[PATCH 1/4] perf/x86_64: get_regs_user: Do not guess user_regs->cs,ss,sp

[PATCH 1/4] perf/x86_64: get_regs_user: Do not guess user_regs->cs,ss,sp

[Denys Vlasenko]

After recent changes to syscall entry points, user_regs->{cs,ss,sp}
are always correct. (They used to be undefined while in syscalls).

We can report them reliably, without guessing.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
CC: Jiri Olsa <jolsa@redhat.com>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Paul Mackerras <paulus@samba.org>
CC: Ingo Molnar <mingo@redhat.com>
CC: Arnaldo Carvalho de Melo <acme@kernel.org>
CC: x86@kernel.org
CC: linux-kernel@vger.kernel.org
---
 arch/x86/kernel/perf_regs.c | 23 +++++++++--------------
 1 file changed, 9 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kernel/perf_regs.c b/arch/x86/kernel/perf_regs.c
index 02a8720..7ab198a 100644
--- a/arch/x86/kernel/perf_regs.c
+++ b/arch/x86/kernel/perf_regs.c
@@ -131,8 +131,8 @@ void perf_get_regs_user(struct perf_regs *regs_user,
 	}
 
 	/*
-	 * RIP, flags, and the argument registers are usually saved.
-	 * orig_ax is probably okay, too.
+	 * These registers are always saved on 64-bit syscall entry.
+	 * On 32-bit entry points, they are saved too except r8..r11.
 	 */
 	regs_user_copy->ip = user_regs->ip;
 	regs_user_copy->cx = user_regs->cx;
@@ -145,9 +145,12 @@ void perf_get_regs_user(struct perf_regs *regs_user,
 	regs_user_copy->r11 = user_regs->r11;
 	regs_user_copy->orig_ax = user_regs->orig_ax;
 	regs_user_copy->flags = user_regs->flags;
+	regs_user_copy->sp = user_regs->sp;
+	regs_user_copy->cs = user_regs->cs;
+	regs_user_copy->ss = user_regs->ss;
 
 	/*
-	 * Don't even try to report the "rest" regs.
+	 * Most system calls don't save these registers, don't report them.
 	 */
 	regs_user_copy->bx = -1;
 	regs_user_copy->bp = -1;
@@ -158,7 +161,7 @@ void perf_get_regs_user(struct perf_regs *regs_user,
 
 	/*
 	 * For this to be at all useful, we need a reasonable guess for
-	 * sp and the ABI.  Be careful: we're in NMI context, and we're
+	 * the ABI.  Be careful: we're in NMI context, and we're
 	 * considering current to be the current task, so we should
 	 * be careful not to look at any other percpu variables that might
 	 * change during context switches.
@@ -167,9 +170,6 @@ void perf_get_regs_user(struct perf_regs *regs_user,
 	    task_thread_info(current)->status & TS_COMPAT) {
 		/* Easy case: we're in a compat syscall. */
 		regs_user->abi = PERF_SAMPLE_REGS_ABI_32;
-		regs_user_copy->sp = user_regs->sp;
-		regs_user_copy->cs = user_regs->cs;
-		regs_user_copy->ss = user_regs->ss;
 	} else if (user_regs->orig_ax != -1) {
 		/*
 		 * We're probably in a 64-bit syscall.
@@ -177,17 +177,12 @@ void perf_get_regs_user(struct perf_regs *regs_user,
 		 * than just blindly copying user_regs.
 		 */
 		regs_user->abi = PERF_SAMPLE_REGS_ABI_64;
-		regs_user_copy->sp = user_regs->sp;
-		regs_user_copy->cs = __USER_CS;
-		regs_user_copy->ss = __USER_DS;
-		regs_user_copy->cx = -1;  /* usually contains garbage */
+		/* usually contains return address (same as ->ip) */
+		regs_user_copy->cx = -1;
 	} 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_copy->sp = user_regs->sp;
-		regs_user_copy->cs = user_regs->cs;
-		regs_user_copy->ss = user_regs->ss;
 	}
 
 	regs_user->regs = regs_user_copy;
-- 
1.8.1.4

[PATCH 2/4] perf/x86_64: get_regs_user: Do report user_regs->cx while we are in syscall

[Denys Vlasenko]

Yes, it is true that cx contains return address.
It's not clear why we trash it.
Stop doing that.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
CC: Jiri Olsa <jolsa@redhat.com>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Paul Mackerras <paulus@samba.org>
CC: Ingo Molnar <mingo@redhat.com>
CC: Arnaldo Carvalho de Melo <acme@kernel.org>
CC: x86@kernel.org
CC: linux-kernel@vger.kernel.org
---
 arch/x86/kernel/perf_regs.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/x86/kernel/perf_regs.c b/arch/x86/kernel/perf_regs.c
index 7ab198a..a8d4e48 100644
--- a/arch/x86/kernel/perf_regs.c
+++ b/arch/x86/kernel/perf_regs.c
@@ -177,8 +177,6 @@ void perf_get_regs_user(struct perf_regs *regs_user,
 		 * than just blindly copying user_regs.
 		 */
 		regs_user->abi = PERF_SAMPLE_REGS_ABI_64;
-		/* usually contains return address (same as ->ip) */
-		regs_user_copy->cx = -1;
 	} else {
 		/* We're probably in an interrupt or exception. */
 		regs_user->abi = user_64bit_mode(user_regs) ?
-- 
1.8.1.4

