Commit cd45f6
2026-09-11 09:47:41 Bob Green: -/-| /dev/null .. programming/assembly language.md | |
| @@ 0,0 1,46 @@ | |
| + | # Assembly Language |
| + | |
| + | This page describes how gcc passes arguments, which is required when accessing those arguments from inside a piece of assembly. |
| + | |
| + | Here's an example of how gcc compiled a function |
| + | ``` |
| + | 00c06950 <zobbo>: |
| + | |
| + | int __attribute__ ((noinline)) zobbo(uint8_t drive_num, uint32_t block_num, uint8_t *buffer) { |
| + | drive_num++; |
| + | |
| + | if (drive_num == 42) { |
| + | c06950: 0c2f 0029 0007 cmpib #41,%sp@(7) |
| + | c06956: 671e beqs c06976 <zobbo+0x26> |
| + | return NOT_OK; |
| + | } |
| + | |
| + | block_num--; |
| + | |
| + | if (block_num == 99) { |
| + | c06958: 7064 moveq #100,%d0 |
| + | c0695a: b0af 0008 cmpl %sp@(8),%d0 |
| + | c0695e: 670e beqs c0696e <zobbo+0x1e> |
| + | errno = 99; |
| + | return NOT_OK; |
| + | } |
| + | |
| + | if (*buffer == '!') { |
| + | c06960: 206f 000c moveal %sp@(12),%a0 |
| + | c06964: 0c10 0021 cmpib #33,%a0@ |
| + | c06968: 57c0 seq %d0 |
| + | c0696a: 49c0 extbl %d0 |
| + | return NOT_OK; |
| + | } |
| + | |
| + | return OK; |
| + | } |
| + | c0696c: 4e75 rts |
| + | errno = 99; |
| + | c0696e: 7063 moveq #99,%d0 |
| + | c06970: 23c0 0000 1160 movel %d0,1160 <errno> |
| + | return NOT_OK; |
| + | c06976: 70ff moveq #-1,%d0 |
| + | } |
| + | c06978: 4e75 rts |
| + | ``` |