Hi Andy, On 09.05.2018 17:54, Peter Zijlstra wrote: > On Tue, May 08, 2018 at 06:21:36PM +0300, Alexey Budankov wrote: >> >> Store user space frame-pointer value (BP register) into 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.budan...@linux.intel.com> >> --- >> arch/x86/kernel/perf_regs.c | 8 +++++++- >> 1 file changed, 7 insertions(+), 1 deletion(-) >> >> diff --git a/arch/x86/kernel/perf_regs.c b/arch/x86/kernel/perf_regs.c >> index e47b2dbbdef3..8d68658eff7f 100644 >> --- a/arch/x86/kernel/perf_regs.c >> +++ b/arch/x86/kernel/perf_regs.c >> @@ -156,7 +156,13 @@ void perf_get_regs_user(struct perf_regs *regs_user, > > >> * Most system calls don't save these registers, don't report them. > > ^^^ that worries me and is the reason for the '-1's below. However I > think with all the PTI rework this might no longer be true. > > The Changelog needs to state that user_regs->bp is in fact valid and > ideally point to the commits that makes it so. Also this patch should > update that comment. > > Cc Andy who keeps better track of all that than me.
Are there any thoughts so far? Feedback on the matter above is highly appreciated. Thanks, Alexey > >> */ >> regs_user_copy->bx = -1; >> - regs_user_copy->bp = -1; >> + /* >> + * 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->r12 = -1; >> regs_user_copy->r13 = -1; >> regs_user_copy->r14 = -1; >