[tip:x86/asm] perf/x86/64: Do report user_regs-> cx while we are in syscall, in get_regs_user()

[tip-bot for Denys Vlasenko]

Commit-ID:  5df71b396b2d1fdd9d9f5a33e2eda5dc27c5632d
Gitweb:     http://git.kernel.org/tip/5df71b396b2d1fdd9d9f5a33e2eda5dc27c5632d
Author:     Denys Vlasenko <dvlasenk@redhat.com>
AuthorDate: Fri, 10 Apr 2015 15:06:57 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Sat, 11 Apr 2015 13:08:53 +0200

perf/x86/64: Do report user_regs->cx while we are in syscall, in get_regs_user()

Yes, it is true that cx contains return address.
It's not clear why we trash it.
Stop doing that.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1428671219-29341-2-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/perf_regs.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/arch/x86/kernel/perf_regs.c b/arch/x86/kernel/perf_regs.c
index 7ab198a..a8d4e48 100644
--- a/arch/x86/kernel/perf_regs.c
+++ b/arch/x86/kernel/perf_regs.c
@@ -177,8 +177,6 @@ void perf_get_regs_user(struct perf_regs *regs_user,
 		 * than just blindly copying user_regs.
 		 */
 		regs_user->abi = PERF_SAMPLE_REGS_ABI_64;
-		/* usually contains return address (same as ->ip) */
-		regs_user_copy->cx = -1;
 	} else {
 		/* We're probably in an interrupt or exception. */
 		regs_user->abi = user_64bit_mode(user_regs) ?

[PATCH 3/4] perf/x86_64: get_regs_user: Simplify regs_user->abi setting code

[Denys Vlasenko]

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@redhat.com>
CC: Jiri Olsa <jolsa@redhat.com>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Paul Mackerras <paulus@samba.org>
CC: Ingo Molnar <mingo@redhat.com>
CC: Arnaldo Carvalho de Melo <acme@kernel.org>
CC: x86@kernel.org
CC: linux-kernel@vger.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

[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@redhat.com>
AuthorDate: Fri, 10 Apr 2015 15:06:58 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
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@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1428671219-29341-3-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@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;
 }

[PATCH 4/4] perf/x86_64: get_regs_user: Report regs_user->ax too

[Denys Vlasenko]

I don't see why we report e.g. orix_ax, which is not always meaningful,
but don't report ax, which is meaningful.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
CC: Jiri Olsa <jolsa@redhat.com>
CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
CC: Paul Mackerras <paulus@samba.org>
CC: Ingo Molnar <mingo@redhat.com>
CC: Arnaldo Carvalho de Melo <acme@kernel.org>
CC: x86@kernel.org
CC: linux-kernel@vger.kernel.org
---
 arch/x86/kernel/perf_regs.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/perf_regs.c b/arch/x86/kernel/perf_regs.c
index 8157d39..da8cb98 100644
--- a/arch/x86/kernel/perf_regs.c
+++ b/arch/x86/kernel/perf_regs.c
@@ -135,6 +135,7 @@ void perf_get_regs_user(struct perf_regs *regs_user,
 	 * On 32-bit entry points, they are saved too except r8..r11.
 	 */
 	regs_user_copy->ip = user_regs->ip;
+	regs_user_copy->ax = user_regs->ax;
 	regs_user_copy->cx = user_regs->cx;
 	regs_user_copy->dx = user_regs->dx;
 	regs_user_copy->si = user_regs->si;
-- 
1.8.1.4

[tip:x86/asm] perf/x86/64: Report regs_user-> ax too in get_regs_user()

[tip-bot for Denys Vlasenko]

Commit-ID:  3b75232d55680ca166dffa274d0587d5faf0a016
Gitweb:     http://git.kernel.org/tip/3b75232d55680ca166dffa274d0587d5faf0a016
Author:     Denys Vlasenko <dvlasenk@redhat.com>
AuthorDate: Fri, 10 Apr 2015 15:06:59 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Sat, 11 Apr 2015 13:08:53 +0200

perf/x86/64: Report regs_user->ax too in get_regs_user()

