On 10/15/2015 12:18 PM, Stephen Rothwell wrote: > Hi Andrey, > > On Tue, 13 Oct 2015 18:28:07 +0300 Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> wrote: >> >> Some code may perform racy by design memory reads. This could be harmless, >> yet such code may produce KASAN warnings. >> >> To hide such accesses from KASAN this patch introduces READ_ONCE_NOCHECK() >> macro. KASAN will not check the memory accessed by READ_ONCE_NOCHECK(). >> >> This patch creates __read_once_size_nocheck() a clone of >> __read_once_size_check() (renamed __read_once_size()). >> The only difference between them is 'no_sanitized_address' attribute >> appended to '*_nocheck' function. This attribute tells the compiler that >> instrumentation of memory accesses should not be applied to that function. >> We declare it as static '__maybe_unsed' because GCC is not capable to >> inline such function: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67368 >> >> With KASAN=n READ_ONCE_NOCHECK() is just a clone of READ_ONCE(). >> >> Signed-off-by: Andrey Ryabinin <aryabinin@xxxxxxxxxxxxx> >> --- >> include/linux/compiler-gcc.h | 13 ++++++++++ >> include/linux/compiler.h | 60 ++++++++++++++++++++++++++++++++++---------- >> 2 files changed, 60 insertions(+), 13 deletions(-) > > I am pretty sure that this patch is causing quite a bit of compile > breakage in linux-next today. During the day I compile with gcc 4.9.0 > and did not see any problems with c86_64 allmodconfig, or i386 > defconfig etc, but overnight we compile with older compilers (gcc 4.6.3 > in particular) and are getting quite a few errors: > Looks like that older GCC doesn't like __alias (or combination of static __always_inline __alias). It creates outline and unused copy of __read_once_size_check() function in the object file. Should be easy to work around this. > From an i386 allnoconfig build: > > arch/x86/entry/vdso/vdso32.so.dbg: undefined symbols found > /home/kisskb/slave/src/arch/x86/entry/vdso/Makefile:154: recipe for target 'arch/x86/entry/vdso/vdso32.so.dbg' failed > > From an x86_64 allnoconfig build: > > arch/x86/entry/vdso/vclock_gettime.o: In function `__read_once_size_check': > vclock_gettime.c:(.text+0x5f): undefined reference to `memcpy' > arch/x86/entry/vdso/vgetcpu.o: In function `__read_once_size_check': > vgetcpu.c:(.text+0x2f): undefined reference to `memcpy' > > and several others ... > -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
