Messages in this thread | | | Date | Thu, 29 Aug 2019 22:21:25 +0200 | From | Stefan Agner <> | Subject | Re: [PATCH] ARM: Emit __gnu_mcount_nc when using Clang 10.0.0 or newer |
| |
On 2019-08-29 21:34, Nathan Chancellor wrote: > On Thu, Aug 29, 2019 at 10:55:28AM -0700, Nick Desaulniers wrote: >> 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. > > I will test with or without CONFIG_AEABI like Matthias asked and I will > implement your Kconfig suggestion if it passes all of my tests. The > reason that I did it this way is because I didn't want a user to end up > with a non-booting kernel since -meabi gnu works with older versions of > clang at build time, the issue happens at boot time but the Kconfig > suggestion + cc-option should fix that.
I agree with Nathan here, I'd rather prefer the build system to fail building rather than runtime error.
If we decide we want to have it building despite it not building a functional kernel, we should at least add a #warning...
-- Stefan
> > I should have a v2 out this evening. > > Cheers, > Nathan
| |