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MIPS: Support for 64-bit FP with O32 binaries

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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: Paul 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: Ralf Baechle <ralf@linux-mips.org>
This commit is contained in:
Paul Burton
2013-11-22 13:12:07 +00:00
committed by Ralf Baechle
parent 56a22d21bf
commit 597ce1723e
19 changed files with 449 additions and 236 deletions
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14
arch/mips/kernel/binfmt_elfo32.c
View File

@@ -27,6 +27,18 @@ typedef elf_greg_t elf_gregset_t[ELF_NGREG];
typedef double elf_fpreg_t;
typedef elf_fpreg_t elf_fpregset_t[ELF_NFPREG];
/*
* In order to be sure that we don't attempt to execute an O32 binary which
* requires 64 bit FP (FR=1) on a system which does not support it we refuse
* to execute any binary which has bits specified by the following macro set
* in its ELF header flags.
*/
#ifdef CONFIG_MIPS_O32_FP64_SUPPORT
# define __MIPS_O32_FP64_MUST_BE_ZERO 0
#else
# define __MIPS_O32_FP64_MUST_BE_ZERO EF_MIPS_FP64
#endif
/*
* This is used to ensure we don't load something for the wrong architecture.
*/
@@ -43,6 +55,8 @@ typedef elf_fpreg_t elf_fpregset_t[ELF_NFPREG];
__res = 0; \
if (((__h->e_flags & EF_MIPS_ABI) != 0) && \
((__h->e_flags & EF_MIPS_ABI) != EF_MIPS_ABI_O32)) \
__res = 0; \
if (__h->e_flags & __MIPS_O32_FP64_MUST_BE_ZERO) \
__res = 0; \
\
__res; \