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In case of an error, you might find an answer of how to deal with it here.

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Building Ladybird

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CMake fails to configure the build because it’s outdated

Ensure your CMake version is >= 3.30 with cmake --version. If your system doesn’t provide a suitable version of CMake, you can download a binary release from the CMake website.
CMake 3.30 or newer is required to build Ladybird.

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GCC is missing or is outdated

Ensure your gcc version is supported by the build system with gcc --version. Otherwise, install it. If your gcc binary is not called gcc you have to specify the names of your C and C++ compiler when you run cmake: 
cmake ../.. -GNinja -DCMAKE_C_COMPILER=gcc-13 -DCMAKE_CXX_COMPILER=g++-13
See the build instructions for supported compiler versions.

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Legacy renegotiation is disabled

Ensure your /etc/ssl/openssl.cnf file has the following options: 
[openssl_init]
ssl_conf = ssl_sect

[ssl_sect]
system_default = system_default_sect

[system_default_sect]
MinProtocol = TLSv1.2
CipherString = DEFAULT@SECLEVEL=1
Options = UnsafeLegacyRenegotiation
When building with the Qt UI on macOS, you may encounter the following message: 
CMake Warning at /opt/homebrew/Cellar/qt/6.7.0_1/lib/cmake/Qt6/FindWrapOpenGL.cmake:48 (target_link_libraries):
Target "ladybird" requests linking to directory "/usr/X11R6/lib". Targets
may link only to libraries. CMake is dropping the item.
…followed by 14-line stack trace, the top of which is this: 
Build/vcpkg/scripts/buildsystems/vcpkg.cmake:859 (_find_package)
Despite the warning message shown in bright yellow, you’ll be able to build successfully with the Qt UI. This warning can be safely ignored.

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Running Ladybird

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Race condition on exit when running headless on systems with llvmpipe

When running --headless=text or --headless=layout-tree on a UNIX system with the llvmpipe software rasterizer (common default on virtual machines), Ladybird will occasionally terminate with: 
double free or corruption (!prev)
Solution: Run Ladybird with --force-cpu-painting to make that go away. 
./Build/release/bin/Ladybird --force-cpu-painting --headless=text
Likely explanation: atexit handlers are registered twice possibly due to llvmpipe and fork/exec interaction issues when starting WebContent process.

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