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>
---
 BaseTools/Source/C/Makefiles/header.makefile | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/BaseTools/Source/C/Makefiles/header.makefile b/BaseTools/Source/C/Makefiles/header.makefile
index 550f8b35bce2..065a998bf5de 100644
--- a/BaseTools/Source/C/Makefiles/header.makefile
+++ b/BaseTools/Source/C/Makefiles/header.makefile
@@ -71,9 +71,9 @@ INCLUDE = $(TOOL_INCLUDE) -I $(MAKEROOT) -I $(MAKEROOT)/Include/Common -I $(MAKE
 BUILD_CPPFLAGS = $(INCLUDE) -O2
 ifeq ($(DARWIN),Darwin)
 # assume clang or clang compatible flags on OS X
-BUILD_CFLAGS = -MD -fshort-wchar -fno-strict-aliasing -Wall -Werror -Wno-deprecated-declarations -Wno-stringop-truncation -Wno-self-assign -Wno-unused-result -nostdlib -c -g
+BUILD_CFLAGS = -MD -fshort-wchar -fno-strict-aliasing -Wall -Werror -Wno-deprecated-declarations -Wno-stringop-truncation -Wno-restrict -Wno-self-assign -Wno-unused-result -nostdlib -c -g
 else
-BUILD_CFLAGS = -MD -fshort-wchar -fno-strict-aliasing -Wall -Werror -Wno-deprecated-declarations -Wno-stringop-truncation -Wno-unused-result -nostdlib -c -g
+BUILD_CFLAGS = -MD -fshort-wchar -fno-strict-aliasing -Wall -Werror -Wno-deprecated-declarations -Wno-stringop-truncation -Wno-restrict -Wno-unused-result -nostdlib -c -g
 endif
 BUILD_LFLAGS =
 BUILD_CXXFLAGS = -Wno-unused-result
-- 
2.14.1.3.gb7cf6e02401b


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