linux-kernel - [PATCH 1/9] perf/x86: Always store regs->ip in perf_callchain

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Message-Id: <3fc9271e95c87a4c31d8184514b8667007cb9540.1560431531.git.jpoimboe@redhat.com>
Date:   Thu, 13 Jun 2019 08:20:58 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
        Song Liu <songliubraving@...com>,
        Kairui Song <kasong@...hat.com>
Subject: [PATCH 1/9] perf/x86: Always store regs->ip in perf_callchain_kernel()

From: Song Liu <songliubraving@...com>

The stacktrace_map_raw_tp BPF selftest is failing because the RIP saved
by perf_arch_fetch_caller_regs() isn't getting saved by
perf_callchain_kernel().

This was broken by the following commit:

  d15d356887e7 ("perf/x86: Make perf callchains work without CONFIG_FRAME_POINTER")

With that change, when starting with non-HW regs, the unwinder starts
with the current stack frame and unwinds until it passes up the frame
which called perf_arch_fetch_caller_regs().  So regs->ip needs to be
saved deliberately.

Fixes: d15d356887e7 ("perf/x86: Make perf callchains work without CONFIG_FRAME_POINTER")
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 arch/x86/events/core.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index f0e4804515d8..6a7cfcadfc1e 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2328,13 +2328,13 @@ perf_callchain_kernel(struct perf_callchain_entry_ctx *entry, struct pt_regs *re
 		return;
 	}
 
-	if (perf_hw_regs(regs)) {
-		if (perf_callchain_store(entry, regs->ip))
-			return;
+	if (perf_callchain_store(entry, regs->ip))
+		return;
+
+	if (perf_hw_regs(regs))
 		unwind_start(&state, current, regs, NULL);
-	} else {
+	else
 		unwind_start(&state, current, NULL, (void *)regs->sp);
-	}
 
 	for (; !unwind_done(&state); unwind_next_frame(&state)) {
 		addr = unwind_get_return_address(&state);
-- 
2.20.1