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SubjectRe: ancient portmap segfault
Andi,
thanks for the response.

The code forks immediately and the new process segfaults immediately.
From an inspection of 'strace -f' on a working version, the next call
would have been setsid() . (The library call in the code is daemon(0,0)).
The original Makefile has an LDFLAG of -N (OMAGIC: make text secion writable,
don't page-align the data section.... No idea why).
If I compile with ancient gcc/ld,
it works after compiling without -N and segfaults when compiling with -N.
If I compile with a recent gcc/ld, it works fine.

here's an objump of the segfaulting portmap
------------------------------------------------
> objdump -x /usr/sbin/portmap
/usr/sbin/portmap: file format a.out-i386-linux
/usr/sbin/portmap
architecture: i386, flags 0x00000002:
EXEC_P
start address 0x00000000
Sections:
Idx Name Size VMA LMA File off Algn
0 .text 00000f7c 00000000 00000000 00000020 2**2
CONTENTS, ALLOC, LOAD, CODE
1 .data 00000110 00000f7c 00000f7c 00000f9c 2**2
CONTENTS, ALLOC, LOAD, DATA
2 .bss 00000018 0000108c 0000108c 00000000 2**2
ALLOC
SYMBOL TABLE:
no symbols
-------------------
and here's the objdump of the test without -N
> objdump -h a.out

a.out: file format a.out-i386-linux

Sections:
Idx Name Size VMA LMA File off Algn
0 .text 00001fe0 00001020 00001020 00000020 2**3
CONTENTS, ALLOC, LOAD, CODE
1 .data 00001000 00003000 00003000 00002000 2**3
CONTENTS, ALLOC, LOAD, DATA
2 .bss 00000000 00004000 00004000 00000000 2**3
ALLOC


--------------------------------------------------
so maybe the alignment difference is the problem?
as I said before, I have things working, only reporting this on the possibility
that it's a bug worth investigating.

thanks
mds


Andi Kleen wrote:
> Mark Studebaker <mds@mds.gotdns.com> writes:
>
>
>>I upgraded from 2.6.5 to 2.6.11.2 and my ancient (libc4 a.out) /sbin/portmap from 1994 that's been running without complaint
>>on kernels for 11 years now consistently segfaults.
>>
>>I upgraded to a version 4 RPM (circa 2002) and that fixed it.
>>
>>If some compatibility was broken on purpose, that's fine, although I couldn't find anything in the kernel docs.
>>I know, I should upgrade everything, but that can break a lot of things too...
>>Thought I'd mention it though in case it's a bug or somebody else has the same problem.
>
>
> It's probably a bug, but your bug report doesn't have enough details
> to track it down. Do you have a a.out strace and could send an strace log
> with the segfault and the last tens of system calls before it?
>
> -Andi


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