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Fix the DLL (re)basing problem in Cygwin / MSYS2

Author: AlexVie
Title: Fix DLL rebasing problems in Cygwin and MSYS2
Language: en-US
Created: 01:33 on Wednesday, 18. October 2017
Modified: 01:33 on Wednesday, 18. October 2017

Sometimes, when launching new programs under Cygwin or MSYS2, you may encounter an error like this:

0 [main] zsh 8712 child_info_fork::abort: address space needed by ‘datetime.dll’ (0x3F0000) is already occupied

This means, a by default non-rebaseable DLL cannot be loaded into the address space it wants to go.

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  • can affect Cygwin and MSYS2
  • is much more likely to occur in the 32bit versions
  • can be fixed easily

DLL memory management problems are known issues that plague Cygwin and MSYS2 for quite a while and particularly affect the 32bit versions. The 64bit versions benefit from the much larger address space, so collisions are less likely to occur. It is therefore strongly recommended to use the 64bit versions of Cygwin or MSYS2 whenever possible. The requirements for the 64bit versions are not steep, it’s basically just a 64bit Windows OS and slightly more RAM than the 32bit versions would use.

I ran into the problem when I recently installed MSYS2 on an old laptop which still runs 32bit Windows 7 and has only 4 GB of RAM, so using the 64bit version of MSYS2 was not an option. Upgrading the OS to a 64bit variant does not make a lot of sense nor would it bring benefits to that somewhat ancient hardware.

The error message

0 [main] zsh 8712 child_info_fork::abort: address space needed by 'parameter.dll' (0x3F0000) is already occupied
/home/myusername/.zsh/tools/ fork failed: resource temporarily unavailable

Obviously, the process names and address values can vary and it can occur with any process that tries to load a DLL, that is not re-baseable, into memory. The virtual address space it claims being already occupied by another process is the most (or only) common cause for the error.

Easily fixable

Fortunately, the issue is easily fixable and only requires that the DLL in question must be marked as re-baseable, which can be done using the peflags and rebase commands. These should be part of every standard Cygwin / MSYS2 installation.

$ peflags -d1 /usr/lib/zsh/5.4.2/zsh/parameter.dll
$ rebase /usr/lib/zsh/5.4.2/zsh/parameter.dll

Note that in order to mark a DLL as re-baseable, it must not be in use, so for best results, you should do this using /usr/bin/dash (a minimalistic shell that does not depend on DLLs).

/usr/lib/zsh/5.4.2/zsh/parameter.dll: skipped because could not open

When using peflags or rebase on it is a good sign for a DLL being in use. To fix, terminate all running Cygwin/MSYS2 processes, start /usr/bin/dash (from windows desktop or command line) and try again.

The command peflags accepts wild cards and instead of rebase you can use rebaseall -v which will try to re-base every executable file that is marked as re-baseable.