[tip:x86/asm] x86/dumpstack: Print orig_ax in __show_regs()

[tip-bot for Josh Poimboeuf]

Commit-ID:  6fa81a12b3f1834a22167aa2d7b24dcc4bf884e3
Gitweb:     http://git.kernel.org/tip/6fa81a12b3f1834a22167aa2d7b24dcc4bf884e3
Author:     Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
AuthorDate: Thu, 20 Oct 2016 11:34:45 -0500
Committer:  Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Fri, 21 Oct 2016 09:26:05 +0200

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@xxxxxxxxxxxxxx>
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Brian Gerst <brgerst@xxxxxxxxx>
Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/93f0fe0307a4af884d3fca00edabcc8cff236002.1476973742.git.jpoimboe@xxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
 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 b3b50ac..f1c36da 100644
--- a/arch/x86/kernel/process_64.c
+++ b/arch/x86/kernel/process_64.c
@@ -63,8 +63,13 @@ 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",