linux-kernel - [RFC PATCH 04/21] x86/hweight: Add stack frame dependency for __arch

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Date:	Fri, 17 Jul 2015 11:47:20 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	Michal Marek <mmarek@...e.cz>,
	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Pedro Alves <palves@...hat.com>, x86@...nel.org,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH 04/21] x86/hweight: Add stack frame dependency for __arch_hweight*()

If __arch_hweight32() or __arch_hweight64() is inlined at the beginning
of a function, gcc can insert the call instruction before setting up a
stack frame, which breaks frame pointer convention if
CONFIG_FRAME_POINTER is enabled and can result in a bad stack trace.

Force a stack frame to be created if CONFIG_FRAME_POINTER is enabled by
listing the stack pointer as an output operand for the inline asm
statement.

Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 arch/x86/include/asm/arch_hweight.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/arch_hweight.h b/arch/x86/include/asm/arch_hweight.h
index 9686c3d..e438a0d 100644
--- a/arch/x86/include/asm/arch_hweight.h
+++ b/arch/x86/include/asm/arch_hweight.h
@@ -23,10 +23,11 @@
  */
 static inline unsigned int __arch_hweight32(unsigned int w)
 {
+	register void *__sp asm("esp");
 	unsigned int res = 0;
 
 	asm (ALTERNATIVE("call __sw_hweight32", POPCNT32, X86_FEATURE_POPCNT)
-		     : "="REG_OUT (res)
+		     : "="REG_OUT (res), "+r" (__sp)
 		     : REG_IN (w));
 
 	return res;
@@ -44,6 +45,7 @@ static inline unsigned int __arch_hweight8(unsigned int w)
 
 static inline unsigned long __arch_hweight64(__u64 w)
 {
+	register void __maybe_unused *__sp asm("rsp");
 	unsigned long res = 0;
 
 #ifdef CONFIG_X86_32
@@ -51,7 +53,7 @@ static inline unsigned long __arch_hweight64(__u64 w)
 		__arch_hweight32((u32)(w >> 32));
 #else
 	asm (ALTERNATIVE("call __sw_hweight64", POPCNT64, X86_FEATURE_POPCNT)
-		     : "="REG_OUT (res)
+		     : "="REG_OUT (res), "+r" (__sp)
 		     : REG_IN (w));
 #endif /* CONFIG_X86_32 */
 
-- 
2.1.0

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