From: Jisheng Zhang jszhang@kernel.org
[ Upstream commit 50f4dd657a0fcf90aa8da8dc2794a8100ff4c37c ]
Even after commit 89fd4a1df829 ("riscv: jump_label: mark arguments as const to satisfy asm constraints"), building with CC_OPTIMIZE_FOR_SIZE + LLVM=1 can reproduce below build error:
CC arch/riscv/kernel/vdso/vgettimeofday.o In file included from <built-in>:4: In file included from lib/vdso/gettimeofday.c:5: In file included from include/vdso/datapage.h:17: In file included from include/vdso/processor.h:10: In file included from arch/riscv/include/asm/vdso/processor.h:7: In file included from include/linux/jump_label.h:112: arch/riscv/include/asm/jump_label.h:42:3: error: invalid operand for inline asm constraint 'i' " .option push \n\t" ^ 1 error generated.
I think the problem is when "-Os" is passed as CFLAGS, it's removed by "CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os" which is introduced in commit e05d57dcb8c7 ("riscv: Fixup __vdso_gettimeofday broke dynamic ftrace"), thus no optimization at all for vgettimeofday.c arm64 does remove "-Os" as well, but it forces "-O2" after removing "-Os".
I compared the generated vgettimeofday.o with "-O2" and "-Os", I think no big performance difference. So let's tell the kbuild not to remove "-Os" rather than follow arm64 style.
vdso related performance can be improved a lot when building kernel with CC_OPTIMIZE_FOR_SIZE after this commit, ("-Os" VS no optimization)
Fixes: e05d57dcb8c7 ("riscv: Fixup __vdso_gettimeofday broke dynamic ftrace") Signed-off-by: Jisheng Zhang jszhang@kernel.org Tested-by: Conor Dooley conor.dooley@microchip.com Link: https://lore.kernel.org/r/20221031182943.2453-1-jszhang@kernel.org Signed-off-by: Palmer Dabbelt palmer@rivosinc.com Signed-off-by: Sasha Levin sashal@kernel.org --- arch/riscv/kernel/vdso/Makefile | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile index 24d936c147cd..926ab3960f9e 100644 --- a/arch/riscv/kernel/vdso/Makefile +++ b/arch/riscv/kernel/vdso/Makefile @@ -30,7 +30,7 @@ obj-y += vdso.o vdso-syms.o CPPFLAGS_vdso.lds += -P -C -U$(ARCH)
# Disable -pg to prevent insert call site -CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os +CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE)
# Disable profiling and instrumentation for VDSO code GCOV_PROFILE := n