UPX - a powerful executable packer

FYI, there are currently no plans to enhance --exact beyond what's
implemented in UPX 3.02. This has both technical (high impact on source
code) and political (e.g. Anti-Virus vendor support) reasons.

Authors who really care about byte-identical versions should use the
one-time compress-decompress workaround mentioned in the docs.

~Markus

Yes, UPX strips some unneeded information from the file it compresses (in
the case of PE format). This improves the compression ratio.

Laszlo

Is the same information lost regardless of compression options?

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There are currently no plans to enhance --exact beyond what's implemented
in UPX 3.01. This has both technical (high impact on source code) and
political (e.g. Anti-Virus vendor support) reasons.

Authors who really care should use the one-time compress-decompress
workaround mentioned in the docs.

I see that UPX 3.01 will refuse to compress a w32 exe if given the --exact
switch (before DLLs were refused, but not EXEs). Good.

When is support for win32/pe planned?

Please have a look at the updated docs about --exact in UPX 3.01 - maybe
that workaround does suit your needs.

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I want to add that MD5 signatures of files before UPX compression and
after compress-uncompress sequence are not same.

We still need to add several throwCantPackExact() statements so that
people at least get warned that --exact does not for all formats as
expected.

The --exact option is not yet supported by all formats. win32/PE is one
those. We've already added a comment about this into the documentation.

The bug is postponed.

Laszlo

I came here to report the same. I hope this will be fixed in next release.