Rich Felker
370679ba98
mips32 has two fpu register file variants: FR=0 with 32 32-bit registers, where pairs of neighboring even/odd registers are used to represent doubles, and FR=1 with 32 64-bit registers, each of which can store a single or double. up through r5 (our "mips" arch), the supported ABI uses FR=0, but modern compilers generate "fpxx" model code that can safely operate with either model. r6, which is an incompatible but similar ISA, drops FR=0 and only provides the FR=1 model. as such, setjmp and longjmp, which depended on being able to save and restore call-saved doubles by storing and loading their 32-bit halves, were completely broken in the presence of floating point code on mips r6. to fix this, use the s.d and l.d mnemonics to store and load fpu registers. these expand to the existing swc1 and lwc1 instructions for pairs of 32-bit fpu registers on mips1, but on mips2 and later they translate directly to the 64-bit sdc1 and ldc1. with FR=0, sdc1 and ldc1 behave just like the pairs of swc1 and lwc1 instructions they replace, storing or loading the even/odd pair of fpu registers that can be treated as separate single-precision floats or as a unit representing a double. but with FR=1, they store/load individual 64-bit registers. this yields the ABI-correct behavior on mips r6, and should make linking of pre-r6 (plain "mips") code with "fp64" model code workable, although this is and will likely remain unsupported usage. in addition to the mips r6 problem this change fixes, reportedly clang's internal assembler refuses to assemble swc1 and lwc1 instructions for odd register indices when building for "fpxx" model (the default). this caused setjmp and longjmp not to build. by using the s.d and l.d forms, this problem is avoided too. as a bonus, code size is reduced everywhere but mips1.
musl libc
musl, pronounced like the word "mussel", is an MIT-licensed
implementation of the standard C library targetting the Linux syscall
API, suitable for use in a wide range of deployment environments. musl
offers efficient static and dynamic linking support, lightweight code
and low runtime overhead, strong fail-safe guarantees under correct
usage, and correctness in the sense of standards conformance and
safety. musl is built on the principle that these goals are best
achieved through simple code that is easy to understand and maintain.
The 1.1 release series for musl features coverage for all interfaces
defined in ISO C99 and POSIX 2008 base, along with a number of
non-standardized interfaces for compatibility with Linux, BSD, and
glibc functionality.
For basic installation instructions, see the included INSTALL file.
Information on full musl-targeted compiler toolchains, system
bootstrapping, and Linux distributions built on musl can be found on
the project website:
http://www.musl-libc.org/