diff mbox series

[v15,09/19] tracing: Add ftrace_fill_perf_regs() for perf event

Message ID 172639147435.366111.834128908630424679.stgit@devnote2 (mailing list archive)
State Superseded
Headers show
Series tracing: fprobe: function_graph: Multi-function graph and fprobe on fgraph | expand

Commit Message

Masami Hiramatsu (Google) Sept. 15, 2024, 9:11 a.m. UTC 
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Add ftrace_fill_perf_regs() which should be compatible with the
perf_fetch_caller_regs(). In other words, the pt_regs returned from the
ftrace_fill_perf_regs() must satisfy 'user_mode(regs) == false' and can be
used for stack tracing.

Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
  Changes from previous series: NOTHING, just forward ported.
---
 arch/arm64/include/asm/ftrace.h   |    7 +++++++
 arch/powerpc/include/asm/ftrace.h |    7 +++++++
 arch/s390/include/asm/ftrace.h    |    5 +++++
 arch/x86/include/asm/ftrace.h     |    7 +++++++
 include/linux/ftrace.h            |   31 +++++++++++++++++++++++++++++++
 5 files changed, 57 insertions(+)

Comments

Heiko Carstens Oct. 9, 2024, 10:05 a.m. UTC | #1 
On Sun, Sep 15, 2024 at 06:11:14PM +0900, Masami Hiramatsu (Google) wrote:
> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> 
> Add ftrace_fill_perf_regs() which should be compatible with the
> perf_fetch_caller_regs(). In other words, the pt_regs returned from the
> ftrace_fill_perf_regs() must satisfy 'user_mode(regs) == false' and can be
> used for stack tracing.
> 
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
...
>  arch/s390/include/asm/ftrace.h    |    5 +++++
...
> diff --git a/arch/s390/include/asm/ftrace.h b/arch/s390/include/asm/ftrace.h
> index 9cdd48a46bf7..0d9f6df21f81 100644
> --- a/arch/s390/include/asm/ftrace.h
> +++ b/arch/s390/include/asm/ftrace.h
> @@ -84,6 +84,11 @@ ftrace_regs_get_frame_pointer(struct ftrace_regs *fregs)
>  	return sp[0];	/* return backchain */
>  }
>  
> +#define arch_ftrace_fill_perf_regs(fregs, _regs)	 do {		\
> +		(_regs)->psw.addr = (fregs)->regs.psw.addr;		\
> +		(_regs)->gprs[15] = (fregs)->regs.gprs[15];		\
> +	} while (0)

After reading your commit description and looking at the code I think the
s390 implementation of perf_arch_fetch_caller_regs() is at least
suboptimal: it is not possible to tell if an address belongs to user or
kernel space by looking only at the address (psw.addr); this also requires
to look at psw.mask. It _looks_ like all current callers of
perf_arch_fetch_caller_regs() initialize the passed in pt_regs to zero,
which of course also sets psw.mask to zero, and therefore
user_mode(regs) == false is satisfied.

However I'd rather make that explicit and don't want to rely on
callers. Therefore the above arch_ftrace_fill_perf_regs() should
set the mask to zero

		(_regs)->psw.mask = 0;

I will change perf_arch_fetch_caller_regs() accordingly.
diff mbox series

Patch

diff --git a/arch/arm64/include/asm/ftrace.h b/arch/arm64/include/asm/ftrace.h
index 5cd587afab6d..14ecb9a418d9 100644
--- a/arch/arm64/include/asm/ftrace.h
+++ b/arch/arm64/include/asm/ftrace.h
@@ -143,6 +143,13 @@  ftrace_partial_regs(const struct ftrace_regs *fregs, struct pt_regs *regs)
 	return regs;
 }
 
+#define arch_ftrace_fill_perf_regs(fregs, _regs) do {		\
+		(_regs)->pc = (fregs)->pc;			\
+		(_regs)->regs[29] = (fregs)->fp;		\
+		(_regs)->sp = (fregs)->sp;			\
+		(_regs)->pstate = PSR_MODE_EL1h;		\
+	} while (0)
+
 int ftrace_regs_query_register_offset(const char *name);
 
 int ftrace_init_nop(struct module *mod, struct dyn_ftrace *rec);
diff --git a/arch/powerpc/include/asm/ftrace.h b/arch/powerpc/include/asm/ftrace.h
index 23d26f3afae4..e6ff6834bf7e 100644
--- a/arch/powerpc/include/asm/ftrace.h
+++ b/arch/powerpc/include/asm/ftrace.h
@@ -42,6 +42,13 @@  static __always_inline struct pt_regs *arch_ftrace_get_regs(struct ftrace_regs *
 	return fregs->regs.msr ? &fregs->regs : NULL;
 }
 
