On Sun, Dec 16, 2018 at 07:33:11PM +0100, Arnd Bergmann wrote: > Hi Josh, > > In randconfig tests with gcc-8.1, I get this warning every > few hundred builds, tried it on both next/master and 4.19.y-stable: > > kernel/trace/trace_selftest_dynamic.o: warning: objtool: > trace_selftest_dynamic_test_func()+0x5: call without frame pointer > save/setup > kernel/trace/trace_selftest_dynamic.o: warning: objtool: > trace_selftest_dynamic_test_func2()+0x5: call without frame pointer > save/setup > > $ objdump -dr > build/x86/0x90C84554_defconfig/kernel/trace/trace_selftest_dynamic.o > > build/x86/0x90C84554_defconfig/kernel/trace/trace_selftest_dynamic.o: > file format elf64-x86-64 > > Disassembly of section .text: > > 0000000000000000 <trace_selftest_dynamic_test_func>: > 0: e8 00 00 00 00 callq 5 > <trace_selftest_dynamic_test_func+0x5> > 1: R_X86_64_PC32 __fentry__-0x4 > 5: e8 00 00 00 00 callq a > <trace_selftest_dynamic_test_func+0xa> > 6: R_X86_64_PC32 __sanitizer_cov_trace_pc-0x4 > a: 31 c0 xor %eax,%eax > c: c3 retq > d: 0f 1f 00 nopl (%rax) > > 0000000000000010 <trace_selftest_dynamic_test_func2>: > 10: e8 00 00 00 00 callq 15 > <trace_selftest_dynamic_test_func2+0x5> > 11: R_X86_64_PC32 __fentry__-0x4 > 15: e8 00 00 00 00 callq 1a > <trace_selftest_dynamic_test_func2+0xa> > 16: R_X86_64_PC32 __sanitizer_cov_trace_pc-0x4 > 1a: 31 c0 xor %eax,%eax > 1c: c3 retq > > I found this reported in > http://kisskb.ellerman.id.au/kisskb/buildresult/13499139/, but could > not find an existing fix or analysis.
Thanks for reporting this Arnd. The problem is that, for some reason, __noclone is preventing GCC from creating frame pointers for these functions. Miroslav said that __noclone is not recommended by GCC developers, and that __used can be used instead for the same purpose: https://lkml.kernel.org/r/alpine.lsu.2.21.1812171256390.3...@pobox.suse.cz Andi, is __noclone really needed here, since the functions aren't static? Or does LTO cause them to be treated like static functions? Or if it is really needed, would __used be sufficient instead? noinline __noclone int DYN_FTRACE_TEST_NAME(void) { /* used to call mcount */ return 0; } noinline __noclone int DYN_FTRACE_TEST_NAME2(void) { /* used to call mcount */ return 0; } -- Josh
