[PATCH v2] procfs: Fix /proc/self/maps output for 32-bit kernel and compat tasks

[Helge Deller <deller@gmx.de>]

On a 32-bit kernel addresses should be shown with 8 hex digits, e.g.:

root@debian:~# cat /proc/self/maps
00010000-00019000 r-xp 00000000 08:05 787324     /usr/bin/cat
00019000-0001a000 rwxp 00009000 08:05 787324     /usr/bin/cat
0001a000-0003b000 rwxp 00000000 00:00 0          [heap]
f7551000-f770d000 r-xp 00000000 08:05 794765     /usr/lib/hppa-linux-gnu/libc.so.6
f770d000-f770f000 r--p 001bc000 08:05 794765     /usr/lib/hppa-linux-gnu/libc.so.6
f770f000-f7714000 rwxp 001be000 08:05 794765     /usr/lib/hppa-linux-gnu/libc.so.6
f7d39000-f7d68000 r-xp 00000000 08:05 794759     /usr/lib/hppa-linux-gnu/ld.so.1
f7d68000-f7d69000 r--p 0002f000 08:05 794759     /usr/lib/hppa-linux-gnu/ld.so.1
f7d69000-f7d6d000 rwxp 00030000 08:05 794759     /usr/lib/hppa-linux-gnu/ld.so.1
f7ea9000-f7eaa000 r-xp 00000000 00:00 0          [vdso]
f8565000-f8587000 rwxp 00000000 00:00 0          [stack]

But since commmit 0e3dc0191431 ("procfs: add seq_put_hex_ll to speed up
/proc/pid/maps") even on native 32-bit kernels the output looks like this:

root@debian:~# cat /proc/self/maps
0000000010000-0000000019000 r-xp 00000000 000000008:000000005 787324  /usr/bin/cat
0000000019000-000000001a000 rwxp 000000009000 000000008:000000005 787324  /usr/bin/cat
000000001a000-000000003b000 rwxp 00000000 00:00 0  [heap]
00000000f73d1000-00000000f758d000 r-xp 00000000 000000008:000000005 794765  /usr/lib/hppa-linux-gnu/libc.so.6
00000000f758d000-00000000f758f000 r--p 000000001bc000 000000008:000000005 794765  /usr/lib/hppa-linux-gnu/libc.so.6
00000000f758f000-00000000f7594000 rwxp 000000001be000 000000008:000000005 794765  /usr/lib/hppa-linux-gnu/libc.so.6
00000000f7af9000-00000000f7b28000 r-xp 00000000 000000008:000000005 794759  /usr/lib/hppa-linux-gnu/ld.so.1
00000000f7b28000-00000000f7b29000 r--p 000000002f000 000000008:000000005 794759  /usr/lib/hppa-linux-gnu/ld.so.1
00000000f7b29000-00000000f7b2d000 rwxp 0000000030000 000000008:000000005 794759  /usr/lib/hppa-linux-gnu/ld.so.1
00000000f7e0c000-00000000f7e0d000 r-xp 00000000 00:00 0  [vdso]
00000000f9061000-00000000f9083000 rwxp 00000000 00:00 0  [stack]

This patch brings back the old default 8-hex digit output for
32-bit kernels and compat tasks.

Fixes: 0e3dc0191431 ("procfs: add seq_put_hex_ll to speed up /proc/pid/maps")
Cc: Andrei Vagin <avagin@openvz.org>
Signed-off-by: Helge Deller <deller@gmx.de>

---
v2:
- Linux kernel test robot complained that is_compat_task() isn't known.
  Use in_compat_syscall() instead and check for 32-bit kernel with
  !IS_ENABLED(CONFIG_64BIT)

---

diff --git a/fs/seq_file.c b/fs/seq_file.c
index f5fdaf3b1572..52a0ea05cad2 100644
--- a/fs/seq_file.c
+++ b/fs/seq_file.c
@@ -19,6 +19,7 @@
 #include <linux/printk.h>
 #include <linux/string_helpers.h>
 #include <linux/uio.h>
+#include <linux/compat.h>
 
 #include <linux/uaccess.h>
 #include <asm/page.h>
@@ -759,8 +760,9 @@ void seq_put_hex_ll(struct seq_file *m, const char *delimiter,
 			seq_puts(m, delimiter);
 	}
 
-	/* If x is 0, the result of __builtin_clzll is undefined */
-	if (v == 0)
+	/* If v is 0, the result of __builtin_clzll is undefined */
+	/* Use provided width on 32-bit kernel and compat mode */
+	if (v == 0 || !IS_ENABLED(CONFIG_64BIT) || in_compat_syscall())
 		len = 1;
 	else
 		len = (sizeof(v) * 8 - __builtin_clzll(v) + 3) / 4;