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From: Will Deacon <will@kernel.org>
To: linux-arm-kernel@lists.infradead.org
Cc: Will Deacon <will@kernel.org>,
	Tamas Zsoldos <tamas.zsoldos@arm.com>,
	Mark Brown <broonie@kernel.org>,
	kernel-team@android.com, Dave Martin <dave.martin@arm.com>,
	Daniel Kiss <daniel.kiss@arm.com>
Subject: [PATCH 3/3] arm64: vdso: Fix CFI directives in sigreturn trampoline
Date: Tue, 19 May 2020 13:18:18 +0100	[thread overview]
Message-ID: <20200519121818.14511-4-will@kernel.org> (raw)
In-Reply-To: <20200519121818.14511-1-will@kernel.org>

Daniel reports that the .cfi_startproc is misplaced for the sigreturn
trampoline, which causes LLVM's unwinder to misbehave:

  | I run into this with LLVM’s unwinder.
  | This combination was always broken.

This prompted Dave to realise that our CFI directives are contradictory,
as we specify both .cfi_signal_frame *and* .cfi_def_cfa, with the latter
unconditionally identifying the interrupted context as opposed to the
values in the sigcontext.

Rework the CFI directives so that we only use .cfi_signal_frame, and
include the "mysterious NOP" as part of the .cfi_{start,end}proc block.

Cc: Tamas Zsoldos <tamas.zsoldos@arm.com>
Reported-by: Dave Martin <dave.martin@arm.com>
Reported-by: Daniel Kiss <daniel.kiss@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>
---
 arch/arm64/kernel/vdso/sigreturn.S | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/vdso/sigreturn.S b/arch/arm64/kernel/vdso/sigreturn.S
index 7853fa9692f6..28b33f7d0604 100644
--- a/arch/arm64/kernel/vdso/sigreturn.S
+++ b/arch/arm64/kernel/vdso/sigreturn.S
@@ -14,6 +14,9 @@
 
 	.text
 
+/* Ensure that the mysterious NOP can be associated with a function. */
+	.cfi_startproc
+	.cfi_signal_frame
 /*
  * This mysterious NOP is required for some unwinders that subtract one from
  * the return address in order to identify the calling function.
@@ -28,11 +31,6 @@
  * is perfectly fine.
  */
 SYM_START(__kernel_rt_sigreturn, SYM_L_GLOBAL, SYM_A_ALIGN)
-	.cfi_startproc
-	.cfi_signal_frame
-	.cfi_def_cfa	x29, 0
-	.cfi_offset	x29, 0 * 8
-	.cfi_offset	x30, 1 * 8
 	mov	x8, #__NR_rt_sigreturn
 	svc	#0
 	.cfi_endproc
-- 
2.26.2.761.g0e0b3e54be-goog


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  parent reply	other threads:[~2020-05-19 12:19 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-19 12:18 [PATCH 0/3] arm64 sigreturn unwinding fixes Will Deacon
2020-05-19 12:18 ` [PATCH 1/3] arm64: vdso: Don't prefix sigreturn trampoline with a BTI C instruction Will Deacon
2020-05-19 12:38   ` Mark Brown
2020-05-19 13:25     ` Dave Martin
2020-05-19 14:35       ` Mark Brown
2020-05-19 14:55         ` Dave Martin
2020-05-19 15:42           ` Mark Brown
2020-05-20  9:48             ` Dave Martin
2020-05-20 10:46               ` Mark Brown
2020-05-20 11:08                 ` Dave Martin
2020-05-19 15:26     ` Will Deacon
2020-05-19 13:21   ` Dave Martin
2020-05-19 13:29     ` Will Deacon
2020-05-19 12:18 ` [PATCH 2/3] arm64: vdso: Add a comment to justify the mysterious NOP in sigreturn Will Deacon
2020-05-19 13:26   ` Dave Martin
2020-05-19 12:18 ` Will Deacon [this message]
2020-05-19 13:09   ` [PATCH 3/3] arm64: vdso: Fix CFI directives in sigreturn trampoline Dave P Martin
2020-05-19 13:39     ` Will Deacon
2020-05-19 13:55       ` Dave Martin
2020-05-19 15:24         ` Will Deacon
2020-05-19 15:30         ` Daniel Kiss
2020-05-19 15:55           ` Will Deacon

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