// We look at the ARMv8 CPU instruction set, used by Apple Silicon M1 and subsequent Aarch64 chips.

sergey@snowball armv8 % cat hello-loop.c 
#include <stdio.h>

int main()
{
     int i = 10;
     
     while( i >= 0 ){
          i = i - 1;
	  puts( "Hello" );
     }

     return 42;
}

sergey@snowball armv8 % gcc -v
Configured with: --prefix=/Library/Developer/CommandLineTools/usr --with-gxx-include-dir=/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/c++/4.2.1
Apple clang version 13.0.0 (clang-1300.0.29.30)
Target: arm64-apple-darwin20.6.0
Thread model: posix
InstalledDir: /Library/Developer/CommandLineTools/usr/bin

sergey@snowball armv8 % gcc -Wall -o h hello-loop.c

// Mach-O is a cousin of ELF and PE executable and linkable file formats, used by Linux
/    and Windows respectively.


sergey@snowball armv8 % file h
h: Mach-O 64-bit arm64 executable, flags:<NOUNDEFS|DYLDLINK|TWOLEVEL|PIE>

sergey@snowball armv8 % lldb ./h
(lldb) target create "./h"
Current executable set to '/Users/user/cs59/armv8/h' (arm64).

(lldb) disas -n main
h`main:
h[0x100003f34] <+0>:  sub    sp, sp, #0x20             ; =0x20 
h[0x100003f38] <+4>:  stp    x29, x30, [sp, #0x10]
h[0x100003f3c] <+8>:  add    x29, sp, #0x10            ; =0x10 
h[0x100003f40] <+12>: stur   wzr, [x29, #-0x4]
h[0x100003f44] <+16>: mov    w8, #0xa
h[0x100003f48] <+20>: str    w8, [sp, #0x8]
h[0x100003f4c] <+24>: ldr    w8, [sp, #0x8]
h[0x100003f50] <+28>: tbnz   w8, #0x1f, 0x100003f70    ; <+60>
h[0x100003f54] <+32>: ldr    w8, [sp, #0x8]
h[0x100003f58] <+36>: subs   w8, w8, #0x1              ; =0x1 
h[0x100003f5c] <+40>: str    w8, [sp, #0x8]
h[0x100003f60] <+44>: adrp   x0, 0
h[0x100003f64] <+48>: add    x0, x0, #0xfb0            ; =0xfb0 
h[0x100003f68] <+52>: bl     0x100003f80               ; symbol stub for: puts
h[0x100003f6c] <+56>: b      0x100003f4c               ; <+24>
h[0x100003f70] <+60>: mov    w0, #0x2a
h[0x100003f74] <+64>: ldp    x29, x30, [sp, #0x10]
h[0x100003f78] <+68>: add    sp, sp, #0x20             ; =0x20 
h[0x100003f7c] <+72>: ret    

// ARM instructions have a uniform encoded length of 4 bytes, unlike x86 variable-length
//    instructions.

(lldb) disas -b -n main
h`main:
h[0x100003f34] <+0>:  0xd10083ff   sub    sp, sp, #0x20             ; =0x20 
h[0x100003f38] <+4>:  0xa9017bfd   stp    x29, x30, [sp, #0x10]
h[0x100003f3c] <+8>:  0x910043fd   add    x29, sp, #0x10            ; =0x10 
h[0x100003f40] <+12>: 0xb81fc3bf   stur   wzr, [x29, #-0x4]
h[0x100003f44] <+16>: 0x52800148   mov    w8, #0xa
h[0x100003f48] <+20>: 0xb9000be8   str    w8, [sp, #0x8]
h[0x100003f4c] <+24>: 0xb9400be8   ldr    w8, [sp, #0x8]
h[0x100003f50] <+28>: 0x37f80108   tbnz   w8, #0x1f, 0x100003f70    ; <+60>
h[0x100003f54] <+32>: 0xb9400be8   ldr    w8, [sp, #0x8]
h[0x100003f58] <+36>: 0x71000508   subs   w8, w8, #0x1              ; =0x1 
h[0x100003f5c] <+40>: 0xb9000be8   str    w8, [sp, #0x8]
h[0x100003f60] <+44>: 0x90000000   adrp   x0, 0
h[0x100003f64] <+48>: 0x913ec000   add    x0, x0, #0xfb0            ; =0xfb0 
h[0x100003f68] <+52>: 0x94000006   bl     0x100003f80               ; symbol stub for: puts
h[0x100003f6c] <+56>: 0x17fffff8   b      0x100003f4c               ; <+24>
h[0x100003f70] <+60>: 0x52800540   mov    w0, #0x2a
h[0x100003f74] <+64>: 0xa9417bfd   ldp    x29, x30, [sp, #0x10]
h[0x100003f78] <+68>: 0x910083ff   add    sp, sp, #0x20             ; =0x20 
h[0x100003f7c] <+72>: 0xd65f03c0   ret    

(lldb) b main
Breakpoint 1: where = h`main, address = 0x0000000100003f34

(lldb) r
Process 17477 launched: '/Users/user/cs59/armv8/h' (arm64)
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 1.1
    frame #0: 0x0000000100003f34 h`main
h`main:
->  0x100003f34 <+0>:  sub    sp, sp, #0x20             ; =0x20 
    0x100003f38 <+4>:  stp    x29, x30, [sp, #0x10]
    0x100003f3c <+8>:  add    x29, sp, #0x10            ; =0x10 
    0x100003f40 <+12>: stur   wzr, [x29, #-0x4]
Target 0: (h) stopped.

// The three top instructions make the stack frame for main():

low addr                                                              high addr
SP               SP+0x8       SP+0xC       SP+0x10           SP+0x18           SP+0x20
 |                 |            |            |                 |                 |
 v                 v            v            v                 v                 v
 +--------+--------+------------+------------+-----------------+-----------------+
 |  unused (pad)   |  local "i" | 0-ed,unused|   saved X29     |   saved X30     |
 |   8 bytes       |  4 bytes   |   4 bytes  |   (old FP)      |   (LR / ret)    |
 +-----------------+------------+------------+-----------------+-----------------+
                                             ^
                                            X29 (FP) points here after 0x100003f3c

(lldb) reg r $sp
      sp = 0x000000016fdff470

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f38 h`main + 4
h`main:
->  0x100003f38 <+4>:  stp    x29, x30, [sp, #0x10]
    0x100003f3c <+8>:  add    x29, sp, #0x10            ; =0x10 
    0x100003f40 <+12>: stur   wzr, [x29, #-0x4]
    0x100003f44 <+16>: mov    w8, #0xa
Target 0: (h) stopped.

