Messages in this thread | | | From | Nick Desaulniers <> | Date | Thu, 29 Aug 2019 10:55:28 -0700 | Subject | Re: [PATCH] ARM: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer |
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On Wed, Aug 28, 2019 at 11:27 PM Nathan Chancellor <natechancellor@gmail.com> wrote: > > Currently, multi_v7_defconfig + CONFIG_FUNCTION_TRACER fails to build > with clang: > > arm-linux-gnueabi-ld: kernel/softirq.o: in function `_local_bh_enable': > softirq.c:(.text+0x504): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o: in function `__local_bh_enable_ip': > softirq.c:(.text+0x58c): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o: in function `do_softirq': > softirq.c:(.text+0x6c8): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_enter': > softirq.c:(.text+0x75c): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o: in function `irq_exit': > softirq.c:(.text+0x840): undefined reference to `mcount' > arm-linux-gnueabi-ld: kernel/softirq.o:softirq.c:(.text+0xa50): more undefined references to `mcount' follow > > clang can emit a working mcount symbol, __gnu_mcount_nc, when > '-meabi gnu' is passed to it. Until r369147 in LLVM, this was > broken and caused the kernel not to boot because the calling > convention was not correct. Now that it is fixed, add this to > the command line when clang is 10.0.0 or newer so everything > works properly. > > Link: https://github.com/ClangBuiltLinux/linux/issues/35 > Link: https://bugs.llvm.org/show_bug.cgi?id=33845 > Link: https://github.com/llvm/llvm-project/commit/16fa8b09702378bacfa3d07081afe6b353b99e60 > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> > --- > arch/arm/Makefile | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/arch/arm/Makefile b/arch/arm/Makefile > index c3624ca6c0bc..7b5a26a866fc 100644 > --- a/arch/arm/Makefile > +++ b/arch/arm/Makefile > @@ -112,6 +112,12 @@ ifeq ($(CONFIG_ARM_UNWIND),y) > CFLAGS_ABI +=-funwind-tables > endif > > +ifeq ($(CONFIG_CC_IS_CLANG),y) > +ifeq ($(shell test $(CONFIG_CLANG_VERSION) -ge 100000; echo $$?),0) > +CFLAGS_ABI +=-meabi gnu > +endif > +endif > +
Thanks for the patch! I think this is one of the final issues w/ 32b ARM configs when building w/ Clang.
I'm not super enthused about the version check. The flag is indeed not recognized by GCC, but I think it would actually be more concise with $(cc-option) and no compiler or version check.
Further, I think that the working __gnu_mcount_nc in Clang would better be represented as marking the arch/arm/KConfig option for CONFIG_FUNCTION_TRACER for dependent on a version of Clang greater than or equal to Clang 10, not conditionally adding this flag. (We should always add the flag when supported, IMO. __gnu_mcount_nc's calling convention being broken is orthogonal to the choice of __gnu_mcount_nc vs mcount, and it's the former's that should be checked, not the latter as in this patch.
> # Accept old syntax despite ".syntax unified" > AFLAGS_NOWARN :=$(call as-option,-Wa$(comma)-mno-warn-deprecated,-Wa$(comma)-W) > > -- > 2.23.0 >
-- Thanks, ~Nick Desaulniers
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