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

[Christian Jullien]

Ok I fixed it taking care of gcc version.

http://repo.or.cz/tinycc.git/commitdiff/ed99f3608df3d6dd4c8c7d52d608a8212203
dfe4

Looks good now on Fedora 25.

C.

-----Original Message-----
From: Tinycc-devel [mailto:address@hidden
On Behalf Of grischka
Sent: mardi 29 novembre 2016 12:20
To: address@hidden
Subject: Re: [Tinycc-devel] '__builtin_frame_address' warning about
suspicious use of this call

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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