r2: expanding a file size not working as expected
Author: afiskonCreated Oct 14, 2024Updated Apr 12, 2026
Environment
eax@z930:~$ date
Mon Oct 14 15:00:03 MSK 2024
eax@z930:~$ r2 -v
radare2 5.9.7 32724 @ linux-x86-64
birth: git.5.9.6-5-g1cbab0f485 2024-10-14__14:39:51
commit: 1cbab0f48541e30a975154e953fb2fc9852263bb
options: gpl -O? cs:5 cl:2 make
eax@z930:~$ uname -ms
Linux x86_64Description
I'm using r2 as a simple hex editor. While doing so I noticed that expending a binary file with r and checking the result with px shows that the file size was not affected. The w command doesn't seem to be aware of the additionally allocated space too. If I quit with q and open the same file again I see that the size was changed correctly. Truncating the file with r seems to work properly.
Test
echo aaa > test.bin
r2 -w test.bin
[0x00000000]> px 010
- offset - 0 1 2 3 4 5 6 7 8 9 A B C D E F 0123456789ABCDEF
0x00000000 6161 610a ffff ffff aaa.....
[0x00000000]> px 0x10
- offset - 0 1 2 3 4 5 6 7 8 9 A B C D E F 0123456789ABCDEF
0x00000000 6161 610a ffff ffff ffff ffff ffff ffff aaa.............
[0x00000000]> r 0x10
[0x00000000]> r
16
[0x00000000]> px 0x10
- offset - 0 1 2 3 4 5 6 7 8 9 A B C D E F 0123456789ABCDEF
0x00000000 6161 610a ffff ffff ffff ffff ffff ffff aaa.............
[0x00000000]> wx 11 22 33 44 55
[0x00000000]> px 0x10
- offset - 0 1 2 3 4 5 6 7 8 9 A B C D E F 0123456789ABCDEF
0x00000000 1122 3344 ffff ffff ffff ffff ffff ffff ."3D............
[0x00000000]> q
r2 -w test.bin
[0x00000000]> px 0x10
- offset - 0 1 2 3 4 5 6 7 8 9 A B C D E F 0123456789ABCDEF
0x00000000 1122 3344 0000 0000 0000 0000 0000 0000 ."3D............Source: radareorg/radare2