| From 97e026dff6906b0f61449315386c7ad3025d48e3 Mon Sep 17 00:00:00 2001 |
| From: Sasha Levin <sashal@kernel.org> |
| Date: Tue, 15 Feb 2022 22:28:58 +1100 |
| Subject: powerpc/Makefile: Don't pass -mcpu=powerpc64 when building 32-bit |
| |
| From: Michael Ellerman <mpe@ellerman.id.au> |
| |
| [ Upstream commit 2863dd2db23e0407f6c50b8ba5c0e55abef894f1 ] |
| |
| When CONFIG_GENERIC_CPU=y (true for all our defconfigs) we pass |
| -mcpu=powerpc64 to the compiler, even when we're building a 32-bit |
| kernel. |
| |
| This happens because we have an ifdef CONFIG_PPC_BOOK3S_64/else block in |
| the Makefile that was written before 32-bit supported GENERIC_CPU. Prior |
| to that the else block only applied to 64-bit Book3E. |
| |
| The GCC man page says -mcpu=powerpc64 "[specifies] a pure ... 64-bit big |
| endian PowerPC ... architecture machine [type], with an appropriate, |
| generic processor model assumed for scheduling purposes." |
| |
| It's unclear how that interacts with -m32, which we are also passing, |
| although obviously -m32 is taking precedence in some sense, as the |
| 32-bit kernel only contains 32-bit instructions. |
| |
| This was noticed by inspection, not via any bug reports, but it does |
| affect code generation. Comparing before/after code generation, there |
| are some changes to instruction scheduling, and the after case (with |
| -mcpu=powerpc64 removed) the compiler seems more keen to use r8. |
| |
| Fix it by making the else case only apply to Book3E 64, which excludes |
| 32-bit. |
| |
| Fixes: 0e00a8c9fd92 ("powerpc: Allow CPU selection also on PPC32") |
| Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> |
| Link: https://lore.kernel.org/r/20220215112858.304779-1-mpe@ellerman.id.au |
| Signed-off-by: Sasha Levin <sashal@kernel.org> |
| --- |
| arch/powerpc/Makefile | 2 +- |
| 1 file changed, 1 insertion(+), 1 deletion(-) |
| |
| diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile |
| index e02568f17334..3d2e74ebc014 100644 |
| --- a/arch/powerpc/Makefile |
| +++ b/arch/powerpc/Makefile |
| @@ -171,7 +171,7 @@ else |
| CFLAGS-$(CONFIG_GENERIC_CPU) += $(call cc-option,-mtune=power7,$(call cc-option,-mtune=power5)) |
| CFLAGS-$(CONFIG_GENERIC_CPU) += $(call cc-option,-mcpu=power5,-mcpu=power4) |
| endif |
| -else |
| +else ifdef CONFIG_PPC_BOOK3E_64 |
| CFLAGS-$(CONFIG_GENERIC_CPU) += -mcpu=powerpc64 |
| endif |
| |
| -- |
| 2.34.1 |
| |
