perf/x86: Store user space frame-pointer value on a sample

Store user space frame-pointer value (BP register) into the perf trace
on a sample for a process so the value becomes available when
unwinding call stacks for functions gaining event samples.

Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: http://lkml.kernel.org/r/311d4a34-f81b-5535-3385-01427ac73b41@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/kernel/perf_regs.c

@@ -151,17 +151,19 @@ void perf_get_regs_user(struct perf_regs *regs_user,
 	regs_user_copy->sp = user_regs->sp;
 	regs_user_copy->cs = user_regs->cs;
 	regs_user_copy->ss = user_regs->ss;
-
 	/*
-	 * Most system calls don't save these registers, don't report them.
+	 * Store user space frame-pointer value on sample
+	 * to facilitate stack unwinding for cases when
+	 * user space executable code has such support
+	 * enabled at compile time:
 	 */
+	regs_user_copy->bp = user_regs->bp;
+
 	regs_user_copy->bx = -1;
-	regs_user_copy->bp = -1;
 	regs_user_copy->r12 = -1;
 	regs_user_copy->r13 = -1;
 	regs_user_copy->r14 = -1;
 	regs_user_copy->r15 = -1;
-
 	/*
 	 * For this to be at all useful, we need a reasonable guess for
 	 * the ABI.  Be careful: we're in NMI context, and we're