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


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