MIPS: Support for 64-bit FP with O32 binaries
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>
diff --git a/arch/mips/include/asm/elf.h b/arch/mips/include/asm/elf.h
index a66359e..d414405 100644
--- a/arch/mips/include/asm/elf.h
+++ b/arch/mips/include/asm/elf.h
@@ -36,6 +36,7 @@
#define EF_MIPS_ABI2 0x00000020
#define EF_MIPS_OPTIONS_FIRST 0x00000080
#define EF_MIPS_32BITMODE 0x00000100
+#define EF_MIPS_FP64 0x00000200
#define EF_MIPS_ABI 0x0000f000
#define EF_MIPS_ARCH 0xf0000000
@@ -176,6 +177,18 @@
#ifdef CONFIG_32BIT
/*
+ * 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.
*/
#define elf_check_arch(hdr) \
@@ -192,6 +205,8 @@
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; \
})
@@ -249,6 +264,11 @@
#define SET_PERSONALITY(ex) \
do { \
+ if ((ex).e_flags & EF_MIPS_FP64) \
+ clear_thread_flag(TIF_32BIT_FPREGS); \
+ else \
+ set_thread_flag(TIF_32BIT_FPREGS); \
+ \
if (personality(current->personality) != PER_LINUX) \
set_personality(PER_LINUX); \
\
@@ -271,14 +291,18 @@
#endif
#ifdef CONFIG_MIPS32_O32
-#define __SET_PERSONALITY32_O32() \
+#define __SET_PERSONALITY32_O32(ex) \
do { \
set_thread_flag(TIF_32BIT_REGS); \
set_thread_flag(TIF_32BIT_ADDR); \
+ \
+ if (!((ex).e_flags & EF_MIPS_FP64)) \
+ set_thread_flag(TIF_32BIT_FPREGS); \
+ \
current->thread.abi = &mips_abi_32; \
} while (0)
#else
-#define __SET_PERSONALITY32_O32() \
+#define __SET_PERSONALITY32_O32(ex) \
do { } while (0)
#endif
@@ -289,7 +313,7 @@
((ex).e_flags & EF_MIPS_ABI) == 0) \
__SET_PERSONALITY32_N32(); \
else \
- __SET_PERSONALITY32_O32(); \
+ __SET_PERSONALITY32_O32(ex); \
} while (0)
#else
#define __SET_PERSONALITY32(ex) do { } while (0)
@@ -300,6 +324,7 @@
unsigned int p; \
\
clear_thread_flag(TIF_32BIT_REGS); \
+ clear_thread_flag(TIF_32BIT_FPREGS); \
clear_thread_flag(TIF_32BIT_ADDR); \
\
if ((ex).e_ident[EI_CLASS] == ELFCLASS32) \