Messages in this thread | | | Date | Mon, 21 Aug 2023 10:41:33 +0200 | Subject | Re: [PATCH] procfs: Fix /proc/self/maps output for 32-bit kernel and compat tasks | From | Vegard Nossum <> |
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On 8/19/23 11:21, Helge Deller 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. > > Signed-off-by: Helge Deller <deller@gmx.de> > Fixes: 0e3dc0191431 ("procfs: add seq_put_hex_ll to speed up /proc/pid/maps") > Cc: Andrei Vagin <avagin@openvz.org> > > diff --git a/fs/seq_file.c b/fs/seq_file.c > index f5fdaf3b1572..1a15b531aede 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> > @@ -759,11 +760,16 @@ void seq_put_hex_ll(struct seq_file *m, const char *delimiter, > seq_puts(m, delimiter); > } > > +#ifdef CONFIG_64BIT > /* If x is 0, the result of __builtin_clzll is undefined */ > - if (v == 0) > + if (v == 0 || is_compat_task()) > len = 1; > else > len = (sizeof(v) * 8 - __builtin_clzll(v) + 3) / 4; > +#else > + /* On 32-bit kernel always use provided width */ > + len = 1; > +#endif > > if (len < width) > len = width;
Hi,
I think this is fixing the wrong thing.
seq_put_hex_ll() is a generic routine so the #ifdef/is_compat_task() doesn't seem to belong there.
Moreover, the kerneldoc comment on this function states:
* seq_put_hex_ll(m, "", v, 8) is equal to seq_printf(m, "%08llx", v)
The seq_put_hex_ll() call from show_vma_header_prefix() is calling this with the last argument (minimum padding length) being 8, so why is it padding to more than that in the first place?
Look at your example:
> root@debian:~# cat /proc/self/maps > 0000000010000-0000000019000 r-xp 00000000 000000008:000000005 787324 /usr/bin/cat
that's padded to... 13 hex characters? Huh?
Even on my x86_64, short addresses are only padded to 8 bytes, as they should be in all cases. Could there possibly be a bug in parisc __builtin_clzll()...?
Vegard
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