On Fri, Aug 30, 2019 at 11:05:31PM -0700, Nathan Chancellor 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 with '-pg' because the > calling convention was not correct. Always build with '-meabi gnu' > when using clang but ensure that '-pg' (which is added with > CONFIG_FUNCTION_TRACER and its prereq CONFIG_HAVE_FUNCTION_TRACER) > cannot be added with it unless this is fixed (which means using > clang 10.0.0 and newer). > > 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 > Reviewed-by: Nick Desaulniers <ndesaulni...@google.com> > Reviewed-by: Stefan Agner <ste...@agner.ch> > Signed-off-by: Nathan Chancellor <natechancel...@gmail.com>
Reviewed-by: Matthias Kaehlcke <m...@chromium.org>
