• Paul Burton's avatar
    MIPS: Support for 64-bit FP with O32 binaries · 597ce172
    Paul Burton authored
    CPUs implementing MIPS32 R2 may include a 64-bit FPU, just as MIPS64 CPUs
    do. In order to preserve backwards compatibility a 64-bit FPU will act
    like a 32-bit FPU (by accessing doubles from the least significant 32
    bits of an even-odd pair of FP registers) when the Status.FR bit is
    zero, again just like a mips64 CPU. The standard O32 ABI is defined
    expecting a 32-bit FPU, however recent toolchains support use of a
    64-bit FPU from an O32 MIPS32 executable. When an ELF executable is
    built to use a 64-bit FPU a new flag (EF_MIPS_FP64) is set in the ELF
    header.
    
    With this patch the kernel will check the EF_MIPS_FP64 flag when
    executing an O32 binary, and set Status.FR accordingly. The addition
    of O32 64-bit FP support lessens the opportunity for optimisation in
    the FPU emulator, so a CONFIG_MIPS_O32_FP64_SUPPORT Kconfig option is
    introduced to allow this support to be disabled for those that don't
    require it.
    
    Inspired by an earlier patch by Leonid Yegoshin, but implemented more
    cleanly & correctly.
    Signed-off-by: default avatarPaul Burton <paul.burton@imgtec.com>
    Cc: linux-mips@linux-mips.org
    Cc: Paul Burton <paul.burton@imgtec.com>
    Patchwork: https://patchwork.linux-mips.org/patch/6154/Signed-off-by: default avatarRalf Baechle <ralf@linux-mips.org>
    597ce172
binfmt_elfo32.c 5.25 KB