Hi Steve, Nicholas, I stumbled across this while working on livepatch self-tests, which like the ftrace self-tests, specify $(CC_FLAGS_FTRACE) to ensure that target functions are indeed trace-able.
On ppc64le, v5.0 fails the self-tests on my machine: % gcc --version gcc (GCC) 8.2.1 20180905 (Red Hat 8.2.1-3) % git checkout v5.0 % grep FTRACE_SELFTEST .config CONFIG_FTRACE_SELFTEST=y After building the kernel, I noticed no mcount sections and of course the self-tests fail as it can't hook functions: % readelf --sections kernel/trace/trace_selftest_dynamic.o | grep mcount (nothing) [ ... snip ... ] [ 126.147892] Testing all events: OK [ 126.390487] WARNING: CPU: 0 PID: 1 at kernel/trace/trace_events.c:3421 event_trace_self_tests_init+0x94/0xf4 [ 126.390498] Modules linked in: [ 126.390510] CPU: 0 PID: 1 Comm: swapper/0 Tainted: G W 5.0.0 #10 [ 126.390520] NIP: c000000000f044d4 LR: c000000000f044cc CTR: c000000000b63d70 [ 126.390530] REGS: c0000001fb183910 TRAP: 0700 Tainted: G W (5.0.0) [ 126.390540] MSR: 8000000002029033 <SF,VEC,EE,ME,IR,DR,RI,LE> CR: 28000222 XER: 20040007 [ 126.390564] CFAR: c00000000025b1f4 IRQMASK: 0 [ 126.390564] GPR00: c000000000f044cc c0000001fb183ba0 c000000001453c00 ffffffffffffffed [ 126.390564] GPR04: 0000000000000000 c0000000017a0aac 000000000000037d c0000001fb142d00 [ 126.390564] GPR08: 0000000000000000 0000000000000001 0000000000000000 0000000000000000 [ 126.390564] GPR12: 0000000000000000 c000000001880000 c000000000010530 0000000000000000 [ 126.390564] GPR16: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 [ 126.390564] GPR20: 0000000000000000 0000000000000000 0000000000000000 0000000000000000 [ 126.390564] GPR24: 0000000000000000 0000000000000000 c000000000eb8908 c000000000f4ea68 [ 126.390564] GPR28: c000000000f4eaa8 0000000000000000 c000000000f04440 c000000000f581a8 [ 126.390662] NIP [c000000000f044d4] event_trace_self_tests_init+0x94/0xf4 [ 126.390672] LR [c000000000f044cc] event_trace_self_tests_init+0x8c/0xf4 [ 126.390682] Call Trace: [ 126.390690] [c0000001fb183ba0] [c000000000f044cc] event_trace_self_tests_init+0x8c/0xf4 (unreliable) [ 126.390705] [c0000001fb183c10] [c000000000010134] do_one_initcall+0x64/0x264 [ 126.390719] [c0000001fb183ce0] [c000000000ed443c] kernel_init_freeable+0x36c/0x470 [ 126.390731] [c0000001fb183db0] [c000000000010554] kernel_init+0x2c/0x148 [ 126.390744] [c0000001fb183e20] [c00000000000b65c] ret_from_kernel_thread+0x5c/0x80 [ 126.390755] Instruction dump: [ 126.390765] 3fe2ffb0 f9284578 3bff3d50 794ad182 0b0a0000 2fa90000 419e0058 3bff0858 [ 126.390789] 7fe3fb78 4b356cc1 60000000 54690ffe <0b090000> 2f830000 409c0018 3c62ff96 [ 126.390814] ---[ end trace b5898e7f7f73e163 ]--- [ 126.390822] Failed to enable function tracer for event tests I git bisected to 6977f95e63b9 ("powerpc: avoid -mno-sched-epilog on GCC 4.9 and newer"). Reverting this change and rebuilding, I could see the mcount sections once again: % readelf --sections kernel/trace/trace_selftest_dynamic.o | grep mcount [ 3] __mcount_loc PROGBITS 0000000000000000 00000060 [ 4] .rela__mcount_loc RELA 0000000000000000 000258c8 Reboot and the self-test now passes. Perhaps this is gcc version specific? I didn't see any other reports, so maybe its specific to my config. If I run make V=1, I can see that gcc is called with '-pg -mprofile-kernel', but then the record_mcount script is skipped. Any ideas? Regards, -- Joe