+#define arch_ftrace_fill_perf_regs(fregs, _regs) do {		\
+		(_regs)->result = 0;				\
+		(_regs)->nip = (fregs)->regs.nip;		\
+		(_regs)->gpr[1] = (fregs)->regs.gpr[1];		\
+		asm volatile("mfmsr %0" : "=r" ((_regs)->msr));	\
+	} while (0)
+
 static __always_inline void
 ftrace_regs_set_instruction_pointer(struct ftrace_regs *fregs,
 				    unsigned long ip)
diff --git a/arch/s390/include/asm/ftrace.h b/arch/s390/include/asm/ftrace.h
index 9cdd48a46bf7..0d9f6df21f81 100644
--- a/arch/s390/include/asm/ftrace.h
+++ b/arch/s390/include/asm/ftrace.h
@@ -84,6 +84,11 @@  ftrace_regs_get_frame_pointer(struct ftrace_regs *fregs)
 	return sp[0];	/* return backchain */
 }
 
+#define arch_ftrace_fill_perf_regs(fregs, _regs)	 do {		\
+		(_regs)->psw.addr = (fregs)->regs.psw.addr;		\
+		(_regs)->gprs[15] = (fregs)->regs.gprs[15];		\
+	} while (0)
+
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
 /*
  * When an ftrace registered caller is tracing a function that is
diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
index 669771ef3b5b..1f4d1f7b19ed 100644
--- a/arch/x86/include/asm/ftrace.h
+++ b/arch/x86/include/asm/ftrace.h
@@ -46,6 +46,13 @@  arch_ftrace_get_regs(struct ftrace_regs *fregs)
 	return &fregs->regs;
 }
 
+#define arch_ftrace_fill_perf_regs(fregs, _regs) do {	\
+		(_regs)->ip = (fregs)->regs.ip;		\
+		(_regs)->sp = (fregs)->regs.sp;		\
+		(_regs)->cs = __KERNEL_CS;		\
+		(_regs)->flags = 0;			\
+	} while (0)
+
 #define ftrace_regs_set_instruction_pointer(fregs, _ip)	\
 	do { (fregs)->regs.ip = (_ip); } while (0)
 
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index d6b92a4091b9..cc6bf05a9992 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -193,6 +193,37 @@  ftrace_partial_regs(struct ftrace_regs *fregs, struct pt_regs *regs)
 
 #endif /* !CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS || CONFIG_HAVE_PT_REGS_TO_FTRACE_REGS_CAST */
 
+#ifdef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS
+
+/*
+ * Please define arch dependent pt_regs which compatible to the
+ * perf_arch_fetch_caller_regs() but based on ftrace_regs.
+ * This requires
+ *   - user_mode(_regs) returns false (always kernel mode).
+ *   - able to use the _regs for stack trace.
+ */
+#ifndef arch_ftrace_fill_perf_regs
+/* As same as perf_arch_fetch_caller_regs(), do nothing by default */
+#define arch_ftrace_fill_perf_regs(fregs, _regs) do {} while (0)
+#endif
+
+static __always_inline struct pt_regs *
+ftrace_fill_perf_regs(struct ftrace_regs *fregs, struct pt_regs *regs)
+{
+	arch_ftrace_fill_perf_regs(fregs, regs);
+	return regs;
+}
+
+#else /* !CONFIG_HAVE_DYNAMIC_FTRACE_WITH_ARGS */
+
+static __always_inline struct pt_regs *
+ftrace_fill_perf_regs(struct ftrace_regs *fregs, struct pt_regs *regs)
+{
+	return &fregs->regs;
+}
+
+#endif
+
 /*
  * When true, the ftrace_regs_{get,set}_*() functions may be used on fregs.
  * Note: this can be true even when ftrace_get_regs() cannot provide a pt_regs.