Dos and don'ts while removing multilib
An RFC discusses how to properly remove multilib support for s390 after dropping 31-bit support, while maintaining library directory conventions.
Stefan Schulze Frielinghaus is preparing a patch to remove -m31 support for s390, which would make multilib obsolete. The author seeks guidance on how to remove multilib while preserving the convention of installing 64-bit libraries under /usr/lib64 instead of /usr/lib. Andreas Schwab notes that alpha-linux and ia64-linux place their libraries in /lib, even without multilib.
- proposer
Seeks advice on removing multilib support for s390 while maintaining the convention of using /usr/lib64 for 64-bit libraries.
“Naively removing MULTILIB_{OPTIONS,DIRNAMES,OSDIRNAMES} from Makefile config/s390/t-linux64 and the define MULTILIB_DEFAULTS results in choosing the wrong library dir `lib` instead of `lib64`.”
- other
Points out that alpha-linux and ia64-linux, also 64-bit targets without multilib, put their libraries in /lib.
“There are two other 64-bit targets without multilib: alpha-linux and ia64-linux. But both of them put their libraries in /lib, not /lib64.”
Technical Tradeoffs
- Removing multilib support simplifies the build process but requires careful configuration to ensure libraries are installed in the correct directories.
- Maintaining the /usr/lib64 convention may require custom configuration beyond simply removing multilib macros.
In Details
Multilib in GCC allows building code for multiple target architectures from a single source tree. It uses macros like MULTILIB_OPTIONS and MULTILIB_DIRNAMES to configure the build process and library installation paths. Removing multilib requires careful adjustment of these macros to ensure correct library placement.
For Context
Multilib is a mechanism that allows a single compiler to build binaries for multiple target architectures. This is useful when an operating system supports both 32-bit and 64-bit applications. It involves configuring the compiler to generate code for different architectures and placing the resulting libraries in separate directories to avoid conflicts during linking. The configuration files need to be adjusted to ensure libraries are placed in their correct directories. This proposal discusses how to handle library installation directories after only one architecture is supported.