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From: Victor Kamensky <kamensky@cisco.com>
To: linux-mips@vger.kernel.org
Cc: Ralf Baechle <ralf@linux-mips.org>,
	Paul Burton <paulburton@kernel.org>,
	James Hogan <jhogan@kernel.org>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	bruce.ashfield@gmail.com, richard.purdie@linuxfoundation.org
Subject: [PATCH 1/2] mips: vdso: fix 'jalr t9' crash in vdso code
Date: Mon,  3 Feb 2020 15:31:32 -0800	[thread overview]
Message-ID: <20200203233133.38613-2-kamensky@cisco.com> (raw)
In-Reply-To: <20200203233133.38613-1-kamensky@cisco.com>

Observed that when kernel is built with Yocto mips64-poky-linux-gcc,
and mips64-poky-linux-gnun32-gcc toolchain, resulting vdso contains
'jalr t9' instructions in its code and since in vdso case nobody
sets GOT table code crashes when instruction reached. On other hand
observed that when kernel is built mips-poky-linux-gcc toolchain, the
same 'jalr t9' instruction are replaced with PC relative function
calls using 'bal' instructions.

The difference boils down to -mrelax-pic-calls and -mexplicit-relocs
gcc options that gets different default values depending on gcc
target triplets and corresponding binutils. -mrelax-pic-calls got
enabled by default only in mips-poky-linux-gcc case. MIPS binuitls
ld relies on R_MIPS_JALR relocation to convert 'jalr t9' into 'bal'
and such relocation is generated only if -mrelax-pic-calls option
is on.

Solution call out -mrelax-pic-calls and -mexplicit-relocs options
explicitily while compiling MIPS vdso code. That would get correct
and consistent between different toolchains behaviour.

Reported-by: Bruce Ashfield <bruce.ashfield@gmail.com>
Signed-off-by: Victor Kamensky <kamensky@cisco.com>
---
 arch/mips/vdso/Makefile | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
index b2a2e032dc99..ec6c5c645edd 100644
--- a/arch/mips/vdso/Makefile
+++ b/arch/mips/vdso/Makefile
@@ -35,7 +35,9 @@ cflags-vdso := $(ccflags-vdso) \
 	-O3 -g -fPIC -fno-strict-aliasing -fno-common -fno-builtin -G 0 \
 	-fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \
 	$(call cc-option, -fno-asynchronous-unwind-tables) \
-	$(call cc-option, -fno-stack-protector)
+	$(call cc-option, -fno-stack-protector) \
+	$(call cc-option, -mrelax-pic-calls) \
+	$(call cc-option, -mexplicit-relocs)
 aflags-vdso := $(ccflags-vdso) \
 	-D__ASSEMBLY__ -Wa,-gdwarf-2
 
-- 
2.21.1


  reply	other threads:[~2020-02-03 23:38 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-03 23:31 [PATCH 0/2] mips: vdso: fix 'jalr t9' crash in vdso code Victor Kamensky
2020-02-03 23:31 ` Victor Kamensky [this message]
2020-02-10 19:14   ` [PATCH 1/2] " Paul Burton
2020-02-10 19:33     ` Paul Burton
2020-02-10 21:12       ` Victor Kamensky (kamensky)
2020-02-10 22:52         ` Paul Burton
2020-02-10 23:11           ` Paul Burton
2020-02-11 16:55           ` Victor Kamensky (kamensky)
2020-02-11 17:01             ` Paul Burton
2020-02-17 13:38               ` Maciej W. Rozycki
2020-02-03 23:31 ` [PATCH 2/2] mips: vdso: add build time check that no 'jalr t9' calls left Victor Kamensky

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