Re: [PATCH v4 5/6] powerpc: Add show_user_instructions()

Hi, Christophe.

On Thu, Aug 02, 2018 at 07:26:20AM +0200, Christophe LEROY wrote:

Le 01/08/2018 à 23:33, Murilo Opsfelder Araujo a écrit :

quoted

show_user_instructions() is a slightly modified version of
show_instructions() that allows userspace instruction dump.

This will be useful within show_signal_msg() to dump userspace
instructions of the faulty location.

Here is a sample of what show_user_instructions() outputs:

   pandafault[10850]: code: 4bfffeec 4bfffee8 3c401002 38427f00 fbe1fff8 f821ffc1 7c3f0b78 3d22fffe
   pandafault[10850]: code: 392988d0 f93f0020 e93f0020 39400048 <99490000> 39200000 7d234b78 383f0040

The current->comm and current->pid printed can serve as a glue that
links the instructions dump to its originator, allowing messages to be
interleaved in the logs.

Signed-off-by: Murilo Opsfelder Araujo <redacted>
---
  arch/powerpc/include/asm/stacktrace.h | 13 +++++++++
  arch/powerpc/kernel/process.c         | 40 +++++++++++++++++++++++++++
  2 files changed, 53 insertions(+)
  create mode 100644 arch/powerpc/include/asm/stacktrace.h

diff --git a/arch/powerpc/include/asm/stacktrace.h b/arch/powerpc/include/asm/stacktrace.h
new file mode 100644
index 000000000000..6149b53b3bc8
--- /dev/null
+++ b/arch/powerpc/include/asm/stacktrace.h

@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Stack trace functions.
+ *
+ * Copyright 2018, Murilo Opsfelder Araujo, IBM Corporation.
+ */
+
+#ifndef _ASM_POWERPC_STACKTRACE_H
+#define _ASM_POWERPC_STACKTRACE_H
+
+void show_user_instructions(struct pt_regs *regs);
+
+#endif /* _ASM_POWERPC_STACKTRACE_H */

diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index e9533b4d2f08..364645ac732c 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c

@@ -1299,6 +1299,46 @@ static void show_instructions(struct pt_regs *regs)
  	pr_cont("\n");
  }
+void show_user_instructions(struct pt_regs *regs)
+{
+	int i;
+	const char *prefix = KERN_INFO "%s[%d]: code: ";
+	unsigned long pc = regs->nip - (instructions_to_print * 3 / 4 *
+					sizeof(int));
+
+	printk(prefix, current->comm, current->pid);

Why not use pr_info() and remove KERN_INFO from *prefix ?

Because it doesn't compile:

  arch/powerpc/kernel/process.c:1317:10: error: expected ‘)’ before ‘prefix’
    pr_info(prefix, current->comm, current->pid);
            ^
  ./include/linux/printk.h:288:21: note: in definition of macro ‘pr_fmt’
   #define pr_fmt(fmt) fmt
                     ^

`pr_info(prefix, ...)` expands to `printk("\001" "6" prefix, ...)`,
which is an invalid string concatenation.

`pr_info("%s", ...)` expands to `printk("\001" "6" "%s", ...)`, which is
valid.

quoted

+
+	for (i = 0; i < instructions_to_print; i++) {
+		int instr;
+
+		if (!(i % 8) && (i > 0)) {
+			pr_cont("\n");
+			printk(prefix, current->comm, current->pid);
+		}
+
+#if !defined(CONFIG_BOOKE)
+		/* If executing with the IMMU off, adjust pc rather
+		 * than print XXXXXXXX.
+		 */
+		if (!(regs->msr & MSR_IR))
+			pc = (unsigned long)phys_to_virt(pc);

Shouldn't this be done outside of the loop, only once ?

I don't think so.

pc gets incremented at the bottom of the loop:

  pc += sizeof(int);

Adjusting pc is necessary at each iteration.  Leaving this block inside
the loop seems correct.

Cheers
Murilo