I don't see why we report e.g. orix_ax, which is not always
meaningful, but don't report ax, which is meaningful.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1428671219-29341-4-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/perf_regs.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/kernel/perf_regs.c b/arch/x86/kernel/perf_regs.c
index 8157d39..da8cb98 100644
--- a/arch/x86/kernel/perf_regs.c
+++ b/arch/x86/kernel/perf_regs.c
@@ -135,6 +135,7 @@ void perf_get_regs_user(struct perf_regs *regs_user,
 	 * On 32-bit entry points, they are saved too except r8..r11.
 	 */
 	regs_user_copy->ip = user_regs->ip;
+	regs_user_copy->ax = user_regs->ax;
 	regs_user_copy->cx = user_regs->cx;
 	regs_user_copy->dx = user_regs->dx;
 	regs_user_copy->si = user_regs->si;

[tip:x86/asm] perf/x86/64: Do not guess user_regs->cs, ss, sp in get_regs_user()

[tip-bot for Denys Vlasenko]

Commit-ID:  aa21df0424468dbd991440d41ba0f700c5997103
Gitweb:     http://git.kernel.org/tip/aa21df0424468dbd991440d41ba0f700c5997103
Author:     Denys Vlasenko <dvlasenk@redhat.com>
AuthorDate: Fri, 10 Apr 2015 15:06:56 +0200
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Sat, 11 Apr 2015 13:08:52 +0200

perf/x86/64: Do not guess user_regs->cs, ss, sp in get_regs_user()

After recent changes to syscall entry points,
user_regs->{cs,ss,sp} are always correct. (They used to be
undefined while in syscalls).

We can report them reliably, without guessing.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1428671219-29341-1-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/kernel/perf_regs.c | 23 +++++++++--------------
 1 file changed, 9 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kernel/perf_regs.c b/arch/x86/kernel/perf_regs.c
index 02a8720..7ab198a 100644
--- a/arch/x86/kernel/perf_regs.c
+++ b/arch/x86/kernel/perf_regs.c
@@ -131,8 +131,8 @@ void perf_get_regs_user(struct perf_regs *regs_user,
 	}
 
 	/*
-	 * RIP, flags, and the argument registers are usually saved.
-	 * orig_ax is probably okay, too.
+	 * These registers are always saved on 64-bit syscall entry.
+	 * On 32-bit entry points, they are saved too except r8..r11.
 	 */
 	regs_user_copy->ip = user_regs->ip;
 	regs_user_copy->cx = user_regs->cx;
@@ -145,9 +145,12 @@ void perf_get_regs_user(struct perf_regs *regs_user,
 	regs_user_copy->r11 = user_regs->r11;
 	regs_user_copy->orig_ax = user_regs->orig_ax;
 	regs_user_copy->flags = user_regs->flags;
+	regs_user_copy->sp = user_regs->sp;
+	regs_user_copy->cs = user_regs->cs;
+	regs_user_copy->ss = user_regs->ss;
 
 	/*
-	 * Don't even try to report the "rest" regs.
+	 * Most system calls don't save these registers, don't report them.
 	 */
 	regs_user_copy->bx = -1;
 	regs_user_copy->bp = -1;
@@ -158,7 +161,7 @@ void perf_get_regs_user(struct perf_regs *regs_user,
 
 	/*
 	 * For this to be at all useful, we need a reasonable guess for
-	 * sp and the ABI.  Be careful: we're in NMI context, and we're
+	 * the ABI.  Be careful: we're in NMI context, and we're
 	 * considering current to be the current task, so we should
 	 * be careful not to look at any other percpu variables that might
 	 * change during context switches.
@@ -167,9 +170,6 @@ void perf_get_regs_user(struct perf_regs *regs_user,
 	    task_thread_info(current)->status & TS_COMPAT) {
 		/* Easy case: we're in a compat syscall. */
 		regs_user->abi = PERF_SAMPLE_REGS_ABI_32;
-		regs_user_copy->sp = user_regs->sp;
-		regs_user_copy->cs = user_regs->cs;
-		regs_user_copy->ss = user_regs->ss;
 	} else if (user_regs->orig_ax != -1) {
 		/*
 		 * We're probably in a 64-bit syscall.
@@ -177,17 +177,12 @@ void perf_get_regs_user(struct perf_regs *regs_user,
 		 * than just blindly copying user_regs.
 		 */
 		regs_user->abi = PERF_SAMPLE_REGS_ABI_64;
-		regs_user_copy->sp = user_regs->sp;
-		regs_user_copy->cs = __USER_CS;
-		regs_user_copy->ss = __USER_DS;
-		regs_user_copy->cx = -1;  /* usually contains garbage */
+		/* usually contains return address (same as ->ip) */
+		regs_user_copy->cx = -1;
 	} 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_copy->sp = user_regs->sp;
-		regs_user_copy->cs = user_regs->cs;
-		regs_user_copy->ss = user_regs->ss;
 	}
 
 	regs_user->regs = regs_user_copy;