[PATCH] vsprintf: replace space with readable '=' before crng is ready

Shunyong Yang
2018-02-13T06:23:38Z

Before crng is ready, output of "%p" composes of "(ptrval)" and
left padding spaces for alignment as no random address can be
generated. This seems a little strange when default string width
is larger than strlen("(ptrval)").

For example, when irq domain names are built with "%p", the nodes
under /sys/kernel/debug/irq/domains like this on AArch64 system,

[root@y irq]# ls domains/
default irqchip@ (ptrval)-2
irqchip@ (ptrval)-4 \_SB_.TCS0.QIC1 \_SB_.TCS0.QIC3
irqchip@ (ptrval) irqchip@ (ptrval)-3
\_SB_.TCS0.QIC0 \_SB_.TCS0.QIC2

The name "irqchip@ (ptrval)-2" is not so readable in console
output.

This patch replaces space with readable "=" when output needs padding.
Following is the output after applying the patch,

[root@y domains]# ls
default irqchip@(====ptrval====)-2
irqchip@(====ptrval====)-4 \_SB_.TCS0.QIC1 \_SB_.TCS0.QIC3
irqchip@(====ptrval====) irqchip@(====ptrval====)-3 \_SB_.TCS0.QIC0
\_SB_.TCS0.QIC2

There is same problem in some subsystem's dmesg output. Moreover,
someone may call "%p" in a similar case. In addition, the timing of
crng initialization done may vary on different system. So, the change
is made in vsprintf.c.

Link: https://patchwork.kernel.org/patch/10185199/

Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Joey Zheng <yu.zheng@hxt-semitech.com>
Suggested-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Shunyong Yang <shunyong.yang@hxt-semitech.com>
---
lib/vsprintf.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 77ee6ced11b1..9fdc8376752a 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1700,9 +1700,25 @@ static char *ptr_to_id(char *buf, char *end, void *ptr, struct printf_spec spec)
const int default_width = 2 * sizeof(ptr);

if (unlikely(!have_filled_random_ptr_key)) {
+ char *ptrval_str = "(ptrval)";
+ char str[default_width + 1];
+ int len = strlen(ptrval_str);
+
+ if (default_width > len) {
+ int pos;
+
+ pos = (default_width - len) / 2;
+ memset(str, '=', default_width);
+ memcpy(str + pos + 1, ptrval_str + 1, len - 2);
+ str[0] = '(';
+ str[default_width - 1] = ')';
+ str[default_width] = 0;
+ ptrval_str = str;
+ }
+
spec.field_width = default_width;
/* string length must be less than default_width */
- return string(buf, end, "(ptrval)", spec);
+ return string(buf, end, ptrval_str, spec);
}

#ifdef CONFIG_64BIT
--
1.8.3.1