Looks like an embedded timestamp:
--8<---cut here---start->8---
$ diff -ru --no-dereference
/gnu/store/8pskv4xpdjg1grx3c2an3g5fqj8pcrgh-gdbm-1.12{,-check}
Binary files
/gnu/store/8pskv4xpdjg1grx3c2an3g5fqj8pcrgh-gdbm-1.12/lib/libgdbm.a and
/gnu/store/8pskv4xpdjg1grx3c2an3g5fqj8pcrgh-gdbm-1.12-check/lib/libgdbm.a differ
Binary files
/gnu/store/8pskv4xpdjg1grx3c2an3g5fqj8pcrgh-gdbm-1.12/lib/libgdbm.so.4.0.0 and
/gnu/store/8pskv4xpdjg1grx3c2an3g5fqj8pcrgh-gdbm-1.12-check/lib/libgdbm.so.4.0.0
differ
$ git describe
v0.11.0-2-g8aceca5
$ diffoscope /gnu/store/8pskv4xpdjg1grx3c2an3g5fqj8pcrgh-gdbm-1.12{,-check}/lib
--- /gnu/store/8pskv4xpdjg1grx3c2an3g5fqj8pcrgh-gdbm-1.12/lib
+++ /gnu/store/8pskv4xpdjg1grx3c2an3g5fqj8pcrgh-gdbm-1.12-check/lib
[...]
├── libgdbm.a
│┄ xxd not available in path. Falling back to Python hexlify.
│┄ No differences found inside, yet data differs
│ @@ -2892,15 +2892,15 @@
│ 2020302020202020202020202020302020202020302020202020363434202020
│ 202031373834202020202020600a7f454c46020101000100
│ 3e0001003803
│ 40004f000c008b163917b801007f2d7c238b4e04394f
│ 047f237c198b4e08394f087f190f9cc00fb6c0f7d8c30f1f8400b8ff
│ ff0f1f00f3c301000c00
│ 4744424d2076657273696f6e20312e31322e2031362f30352f32
│ -30313620286275696c74204a756e20313320323031362032313a32343a323729
│ +30313620286275696c742041756720203320323031362030393a30363a353729
│ 4743433a2028474e552920342e392e331400017a
│ 5200017810011b0c0708900114001c003a00
│ 002e73796d746162002e737472746162002e7368737472746162
│ 002e74657874002e72656c612e64617461002e627373002e746578742e756e6c
│ 696b656c79002e726f64617461002e726f646174612e737472312e38002e636f
│ 6d6d656e74002e6e6f74652e474e552d737461636b002e72656c612e65685f66
│ 72616d65
[...]
├── libgdbm.so.4.0.0
│ ├── readelf --wide --hex-dump=.rodata {}
│ │ @@ -98,10 +98,10 @@
│ │0x8c30 7778797a 30313233 34353637 38392b2f wxyz0123456789+/
│ │0x8c40 00636f75 6c646e27 7420696e 69742063 .couldn't init c
│ │0x8c50 61636865 006d616c 6c6f6320 6661696c ache.malloc fail
│ │0x8c60 65640067 64626d20 66617461 6c3a2025 ed.gdbm fatal: %
│ │0x8c70 730a 0100 0c00 s...
│ │0x8c80 4744424d 20766572 73696f6e 20312e31 GDBM version 1.1
│ │0x8c90 322e2031 362f3035 2f323031 36202862 2. 16/05/2016 (b
│ │ - 0x8ca0 75696c74 204a756e 20313320 32303136 uilt Jun 13 2016
│ │ - 0x8cb0 2032313a 32343a32 3729 21:24:27)..
│ │ + 0x8ca0 75696c74 20417567 20203320 32303136 uilt Aug 3 2016
│ │ + 0x8cb0 2030393a 30363a35 3729 09:06:57)..
--8<---cut here---end--->8---
Ludo’.