// ..and now the notional frame is created:

(lldb) reg r $sp
      sp = 0x000000016fdff450

// FP and LR (x29 and x30) will be saved next:

(lldb) x/10gx $sp
0x16fdff450: 0x0000000000000000 0x0000000000000000
0x16fdff460: 0x000000016fdff480 0xc902000100011038    // <-- saved FP & LR will go here
0x16fdff470: 0x0000000197c7d430 0x0000000000000000
0x16fdff480: 0x0000000000000000 0x0000000000000000
0x16fdff490: 0x0000000000000000 0x0000000100000000

(lldb) reg r $x29 $x30 
      fp = 0x000000016fdff480
      lr = 0x0000000197c7d430  libdyld.dylib`start + 4

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f3c h`main + 8
h`main:
->  0x100003f3c <+8>:  add    x29, sp, #0x10            ; =0x10 
    0x100003f40 <+12>: stur   wzr, [x29, #-0x4]
    0x100003f44 <+16>: mov    w8, #0xa
    0x100003f48 <+20>: str    w8, [sp, #0x8]
Target 0: (h) stopped.

(lldb) x/10gx $sp
0x16fdff450: 0x0000000000000000 0x0000000000000000
0x16fdff460: 0x000000016fdff480 0x0000000197c7d430    // <--- ..and they did
0x16fdff470: 0x0000000197c7d430 0x0000000000000000
0x16fdff480: 0x0000000000000000 0x0000000000000000
0x16fdff490: 0x0000000000000000 0x0000000100000000

// The FP for this frame will be set now:

(lldb) dis
h`main:
    0x100003f34 <+0>:  sub    sp, sp, #0x20             ; =0x20 
    0x100003f38 <+4>:  stp    x29, x30, [sp, #0x10]
->  0x100003f3c <+8>:  add    x29, sp, #0x10            ; =0x10 
    0x100003f40 <+12>: stur   wzr, [x29, #-0x4]
    0x100003f44 <+16>: mov    w8, #0xa
    0x100003f48 <+20>: str    w8, [sp, #0x8]
    0x100003f4c <+24>: ldr    w8, [sp, #0x8]
    0x100003f50 <+28>: tbnz   w8, #0x1f, 0x100003f70    ; <+60>
    0x100003f54 <+32>: ldr    w8, [sp, #0x8]
    0x100003f58 <+36>: subs   w8, w8, #0x1              ; =0x1 
    0x100003f5c <+40>: str    w8, [sp, #0x8]
    0x100003f60 <+44>: adrp   x0, 0
    0x100003f64 <+48>: add    x0, x0, #0xfb0            ; =0xfb0 
    0x100003f68 <+52>: bl     0x100003f80               ; symbol stub for: puts
    0x100003f6c <+56>: b      0x100003f4c               ; <+24>
    0x100003f70 <+60>: mov    w0, #0x2a
    0x100003f74 <+64>: ldp    x29, x30, [sp, #0x10]
    0x100003f78 <+68>: add    sp, sp, #0x20             ; =0x20 
    0x100003f7c <+72>: ret    

(lldb) reg r $x29 $x30
      fp = 0x000000016fdff480
      lr = 0x0000000197c7d430  libdyld.dylib`start + 4

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f40 h`main + 12
h`main:
->  0x100003f40 <+12>: stur   wzr, [x29, #-0x4]
    0x100003f44 <+16>: mov    w8, #0xa
    0x100003f48 <+20>: str    w8, [sp, #0x8]
    0x100003f4c <+24>: ldr    w8, [sp, #0x8]
Target 0: (h) stopped.

// Now FP is pointing to its intended place in the frame. Note that since SP
//  doesn't move during the function, the compiler keeps addressing locals
//  off of SP, and ignored FP. That would not be the case if the function
//  needed to save more things on the stack, which would move SP but keep FP put.

(lldb) reg r $x29 $x30
      fp = 0x000000016fdff460
      lr = 0x0000000197c7d430  libdyld.dylib`start + 4

(lldb) reg r $sp
      sp = 0x000000016fdff450

// I haven't found a reason for zeroing out these 4 bytes. Claude suggests
//   these are for storing a "result" variable, but I doubt it. The local variable
//   "i" could live there, but I think the compiler prefers to have it at 
//   the 8-byte alignment.

(lldb) dis
h`main:
    0x100003f34 <+0>:  sub    sp, sp, #0x20             ; =0x20 
    0x100003f38 <+4>:  stp    x29, x30, [sp, #0x10]
    0x100003f3c <+8>:  add    x29, sp, #0x10            ; =0x10 
->  0x100003f40 <+12>: stur   wzr, [x29, #-0x4]
    0x100003f44 <+16>: mov    w8, #0xa
    0x100003f48 <+20>: str    w8, [sp, #0x8]    // <<-- behold:  i = 10
    0x100003f4c <+24>: ldr    w8, [sp, #0x8]    //   this instruction is redundant and can be optimized away, but I didn't ask for optimization yet 
    0x100003f50 <+28>: tbnz   w8, #0x1f, 0x100003f70    ; <+60>  // check for  i >= 0, jump to the end of the function if the sign bit (bit 31) of w8 is set  
    0x100003f54 <+32>: ldr    w8, [sp, #0x8]    // ARM can only do arithmetic in registers     
    0x100003f58 <+36>: subs   w8, w8, #0x1              ; =0x1  // i = i-1 
    0x100003f5c <+40>: str    w8, [sp, #0x8]    //  .. store the new value of i  
    0x100003f60 <+44>: adrp   x0, 0             //  data addresses like the pointer to "Hello"
                                                //    must be built up by two instructions
						//    due to ARM's fixed-length instruction encoding
    0x100003f64 <+48>: add    x0, x0, #0xfb0            ; =0xfb0 
    0x100003f68 <+52>: bl     0x100003f80               ; symbol stub for: puts
    0x100003f6c <+56>: b      0x100003f4c               ; <+24>  // jump back to the top of while()
    0x100003f70 <+60>: mov    w0, #0x2a
    0x100003f74 <+64>: ldp    x29, x30, [sp, #0x10]
    0x100003f78 <+68>: add    sp, sp, #0x20             ; =0x20 
    0x100003f7c <+72>: ret    

