Using libfaketime to manipulate the system time for applications #faketime #wine #debug #commandlinefu

libfaketime_usage.md

Using libfaketime to manipulate the system time for applications

See libfaketime on github for upstream project site general overview.

Build in multilib environment

#!/usr/bin/env bash

set -Eeuo pipefail

LIBFAKETIME_SOURCE_PATH=$PWD/libfaketime
LIBFAKETIME_INSTALL32_PREFIX=$PWD/install-x86
LIBFAKETIME_INSTALL64_PREFIX=$PWD/install-x86_64

[[ -d $LIBFAKETIME_SOURCE_PATH ]] || git clone https://github.com/wolfcw/libfaketime.git
make -C $LIBFAKETIME_SOURCE_PATH PREFIX=$LIBFAKETIME_INSTALL64_PREFIX distclean install | tee build64.log
CFLAGS="-m32" LDFLAGS="-m32" make -C $LIBFAKETIME_SOURCE_PATH PREFIX=$LIBFAKETIME_INSTALL32_PREFIX distclean install | tee build32.log

# generate scripts for shell environment
echo "export LD_PRELOAD=$LIBFAKETIME_INSTALL32_PREFIX/lib/faketime/libfaketime.so.1" > libfaketime32.env
echo "export LD_PRELOAD=$LIBFAKETIME_INSTALL64_PREFIX/lib/faketime/libfaketime.so.1" > libfaketime64.env

Usage in Wine to fake system time for Windows applications

64-bit application in 64-bit WINEPREFIX:

$ date
Sat Oct 19 19:11:58 CEST 2019

$ (source libfaketime64.env ; FAKETIME="-1y" wine64 "c:/windows/system32/cmd.exe" /c date /t)
Current Date is 10/19/2018

32-bit application in 64-bit WINEPREFIX:

$ date
Sat Oct 19 19:11:58 CEST 2019

$ (source libfaketime32.env ; FAKETIME="-1y" wine "c:/windows/syswow64/cmd.exe" /c date /t)
Current Date is 10/19/2018

NOTE: Since Wine 7.2, libfaketime doesn't work anymore for 32-bit processes due to missing 64-bit time_t support. See my comment

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Links

• libfaketime on github

Hi,

just to clear things up. You are referring to the new experimental WoW64 mode.
Wine has Wow64 implemented since like 15 years which required a multilib host with 32-bit and 64-bit dependencies.
With the new experimental WoW64 mode, the 32-bit native host (and build) dependencies are no longer needed.
The 32-bit executables run in a 64-bit process.

Since I always build Wine on my own (I can still build all Wine versions down to Wine 1.3.x on the same Fedora 41 machine), I have those experimental wow64 builds as well, along with the traditional Wow64 32/64-bit multilib.

The new WoW64 is the way and follows what Windows natively does.
Output from my "new" wow64 mode build, showing it works:

$ source libfaketime64.env

$ wine --version
wine-10.0-127-g1f23d893483

$ FAKETIME="-1y" wine "c:/windows/syswow64/cmd.exe" /c date /t
0174:err:environ:init_peb starting L"C:\\windows\\syswow64\\cmd.exe" in experimental wow64 mode
Current Date is 1/25/2024

Not sure when they are provided as alternative/default to distros as well from WineHQ (https://gitlab.winehq.org/wine/wine/-/wikis/Download).
There are several third-party projects which provide own "custom" builds of various Wine flavours, including experimental WoW64 mode enabled ones. Example:

https://github.com/Kron4ek/Wine-Builds

Note, I don't use it/nor can comment on it, just listed as example.

Regards