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Date: Wed, 21 Sep 2022 20:51:26 +0800
From: Chen Zhongjin <chenzhongjin@...wei.com>
To: <linux-kernel@...r.kernel.org>, <linux-riscv@...ts.infradead.org>,
<linux-perf-users@...r.kernel.org>
CC: <paul.walmsley@...ive.com>, <palmer@...belt.com>,
<aou@...s.berkeley.edu>, <peterz@...radead.org>,
<mingo@...hat.com>, <acme@...nel.org>, <mark.rutland@....com>,
<alexander.shishkin@...ux.intel.com>, <namhyung@...nel.org>,
<jolsa@...nel.org>, <guoren@...nel.org>, <frederic@...nel.org>,
<vincent.chen@...ive.com>, <ardb@...nel.org>,
<mhiramat@...nel.org>, <rostedt@...dmis.org>,
<keescook@...omium.org>, <catalin.marinas@....com>,
<chenzhongjin@...wei.com>
Subject: [PATCH for-next v2 3/4] riscv: stacktrace: Save pt_regs in ENCODE_FRAME_POINTER
To support stack unwinding when there is a pt_regs on stack, the position
of pt_regs is nessesary. Because for some functions, compiler only push
s0/fp on stack without ra.
As the situation described in
commit f766f77a74f5("riscv/stacktrace: Fix stack output without ra on the stack top")
When irq happens there, the function frame looks like:
prev function | ... |
| |
normal function +-----------------+
| ra to prev |
| s0 of prev |
| ... |<-+
leaf function +-----------------+ |
| s0 of normal | |
| empty slot | |
irq pt_regs +-----------------+ |
| epc (ra to leaf)| |
| ra (ra to norm)| |
| ... | |
| s0 of leaf |--+
| ... |
+-----------------+
When unwinding from unwinding from leaf to normal, beacause (ra to norm)
is saved in pt_regs, but not stackframe of leaf, we have to get pt_regs
for that.
To get pt_regs position on stack, we can save the encoded *pt_regs
in s0, as x86 architecture did. Then we can get s0, epc and ra
easily.
Add ENCODE_FRAME_POINTER in irq, ftrace and kretprobe trampoline entries.
For ftrace and kretprobes we should also set pt_regs as kernel mode
so that they are not mistaken as user_mode pt_regs.
Signed-off-by: Chen Zhongjin <chenzhongjin@...wei.com>
Reviewed-by: Guo Ren <guoren@...nel.org>
---
arch/riscv/include/asm/frame.h | 45 +++++++++++++++++++
arch/riscv/kernel/entry.S | 3 ++
arch/riscv/kernel/mcount-dyn.S | 7 +++
arch/riscv/kernel/probes/kprobes_trampoline.S | 7 +++
4 files changed, 62 insertions(+)
create mode 100644 arch/riscv/include/asm/frame.h
diff --git a/arch/riscv/include/asm/frame.h b/arch/riscv/include/asm/frame.h
new file mode 100644
index 000000000000..2a1f45cf3a4e
--- /dev/null
+++ b/arch/riscv/include/asm/frame.h
@@ -0,0 +1,45 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_RISCV_FRAME_H
+#define _ASM_RISCV_FRAME_H
+
+#include <asm/asm.h>
+
+#ifdef CONFIG_FRAME_POINTER
+
+#ifdef __ASSEMBLY__
+
+/*
+ * This is a sneaky trick to help the unwinder find pt_regs on the stack. The
+ * frame pointer is replaced with an encoded pointer to pt_regs. The encoding
+ * is just setting the LSB, which makes it an invalid stack address and is also
+ * a signal to the unwinder that it's a pt_regs pointer in disguise.
+ *
+ * This macro must be used when sp point to pt_regs
+ */
+.macro ENCODE_FRAME_POINTER
+ add s0, sp, 0x1
+.endm
+
+#else /* !__ASSEMBLY__ */
+
+#define ENCODE_FRAME_POINTER \
+ "add s0, sp, 0x1\n\t"
+
+#endif /* __ASSEMBLY__ */
+
+#else /* !CONFIG_FRAME_POINTER */
+
+#ifdef __ASSEMBLY__
+
+.macro ENCODE_FRAME_POINTER ptregs_offset=0
+.endm
+
+#else /* !__ASSEMBLY */
+
+#define ENCODE_FRAME_POINTER
+
+#endif /* !__ASSEMBLY */
+
+#endif /* CONFIG_FRAME_POINTER */
+
+#endif /* _ASM_RISCV_FRAME_H */
diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index b9eda3fcbd6d..ecb15c7430b4 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -13,6 +13,7 @@
#include <asm/thread_info.h>
#include <asm/asm-offsets.h>
#include <asm/errata_list.h>
+#include <asm/frame.h>
#if !IS_ENABLED(CONFIG_PREEMPTION)
.set resume_kernel, restore_all
@@ -95,6 +96,8 @@ _save_context:
REG_S s4, PT_CAUSE(sp)
REG_S s5, PT_TP(sp)
+ ENCODE_FRAME_POINTER
+
/*
* Set the scratch register to 0, so that if a recursive exception
* occurs, the exception vector knows it came from the kernel
diff --git a/arch/riscv/kernel/mcount-dyn.S b/arch/riscv/kernel/mcount-dyn.S
index d171eca623b6..a362521e030e 100644
--- a/arch/riscv/kernel/mcount-dyn.S
+++ b/arch/riscv/kernel/mcount-dyn.S
@@ -10,6 +10,8 @@
#include <asm/asm-offsets.h>
#include <asm-generic/export.h>
#include <asm/ftrace.h>
+#include <asm/frame.h>
+#include <asm/csr.h>
.text
@@ -172,6 +174,11 @@ ENDPROC(ftrace_caller)
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
ENTRY(ftrace_regs_caller)
SAVE_ALL
+#ifdef CONFIG_FRAME_POINTER
+ li s0, SR_PP
+ REG_S s0, PT_STATUS(sp)
+ ENCODE_FRAME_POINTER
+#endif
addi a0, ra, -FENTRY_RA_OFFSET
la a1, function_trace_op
diff --git a/arch/riscv/kernel/probes/kprobes_trampoline.S b/arch/riscv/kernel/probes/kprobes_trampoline.S
index 7bdb09ded39b..70760a16784f 100644
--- a/arch/riscv/kernel/probes/kprobes_trampoline.S
+++ b/arch/riscv/kernel/probes/kprobes_trampoline.S
@@ -6,6 +6,8 @@
#include <asm/asm.h>
#include <asm/asm-offsets.h>
+#include <asm/frame.h>
+#include <asm/csr.h>
.text
.altmacro
@@ -78,6 +80,11 @@
ENTRY(__kretprobe_trampoline)
addi sp, sp, -(PT_SIZE_ON_STACK)
save_all_base_regs
+#ifdef CONFIG_FRAME_POINTER
+ li s0, SR_PP
+ REG_S s0, PT_STATUS(sp)
+ ENCODE_FRAME_POINTER
+#endif
move a0, sp /* pt_regs */
--
2.17.1
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