Support dynamically-linked and/or native musl targets #40113
Commits on Aug 22, 2017
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Remove incorrect special case of mips-musl
The libdl/librt/libpthread provided by musl are no-op (empty static libraries) on all architectures, mips included.
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Copy musl startup objects before building std
They are required for linking it, even though it is a library, because crtn.o in post_link_objects, as hardcoded in src/librustc_back/target/ linux_musl_base.rs, is added to the linker command line for both executables and libraries.
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Introduce crt_static target option in config.toml
This controls the value of the crt-static feature used when building the standard library for a target, as well as the compiler itself when that target is the host.
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Inline crt-static choice for pc-windows-msvc
This avoids the possibility of a duplicate or conflicting crt-static command line option sent to rustc.
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Factor out a helper for the getting C runtime linkage
This commit makes no functional changes.
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Introduce temporary target feature crt_static_respected
This feature allows targets to opt in to full support of the crt-static feature. Currently, crt-static is allowed on all targets, even those that really can't or really shouldn't support it. This works because it is very loose in the specification of its effects. Changing the behavior of crt-static to be more strict in how it chooses libraries and links executables would likely cause compilation to fail on these platforms. To avoid breaking existing uses of crt-static, whitelist targets that support the new, stricter behavior. For all other targets, this changes crt-static from being "mostly a no-op" to "explicitly a no-op".
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Introduce target feature crt_static_allows_dylibs
Most UNIX-like platforms do not allow shared libraries to statically link their own libc, as libc expects to have consistent process-global state. On those platforms, when we do not have a shared libc available, we must not attempt to link dylibs or cdylibs. On Windows, however, it is expected to statically link the CRT into dynamic libraries. This feature is only relevant for targets that support both fully-static and fully-dynamic linkage, such as musl on Linux.
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Disable PIE when linking statically
Static PIE support, while supported on musl, requires a patch to GCC. Until/unless it is merged, adding '-pie' to the linker command line will override '-static' and create a binary that requires a dynamic interpreter (ld.so).
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Tell the linker when we want to link a static executable
If the C runtime is linked statically, explicitly tell the linker that the executable should be static.
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Update libunwind dependencies for musl
Use libgcc_s when linking dynamically. Convert the static libunwind to static-nobundle, as libunwind.a is copied from musl_root and available in the library search path.
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Support dynamic linking for musl-based targets
Note that this commit does not affect mips-musl targets, as they do not inherit from linux_musl_base.
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Update ignored tests for dynamic musl
Now that musl supports dynamic libraries (although not by default) enable the tests that now pass. Additional currently-ignored tests will pass if rustc is built with crt_static=false in config.toml.
