https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103882
Jose Silva <krystalgamer at protonmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|RESOLVED |UNCONFIRMED
Resolution|INVALID |---
--- Comment #2 from Jose Silva <krystalgamer at protonmail dot com> ---
Marking as noinline does not help.
See the generated code:
```
0040014c <example>:
40014c: 27bdffe0 addiu sp,sp,-32
400150: afbf001c sw ra,28(sp)
400154: 0c100050 jal 400140 <fail>
400158: 00000000 nop
40015c: 80820000 lb v0,0(a0)
400160: 8fbf001c lw ra,28(sp)
400164: 27bd0020 addiu sp,sp,32
400168: 38420061 xori v0,v0,0x61
40016c: 03e00008 jr ra
400170: 2c420001 sltiu v0,v0,1
```
The marking as a clobbered does work, but it doesn't fix the underlying issue.
On my original code I had a `syscall`, which passes the code execution to the
kernel that I have no control over or know the full implementation.
The specific syscall was overwriting the $a0 register which I simplified in my
example.
GCC when -O2 is enabled is making too strong assumptions about the code. To
better illustrate the issue, let me give another example. If I call a function
via a function pointer regardless of the optimization level, GCC will save all
caller-saved registers in use. But when it encounters an ASM statement it
treats it like it doesn't exist. In my opinion, the same assumptions made when
calling from a function pointer should apply when calling a function with
inline-asm*.
* Manually indicating the clobbered registers could override this behaviour
