When building using GCC 4.7 or older, -ffunction-sections & the -pg flag used by ftrace are incompatible. This causes warnings or build failures (where -Werror applies) such as the following:
arch/mips/generic/init.c: error: -ffunction-sections disabled; it makes profiling impossible
This used to be taken into account by the ordering of calls to cc-option from within the top-level Makefile, which was introduced by commit 90ad4052e85c ("kbuild: avoid conflict between -ffunction-sections and -pg on gcc-4.7"). Unfortunately this was broken when the CONFIG_LD_DEAD_CODE_DATA_ELIMINATION cc-option check was moved to Kconfig in commit e85d1d65cd8a ("kbuild: test dead code/data elimination support in Kconfig"), because the flags used by this check no longer include -pg.
Fix this by not allowing CONFIG_LD_DEAD_CODE_DATA_ELIMINATION to be enabled at the same time as ftrace/CONFIG_FUNCTION_TRACER when building using GCC 4.7 or older.
Signed-off-by: Paul Burton paul.burton@mips.com Fixes: e85d1d65cd8a ("kbuild: test dead code/data elimination support in Kconfig") Reported-by: Geert Uytterhoeven geert@linux-m68k.org Cc: Masahiro Yamada yamada.masahiro@socionext.com Cc: Nicholas Piggin npiggin@gmail.com Cc: stable@vger.kernel.org # v4.19+ --- init/Kconfig | 1 + 1 file changed, 1 insertion(+)
diff --git a/init/Kconfig b/init/Kconfig index d47cb77a220e..c787f782148d 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1124,6 +1124,7 @@ config LD_DEAD_CODE_DATA_ELIMINATION bool "Dead code and data elimination (EXPERIMENTAL)" depends on HAVE_LD_DEAD_CODE_DATA_ELIMINATION depends on EXPERT + depends on !FUNCTION_TRACER || !CC_IS_GCC || GCC_VERSION >= 40800 depends on $(cc-option,-ffunction-sections -fdata-sections) depends on $(ld-option,--gc-sections) help