[bug][Solved in FASM 1.71.16] invalid ELF file generated

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JohnFound

Joined: 16 Jun 2003
Posts: 3499
Location: Bulgaria

JohnFound 29 Oct 2013, 21:41

Hi, Tomasz.

It is very old problem, that I get from time to time invalid ELF file generated.

The sources where this happened were pretty big and it was impossible to search the reasons for such strange behavior.

Fortunately, today I managed to construct very small source, where the bug appears and can be reproduced. The example is artificial and does not compile to valid program:

Code:

        format ELF executable 3
        entry start

        segment readable writeable executable
start:
        int3

        align 4   ; comment this line in order to get valid elf.
        rb  16

        segment interpreter readable
        db '******************', 0

        segment dynamic readable
        db 8 dup('.')

        segment readable writeable
        db 8 dup '?'

The source is compiled to ELF file with size 197 bytes, where the asterisk string '******************',0 misses at all.

After commenting out the 'align 4' directive, the source compiles to ELF file with size 216 bytes (!) where the mentioned string exists.

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Last edited by JohnFound on 30 Oct 2013, 12:46; edited 2 times in total

29 Oct 2013, 21:41

HaHaAnonymous

Joined: 02 Dec 2012
Posts: 1178
Location: Unknown

HaHaAnonymous 29 Oct 2013, 22:24

[ Post removed by author. ]

Last edited by HaHaAnonymous on 28 Feb 2015, 19:15; edited 1 time in total

29 Oct 2013, 22:24

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20339
Location: In your JS exploiting you and your system

revolution 30 Oct 2013, 01:27

Confirmed. I made it sticky.

30 Oct 2013, 01:27

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8353
Location: Kraków, Poland

Tomasz Grysztar 30 Oct 2013, 11:26

While testing the fix for this problem I have also found another bug - one that made the addresses to be generated incorrectly if you used the default segment (that is: start code right away after "format ELF executable", without a segment directive). I fixed them both. Please try 1.71.16.

30 Oct 2013, 11:26

JohnFound

Joined: 16 Jun 2003
Posts: 3499
Location: Bulgaria

JohnFound 30 Oct 2013, 12:18

Everything seems to be OK now. Two bugs less in FASM - one more step towards the perfect assembler. Smile

30 Oct 2013, 12:18

HaHaAnonymous

Joined: 02 Dec 2012
Posts: 1178
Location: Unknown

HaHaAnonymous 30 Oct 2013, 15:00

[ Post removed by author. ]

Last edited by HaHaAnonymous on 28 Feb 2015, 19:14; edited 1 time in total

30 Oct 2013, 15:00

revolution
When all else fails, read the source

Joined: 24 Aug 2004
Posts: 20339
Location: In your JS exploiting you and your system

revolution 30 Oct 2013, 15:05

HaHaAnonymous wrote:

Humans will never meet perfection.

That depends upon how you define perfection.

30 Oct 2013, 15:05

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