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Subject[PATCH] perf: x86: fix callgraphs of 32-bit processes on 64-bit kernels V2.
Date
When profiling a 32-bit process on a 64-bit kernel, callgraph tracing
stopped after the first function, because it has seen a garbage memory address
(tried to interpret the frame pointer, and return address as a 64-bit pointer).

Fix this by using a struct stack_frame with 32-bit pointers when the TIF_IA32 flag is set.

Note that TIF_IA32 flag must be used, and not is_compat_task(), because the
latter is only set when the 32-bit process is executing a syscall,
which may not always be the case (when tracing page fault events for example).

Signed-off-by: Török Edwin <edwintorok@gmail.com>
---
arch/x86/kernel/cpu/perf_event.c | 33 +++++++++++++++++++++++++++++++++
1 files changed, 33 insertions(+), 0 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 8c1c070..b85ea9f 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -2401,6 +2401,20 @@ static int copy_stack_frame(const void __user *fp, struct stack_frame *frame)
return bytes == sizeof(*frame);
}

+struct stack_frame_ia32 {
+ u32 next_frame;
+ u32 return_address;
+};
+
+static int copy_stack_frame_ia32(u32 fp, struct stack_frame_ia32 *frame)
+{
+ unsigned long bytes;
+
+ bytes = copy_from_user_nmi(frame, (const void __user*)(unsigned long)fp, sizeof(*frame));
+
+ return bytes == sizeof(*frame);
+}
+
static void
perf_callchain_user(struct pt_regs *regs, struct perf_callchain_entry *entry)
{
@@ -2414,6 +2428,25 @@ perf_callchain_user(struct pt_regs *regs, struct perf_callchain_entry *entry)

callchain_store(entry, PERF_CONTEXT_USER);
callchain_store(entry, regs->ip);
+ if (test_thread_flag(TIF_IA32)) {
+ /* 32-bit process in 64-bit kernel. */
+ u32 fp = regs->bp;
+ struct stack_frame_ia32 frame;
+ while (entry->nr < PERF_MAX_STACK_DEPTH) {
+ frame.next_frame = 0;
+ frame.return_address = 0;
+
+ if (!copy_stack_frame_ia32(fp, &frame))
+ break;
+
+ if (fp < (u32)regs->sp)
+ break;
+
+ callchain_store(entry, frame.return_address);
+ fp = frame.next_frame;
+ }
+ return;
+ }

while (entry->nr < PERF_MAX_STACK_DEPTH) {
frame.next_frame = NULL;
--
1.7.0
--
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