linux-kernel - [PATCH] arm64: vdso32: force vdso32 to be compiled as -marm

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Date:   Tue, 26 May 2020 10:31:14 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>
Cc:     Nick Desaulniers <ndesaulniers@...gle.com>,
        Stephen Boyd <swboyd@...gle.com>,
        Luis Lozano <llozano@...gle.com>,
        Manoj Gupta <manojgupta@...gle.com>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Nathan Chancellor <natechancellor@...il.com>,
        Naohiro Aota <naohiro.aota@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] arm64: vdso32: force vdso32 to be compiled as -marm

Custom toolchains that modify the default target to -mthumb cannot
compile the arm64 compat vdso32, as
arch/arm64/include/asm/vdso/compat_gettimeofday.h
contains assembly that's invalid in -mthumb.  Force the use of -marm,
always.

Link: https://bugs.chromium.org/p/chromium/issues/detail?id=1084372
Cc: Stephen Boyd <swboyd@...gle.com>
Reported-by: Luis Lozano <llozano@...gle.com>
Tested-by: Manoj Gupta <manojgupta@...gle.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@...gle.com>
---
Surgeon General's Warning: changing the compiler defaults is not
recommended and can lead to spooky bugs that are hard to reproduce
upstream.

 arch/arm64/kernel/vdso32/Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/arm64/kernel/vdso32/Makefile b/arch/arm64/kernel/vdso32/Makefile
index 3964738ebbde..c449a293d81e 100644
--- a/arch/arm64/kernel/vdso32/Makefile
+++ b/arch/arm64/kernel/vdso32/Makefile
@@ -104,6 +104,8 @@ VDSO_CFLAGS += -D__uint128_t='void*'
 # (on GCC 4.8 or older, there is unfortunately no way to silence this warning)
 VDSO_CFLAGS += $(call cc32-disable-warning,shift-count-overflow)
 VDSO_CFLAGS += -Wno-int-to-pointer-cast
+# Force vdso to be compiled in ARM mode, not THUMB.
+VDSO_CFLAGS += -marm
 
 VDSO_AFLAGS := $(VDSO_CAFLAGS)
 VDSO_AFLAGS += -D__ASSEMBLY__
-- 
2.27.0.rc0.183.gde8f92d652-goog