What's gcj?
gcj (src: gcc-whatever) compiles (something resembling) Java to native binaries.
It's used, in Debian, mostly to produce versions of build tools which don't depend on having default-jre installed (probably because default-jre is order-of 100MB).
Detection
debbindiff finds a Build Id: variation during readelf, probably for a file named something.jar.so.
Cause
Unknown.
$ sudo apt-get install gcj-4.9-jdk
...
$ echo 'public class A { public static void main(String[] s) { System.out.println("Hello world."); } }' > A.java
$ gcj-4.9 -c A.java && readelf --all A.o > 1
$ gcj-4.9 -c A.java && readelf --all A.o > 2
$ diff -u 1 2
@@ -169,7 +169,7 @@
Symbol table '.symtab' contains 47 entries:
Num: Value Size Type Bind Vis Ndx Name
0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND
- 1: 0000000000000000 0 FILE LOCAL DEFAULT ABS cce7CLvy.jar
+ 1: 0000000000000000 0 FILE LOCAL DEFAULT ABS ccCSg3WR.jar
2: 0000000000000000 0 SECTION LOCAL DEFAULT 1
3: 0000000000000000 0 SECTION LOCAL DEFAULT 3
4: 0000000000000000 0 SECTION LOCAL DEFAULT 5
... but also sometimes:
@@ -137,14 +137,14 @@
Relocation section '.rela.debug_info' at offset 0x1210 contains 12 entries:
Offset Info Type Sym. Value Sym. Name + Addend
000000000006 00150000000a R_X86_64_32 0000000000000000 .debug_abbrev + 0
-00000000000c 00180000000a R_X86_64_32 0000000000000000 .debug_str + 47
-000000000011 00180000000a R_X86_64_32 0000000000000000 .debug_str + 40
-000000000015 00180000000a R_X86_64_32 0000000000000000 .debug_str + 2a
+00000000000c 00180000000a R_X86_64_32 0000000000000000 .debug_str + 25
+000000000011 00180000000a R_X86_64_32 0000000000000000 .debug_str + 157
+000000000015 00180000000a R_X86_64_32 0000000000000000 .debug_str + 141
000000000019 000200000001 R_X86_64_64 0000000000000000 .text + 0
000000000029 00170000000a R_X86_64_32 0000000000000000 .debug_line + 0
00000000002e 00180000000a R_X86_64_32 0000000000000000 .debug_str + 0
000000000034 000200000001 R_X86_64_64 0000000000000000 .text + 0
-000000000047 00180000000a R_X86_64_32 0000000000000000 .debug_str + 25
+000000000047 00180000000a R_X86_64_32 0000000000000000 .debug_str + 15e
00000000004d 000200000001 R_X86_64_64 0000000000000000 .text + 22
000000000060 00180000000a R_X86_64_32 0000000000000000 .debug_str + 7
000000000064 000200000001 R_X86_64_64 0000000000000000 .text + 8b