Re: [Tinycc-devel] '__builtin_frame_address' warning about suspicious use of this call

[grischka]

Christian Jullien wrote:
> GCC documentation says:

> Calling this function with a nonzero argument can have unpredictable
> effects, including crashing the calling program. As a result, calls that are
> considered unsafe are diagnosed when the -Wframe-address option is in
> effect. Such calls should only be made in debugging situations. 
>
> ^^^^^ This latest sentence makes me afraid!

Actually we are in a "debugging situation" with bcheck.c which
is helper code for the tcc -b switch.

Also, in our case the result is not unpredictable because these
functions are used in a controlled way by calls inserted by the
compiler (tcc).

If you use
    #pragma GCC diagnostic ignored "-Wframe-address"
it will probably just trigger another warning
    xxx.c:00: warning: ignoring #pragma GCC diagnostic
with most versions of gcc.

Alternatively we could just use tcc to compile the library
which you get by commenting out the lines
     XCC = $(CC)
near the top of lib/Makefile for i386/x86_84.

Feel free to make such change to mob, if it works.

Thanks,

--- grischka

> Two questions here:
>
> Q1. Should we really call this function with one arg?
>
>  
>
> Q2. If safe, we should make this change to avoid this warning:
>
>  
>
> diff --git a/lib/bcheck.c b/lib/bcheck.c
>
> index 756c539..8a75654 100644
>
> --- a/lib/bcheck.c
>
> +++ b/lib/bcheck.c
>
> @@ -240,6 +240,9 @@ BOUND_PTR_INDIR(16)
>
>      fp = (size_t)__builtin_frame_address(1);\
>
> }
>
> +#pragma GCC diagnostic push
>
> +#pragma GCC diagnostic ignored "-Wframe-address"
>
> +
>
> /* called when entering a function to add all the local regions */
>
> void FASTCALL __bound_local_new(void *p1) 
>
>  {
>
> @@ -273,6 +276,7 @@ void FASTCALL __bound_local_delete(void *p1)
>
>          __bound_delete_region((void *)addr);
>
>      }
>
> }
>
> +#pragma GCC diagnostic pop
>
>  static BoundEntry *__bound_new_page(void)
>
> {
>
>
>
>
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>
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