linux-kernel - [PATCH 1/3] x86/unwind: properly zero-pad 32-bit values in unwind

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Date:   Tue, 18 Apr 2017 08:12:56 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH 1/3] x86/unwind: properly zero-pad 32-bit values in unwind_dump()

On x86-32, 32-bit stack values printed by unwind_dump() are confusingly
zero-padded to 16 characters (64 bits):

  unwind stack type:0 next_sp:  (null) mask:a graph_idx:0
  f50cdebc: 00000000f50cdec4 (0xf50cdec4)
  f50cdec0: 00000000c40489b7 (irq_exit+0x87/0xa0)
  ...

Instead, base the field width on the size of a long integer so that it
looks right on both x86-32 and x86-64.

x86-32:

  unwind stack type:1 next_sp:  (null) mask:0x2 graph_idx:0
  c0ee9d98: c0ee9de0 (init_thread_union+0x1de0/0x2000)
  c0ee9d9c: c043fd90 (__save_stack_trace+0x50/0xe0)
  ...

x86-64:

  unwind stack type:1 next_sp:          (null) mask:0x2 graph_idx:0
  ffffffff81e03b88: ffffffff81e03c10 (init_thread_union+0x3c10/0x4000)
  ffffffff81e03b90: ffffffff81048f8e (__save_stack_trace+0x5e/0x100)
  ...

Reported-by: "H. Peter Anvin" <hpa@...or.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 arch/x86/kernel/unwind_frame.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index c461135..3ebe687 100644
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -48,11 +48,13 @@ static void unwind_dump(struct unwind_state *state, unsigned long *sp)

 		if (zero) {
 			if (!prev_zero)
-				printk_deferred("%p: %016x ...\n", sp, 0);
+				printk_deferred("%p: %0*x ...\n",
+						sp, BITS_PER_LONG/4, 0);
 			continue;
 		}

-		printk_deferred("%p: %016lx (%pB)\n", sp, word, (void *)word);
+		printk_deferred("%p: %0*lx (%pB)\n",
+				sp, BITS_PER_LONG/4, word, (void *)word);
 	}
 }

-- 
2.7.4