Re: [PATCH v2 2/4] Consolidate stdio-lock.h

[Florian Weimer <fweimer@redhat.com>]

* Adhemerval Zanella via Libc-alpha:

> diff --git a/sysdeps/generic/stdio-lock.h b/sysdeps/generic/stdio-lock.h
> index 14cf458bdd..fd61f0b5b7 100644
> --- a/sysdeps/generic/stdio-lock.h
> +++ b/sysdeps/generic/stdio-lock.h
> @@ -45,20 +45,13 @@ __libc_lock_define_recursive (typedef, _IO_lock_t)
>  #define _IO_cleanup_region_end(_doit) \
>    __libc_cleanup_region_end (_doit)
>  
> -#if defined _LIBC && IS_IN (libc)
> -
> -# ifdef __EXCEPTIONS
> -# define _IO_acquire_lock(_fp) \
> +#define _IO_acquire_lock(_fp) \
>    do {									      \
> -    FILE *_IO_acquire_lock_file						      \
> -	__attribute__((cleanup (_IO_acquire_lock_fct)))			      \
> -	= (_fp);							      \
> -    _IO_flockfile (_IO_acquire_lock_file);
> -# else
> -#  define _IO_acquire_lock(_fp) _IO_acquire_lock_needs_exceptions_enabled
> -# endif
> -# define _IO_release_lock(_fp) ; } while (0)
> -
> -#endif
> +    _IO_cleanup_region_start((void (*) (void *)) &_IO_funlockfile, _fp);      \
> +    _IO_flockfile (_fp);
> +#define _IO_release_lock(_fp) \
> +    _IO_funlockfile (_fp);						      \
> +    _IO_cleanup_region_end (0);						      \
> +  } while (0)
>  
>  #endif /* stdio-lock.h */

I think this change replaces unwind tables for -fexceptions builds.  If
GCC can't turn the indirect call to the unlock function into a direct
call, this will result in a loss of hardening due to the additional
indirect function call.

This change may also lose C++ unwinding compatibility for some
fopencookie use cases, I think.

Thanks,
Florian