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Subject[PATCH] perf: x86: fix callgraphs of 32-bit processes on 64-bit kernels V4.
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).

Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: x86@kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Török Edwin <edwintorok@gmail.com>
---
arch/x86/kernel/cpu/perf_event.c | 44 +++++++++++++++++++++++++++++++++----
arch/x86/kernel/dumpstack.h | 5 ++++
2 files changed, 44 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 8c1c070..5f97f29 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -26,6 +26,7 @@
#include <asm/apic.h>
#include <asm/stacktrace.h>
#include <asm/nmi.h>
+#include <asm/compat.h>

static u64 perf_event_mask __read_mostly;

@@ -2392,14 +2393,42 @@ copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
return len;
}

-static int copy_stack_frame(const void __user *fp, struct stack_frame *frame)
+#ifdef CONFIG_COMPAT
+static inline int
+perf_callchain_user32(struct pt_regs *regs, struct perf_callchain_entry *entry)
{
- unsigned long bytes;
+ /* 32-bit process in 64-bit kernel. */
+ struct stack_frame_ia32 frame;
+ const void __user *fp;
+
+ if (!test_thread_flag(TIF_IA32))
+ return 0;
+
+ fp = compat_ptr(regs->bp);
+ while (entry->nr < PERF_MAX_STACK_DEPTH) {
+ unsigned long bytes;
+ frame.next_frame = 0;
+ frame.return_address = 0;

- bytes = copy_from_user_nmi(frame, fp, sizeof(*frame));
+ bytes = copy_from_user_nmi(&frame, fp, sizeof(frame));
+ if (bytes != sizeof(frame))
+ break;
+
+ if (fp < compat_ptr(regs->sp))
+ break;

- return bytes == sizeof(*frame);
+ callchain_store(entry, frame.return_address);
+ fp = compat_ptr(frame.next_frame);
+ }
+ return 1;
}
+#else
+static inline int
+perf_callchain_user32(struct pt_regs *regs, struct perf_callchain_entry *entry)
+{
+ return 0;
+}
+#endif

static void
perf_callchain_user(struct pt_regs *regs, struct perf_callchain_entry *entry)
@@ -2415,11 +2444,16 @@ perf_callchain_user(struct pt_regs *regs, struct perf_callchain_entry *entry)
callchain_store(entry, PERF_CONTEXT_USER);
callchain_store(entry, regs->ip);

+ if (perf_callchain_user32(regs, entry))
+ return;
+
while (entry->nr < PERF_MAX_STACK_DEPTH) {
+ unsigned long bytes;
frame.next_frame = NULL;
frame.return_address = 0;

- if (!copy_stack_frame(fp, &frame))
+ bytes = copy_from_user_nmi(&frame, fp, sizeof(frame));
+ if (bytes != sizeof(frame))
break;

if ((unsigned long)fp < regs->sp)
diff --git a/arch/x86/kernel/dumpstack.h b/arch/x86/kernel/dumpstack.h
index 4fd1420..3f0a242 100644
--- a/arch/x86/kernel/dumpstack.h
+++ b/arch/x86/kernel/dumpstack.h
@@ -29,4 +29,9 @@ struct stack_frame {
struct stack_frame *next_frame;
unsigned long return_address;
};
+
+struct stack_frame_ia32 {
+ u32 next_frame;
+ u32 return_address;
+};
#endif
--
1.7.0
--
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