[PATCH] riscv: stacktrace: Add USER_STACKTRACE support

[Jinjie Ruan]

Currently, userstacktrace is unsupported for riscv. So use the
perf_callchain_user() code as blueprint to implement the
arch_stack_walk_user() which add userstacktrace support on riscv.
Meanwhile, we can use arch_stack_walk_user() to simplify the implementation
of perf_callchain_user().

Signed-off-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
---
 arch/riscv/Kconfig                 |  1 +
 arch/riscv/kernel/perf_callchain.c | 46 ++----------------------------
 arch/riscv/kernel/stacktrace.c     | 43 ++++++++++++++++++++++++++++
 3 files changed, 47 insertions(+), 43 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index b94176e25be1..4a7ba6a08dee 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -193,6 +193,7 @@ config RISCV
 	select THREAD_INFO_IN_TASK
 	select TRACE_IRQFLAGS_SUPPORT
 	select UACCESS_MEMCPY if !MMU
+	select USER_STACKTRACE_SUPPORT
 	select ZONE_DMA32 if 64BIT
 
 config CLANG_SUPPORTS_DYNAMIC_FTRACE
diff --git a/arch/riscv/kernel/perf_callchain.c b/arch/riscv/kernel/perf_callchain.c
index 3348a61de7d9..c7468af77c66 100644
--- a/arch/riscv/kernel/perf_callchain.c
+++ b/arch/riscv/kernel/perf_callchain.c
@@ -6,37 +6,9 @@
 
 #include <asm/stacktrace.h>
 
-/*
- * Get the return address for a single stackframe and return a pointer to the
- * next frame tail.
- */
-static unsigned long user_backtrace(struct perf_callchain_entry_ctx *entry,
-				    unsigned long fp, unsigned long reg_ra)
+static bool fill_callchain(void *entry, unsigned long pc)
 {
-	struct stackframe buftail;
-	unsigned long ra = 0;
-	unsigned long __user *user_frame_tail =
-		(unsigned long __user *)(fp - sizeof(struct stackframe));
-
-	/* Check accessibility of one struct frame_tail beyond */
-	if (!access_ok(user_frame_tail, sizeof(buftail)))
-		return 0;
-	if (__copy_from_user_inatomic(&buftail, user_frame_tail,
-				      sizeof(buftail)))
-		return 0;
-
-	if (reg_ra != 0)
-		ra = reg_ra;
-	else
-		ra = buftail.ra;
-
-	fp = buftail.fp;
-	if (ra != 0)
-		perf_callchain_store(entry, ra);
-	else
-		return 0;
-
-	return fp;
+	return perf_callchain_store(entry, pc) == 0;
 }
 
 /*
@@ -56,19 +28,7 @@ static unsigned long user_backtrace(struct perf_callchain_entry_ctx *entry,
 void perf_callchain_user(struct perf_callchain_entry_ctx *entry,
 			 struct pt_regs *regs)
 {
-	unsigned long fp = 0;
-
-	fp = regs->s0;
-	perf_callchain_store(entry, regs->epc);
-
-	fp = user_backtrace(entry, fp, regs->ra);
-	while (fp && !(fp & 0x3) && entry->nr < entry->max_stack)
-		fp = user_backtrace(entry, fp, 0);
-}
-
-static bool fill_callchain(void *entry, unsigned long pc)
-{
-	return perf_callchain_store(entry, pc) == 0;
+	arch_stack_walk_user(fill_callchain, entry, regs);
 }
 
 void perf_callchain_kernel(struct perf_callchain_entry_ctx *entry,
diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
index 528ec7cc9a62..e0f556b680d8 100644
--- a/arch/riscv/kernel/stacktrace.c
+++ b/arch/riscv/kernel/stacktrace.c
@@ -161,3 +161,46 @@ noinline void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie
 {
 	walk_stackframe(task, regs, consume_entry, cookie);
 }
+
+/*
+ * Get the return address for a single stackframe and return a pointer to the
+ * next frame tail.
+ */
+static unsigned long unwind_user_frame(stack_trace_consume_fn consume_entry,
+				       void *cookie, unsigned long fp,
+				       unsigned long reg_ra)
+{
+	struct stackframe buftail;
+	unsigned long ra = 0;
+	unsigned long __user *user_frame_tail =
+		(unsigned long __user *)(fp - sizeof(struct stackframe));
+
+	/* Check accessibility of one struct frame_tail beyond */
+	if (!access_ok(user_frame_tail, sizeof(buftail)))
+		return 0;
+	if (__copy_from_user_inatomic(&buftail, user_frame_tail,
+				      sizeof(buftail)))
+		return 0;
+
+	ra = reg_ra ? : buftail.ra;
+
+	fp = buftail.fp;
+	if (!ra || (ra && !consume_entry(cookie, ra)))
+		return 0;
+
+	return fp;
+}
+
+void arch_stack_walk_user(stack_trace_consume_fn consume_entry, void *cookie,
+			  const struct pt_regs *regs)
+{
+	unsigned long fp = 0;
+
+	fp = regs->s0;
+	if (!consume_entry(cookie, regs->epc))
+		return;
+
+	fp = unwind_user_frame(consume_entry, cookie, fp, regs->ra);
+	while (fp && !(fp & 0x3))
+		fp = unwind_user_frame(consume_entry, cookie, fp, 0);
+}
-- 
2.34.1