Hi Mark,
That might be an interesting alternative. Could you use this for e.g.
inserting a .comment section fragment with an unique (version) string?
That would be stripped away, but should still count for the build-id
hash calculation.
If you know the value you want to store ahead of time, then it is easy:
% cat comment.t
SECTIONS
{
.comment (INFO) :
{
BYTE (0x12);
BYTE (0x34);
BYTE (0x56);
BYTE (0x78);
}
}
% gcc hello.c -Wl,comment.t
% readelf -x.comment a.out
Hex dump of section '.comment':
0x00000000 4743433a 2028474e 55292037 2e332e31 GCC: (GNU) 7.3.1
0x00000010 20323031 38303133 30202852 65642048 20180130 (Red H
0x00000020 61742037 2e332e31 2d322900 4743433a at 7.3.1-2).GCC:
0x00000030 2028474e 55292037 2e322e31 20323031 (GNU) 7.2.1 201
0x00000040 37303931 35202852 65642048 61742037 70915 (Red Hat 7
0x00000050 2e322e31 2d322900 12345678 .2.1-2)..4Vx
(Note how the value has been appended to the .comment section).
Unfortunately the linker does not have a STRING() operator to insert
ascii codes into a section, so you have to construct the bytes by
hand. Eg:
% cat comment.t
SECTIONS
{
.comment (INFO) :
{
BYTE (0x41);
BYTE (0x42);
BYTE (0x43);
BYTE (0x00);
}
}
% gcc hello.c -Wl,comment.t
% readelf -p.comment a.out
String dump of section '.comment':
[ 0] GCC: (GNU) 7.3.1 20180130 (Red Hat 7.3.1-2)
[ 2c] GCC: (GNU) 7.2.1 20170915 (Red Hat 7.2.1-2)
[ 58] ABC
A simple perl or python script could be used to create the comment.t
linker script fragment.
Cheers
Nick