linux-kernel - [PATCH 3/4] perf/x86_64: get_regs_user: Simplify regs

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Date:	Fri, 10 Apr 2015 15:06:58 +0200
From:	Denys Vlasenko <dvlasenk@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Denys Vlasenko <dvlasenk@...hat.com>, Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>, x86@...nel.org
Subject: [PATCH 3/4] perf/x86_64: get_regs_user: Simplify regs_user->abi setting code

user_64bit_mode(regs) basically checks regs->cs to point to a 64-bit segment.
This check used to be unreliable here because regs->cs was not always correct
in syscalls.

Now regs->cs is always correct: in syscalls, in interrupts, in exceptions.
No need to emply heuristics here.

Signed-off-by: Denys Vlasenko <dvlasenk@...hat.com>
CC: Jiri Olsa <jolsa@...hat.com>
CC: Peter Zijlstra <a.p.zijlstra@...llo.nl>
CC: Paul Mackerras <paulus@...ba.org>
CC: Ingo Molnar <mingo@...hat.com>
CC: Arnaldo Carvalho de Melo <acme@...nel.org>
CC: x86@...nel.org
CC: linux-kernel@...r.kernel.org
---
 arch/x86/kernel/perf_regs.c | 18 ++----------------
 1 file changed, 2 insertions(+), 16 deletions(-)

diff --git a/arch/x86/kernel/perf_regs.c b/arch/x86/kernel/perf_regs.c
index a8d4e48..8157d39 100644
--- a/arch/x86/kernel/perf_regs.c
+++ b/arch/x86/kernel/perf_regs.c
@@ -166,22 +166,8 @@ void perf_get_regs_user(struct perf_regs *regs_user,
 	 * be careful not to look at any other percpu variables that might
 	 * change during context switches.
 	 */
-	if (IS_ENABLED(CONFIG_IA32_EMULATION) &&
-	    task_thread_info(current)->status & TS_COMPAT) {
-		/* Easy case: we're in a compat syscall. */
-		regs_user->abi = PERF_SAMPLE_REGS_ABI_32;
-	} else if (user_regs->orig_ax != -1) {
-		/*
-		 * We're probably in a 64-bit syscall.
-		 * Warning: this code is severely racy.  At least it's better
-		 * than just blindly copying user_regs.
-		 */
-		regs_user->abi = PERF_SAMPLE_REGS_ABI_64;
-	} else {
-		/* We're probably in an interrupt or exception. */
-		regs_user->abi = user_64bit_mode(user_regs) ?
-			PERF_SAMPLE_REGS_ABI_64 : PERF_SAMPLE_REGS_ABI_32;
-	}
+	regs_user->abi = user_64bit_mode(user_regs) ?
+		PERF_SAMPLE_REGS_ABI_64 : PERF_SAMPLE_REGS_ABI_32;
 
 	regs_user->regs = regs_user_copy;
 }
-- 
1.8.1.4

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