[PATCH 6/6] x86/dumpstack: print orig_ax in __show_regs()

From: Josh Poimboeuf
Date: Thu Oct 20 2016 - 12:35:29 EST

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>
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 92d3f70..4481e72 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",