Avoiding stack buffer clear being optimised out

[Jonathan Wakely]

On Thu, 1 Dec 2022 at 10:44, Jonny Grant wrote:
> Thank you Jonathan and David for your replies.
>
> That "noipa" looks to have sorted this issue
>
> https://gcc.gnu.org/onlinedocs/gcc/Common-Function-Attributes.html
>
> That page also suggests "noinline" attribute which seems to suggest I'd need to add asm (""); in each wrapper of memset()

I already used the noinline attribute in my example above.

> I'd much rather have memset_s - Jonathan, do you think GCC could add some built-in functions for memset_s ?     __builtin_memset_s() would be great.

No.

But C2x adds a memset_explicit function that does what you want, so
that should arrive in glibc soonish.
I thought it had been added, but was searching the C2x draft for
"memset_secure" and other incorrect names.

https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2631.htm was the
proposal adding it.

>
> There are quite a few similar ones that should be easy to add based on existing
>  (memcpy_s, memmove_s, strcpy_s, strncpy_s, strcat_s, strncat_s, strtok_s, memset_s, strerror_s, strerrorlen_s, strnlen_s).

They're not good APIs. See
https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1967.htm and
https://sourceware.org/legacy-ml/libc-help/2018-01/msg00007.html


> I did speak to someone at LLVM who was considering adding built-ins to clang.
>
> Kind regards
> Jonny
>
>