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From cbbce37ccc6041d3ae3d3cb3b1918a61a39820a0 Mon Sep 17 00:00:00 2001
From: Fang Jia <fang.jia@windriver.com>
Date: Fri, 28 Dec 2018 16:28:34 +0800
Subject: [PATCH] arm64/perf: fix backtrace for AAPCS with FP enabled
This change is for arm64 platform compat mode.
The change for arm32 platform has been included in this commit "perf: fix
backtrace for AAPCS with FP enabled".
This change replaces code designed for the obsolete ARM APCS ABI, which
causes failures of the perf backtrace logic unless the gcc option
-mapcs-frame is used to build all binaries on the platform. This
obsolete gcc option forces the compiler to include the stack pointer
along with the frame pointer and link register in the stack frame
for each funciton call. The current AAPCS ABI document, doesn't
explicitly describe the frame structure when the gcc frame pointer
option, -fno-omit-frame-pointer, is enabled. However, with this option
enabled, examination of the emitted prologue instructions shows that
1) R11 is used as the frame pointer,
2) only the R11 and LR are saved onto the stack, not the stack pointer,
3) after this prologue setup, the frame pointer, R11 points to the
saved location of LR on the stack.
The use of unsigned int arithmetic in the commit is required since
the gcc emitted pointer arithmetic uses 8-byte pointer sizes, which are
incorrect addresses for the 4-byte stack address size.
Signed-off-by: Fang Jia <fang.jia@windriver.com>
Reviewed-by: Jiwei Sun <jiwei.sun@windriver.com>
Signed-off-by: De Huo <de.huo@windriver.com>
---
arch/arm64/kernel/perf_callchain.c | 25 +++++++++++++++----------
1 file changed, 15 insertions(+), 10 deletions(-)
diff --git a/arch/arm64/kernel/perf_callchain.c b/arch/arm64/kernel/perf_callchain.c
index 9d63514b9836..b9bbe0b04fc1 100644
--- a/arch/arm64/kernel/perf_callchain.c
+++ b/arch/arm64/kernel/perf_callchain.c
@@ -54,16 +54,22 @@ user_backtrace(struct frame_tail __user *tail,
#ifdef CONFIG_COMPAT
/*
- * The registers we're interested in are at the end of the variable
- * length saved register structure. The fp points at the end of this
- * structure so the address of this struct is:
- * (struct compat_frame_tail *)(xxx->fp)-1
+ * The AAPCS ABI, the most current replacing the obsolete APCS ABI,
+ * does not specifically describe the stack frame with respect to the
+ * frame pointer. However, the examination of emitted prologue
+ * instructions for ARM implies that with -fno-omit-framepointer,
+ * register R11 is used as the frame pointer register and saved on the
+ * stack, with LR.
*
- * This code has been adapted from the ARM OProfile support.
+ * After the prolog, the FP points to the location of the saved LR and
+ * FP+4 points to the previous frames FP as shown below:
+ * Stack Hi Mem
+ * (Value of FP)+4 Saved FP for caller
+ * (Value of FP) LR set by caller
+ * Stack Lo Mem
*/
struct compat_frame_tail {
compat_uptr_t fp; /* a (struct compat_frame_tail *) in compat mode */
- u32 sp;
u32 lr;
} __attribute__((packed));
@@ -91,11 +97,10 @@ compat_user_backtrace(struct compat_frame_tail __user *tail,
* Frame pointers should strictly progress back up the stack
* (towards higher addresses).
*/
- if (tail + 1 >= (struct compat_frame_tail __user *)
- compat_ptr(buftail.fp))
+ if ((u32)tail + 4 >= buftail.fp)
return NULL;
- return (struct compat_frame_tail __user *)compat_ptr(buftail.fp) - 1;
+ return (struct compat_frame_tail __user *)(buftail.fp - 4);
}
#endif /* CONFIG_COMPAT */
@@ -123,7 +128,7 @@ void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
/* AARCH32 compat mode */
struct compat_frame_tail __user *tail;
- tail = (struct compat_frame_tail __user *)regs->compat_fp - 1;
+ tail = (struct compat_frame_tail __user *)(regs->compat_fp - 4);
while ((entry->nr < entry->max_stack) &&
tail && !((unsigned long)tail & 0x3))
--
2.17.1
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