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author | Masahiro Yamada <yamada.masahiro@socionext.com> | 2018-08-26 03:16:29 +0900 |
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committer | Kees Cook <keescook@chromium.org> | 2018-10-11 08:17:50 -0700 |
commit | 81b45683487a51b0f4d3b29d37f20d6d078544e4 (patch) | |
tree | 96bb8fc0be10e5436b7c16a518a70dcfcf6a82ce /scripts/Makefile.extrawarn | |
parent | 57361846b52bc686112da6ca5368d11210796804 (diff) | |
download | linux-81b45683487a51b0f4d3b29d37f20d6d078544e4.tar.bz2 |
compiler.h: give up __compiletime_assert_fallback()
__compiletime_assert_fallback() is supposed to stop building earlier
by using the negative-array-size method in case the compiler does not
support "error" attribute, but has never worked like that.
You can simply try:
BUILD_BUG_ON(1);
GCC immediately terminates the build, but Clang does not report
anything because Clang does not support the "error" attribute now.
It will later fail at link time, but __compiletime_assert_fallback()
is not working at least.
The root cause is commit 1d6a0d19c855 ("bug.h: prevent double evaluation
of `condition' in BUILD_BUG_ON"). Prior to that commit, BUILD_BUG_ON()
was checked by the negative-array-size method *and* the link-time trick.
Since that commit, the negative-array-size is not effective because
'__cond' is no longer constant. As the comment in <linux/build_bug.h>
says, GCC (and Clang as well) only emits the error for obvious cases.
When '__cond' is a variable,
((void)sizeof(char[1 - 2 * __cond]))
... is not obvious for the compiler to know the array size is negative.
Reverting that commit would break BUILD_BUG() because negative-size-array
is evaluated before the code is optimized out.
Let's give up __compiletime_assert_fallback(). This commit does not
change the current behavior since it just rips off the useless code.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>
Diffstat (limited to 'scripts/Makefile.extrawarn')
0 files changed, 0 insertions, 0 deletions