[PATCH v2] Replace __strcpy_chk with __builtin___strcpy_chk

[Siddhesh Poyarekar]

On 2024-12-17 17:55, H.J. Lu wrote:
> Although _chk functions are exported in libc.so.6, their prototypes aren't
> provided.  Their built versions are supported by compiler.  Replace
> __strcpy_chk with __builtin___strcpy_chk to silence Clang error:
> 
> ./tst-gnuglob-skeleton.c:225:3: error: call to undeclared function '__strcpy_chk'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
>    225 |   __strcpy_chk (dir->d.d_name, filesystem[dir->idx].name, NAME_MAX);
>        |   ^
> 
> Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
> ---
>   posix/tst-glob_lstat_compat.c | 3 ++-
>   posix/tst-gnuglob-skeleton.c  | 3 ++-
>   2 files changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/posix/tst-glob_lstat_compat.c b/posix/tst-glob_lstat_compat.c
> index 6ea3b062f0..752a8c8707 100644
> --- a/posix/tst-glob_lstat_compat.c
> +++ b/posix/tst-glob_lstat_compat.c
> @@ -173,7 +173,8 @@ my_readdir (void *gdir)
>   
>     dir->d.d_type = filesystem[dir->idx].type;
>   
> -  __strcpy_chk (dir->d.d_name, filesystem[dir->idx].name, NAME_MAX);
> +  __builtin___strcpy_chk (dir->d.d_name, filesystem[dir->idx].name,
> +			  NAME_MAX);

So... __builtin___strcpy_chk is not strictly equivalent to __strcpy_chk; 
sorry I should have pointed that out when Sam mentioned it. 
__builtin___strcpy_chk results in a full evaluation of the object size 
argument and consequent replacement with either a strcpy call or a 
__strcpy_chk call depending on whether the access is safe.  __strcpy_chk 
is, well, just __strcpy_chk.

That said though, gcc has a gimple_fold_builtin_stxcpy_chk which folds 
__strcpy_chk calls into a strcpy if the access is known to be safe, so 
from that perspective, it doesn't actually make a difference as far as 
gcc is concerned.  I don't know if clang has similar optimizations.

TL;DR; I think this is fine as far as gcc is concerned.

Thanks,
Sid