[tip:x86/asm] perf/x86/64: Simplify regs_user-> abi setting code in get_regs_user()

[tip-bot for Denys Vlasenko]

Commit-ID:  32caa06091cc59651222cdc971dc21eaab36b097
Gitweb:     http://git.kernel.org/tip/32caa06091cc59651222cdc971dc21eaab36b097
Author:     Denys Vlasenko <dvlasenk@xxxxxxxxxx>
AuthorDate: Fri, 10 Apr 2015 15:06:58 +0200
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Sat, 11 Apr 2015 13:08:53 +0200

perf/x86/64: Simplify regs_user->abi setting code in get_regs_user()

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@xxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Link: http://lkml.kernel.org/r/1428671219-29341-3-git-send-email-dvlasenk@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 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;
 }
--
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