Hello!
I've been interested for a while in making all of my software builds
reproducible [0]. I don't think there's ever been any kind of
written guarantee that the output of javac will be completely
deterministic, but to date it seems like it actually has been. However,
I was a bit disappointed today to find that the output of one of the
builds at AdoptOpenJDK [1] seems to be inserting compiler version
information into compiled module descriptors. It doesn't seem to be
doing this for any other class files.
Here's the output of "openjdk version 10.0.1 2018-04-17" on Linux
(not an AdoptOpenJDK build) when compiling a module descriptor:
---
module com.io7m.jtensors.core
minor version: 0
major version: 53
flags: (0x8000) ACC_MODULE
this_class: #1 // "module-info"
super_class: #0
interfaces: 0, fields: 0, methods: 0, attributes: 2
Constant pool:
#1 = Class #17 // "module-info"
#2 = Utf8 SourceFile
#3 = Utf8 module-info.java
#4 = Utf8 Module
#5 = Module #18 // "com.io7m.jtensors.core"
#6 = Module #19 // "java.base"
#7 = Module #20 // "org.immutables.value"
#8 = Module #21 // "com.io7m.junreachable.core"
#9 = Package #22 // com/io7m/jtensors/core/determinants
#10 = Package #23 // com/io7m/jtensors/core/dotproducts
#11 = Package #24 //
com/io7m/jtensors/core/parameterized/matrices
#12 = Package #25 //
com/io7m/jtensors/core/parameterized/vectors
#13 = Package #26 // com/io7m/jtensors/core/quaternions
#14 = Package #27 //
com/io7m/jtensors/core/unparameterized/matrices
#15 = Package #28 //
com/io7m/jtensors/core/unparameterized/vectors
#16 = Package #29 // com/io7m/jtensors/core
#17 = Utf8 module-info
#18 = Utf8 com.io7m.jtensors.core
#19 = Utf8 java.base
#20 = Utf8 org.immutables.value
#21 = Utf8 com.io7m.junreachable.core
#22 = Utf8 com/io7m/jtensors/core/determinants
#23 = Utf8 com/io7m/jtensors/core/dotproducts
#24 = Utf8 com/io7m/jtensors/core/parameterized/matrices
#25 = Utf8 com/io7m/jtensors/core/parameterized/vectors
#26 = Utf8 com/io7m/jtensors/core/quaternions
#27 = Utf8 com/io7m/jtensors/core/unparameterized/matrices
#28 = Utf8 com/io7m/jtensors/core/unparameterized/vectors
#29 = Utf8 com/io7m/jtensors/core
{
}
SourceFile: "module-info.java"
Module:
#5,0 // "com.io7m.jtensors.core"
#0
3 // requires
#6,8000 // "java.base" ACC_MANDATED
#0
#7,40 // "org.immutables.value"
ACC_STATIC_PHASE
#0
#8,0 // "com.io7m.junreachable.core"
#0
8 // exports
#9,0 //
com/io7m/jtensors/core/determinants
#10,0 //
com/io7m/jtensors/core/dotproducts
#11,0 //
com/io7m/jtensors/core/parameterized/matrices
#12,0 //
com/io7m/jtensors/core/parameterized/vectors
#13,0 //
com/io7m/jtensors/core/quaternions
#14,0 //
com/io7m/jtensors/core/unparameterized/matrices
#15,0 //
com/io7m/jtensors/core/unparameterized/vectors
#16,0 // com/io7m/jtensors/core
0 // opens
0 // uses
0 // provides
---
Here's the same module descriptor compiled on "openjdk version
10-internal" on MacOS (this is actually OpenJDK 10+23):
---
module com.io7m.jtensors.core
minor version: 0
major version: 53
flags: (0x8000) ACC_MODULE
this_class: #1 // "module-info"
super_class: #0
interfaces: 0, fields: 0, methods: 0, attributes: 2
Constant pool:
#1 = Class #18 // "module-info"
#2 = Utf8 SourceFile
#3 = Utf8 module-info.java
#4 = Utf8 Module
#5 = Module #19 // "com.io7m.jtensors.core"
#6 = Module #20 // "java.base"
#7 = Utf8 10-internal
#8 = Module #21 // "org.immutables.value"
#9 = Module #22 // "com.io7m.junreachable.core"
#10 = Package #23 // com/io7m/jtensors/core/determinants
#11 = Package #24 // com/io7m/jtensors/core/dotproducts
#12 = Package #25 //
com/io7m/jtensors/core/parameterized/matrices
#13 = Package #26 //
com/io7m/jtensors/core/parameterized/vectors
#14 = Package #27 // com/io7m/jtensors/core/quaternions
#15 = Package #28 //
com/io7m/jtensors/core/unparameterized/matrices
#16 = Package #29 //
com/io7m/jtensors/core/unparameterized/vectors
#17 = Package #30 // com/io7m/jtensors/core
#18 = Utf8 module-info
#19 = Utf8 com.io7m.jtensors.core
#20 = Utf8 java.base
#21 = Utf8 org.immutables.value
#22 = Utf8 com.io7m.junreachable.core
#23 = Utf8 com/io7m/jtensors/core/determinants
#24 = Utf8 com/io7m/jtensors/core/dotproducts
#25 = Utf8 com/io7m/jtensors/core/parameterized/matrices
#26 = Utf8 com/io7m/jtensors/core/parameterized/vectors
#27 = Utf8 com/io7m/jtensors/core/quaternions
#28 = Utf8 com/io7m/jtensors/core/unparameterized/matrices
#29 = Utf8 com/io7m/jtensors/core/unparameterized/vectors
#30 = Utf8 com/io7m/jtensors/core
{
}
SourceFile: "module-info.java"
Module:
#5,0 // "com.io7m.jtensors.core"
#0
3 // requires
#6,8000 // "java.base" ACC_MANDATED
#7 // 10-internal
#8,40 // "org.immutables.value"
ACC_STATIC_PHASE
#0
#9,0 // "com.io7m.junreachable.core"
#0
8 // exports
#10,0 //
com/io7m/jtensors/core/determinants
#11,0 //
com/io7m/jtensors/core/dotproducts
#12,0 //
com/io7m/jtensors/core/parameterized/matrices
#13,0 //
com/io7m/jtensors/core/parameterized/vectors
#14,0 //
com/io7m/jtensors/core/quaternions
#15,0 //
com/io7m/jtensors/core/unparameterized/matrices
#16,0 //
com/io7m/jtensors/core/unparameterized/vectors
#17,0 // com/io7m/jtensors/core
0 // opens
0 // uses
0 // provides
---
Note the insertion of the "10-internal" string as constant pool entry
7.
Does anyone have any idea why this would happen? I'm considering filing
a bug at the AdoptOpenJDK project, but I'd like to be sure as to
whether or not this is actually intended behaviour by newer compilers.
Inserting version information obviously breaks reproducibility, so it'd
be nice if it could be turned off!
The sources to the above module descriptor are available [2] if anyone
wants to try compiling this for themselves. The SHA256 of the resulting
module-info.class should be
e7a94b5a2788a3c5cd6d7f586e70a0f2138a2eaa0e75144b6a16e75c4b297870 if
your compiler produces the same output as mine.
[0] https://reproducible-builds.org/
[1] https://adoptopenjdk.net/
[2] https://github.com/io7m/jtensors
--
Mark Raynsford | http://www.io7m.com
