From aa21df0424468dbd991440d41ba0f700c5997103 Mon Sep 17 00:00:00 2001 From: Denys Vlasenko Date: Fri, 10 Apr 2015 15:06:56 +0200 Subject: [PATCH] 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 Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Paul Mackerras Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/1428671219-29341-1-git-send-email-dvlasenk@redhat.com Signed-off-by: Ingo Molnar --- 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 02a8720414c0..7ab198acc5b8 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; -- 2.34.1