(lldb) dis -b
h`main:
    0x100003f34 <+0>:  0xd10083ff   sub    sp, sp, #0x20             ; =0x20 
    0x100003f38 <+4>:  0xa9017bfd   stp    x29, x30, [sp, #0x10]
    0x100003f3c <+8>:  0x910043fd   add    x29, sp, #0x10            ; =0x10 
->  0x100003f40 <+12>: 0xb81fc3bf   stur   wzr, [x29, #-0x4]
    0x100003f44 <+16>: 0x52800148   mov    w8, #0xa
    0x100003f48 <+20>: 0xb9000be8   str    w8, [sp, #0x8]
    0x100003f4c <+24>: 0xb9400be8   ldr    w8, [sp, #0x8]
    0x100003f50 <+28>: 0x37f80108   tbnz   w8, #0x1f, 0x100003f70    ; <+60>
    0x100003f54 <+32>: 0xb9400be8   ldr    w8, [sp, #0x8]
    0x100003f58 <+36>: 0x71000508   subs   w8, w8, #0x1              ; =0x1 
    0x100003f5c <+40>: 0xb9000be8   str    w8, [sp, #0x8]
    0x100003f60 <+44>: 0x90000000   adrp   x0, 0
    0x100003f64 <+48>: 0x913ec000   add    x0, x0, #0xfb0            ; =0xfb0 
    0x100003f68 <+52>: 0x94000006   bl     0x100003f80               ; symbol stub for: puts
    0x100003f6c <+56>: 0x17fffff8   b      0x100003f4c               ; <+24>
    0x100003f70 <+60>: 0x52800540   mov    w0, #0x2a
    0x100003f74 <+64>: 0xa9417bfd   ldp    x29, x30, [sp, #0x10]
    0x100003f78 <+68>: 0x910083ff   add    sp, sp, #0x20             ; =0x20 
    0x100003f7c <+72>: 0xd65f03c0   ret    

(lldb) reg r $sp
      sp = 0x000000016fdff450

// Let's see the stack before "i" is saved:

(lldb) x/10gx $sp
0x16fdff450: 0x0000000000000000 0x0000000000000000
0x16fdff460: 0x000000016fdff480 0x0000000197c7d430
0x16fdff470: 0x0000000197c7d430 0x0000000000000000
0x16fdff480: 0x0000000000000000 0x0000000000000000
0x16fdff490: 0x0000000000000000 0x0000000100000000

(lldb) x/10wx $sp
0x16fdff450: 0x00000000 0x00000000 0x00000000 0x00000000
0x16fdff460: 0x6fdff480 0x00000001 0x97c7d430 0x00000001
0x16fdff470: 0x97c7d430 0x00000001

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f44 h`main + 16
h`main:
->  0x100003f44 <+16>: mov    w8, #0xa
    0x100003f48 <+20>: str    w8, [sp, #0x8]
    0x100003f4c <+24>: ldr    w8, [sp, #0x8]
    0x100003f50 <+28>: tbnz   w8, #0x1f, 0x100003f70    ; <+60>
Target 0: (h) stopped.

(lldb) reg r $w8
      w8 = 0x3f9500f0

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f48 h`main + 20
h`main:
->  0x100003f48 <+20>: str    w8, [sp, #0x8]
    0x100003f4c <+24>: ldr    w8, [sp, #0x8]
    0x100003f50 <+28>: tbnz   w8, #0x1f, 0x100003f70    ; <+60>
    0x100003f54 <+32>: ldr    w8, [sp, #0x8]
Target 0: (h) stopped.

(lldb) reg r $w8
      w8 = 0x0000000a

// ... and after 

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f4c h`main + 24
h`main:
->  0x100003f4c <+24>: ldr    w8, [sp, #0x8]
    0x100003f50 <+28>: tbnz   w8, #0x1f, 0x100003f70    ; <+60>
    0x100003f54 <+32>: ldr    w8, [sp, #0x8]
    0x100003f58 <+36>: subs   w8, w8, #0x1              ; =0x1 
Target 0: (h) stopped.

(lldb) x/10gx $sp
0x16fdff450: 0x0000000000000000 0x000000000000000a  <<--- "i"
0x16fdff460: 0x000000016fdff480 0x0000000197c7d430
0x16fdff470: 0x0000000197c7d430 0x0000000000000000
0x16fdff480: 0x0000000000000000 0x0000000000000000
0x16fdff490: 0x0000000000000000 0x0000000100000000

(lldb) x/10wx $sp
0x16fdff450: 0x00000000 0x00000000 0x0000000a 0x00000000  <<-- "i" at exactly SP+8
0x16fdff460: 0x6fdff480 0x00000001 0x97c7d430 0x00000001
0x16fdff470: 0x97c7d430 0x00000001

// Integers are little-endian:

(lldb) x/16bx $sp
0x16fdff450: 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
0x16fdff458: 0x0a 0x00 0x00 0x00 0x00 0x00 0x00 0x00
             ^^^^^^^^^^^^^^^^^^^ "i"
(lldb) dis
h`main:
    0x100003f34 <+0>:  sub    sp, sp, #0x20             ; =0x20 
    0x100003f38 <+4>:  stp    x29, x30, [sp, #0x10]
    0x100003f3c <+8>:  add    x29, sp, #0x10            ; =0x10 
    0x100003f40 <+12>: stur   wzr, [x29, #-0x4]
    0x100003f44 <+16>: mov    w8, #0xa
    0x100003f48 <+20>: str    w8, [sp, #0x8]
->  0x100003f4c <+24>: ldr    w8, [sp, #0x8]
    0x100003f50 <+28>: tbnz   w8, #0x1f, 0x100003f70    ; <+60>
    0x100003f54 <+32>: ldr    w8, [sp, #0x8]
    0x100003f58 <+36>: subs   w8, w8, #0x1              ; =0x1 
    0x100003f5c <+40>: str    w8, [sp, #0x8]
    0x100003f60 <+44>: adrp   x0, 0
    0x100003f64 <+48>: add    x0, x0, #0xfb0            ; =0xfb0 
    0x100003f68 <+52>: bl     0x100003f80               ; symbol stub for: puts
    0x100003f6c <+56>: b      0x100003f4c               ; <+24>
    0x100003f70 <+60>: mov    w0, #0x2a
    0x100003f74 <+64>: ldp    x29, x30, [sp, #0x10]
    0x100003f78 <+68>: add    sp, sp, #0x20             ; =0x20 
    0x100003f7c <+72>: ret    

// We test "i >= 0" and pass:

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f50 h`main + 28
h`main:
->  0x100003f50 <+28>: tbnz   w8, #0x1f, 0x100003f70    ; <+60>
    0x100003f54 <+32>: ldr    w8, [sp, #0x8]
    0x100003f58 <+36>: subs   w8, w8, #0x1              ; =0x1 
    0x100003f5c <+40>: str    w8, [sp, #0x8]
Target 0: (h) stopped.

// And now we do "i = i - 1":

(lldb) 
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f54 h`main + 32
h`main:
->  0x100003f54 <+32>: ldr    w8, [sp, #0x8]
    0x100003f58 <+36>: subs   w8, w8, #0x1              ; =0x1 
    0x100003f5c <+40>: str    w8, [sp, #0x8]
    0x100003f60 <+44>: adrp   x0, 0
Target 0: (h) stopped.

