From: George Guo <[email protected]> arch/loongarch/Makefile uses -fpatchable-function-entry=2 when CONFIG_DYNAMIC_FTRACE is set, but nothing selects FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY, so kbuild falls back to FTRACE_MCOUNT_USE_RECORDMCOUNT and runs recordmcount on every object. The pass is useless here: there are no _mcount calls to find, and the real ftrace sites come from the __patchable_function_entries section anyway.
It is not just wasted time. recordmcount needs a non-weak symbol in each text section, to use as the base of the __mcount_loc relocations it writes (see find_secsym_ndx()). GAS emits a section symbol for every section, so GCC objects always have one. Clang's integrated assembler drops unreferenced section symbols, so a clang object must use the function's own symbol -- but find_secsym_ndx() skips weak symbols. So with -ffunction-sections (which klp-build uses), a __weak function like sched_clock is alone in its section with no usable symbol, and recordmcount fails: Cannot find symbol for section 5: .text.sched_clock. kernel/sched/build_utility.o: failed Select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY like arm64 and riscv do, which disables the recordmcount pass altogether. Reported-by: Joe Lawrence <[email protected]> Suggested-by: Joe Lawrence <[email protected]> Signed-off-by: George Guo <[email protected]> --- arch/loongarch/Kconfig | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig index 1dbf51ba9d6a..a1549003c871 100644 --- a/arch/loongarch/Kconfig +++ b/arch/loongarch/Kconfig @@ -88,6 +88,7 @@ config LOONGARCH select CPU_PM select EDAC_SUPPORT select EFI + select FTRACE_MCOUNT_USE_PATCHABLE_FUNCTION_ENTRY if DYNAMIC_FTRACE select GENERIC_ATOMIC64 if 32BIT select GENERIC_CLOCKEVENTS select GENERIC_CMOS_UPDATE -- 2.25.1
