gas listing option changes the size of the .eh_frame section

[Richard Sharman]

Why does the gas listing option change the size of the .eh_frame section?
[This occurs with gas 2.11.90.0.8, but not with version 2.9.5]


The following example demonstrates what I mean.  
A trivial C++ program is compiled, stopping after the assembler file is
produced.  A copy of it is taken.  When compiling the two assembler
programs with and without the -a option the resulting object files
differ in the .eh_frame section.

The first diff shows the differences of "objdump -h",  showing the
differences in sizes of the section.

The second diff shows the differences of the .eh_frame section itself.

% cat run
#! /bin/sh
set -v
cat a.cc
g++ -S -o a.s a.cc
cp a.s b.s
as -o a.o a.s
as -o b.o -Wa b.s > List
ls -l a.o b.o
objdump -h a.o > D1
objdump -h b.o > D2
diff D1 D2
objdump -j .eh_frame -s -r  a.o > D3
objdump -j .eh_frame -s -r  b.o > D4
diff D3 D4
% ./run
cat a.cc
#include <iostream.h>

int main(void) {
  cout << "hello, world" << endl;
  exit(0);
}
g++ -S -o a.s a.cc
cp a.s b.s
as -o a.o a.s
as -o b.o -Wa b.s > List
ls -l a.o b.o
-rw-r--r--    1 sharman  gx5000       1364 Feb 14 16:37 a.o
-rw-r--r--    1 sharman  gx5000       1376 Feb 14 16:37 b.o
objdump -h a.o > D1
objdump -h b.o > D2
diff D1 D2
2c2
< a.o:     file format elf32-i386
---
> b.o:     file format elf32-i386
16c16
<   5 .eh_frame     00000030  00000000  00000000  000000b4  2**2
---
>   5 .eh_frame     0000003c  00000000  00000000  000000b4  2**2
18c18
<   6 .comment      00000026  00000000  00000000  000000e4  2**0
---
>   6 .comment      00000026  00000000  00000000  000000f0  2**0
objdump -j .eh_frame -s -r  a.o > D3
objdump -j .eh_frame -s -r  b.o > D4
diff D3 D4
2c2
< a.o:     file format elf32-i386
---
> b.o:     file format elf32-i386
11,12c11,13
<  0010 88010000 18000000 18000000 00000000  ................
<  0020 44000000 410e0885 02420d05 582e1000  D...A....B..X...
---
>  0010 88010000 24000000 18000000 00000000  ....$...........
>  0020 44000000 04010000 000e0885 02040200  D...............
>  0030 00000d05 04180000 002e1000           ............    
% 

Versions:

% gcc -v
Reading specs from /usr/local/lib/gcc-lib/i686-pc-linux-gnu/2.95.3/specs
gcc version 2.95.3 20010315 (release)
% as --version
GNU assembler 2.11.90.0.8
Copyright 2001 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License.  This program has absolutely no warranty.
This assembler was configured for a target of `i386-redhat-linux'.
% objdump --version
GNU objdump 2.11.90.0.8
Copyright 1997, 98, 99, 2000, 2001 Free Software Foundation, Inc.
This program is free software; you may redistribute it under the terms of
the GNU General Public License.  This program has absolutely no warranty.
% 

When I tried with 2.9.5 gas the problem did not occur.

Richard Sharman