(lldb) 
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f58 h`main + 36
h`main:
->  0x100003f58 <+36>: subs   w8, w8, #0x1              ; =0x1 
    0x100003f5c <+40>: str    w8, [sp, #0x8]
    0x100003f60 <+44>: adrp   x0, 0
    0x100003f64 <+48>: add    x0, x0, #0xfb0            ; =0xfb0 
Target 0: (h) stopped.
(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f5c h`main + 40
h`main:
->  0x100003f5c <+40>: str    w8, [sp, #0x8]
    0x100003f60 <+44>: adrp   x0, 0
    0x100003f64 <+48>: add    x0, x0, #0xfb0            ; =0xfb0 
    0x100003f68 <+52>: bl     0x100003f80               ; symbol stub for: puts
Target 0: (h) stopped.

// subtraction in register and storage back to the stack frame: 

(lldb) reg r $w8
      w8 = 0x00000009

// Now we load the address of "Hello":

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f60 h`main + 44
h`main:
->  0x100003f60 <+44>: adrp   x0, 0
    0x100003f64 <+48>: add    x0, x0, #0xfb0            ; =0xfb0 
    0x100003f68 <+52>: bl     0x100003f80               ; symbol stub for: puts
    0x100003f6c <+56>: b      0x100003f4c               ; <+24>
Target 0: (h) stopped.

(lldb) x/10gx $sp
0x16fdff450: 0x0000000000000000 0x0000000000000009  // i is 9 now
0x16fdff460: 0x000000016fdff480 0x0000000197c7d430
0x16fdff470: 0x0000000197c7d430 0x0000000000000000
0x16fdff480: 0x0000000000000000 0x0000000000000000
0x16fdff490: 0x0000000000000000 0x0000000100000000
(lldb) reg r $x0
      x0 = 0x0000000000000001

// Loading a data address, such as the pointer to the string "Hello\0", needs two
//  instructions, one for the 4K page address, another for the offset within that page:

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f64 h`main + 48
h`main:
->  0x100003f64 <+48>: add    x0, x0, #0xfb0            ; =0xfb0 
    0x100003f68 <+52>: bl     0x100003f80               ; symbol stub for: puts
    0x100003f6c <+56>: b      0x100003f4c               ; <+24>
    0x100003f70 <+60>: mov    w0, #0x2a
Target 0: (h) stopped.

// Page top:

(lldb) reg r $x0
      x0 = 0x0000000100003000  h`_mh_execute_header + 12288

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f68 h`main + 52
h`main:
->  0x100003f68 <+52>: bl     0x100003f80               ; symbol stub for: puts
    0x100003f6c <+56>: b      0x100003f4c               ; <+24>
    0x100003f70 <+60>: mov    w0, #0x2a
    0x100003f74 <+64>: ldp    x29, x30, [sp, #0x10]
Target 0: (h) stopped.

// The address of "Hello", good to go as the first and only argument to puts(),
//   passed via x0 as per Aarch64 calling convention:

(lldb) reg r $x0
      x0 = 0x0000000100003fb0  "Hello"    // <-- LLDB helpfully shows what's there at that address

(lldb) x/10bx $x0
0x100003fb0: 0x48 0x65 0x6c 0x6c 0x6f 0x00 0x00 0x00
0x100003fb8: 0x01 0x00

// We are now jumping to the "stub" for puts(). Standard library functions are dynamically
//   linked, which means the compiler only provides the stubs for them in the current
//   compilation unit. When called, these stubs will call out to the dynamic linker (DYLD),
//   which will load the right precompiled library and point the stub to it.

// Let's follow these jumps the first time puts() stub is called:

(lldb) x/12i 0x100003f80
    0x100003f80: 0xd503201f   nop    
    0x100003f84: 0x580203f0   ldr    x16, #0x407c              ; (void *)0x0000000100003fa4
    0x100003f88: 0xd61f0200   br     x16
    0x100003f8c: 0x100203f1   adr    x17, #0x407c              ; _dyld_private
    0x100003f90: 0xd503201f   nop    
    0x100003f94: 0xa9bf47f0   stp    x16, x17, [sp, #-0x10]!
    0x100003f98: 0xd503201f   nop    
    0x100003f9c: 0x58000330   ldr    x16, #0x64                ; (void *)0x0000000197c7bbd8: dyld_stub_binder
    0x100003fa0: 0xd61f0200   br     x16
    0x100003fa4: 0x18000050   ldr    w16, 0x100003fac
    0x100003fa8: 0x17fffff9   b      0x100003f8c
    0x100003fac: 0x00000000   udf    #0x0   // <<-- this is 4 bytes of data, read by LDR at 0x100003fa4 . ARM does intersperse data and code  

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f80 h`puts
h`puts:
    0x100003f80 <+0>: nop    
    0x100003f84 <+4>: ldr    x16, #0x407c              ; (void *)0x0000000100003fa4
    0x100003f88 <+8>: br     x16
    0x100003f8c:      adr    x17, #0x407c              ; _dyld_private
Target 0: (h) stopped.

// Note that when puts() is done it will return to here:

(lldb) reg r $x30
      lr = 0x0000000100003f6c  h`main + 56

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f84 h`puts + 4
h`puts:
->  0x100003f84 <+4>: ldr    x16, #0x407c              ; (void *)0x0000000100003fa4
    0x100003f88 <+8>: br     x16
    0x100003f8c:      adr    x17, #0x407c              ; _dyld_private
    0x100003f90:      nop    
Target 0: (h) stopped.

// ..a few more steps into the stub and the dynamic loader:

(lldb) reg r $x16
     x16 = 0x0000000100003f34  h`main

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f88 h`puts + 8
h`puts:
->  0x100003f88 <+8>: br     x16
    0x100003f8c:      adr    x17, #0x407c              ; _dyld_private
    0x100003f90:      nop    
    0x100003f94:      stp    x16, x17, [sp, #-0x10]!
Target 0: (h) stopped.

(lldb) reg r $x16
     x16 = 0x0000000100003fa4  

(lldb) x/1i 0x0000000100003fa4
    0x100003fa4: 0x18000050   ldr    w16, 0x100003fac

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003fa4 h
->  0x100003fa4: ldr    w16, 0x100003fac
    0x100003fa8: b      0x100003f8c
    0x100003fac: udf    #0x0
    0x100003fb0: ldnp   d8, d25, [x10, #-0x140]
Target 0: (h) stopped.

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003fa8 h
->  0x100003fa8: b      0x100003f8c
    0x100003fac: udf    #0x0
    0x100003fb0: ldnp   d8, d25, [x10, #-0x140]
    0x100003fb4: udf    #0x6f
Target 0: (h) stopped.

(lldb) 
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f8c h
    0x100003f8c: adr    x17, #0x407c              ; _dyld_private
    0x100003f90: nop    
    0x100003f94: stp    x16, x17, [sp, #-0x10]!
    0x100003f98: nop    
Target 0: (h) stopped.

