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

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Message-ID: <a7bbca09-b733-2e6e-0662-cb5d7b67d255@gmx.de>
Date:   Fri, 25 Aug 2023 23:09:42 +0200
From:   Helge Deller <deller@....de>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andrei Vagin <avagin@...nvz.org>,
        linux-parisc <linux-parisc@...r.kernel.org>
Subject: Re: [PATCH v2] procfs: Fix /proc/self/maps output for 32-bit kernel
 and compat tasks

On 8/23/23 00:04, Helge Deller wrote:
> 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@....de> wrote:
>>>
>>>> On a 32-bit kernel addresses should be shown with 8 hex digits, e.g.:
>>>>
>>>> root@...ian:~# 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@...ian:~# 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.

To sum up:
It was a bug in the in-kernel __clzdi2() function.
This patch ("lib/clz_ctz.c: Fix __clzdi2() and __ctzdi2() for 32-bit kernels") fixes it:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=382d4cd1847517ffcb1800fd462b625db7b2ebea

Thanks!
Helge