linux-kernel - [PATCH v4 47/57] x86/dumpstack: print orig_ax in __show

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Date:	Thu, 18 Aug 2016 08:06:27 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	"H . Peter Anvin" <hpa@...or.com>
Cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Andy Lutomirski <luto@...capital.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Brian Gerst <brgerst@...il.com>,
	Kees Cook <keescook@...omium.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Byungchul Park <byungchul.park@....com>,
	Nilay Vaish <nilayvaish@...il.com>
Subject: [PATCH v4 47/57] x86/dumpstack: print orig_ax in __show_regs()

The value of regs->orig_ax contains potentially useful debugging data:
For syscalls it contains the syscall number.  For interrupts it contains
the (negated) vector number.  To reduce noise, print it only if it has a
useful value (i.e., something other than -1).

Here's what it looks like for a write syscall:

  RIP: 0033:[<00007f53ad7b1940>] 0x7f53ad7b1940
  RSP: 002b:00007fff8de66558 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
  RAX: ffffffffffffffda RBX: 0000000000000046 RCX: 00007f53ad7b1940
  RDX: 0000000000000002 RSI: 00007f53ae0ca000 RDI: 0000000000000001
  ...

Suggested-by: Andy Lutomirski <luto@...capital.net>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 arch/x86/kernel/process_64.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kernel/process_64.c b/arch/x86/kernel/process_64.c
index 6c43d29..cde6fd0 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -64,8 +64,13 @@ void __show_regs(struct pt_regs *regs, int all)
 
 	printk(KERN_DEFAULT "RIP: %04lx:[<%016lx>] %pS\n", regs->cs & 0xffff,
 			regs->ip, (void *)regs->ip);
-	printk(KERN_DEFAULT "RSP: %04lx:%016lx  EFLAGS: %08lx\n", regs->ss,
+	printk(KERN_DEFAULT "RSP: %04lx:%016lx EFLAGS: %08lx", regs->ss,
 			regs->sp, regs->flags);
+	if (regs->orig_ax != -1)
+		pr_cont(" ORIG_RAX: %016lx\n", regs->orig_ax);
+	else
+		pr_cont("\n");
+
 	printk(KERN_DEFAULT "RAX: %016lx RBX: %016lx RCX: %016lx\n",
 	       regs->ax, regs->bx, regs->cx);
 	printk(KERN_DEFAULT "RDX: %016lx RSI: %016lx RDI: %016lx\n",
-- 
2.7.4