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f90 h
->  0x100003f90: nop    
    0x100003f94: stp    x16, x17, [sp, #-0x10]!
    0x100003f98: nop    
    0x100003f9c: ldr    x16, #0x64                ; (void *)0x0000000197c7bbd8: dyld_stub_binder
Target 0: (h) stopped.

// We let the dynamic loader continue, and will catch the execution after puts() returns:

(lldb) dis -n main
h`main:
    0x100003f34 <+0>:  sub    sp, sp, #0x20             ; =0x20 
    0x100003f38 <+4>:  stp    x29, x30, [sp, #0x10]
    0x100003f3c <+8>:  add    x29, sp, #0x10            ; =0x10 
    0x100003f40 <+12>: stur   wzr, [x29, #-0x4]
    0x100003f44 <+16>: mov    w8, #0xa
    0x100003f48 <+20>: str    w8, [sp, #0x8]
    0x100003f4c <+24>: ldr    w8, [sp, #0x8]
    0x100003f50 <+28>: tbnz   w8, #0x1f, 0x100003f70    ; <+60>
    0x100003f54 <+32>: ldr    w8, [sp, #0x8]
    0x100003f58 <+36>: subs   w8, w8, #0x1              ; =0x1 
    0x100003f5c <+40>: str    w8, [sp, #0x8]
    0x100003f60 <+44>: adrp   x0, 0
    0x100003f64 <+48>: add    x0, x0, #0xfb0            ; =0xfb0 
    0x100003f68 <+52>: bl     0x100003f80               ; symbol stub for: puts
    0x100003f6c <+56>: b      0x100003f4c               ; <+24>
    0x100003f70 <+60>: mov    w0, #0x2a
    0x100003f74 <+64>: ldp    x29, x30, [sp, #0x10]
    0x100003f78 <+68>: add    sp, sp, #0x20             ; =0x20 
    0x100003f7c <+72>: ret    


(lldb) b 0x100003f6c
Breakpoint 2: where = h`main + 56, address = 0x0000000100003f6c

(lldb) c
Process 17477 resuming
Hello
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 2.1
    frame #0: 0x0000000100003f6c h`main + 56
h`main:
->  0x100003f6c <+56>: b      0x100003f4c               ; <+24>
    0x100003f70 <+60>: mov    w0, #0x2a
    0x100003f74 <+64>: ldp    x29, x30, [sp, #0x10]
    0x100003f78 <+68>: add    sp, sp, #0x20             ; =0x20 
Target 0: (h) stopped.

// We go back thought the loop, but puts() will now go straight to its library
//   implementation:

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f4c h`main + 24
h`main:
->  0x100003f4c <+24>: ldr    w8, [sp, #0x8]
    0x100003f50 <+28>: tbnz   w8, #0x1f, 0x100003f70    ; <+60>
    0x100003f54 <+32>: ldr    w8, [sp, #0x8]
    0x100003f58 <+36>: subs   w8, w8, #0x1              ; =0x1 
Target 0: (h) stopped.

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f50 h`main + 28
h`main:
->  0x100003f50 <+28>: tbnz   w8, #0x1f, 0x100003f70    ; <+60>
    0x100003f54 <+32>: ldr    w8, [sp, #0x8]
    0x100003f58 <+36>: subs   w8, w8, #0x1              ; =0x1 
    0x100003f5c <+40>: str    w8, [sp, #0x8]
Target 0: (h) stopped.

(lldb) reg r $w8
      w8 = 0x00000009

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f54 h`main + 32
h`main:
->  0x100003f54 <+32>: ldr    w8, [sp, #0x8]
    0x100003f58 <+36>: subs   w8, w8, #0x1              ; =0x1 
    0x100003f5c <+40>: str    w8, [sp, #0x8]
    0x100003f60 <+44>: adrp   x0, 0
Target 0: (h) stopped.

(lldb) 
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f58 h`main + 36
h`main:
->  0x100003f58 <+36>: subs   w8, w8, #0x1              ; =0x1 
    0x100003f5c <+40>: str    w8, [sp, #0x8]
    0x100003f60 <+44>: adrp   x0, 0
    0x100003f64 <+48>: add    x0, x0, #0xfb0            ; =0xfb0 
Target 0: (h) stopped.

(lldb) 
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f5c h`main + 40
h`main:
->  0x100003f5c <+40>: str    w8, [sp, #0x8]
    0x100003f60 <+44>: adrp   x0, 0
    0x100003f64 <+48>: add    x0, x0, #0xfb0            ; =0xfb0 
    0x100003f68 <+52>: bl     0x100003f80               ; symbol stub for: puts
Target 0: (h) stopped.

(lldb) 
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f60 h`main + 44
h`main:
->  0x100003f60 <+44>: adrp   x0, 0
    0x100003f64 <+48>: add    x0, x0, #0xfb0            ; =0xfb0 
    0x100003f68 <+52>: bl     0x100003f80               ; symbol stub for: puts
    0x100003f6c <+56>: b      0x100003f4c               ; <+24>
Target 0: (h) stopped.

(lldb) 
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f64 h`main + 48
h`main:
->  0x100003f64 <+48>: add    x0, x0, #0xfb0            ; =0xfb0 
    0x100003f68 <+52>: bl     0x100003f80               ; symbol stub for: puts
    0x100003f6c <+56>: b      0x100003f4c               ; <+24>
    0x100003f70 <+60>: mov    w0, #0x2a
Target 0: (h) stopped.

(lldb) 
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f68 h`main + 52
h`main:
->  0x100003f68 <+52>: bl     0x100003f80               ; symbol stub for: puts
    0x100003f6c <+56>: b      0x100003f4c               ; <+24>
    0x100003f70 <+60>: mov    w0, #0x2a
    0x100003f74 <+64>: ldp    x29, x30, [sp, #0x10]
Target 0: (h) stopped.

(lldb) 
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f80 h`puts
h`puts:
    0x100003f80 <+0>: nop    
    0x100003f84 <+4>: ldr    x16, #0x407c              ; (void *)0x0000000197b70004: puts
    0x100003f88 <+8>: br     x16
    0x100003f8c:      adr    x17, #0x407c              ; _dyld_private
Target 0: (h) stopped.

// We are now calling puts(), but look: the next jump will be straight to it:

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f84 h`puts + 4
h`puts:
->  0x100003f84 <+4>: ldr    x16, #0x407c              ; (void *)0x0000000197b70004: puts
    0x100003f88 <+8>: br     x16
    0x100003f8c:      adr    x17, #0x407c              ; _dyld_private
    0x100003f90:      nop    
Target 0: (h) stopped.

(lldb) 
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f88 h`puts + 8
h`puts:
->  0x100003f88 <+8>: br     x16
    0x100003f8c:      adr    x17, #0x407c              ; _dyld_private
    0x100003f90:      nop    
    0x100003f94:      stp    x16, x17, [sp, #-0x10]!
Target 0: (h) stopped.

