gcc-8 (which is part of Fedora 28) enables the new warning
"-Wrestrict" in "-Wall". This warning is documented in detail
at <https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html>; the
introduction says
> Warn when an object referenced by a restrict-qualified parameter (or, in
> C++, a __restrict-qualified parameter) is aliased by another argument,
> or when copies between such objects overlap.
It breaks the BaseTools build (in the Brotli compression library) with:
> In function 'ProcessCommandsInternal',
> inlined from 'ProcessCommands' at dec/decode.c:1828:10:
> dec/decode.c:1781:9: error: 'memcpy' accessing between 17 and
2147483631
> bytes at offsets 16 and 16 overlaps between 17 and
2147483631 bytes at
> offset 16 [-Werror=restrict]
> memcpy(copy_dst + 16, copy_src + 16, (size_t)(i - 16));
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> In function 'ProcessCommandsInternal',
> inlined from 'SafeProcessCommands' at dec/decode.c:1833:10:
> dec/decode.c:1781:9: error: 'memcpy' accessing between 17 and
2147483631
> bytes at offsets 16 and 16 overlaps between 17 and
2147483631 bytes at
> offset 16 [-Werror=restrict]
> memcpy(copy_dst + 16, copy_src + 16, (size_t)(i - 16));
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Paolo Bonzini <pbonzini@redhat.com> analyzed the Brotli source in detail,
and concluded that the warning is a false positive:
> This seems safe to me, because it's preceded by:
>
> uint8_t* copy_dst = &s->ringbuffer[pos];
> uint8_t* copy_src = &s->ringbuffer[src_start];
> int dst_end = pos + i;
> int src_end = src_start + i;
> if (src_end > pos && dst_end > src_start) {
> /* Regions intersect. */
> goto CommandPostWrapCopy;
> }
>
> If [src_start, src_start + i) and [pos, pos + i) don't intersect, then
> neither do [src_start + 16, src_start + i) and [pos + 16, pos + i).
>
> The if seems okay:
>
> (src_start + i > pos && pos + i > src_start)
>
> which can be rewritten to:
>
> (pos < src_start + i && src_start < pos + i)
>
> Then the numbers are in one of these two orders:
>
> pos <= src_start < pos + i <= src_start + i
> src_start <= pos < src_start + i <= pos + i
>
> These two would be allowed by the "if", but they can only happen if pos
> == src_start so they degenerate to the same two orders above:
>
> pos <= src_start < src_start + i <= pos + i
> src_start <= pos < pos + i <= src_start + i
>
> So it is a false positive in GCC.
Disable the warning for now.
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Cole Robinson <crobinso@redhat.com>
Cc: Liming Gao <liming.gao@intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Reported-by: Cole Robinson <crobinso@redhat.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
projects / mirror_edk2.git / commitdiff