| Message ID | 1542349141-7229-1-git-send-email-yamada.masahiro@socionext.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [1/2] build_bug.h: remove negative-array fallback for BUILD_BUG_ON() | expand |
On Fri, Nov 16, 2018 at 12:19 AM, Masahiro Yamada <yamada.masahiro@socionext.com> wrote: > The kernel can only be compiled with an optimization option (-O2, -Os, > or the currently proposed -Og). Hence, __OPTIMIZE__ is always defined > in the kernel source. > > A fallback for -O0 case is just hypothetical and pointless. Moreover, > commit 0bb95f80a38f ("Makefile: Globally enable VLA warning") enabled > -Wvla warning. The use of variable length arrays is banned. > > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> Acked-by: Kees Cook <keescook@chromium.org> -Kees > --- > > include/linux/build_bug.h | 14 -------------- > 1 file changed, 14 deletions(-) > > diff --git a/include/linux/build_bug.h b/include/linux/build_bug.h > index 43d1fd5..d415c64 100644 > --- a/include/linux/build_bug.h > +++ b/include/linux/build_bug.h > @@ -51,23 +51,9 @@ > * If you have some code which relies on certain constants being equal, or > * some other compile-time-evaluated condition, you should use BUILD_BUG_ON to > * detect if someone changes it. > - * > - * The implementation uses gcc's reluctance to create a negative array, but gcc > - * (as of 4.4) only emits that error for obvious cases (e.g. not arguments to > - * inline functions). Luckily, in 4.3 they added the "error" function > - * attribute just for this type of case. Thus, we use a negative sized array > - * (should always create an error on gcc versions older than 4.4) and then call > - * an undefined function with the error attribute (should always create an > - * error on gcc 4.3 and later). If for some reason, neither creates a > - * compile-time error, we'll still have a link-time error, which is harder to > - * track down. > */ > -#ifndef __OPTIMIZE__ > -#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)])) > -#else > #define BUILD_BUG_ON(condition) \ > BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition) > -#endif > > /** > * BUILD_BUG - break compile if used. > -- > 2.7.4 > -- Kees Cook
On Fri, Nov 16, 2018 at 8:01 PM Kees Cook <keescook@chromium.org> wrote: > > On Fri, Nov 16, 2018 at 12:19 AM, Masahiro Yamada > <yamada.masahiro@socionext.com> wrote: > > The kernel can only be compiled with an optimization option (-O2, -Os, > > or the currently proposed -Og). Hence, __OPTIMIZE__ is always defined > > in the kernel source. > > > > A fallback for -O0 case is just hypothetical and pointless. Moreover, > > commit 0bb95f80a38f ("Makefile: Globally enable VLA warning") enabled > > -Wvla warning. The use of variable length arrays is banned. > > > > Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> > > Acked-by: Kees Cook <keescook@chromium.org> Acked-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> Cheers, Miguel
diff --git a/include/linux/build_bug.h b/include/linux/build_bug.h index 43d1fd5..d415c64 100644 --- a/include/linux/build_bug.h +++ b/include/linux/build_bug.h @@ -51,23 +51,9 @@ * If you have some code which relies on certain constants being equal, or * some other compile-time-evaluated condition, you should use BUILD_BUG_ON to * detect if someone changes it. - * - * The implementation uses gcc's reluctance to create a negative array, but gcc - * (as of 4.4) only emits that error for obvious cases (e.g. not arguments to - * inline functions). Luckily, in 4.3 they added the "error" function - * attribute just for this type of case. Thus, we use a negative sized array - * (should always create an error on gcc versions older than 4.4) and then call - * an undefined function with the error attribute (should always create an - * error on gcc 4.3 and later). If for some reason, neither creates a - * compile-time error, we'll still have a link-time error, which is harder to - * track down. */ -#ifndef __OPTIMIZE__ -#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)])) -#else #define BUILD_BUG_ON(condition) \ BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition) -#endif /** * BUILD_BUG - break compile if used.
The kernel can only be compiled with an optimization option (-O2, -Os, or the currently proposed -Og). Hence, __OPTIMIZE__ is always defined in the kernel source. A fallback for -O0 case is just hypothetical and pointless. Moreover, commit 0bb95f80a38f ("Makefile: Globally enable VLA warning") enabled -Wvla warning. The use of variable length arrays is banned. Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com> --- include/linux/build_bug.h | 14 -------------- 1 file changed, 14 deletions(-) -- 2.7.4