// ..and we are now in the standard library puts() implementation: 

(lldb) 
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000197b70004 libsystem_c.dylib`puts
libsystem_c.dylib`puts:
->  0x197b70004 <+0>:  pacibsp 
    0x197b70008 <+4>:  sub    sp, sp, #0x60             ; =0x60 
    0x197b7000c <+8>:  stp    x20, x19, [sp, #0x40]
    0x197b70010 <+12>: stp    x29, x30, [sp, #0x50]
Target 0: (h) stopped.

(lldb) c
Process 17477 resuming
Hello
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 2.1
    frame #0: 0x0000000100003f6c h`main + 56
h`main:
->  0x100003f6c <+56>: b      0x100003f4c               ; <+24>
    0x100003f70 <+60>: mov    w0, #0x2a
    0x100003f74 <+64>: ldp    x29, x30, [sp, #0x10]
    0x100003f78 <+68>: add    sp, sp, #0x20             ; =0x20 
Target 0: (h) stopped.

(lldb) dis -n main
h`main:
    0x100003f34 <+0>:  sub    sp, sp, #0x20             ; =0x20 
    0x100003f38 <+4>:  stp    x29, x30, [sp, #0x10]
    0x100003f3c <+8>:  add    x29, sp, #0x10            ; =0x10 
    0x100003f40 <+12>: stur   wzr, [x29, #-0x4]
    0x100003f44 <+16>: mov    w8, #0xa
    0x100003f48 <+20>: str    w8, [sp, #0x8]
    0x100003f4c <+24>: ldr    w8, [sp, #0x8]
    0x100003f50 <+28>: tbnz   w8, #0x1f, 0x100003f70    ; <+60>
    0x100003f54 <+32>: ldr    w8, [sp, #0x8]
    0x100003f58 <+36>: subs   w8, w8, #0x1              ; =0x1 
    0x100003f5c <+40>: str    w8, [sp, #0x8]
    0x100003f60 <+44>: adrp   x0, 0
    0x100003f64 <+48>: add    x0, x0, #0xfb0            ; =0xfb0 
    0x100003f68 <+52>: bl     0x100003f80               ; symbol stub for: puts
->  0x100003f6c <+56>: b      0x100003f4c               ; <+24>
    0x100003f70 <+60>: mov    w0, #0x2a
    0x100003f74 <+64>: ldp    x29, x30, [sp, #0x10]
    0x100003f78 <+68>: add    sp, sp, #0x20             ; =0x20 
    0x100003f7c <+72>: ret    

// We'll catch the function after the loop exits and it's time to return:

(lldb) b 0x100003f78
Breakpoint 3: where = h`main + 68, address = 0x0000000100003f78

(lldb) c
Process 17477 resuming
Hello
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 2.1
    frame #0: 0x0000000100003f6c h`main + 56
h`main:
->  0x100003f6c <+56>: b      0x100003f4c               ; <+24>
    0x100003f70 <+60>: mov    w0, #0x2a
    0x100003f74 <+64>: ldp    x29, x30, [sp, #0x10]
    0x100003f78 <+68>: add    sp, sp, #0x20             ; =0x20 
Target 0: (h) stopped.

(lldb) breakpoint 
Commands for operating on breakpoints (see 'help b' for shorthand.)

Syntax: breakpoint <subcommand> [<command-options>]

The following subcommands are supported:

      clear   -- Delete or disable breakpoints matching the specified source file and line.
      command -- Commands for adding, removing and listing LLDB commands executed when a
                 breakpoint is hit.
      delete  -- Delete the specified breakpoint(s).  If no breakpoints are specified, delete them
                 all.
      disable -- Disable the specified breakpoint(s) without deleting them.  If none are
                 specified, disable all breakpoints.
      enable  -- Enable the specified disabled breakpoint(s). If no breakpoints are specified,
                 enable all of them.
      list    -- List some or all breakpoints at configurable levels of detail.
      modify  -- Modify the options on a breakpoint or set of breakpoints in the executable.  If
                 no breakpoint is specified, acts on the last created breakpoint.  With the
                 exception of -e, -d and -i, passing an empty argument clears the modification.
      name    -- Commands to manage name tags for breakpoints
      read    -- Read and set the breakpoints previously saved to a file with "breakpoint write".  
      set     -- Sets a breakpoint or set of breakpoints in the executable.
      write   -- Write the breakpoints listed to a file that can be read in with "breakpoint
                 read".  If given no arguments, writes all breakpoints.

For more help on any particular subcommand, type 'help <command> <subcommand>'.

(lldb) breakpoint list
Current breakpoints:
1: name = 'main', locations = 1, resolved = 1, hit count = 1
  1.1: where = h`main, address = 0x0000000100003f34, resolved, hit count = 1 

2: address = h[0x0000000100003f6c], locations = 1, resolved = 1, hit count = 3
  2.1: where = h`main + 56, address = 0x0000000100003f6c, resolved, hit count = 3 

3: address = h[0x0000000100003f78], locations = 1, resolved = 1, hit count = 0
  3.1: where = h`main + 68, address = 0x0000000100003f78, resolved, hit count = 0 

(lldb) break delete 2
1 breakpoints deleted; 0 breakpoint locations disabled.

(lldb) breakpoint list
Current breakpoints:
1: name = 'main', locations = 1, resolved = 1, hit count = 1
  1.1: where = h`main, address = 0x0000000100003f34, resolved, hit count = 1 

3: address = h[0x0000000100003f78], locations = 1, resolved = 1, hit count = 0
  3.1: where = h`main + 68, address = 0x0000000100003f78, resolved, hit count = 0 

(lldb) c
Process 17477 resuming
Hello
Hello
Hello
Hello
Hello
Hello
Hello
Hello
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = breakpoint 3.1
    frame #0: 0x0000000100003f78 h`main + 68
h`main:
->  0x100003f78 <+68>: add    sp, sp, #0x20             ; =0x20 
    0x100003f7c <+72>: ret    

h`puts:
    0x100003f80 <+0>:  nop    
    0x100003f84 <+4>:  ldr    x16, #0x407c              ; (void *)0x0000000197b70004: puts
Target 0: (h) stopped.

// LR points to where main() must return:

(lldb) reg r $x30
      lr = 0x0000000197c7d430  libdyld.dylib`start + 4

// X0 holds the return value, as per ARM calling convention:

(lldb) reg r $x0
      x0 = 0x000000000000002a

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000100003f7c h`main + 72
h`main:
->  0x100003f7c <+72>: ret    

h`puts:
    0x100003f80 <+0>:  nop    
    0x100003f84 <+4>:  ldr    x16, #0x407c              ; (void *)0x0000000197b70004: puts
    0x100003f88 <+8>:  br     x16
Target 0: (h) stopped.

