[libc-commits] [libc] [libc] check a few syscall #'s to avoid wrong syscalls (PR #123100)

[Nick Desaulniers via libc-commits]

nickdesaulniers wrote:

I've been thinking more about how do we better catch the case of:
```c
long mmap_ret_val = syscall_impl<long>(MMAP_SYSCALL_NUMBER, nullptr,
  alloc_size, PROT_READ | PROT_WRITE,                                     
  MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);                                                                                                 
  if (mmap_ret_val < 0 && static_cast<uintptr_t>(mmap_ret_val) > -app.page_size)
    syscall_impl<long>(SYS_exit, 1);
```
when `MMAP_SYSCALL_NUMBER` and `SYS_exit` are both wrong (for the wrong architecture).  I think maybe we could have an internal helper function marked `[[noreturn]]` that checks the return value from the syscall to exit and traps.  That said, perhaps it's possible to have the wrong syscall to exit succeed, so we'd have a false positive there...

https://github.com/llvm/llvm-project/pull/123100