Re: segfault in git-remote-http

> On Wed, Apr 10, 2013 at 02:51:14PM -0400, Jeff King wrote:
> 
> > As for why dmesg reports git-remote-http, I'm not sure. If you
> > "strace -f" the command, you can see that git is running
> > git-remote-https. Why the kernel chooses to report
> > "git-remote-http", I don't know; you'd have to look into how the
> > kernel makes that decision. But I doubt it is related to the reason
> > for the segfault in the first place.
> 
> Ah, I see. The hard links are a red herring. The kernel's message uses
> task->comm, which is presumably set by truncating the basename of the
> program to 15 characters (16 bytes with a trailing NUL).
> 
>   3.6 /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
>   --------------------------------------------------------
>   These files provide a method to access a tasks comm value. It also
>   allows for a task to set its own or one of its thread siblings comm
>   value. The comm value is limited in size compared to the cmdline
>   value, so writing anything longer then the kernel's TASK_COMM_LEN
>   (currently 16 chars) will result in a truncated comm value.
> 
> Try:
> 
>   $ echo 'int main() { sleep(5); *(int *)0=0; }' >foo.c
>   $ gcc -o 12345678901234567890 foo.c
>   $ ./123* &
>   $ cat /proc/$!/comm
>   123456789012345
>   $ sleep 5; dmesg | tail -n 1
>   [2602639.353584] 123456789012345[23062]: segfault at 0 ip
> 0000000000400524 sp 00007fff46bb0700 error 6 in 12345678901234567890
> [400000+1000]
> 
> In both cases we only get the first 15 bytes of the program name. And
> indeed, "git-remote-http" is exactly 15 bytes. So it is dumb luck that
> the limit is such that truncating the name makes it look like another
> program.