// .. and we are now heading back to the shell, via exit()

(lldb) si
Process 17477 stopped
* thread #1, queue = 'com.apple.main-thread', stop reason = instruction step into
    frame #0: 0x0000000197c7d430 libdyld.dylib`start + 4
libdyld.dylib`start:
->  0x197c7d430 <+4>: bl     0x197c9e410               ; symbol stub for: exit
    0x197c7d434 <+8>: brk    #0x3

libdyld.dylib`dyld3::kdebug_trace_dyld_marker:
    0x197c7d438 <+0>: pacibsp 
    0x197c7d43c <+4>: stp    x28, x27, [sp, #-0x60]!
Target 0: (h) stopped.

(lldb) reg r $x30
      lr = 0x0000000197c7d430  libdyld.dylib`start + 4

// Oops, syntax:

(lldb) x/10gx $sp - 0x20
error: memory read takes a start address expression with an optional end address expression.
Expressions should be quoted if they contain spaces or other special characters. 

(lldb) x/10gx $sp-0x20
0x16fdff450: 0x0000000000000000 0x00000000ffffffff  // <<-- note, "i" is now "-1" in 32-bit 2's complement integer encoding, 0xffffffff
0x16fdff460: 0x000000016fdff480 0x0000000197c7d430
0x16fdff470: 0x0000000197c7d430 0x0000000000000000
0x16fdff480: 0x0000000000000000 0x0000000000000000
0x16fdff490: 0x0000000000000000 0x0000000100000000

(lldb) ^D

// Optimized compilation removes most of the compiler template logic that deals
//  with local variables and their storage, etc.:

sergey@snowball armv8 % cat hello-loop.c
#include <stdio.h>

int main()
{
     int i = 10;
     
     while( i >= 0 ){
          i = i - 1;
	  puts( "Hello" );
     }

     return 42;
}

// -O2 is the normal level of optimization:

sergey@snowball armv8 % gcc -O2 -o h2 hello-loop.c

// We see that the loop has been replaced with 11 calls to puts(). This optimization
//  is known as loop unrolling: 

sergey@snowball armv8 % lldb h2  
(lldb) target create "h2"
Current executable set to '/Users/user/cs59/armv8/h2' (arm64).
(lldb) dis -n main
h2`main:
h2[0x100003f04] <+0>:   stp    x20, x19, [sp, #-0x20]!
h2[0x100003f08] <+4>:   stp    x29, x30, [sp, #0x10]
h2[0x100003f0c] <+8>:   add    x29, sp, #0x10            ; =0x10 
h2[0x100003f10] <+12>:  adr    x19, #0xa0                ; "Hello"
h2[0x100003f14] <+16>:  nop    
h2[0x100003f18] <+20>:  mov    x0, x19
h2[0x100003f1c] <+24>:  bl     0x100003f80               ; symbol stub for: puts
h2[0x100003f20] <+28>:  mov    x0, x19
h2[0x100003f24] <+32>:  bl     0x100003f80               ; symbol stub for: puts
h2[0x100003f28] <+36>:  mov    x0, x19
h2[0x100003f2c] <+40>:  bl     0x100003f80               ; symbol stub for: puts
h2[0x100003f30] <+44>:  mov    x0, x19
h2[0x100003f34] <+48>:  bl     0x100003f80               ; symbol stub for: puts
h2[0x100003f38] <+52>:  mov    x0, x19
h2[0x100003f3c] <+56>:  bl     0x100003f80               ; symbol stub for: puts
h2[0x100003f40] <+60>:  mov    x0, x19
h2[0x100003f44] <+64>:  bl     0x100003f80               ; symbol stub for: puts
h2[0x100003f48] <+68>:  mov    x0, x19
h2[0x100003f4c] <+72>:  bl     0x100003f80               ; symbol stub for: puts
h2[0x100003f50] <+76>:  mov    x0, x19
h2[0x100003f54] <+80>:  bl     0x100003f80               ; symbol stub for: puts
h2[0x100003f58] <+84>:  mov    x0, x19
h2[0x100003f5c] <+88>:  bl     0x100003f80               ; symbol stub for: puts
h2[0x100003f60] <+92>:  mov    x0, x19
h2[0x100003f64] <+96>:  bl     0x100003f80               ; symbol stub for: puts
h2[0x100003f68] <+100>: mov    x0, x19
h2[0x100003f6c] <+104>: bl     0x100003f80               ; symbol stub for: puts
h2[0x100003f70] <+108>: mov    w0, #0x2a
h2[0x100003f74] <+112>: ldp    x29, x30, [sp, #0x10]
h2[0x100003f78] <+116>: ldp    x20, x19, [sp], #0x20
h2[0x100003f7c] <+120>: ret    
(lldb) ^D

=====> Annotations stop here, to be continued.


sergey@snowball armv8 % cd ..

sergey@snowball cs59 % cd lisp

sergey@snowball lisp % gcl
GCL (GNU Common Lisp)  2.6.14 Fri Jan 13 10:47:56 AM EST 2023  ANSI    git: Version_2_6_14
Source License: LGPL(gcl,gmp), GPL(unexec,bfd,xgcl)
Binary License:  GPL due to GPL'ed components: (READLINE UNEXEC)
Modifications of this banner must retain notice of a compatible license
Dedicated to the memory of W. Schelter

Use (help) to get some basic information on how to use GCL.
Temporary directory for compiler files:
/var/folders/tp/17fq2kwj13bb2xj7s5hbr0ch0000gn/T/

>1

1

>nil

NIL

>t

T

>10000000000000000000000000000000000

10000000000000000000000000000000000

>10000000000079287589272987529878579857287539287352983752895729875287598753 

10000000000079287589272987529878579857287539287352983752895729875287598753

>(+ 10000000000079287589272987529878579857287539287352983752895729875287598753 1)

10000000000079287589272987529878579857287539287352983752895729875287598754

>(cons + (cons 1 (cons 2 nil)))

((+ 10000000000079287589272987529878579857287539287352983752895729875287598753
    1)
 1 2)

>(cons 1 nil)

(1)

>(cons 1 (cons nil))

Error: 
Fast links are on: do (si::use-fast-links nil) for debugging
Signalled by CONS.

Condition in CONS [or a callee]: INTERNAL-SIMPLE-PROGRAM-ERROR: CONS [or a callee] requires more than one argument.

