[PATCH] src/ext4_resize.c: set errno to 0 before the strtoull call

[xuyang2018.jy@fujitsu.com]

on 2022/1/18 22:02, Florian Weimer wrote:
> * xuyang2018.jy:
> 
>> on 2022/1/18 11:56, Theodore Ts'o wrote:
>>> On Tue, Jan 18, 2022 at 02:43:26AM +0000, xuyang2018.jy@fujitsu.com wrote:
>>>>> You're right of course, but out of curiosity, which C library are you
>>>>> using?
>>>> I use glibc-2.34.
>>>
>>> Hmm, ok.  I'm using glibc 2.31, and in this particular program, errno
>>> shouldn't have been set by any prior system call.  I'm guessing maybe
>>> it was something in crt0 which ended up setting errno?
>> It maybe a glibc bug.
>> I cc glibc mailing list and see whether they have met this problem.
>>
>> @Florian
>>
>> Now, I use glibc-2.34 and run the following program[1] but the errno is
>> not 0 in the beginning. So is this a known bug on glibc-2.34(Theodore
>> doesn't meet this problem on glicb-2.31)?
>>
>> [1]https://git.kernel.org/pub/scm/fs/xfs/xfstests-dev.git/tree/src/ext4_resize.c
> 
> I'm not aware of this issue.  Could you run strace or strace -k to see
> where the failing system call is coming from?  Thanks.
Even before open call, errno is also 1.

The strace output see attachment.

I found the following difference(compare with glibc-2.28, search 'err'
keywords)

bad(glibc-2.34):

map(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0)
= 0x7fdf815a3000
 > /usr/lib64/ld-linux-x86-64.so.2(__mmap+0x26) [0x21c56]
 > /usr/lib64/ld-linux-x86-64.so.2(rtld_malloc+0xa0) [0x1dc50]
 > /usr/lib64/ld-linux-x86-64.so.2(_dl_check_map_versions+0x4ec) [0x121fc]
 > /usr/lib64/ld-linux-x86-64.so.2(_dl_check_all_versions+0x3e) [0x124de]
 > /usr/lib64/ld-linux-x86-64.so.2(version_check_doit+0x1b) [0x1cab]
 > /usr/lib64/ld-linux-x86-64.so.2(_dl_receive_error+0x31) [0x1e811]
 > /usr/lib64/ld-linux-x86-64.so.2(dl_main+0x1e46) [0x4416]
 > /usr/lib64/ld-linux-x86-64.so.2(_dl_sysdep_start+0x3f6) [0x1d696]
 > /usr/lib64/ld-linux-x86-64.so.2(_dl_start+0x217) [0x2097]
 > /usr/lib64/ld-linux-x86-64.so.2(_start+0x7) [0x1097]
 > no matching address range
arch_prctl(ARCH_SET_FS, 0x7fdf815a4480) = 0

good(glibc-2.28):

map(NULL, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0)
= 0x7febd628b000
 > /usr/lib64/ld-2.28.so(__mmap+0x47) [0x1c377]
 > /usr/lib64/ld-2.28.so(malloc+0x8a) [0x1a94a]
 > /usr/lib64/ld-2.28.so(_dl_allocate_tls_storage+0x23) [0x12ac3]
 > /usr/lib64/ld-2.28.so(init_tls+0xa5) [0x1da5]
 > /usr/lib64/ld-2.28.so(dl_main+0x2c6d) [0x51ed]
 > /usr/lib64/ld-2.28.so(_dl_sysdep_start+0x48e) [0x1a14e]
 > /usr/lib64/ld-2.28.so(_dl_start+0x275) [0x2135]
 > /usr/lib64/ld-2.28.so(_start+0x7) [0x1087]
 > No DWARF information found
arch_prctl(ARCH_SET_FS, 0x7febd628b740) = 0

Also if use gcc to compile this c program directly instead of using make
in xfstests testsuite,  the errno value is normal(0).

After tried, I found if using the following command, errno is still 0
gcc ext4_resize.c -g -O2  -D_GNU_SOURCE   -D_FILE_OFFSET_BITS=64
-funsigned-char -fno-strict-aliasing  -Wall -o ext4_resize

But if I used link with lcap, then errno becomes 1 in the beginning.

Even I use lastest upstream libcap, this problem still occurs.

I am still looking into it .

Best Regards
Yang Xu

> 
> Florian
> 

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