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

[Shunyong Yang]

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@xxxxxxxxxxxxxxx>
Cc: Joey Zheng <yu.zheng@xxxxxxxxxxxxxxxx>
Suggested-by: Rasmus Villemoes <linux@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Shunyong Yang <shunyong.yang@xxxxxxxxxxxxxxxx>
---
 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