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Previously, the malloc_conf attribute wasn't as "weak" on MSVC as on other toolchain. While it is possible to override it in an OBJ file - in MSVC, every symbol coming from a LIB file can be overriden from an OBJ file - it isn't possible to override it from another lib file. This makes it impossible to override it from Rust, for instance, as it always generates libs and links them together, instead of linking the obj files directly. While the weak attribute is not supported by MSVC, it can be emulated using the /alternatename linker flag. This flag takes two symbols, and aliases the first symbol to the second if it isn't defined during linking. This ensures that the default value provided by jemalloc can be overridden from all contexts, whether the override comes from an obj or a lib, matching the behavior of gcc's weak attribute. This is supported by MSVC link.exe since time immemorial, and by lld-link since 3.7.0.
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Currently, the
malloc_confattribute isn't "weak" in the same way as on other toolchain. While it is possible to override it in an OBJ file, and the linker will favor the one from the obj file over the symbol from the lib, it isn't possible to override it from another lib file. This makes it impossible to override it from Rust, for instance, as it always generates libs and links them together.While the weak attribute is not supported by MSVC, it can be emulated using the /alternatename linker flag. This flag takes two symbols, and aliases the first symbol to the second if it isn't defined during linking. This ensures that the default value provided by jemalloc can be overridden from all contexts, whether the override comes from an obj or a lib.
This is supported by MSVC link.exe since time immemorial, and by lld-link since 3.7.0.