Broken at CONS.  Type :H for Help.
    1  Return to top level. 
>>1


Top level.
>(cons 1 (cons 2 nil))

(1 2)

>(cons 1 (cons 2 (cons 3 nil)))

(1 2 3)

>(list 1 2 3)

(1 2 3)

>(+ 1 2)

3

>(READ
READ                        READ-FROM-STRING            READER-METHOD-CLASS
READ-BYTE                   READ-LINE                   READTABLE
READ-CHAR                   READ-PRESERVING-WHITESPACE  READTABLE-CASE
READ-CHAR-NO-HANG           READ-SEQUENCE               READTABLEP
READ-DELIMITED-LIST         READER-ERROR                
>(READ-FROM-STRING "(+ 1 2)")

(+ 1 2)
7

>(eval (READ-FROM-STRING "(+ 1 2)"))

3

>(print (eval (READ-FROM-STRING "(+ 1 2)")))

3 
3

>+

(PRINT (EVAL (READ-FROM-STRING "(+ 1 2)")))

>#'+

#<compiled-function +>

>x

Error: 
Fast links are on: do (si::use-fast-links nil) for debugging
Signalled by EVAL.

Condition in EVAL [or a callee]: INTERNAL-SIMPLE-UNBOUND-VARIABLE: Cell error on X: Unbound variable: 

Broken at EVAL.  Type :H for Help.
    1  Return to top level. 
>>1


Top level.
>(+ (* 2 3) 10)

16

>(+ (* 2 3) (- 15 5))

16

>(quote x)

X

>x

Error: 
Fast links are on: do (si::use-fast-links nil) for debugging
Signalled by EVAL.

Condition in EVAL [or a callee]: INTERNAL-SIMPLE-UNBOUND-VARIABLE: Cell error on X: Unbound variable: 

Broken at EVAL.  Type :H for Help.
    1  Return to top level. 
>>1


Top level.
>(set (quote x) 100)

100

>x

100

>(+ x x)

200

>(* x 2)

200

>(consp x)

NIL

>(atom x)

T

>(atom 100)

T

>(atom "foo")

T

>(atom (cons 1 nil))

NIL

>(consp (cons 1 nil))

T

>(if (> x 10) "foo" "bar")

"foo"

>(if (> x 1000) "foo" "bar")

"bar"

>(if (> x 1000) (set (quote y "foo")) (set (quote y) "bar")))

"bar"

>y

"bar"

>(if (> x 10) (set (quote y "foo")) (set (quote y) "bar")))

Error: 
Fast links are on: do (si::use-fast-links nil) for debugging
Signalled by QUOTE.

Condition in QUOTE [or a callee]: INTERNAL-SIMPLE-PROGRAM-ERROR: Too many arguments.

Broken at QUOTE.  Type :H for Help.
    1  Return to top level. 
>>1


Top level.
>(if (> x 10) (set (quote y) "foo")) (set (quote y) "bar")))

"foo"

>
"bar"

>y

"bar"

>x

100

>(if (> x 10) (set (quote y) "foo")) (set (quote y) "bar"))

"foo"

>
"bar"

>y

"bar"

>(if (> x 10) (set (quote y) "foo")) (set (quote y) "bar")))

"foo"

>
"bar"

>y

"bar"

>(if (> x 10) (set (quote y) "foo") (set (quote y) "bar"))

"foo"

>(if (> x 1000) (set (quote y) "foo") (set (quote y) "bar"))

"bar"

>y

"bar"

>(if (> x 10) (set (quote y) "foo") (set (quote y) "bar"))

"foo"

>y

"foo"

>(SETQ  x 200)

200

>x

200

>(defun plus1 (x) (+ x 1)) 

PLUS1

>plus1

Error: 
Fast links are on: do (si::use-fast-links nil) for debugging
Signalled by EVAL.

Condition in EVAL [or a callee]: INTERNAL-SIMPLE-UNBOUND-VARIABLE: Cell error on PLUS1: Unbound variable: 

Broken at EVAL.  Type :H for Help.
    1  Return to top level. 
>>1


Top level.
>(plus1 15)

16

>#'plus1

(SYSTEM:LAMBDA-BLOCK PLUS1 (X) (+ X 1))

>(FUNC
FUNCALL                               FUNCTION
FUNCALLABLE-STANDARD-CLASS            FUNCTION-KEYWORDS
FUNCALLABLE-STANDARD-INSTANCE         FUNCTION-LAMBDA-EXPRESSION
FUNCALLABLE-STANDARD-INSTANCE-ACCESS  FUNCTIONP
>(FUNC
FUNCALL                               FUNCTION
FUNCALLABLE-STANDARD-CLASS            FUNCTION-KEYWORDS
FUNCALLABLE-STANDARD-INSTANCE         FUNCTION-LAMBDA-EXPRESSION
FUNCALLABLE-STANDARD-INSTANCE-ACCESS  FUNCTIONP
>(FUNC
FUNCALL                               FUNCTION
FUNCALLABLE-STANDARD-CLASS            FUNCTION-KEYWORDS
FUNCALLABLE-STANDARD-INSTANCE         FUNCTION-LAMBDA-EXPRESSION
FUNCALLABLE-STANDARD-INSTANCE-ACCESS  FUNCTIONP
>(FUNCALL plus1 10)

Error: 
Fast links are on: do (si::use-fast-links nil) for debugging
Signalled by EVAL.

Condition in EVAL [or a callee]: INTERNAL-SIMPLE-UNBOUND-VARIABLE: Cell error on PLUS1: Unbound variable: 

Broken at FUNCALL.  Type :H for Help.
    1  Return to top level. 
>>1


Top level.
>(FUNCALL 'plus1 10)

11

>(FUNCALL (quote plus1) 10)

11

>(FUNCALL 'plus1 10)

11

>'x

X

>(set 'x 300)

300

>x

300

>(null nil)

T

>(null '())

T

>()

NIL

>(car '(1 2 3))

1

>(cdr '(1 2 3))

(2 3)

>(cdr (cdr '(1 2 3)))

(3)

>(car (cdr (cdr '(1 2 3))))

3

>(car (cdr '(1 2 3)))

2

>(cadr '(1 2 3))

2

>(cddr '(1 2 3))

(3)

>(caddr '(1 2 3))

3

>(cadddr '(1 2 3 4 5 6 7 7 8 9))

4

>(caddddr '(1 2 3 4 5 6 7 7 8 9))

Error: 
Fast links are on: do (si::use-fast-links nil) for debugging
Signalled by EVAL.

Condition in EVAL [or a callee]: INTERNAL-SIMPLE-UNDEFINED-FUNCTION: Cell error on CADDDDR: Undefined function: 

Broken at EVAL.  Type :H for Help.
    1  Return to top level. 
>>1


Top level.
>(defun caddddr (x) (car (cdr (cdddr x))))

CADDDDR

>(caddddr '(1 2 3 4 5 6 7 7 8 9))

5

>(defun len (x) (if (null x) 0  (+ 1 (len (cdr x)))))

LEN

>(len '())

0

>(len '(1))

1

>(len '(1 2))

2

>(len '(1 2 3))

3

>(len '(1 2 3 4))

4

>(len '(1 2 3 4 5 3  3 4 6 8  3 2))

12

====== to be continued ========