From db4b0710fae90a4407bfa77b23db396e580b9e23 Mon Sep 17 00:00:00 2001
From: Mark Rutland <mark.rutland@arm.com>
Date: Thu, 20 Oct 2016 12:23:16 +0100
Subject: [PATCH] arm64: fix show_regs fallout from KERN_CONT changes
Recently in commit 4bcc595ccd80decb ("printk: reinstate KERN_CONT for
printing continuation lines"), the behaviour of printk changed w.r.t.
KERN_CONT. Now, KERN_CONT is mandatory to continue existing lines.
Without this, prefixes are inserted, making output illegible, e.g.
[ 1007.069010] pc : [<ffff00000871898c>] lr : [<ffff000008718948>] pstate: 40000145
[ 1007.076329] sp : ffff000008d53ec0
[ 1007.079606] x29: ffff000008d53ec0 [ 1007.082797] x28: 0000000080c50018
[ 1007.086160]
[ 1007.087630] x27: ffff000008e0c7f8 [ 1007.090820] x26: ffff80097631ca00
[ 1007.094183]
[ 1007.095653] x25: 0000000000000001 [ 1007.098843] x24: 000000ea68b61cac
[ 1007.102206]
... or when dumped with the userpace dmesg tool, which has slightly
different implicit newline behaviour. e.g.
[ 1007.069010] pc : [<ffff00000871898c>] lr : [<ffff000008718948>] pstate: 40000145
[ 1007.076329] sp : ffff000008d53ec0
[ 1007.079606] x29: ffff000008d53ec0
[ 1007.082797] x28: 0000000080c50018
[ 1007.086160]
[ 1007.087630] x27: ffff000008e0c7f8
[ 1007.090820] x26: ffff80097631ca00
[ 1007.094183]
[ 1007.095653] x25: 0000000000000001
[ 1007.098843] x24: 000000ea68b61cac
[ 1007.102206]
We can't simply always use KERN_CONT for lines which may or may not be
continuations. That causes line prefixes (e.g. timestamps) to be
supressed, and the alignment of all but the first line will be broken.
For even more fun, we can't simply insert some dummy empty-string printk
calls, as GCC warns for an empty printk string, and even if we pass
KERN_DEFAULT explcitly to silence the warning, the prefix gets swallowed
unless there is an additional part to the string.
Instead, we must manually iterate over pairs of registers, which gives
us the legible output we want in either case, e.g.
[ 169.771790] pc : [<ffff00000871898c>] lr : [<ffff000008718948>] pstate: 40000145
[ 169.779109] sp : ffff000008d53ec0
[ 169.782386] x29: ffff000008d53ec0 x28: 0000000080c50018
[ 169.787650] x27: ffff000008e0c7f8 x26: ffff80097631de00
[ 169.792913] x25: 0000000000000001 x24: 00000027827b2cf4
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
---
arch/arm64/kernel/process.c | 15 ++++++++++++---
1 file changed, 12 insertions(+), 3 deletions(-)
diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 4f186c56c5eb..01753cd7d3f0 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -187,10 +187,19 @@ void __show_regs(struct pt_regs *regs)
printk("pc : [<%016llx>] lr : [<%016llx>] pstate: %08llx\n",
regs->pc, lr, regs->pstate);
printk("sp : %016llx\n", sp);
- for (i = top_reg; i >= 0; i--) {
+
+ i = top_reg;
+
+ while (i >= 0) {
printk("x%-2d: %016llx ", i, regs->regs[i]);
- if (i % 2 == 0)
- printk("\n");
+ i--;
+
+ if (i % 2 == 0) {
+ pr_cont("x%-2d: %016llx ", i, regs->regs[i]);
+ i--;
+ }
+
+ pr_cont("\n");
}
printk("\n");
}
--
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