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

Helge Deller
2023-08-22T22:05:00Z

On 8/22/23 22:53, Helge Deller wrote:
> On 8/22/23 20:34, Andrew Morton wrote:
>> On Tue, 22 Aug 2023 11:20:36 +0200 Helge Deller <deller@gmx.de> wrote:
>>
>>> 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")
>>
>> That was five years ago.  Given there is some risk of breaking existing
>> parsers, is it worth fixing this?
>
> Huh... that's right!
> Nevertheless, kernel 6.1.45 has it right, which isn't 5 years old.
> I don't see the reason for that change right now, so I'll need to figure out what changed...

It seems to be due to a new bug in gcc's __builtin_clzll()
function (at least on parisc), which seems to return values
for "long" (32bit) instead for "long long" (64bit).

Please ignore this patch for now.

Thanks!
Helge