From bdf80d104021d3405e5ec8ecc08f189b74ae022a Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Sat, 2 May 2015 10:22:45 +0200 Subject: [PATCH] x86/fpu: Document the various fpregs state formats Document all the structures that make up 'struct fpu'. Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar --- arch/x86/include/asm/fpu/types.h | 35 ++++++++++++++++++++++++++++++-- 1 file changed, 33 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h index 261cfb76065f..4c4eceb08a42 100644 --- a/arch/x86/include/asm/fpu/types.h +++ b/arch/x86/include/asm/fpu/types.h @@ -4,6 +4,10 @@ #ifndef _ASM_X86_FPU_H #define _ASM_X86_FPU_H +/* + * The legacy x87 FPU state format, as saved by FSAVE and + * restored by the FRSTOR instructions: + */ struct fregs_state { u32 cwd; /* FPU Control Word */ u32 swd; /* FPU Status Word */ @@ -16,10 +20,16 @@ struct fregs_state { /* 8*10 bytes for each FP-reg = 80 bytes: */ u32 st_space[20]; - /* Software status information [not touched by FSAVE ]: */ + /* Software status information [not touched by FSAVE]: */ u32 status; }; +/* + * The legacy fx SSE/MMX FPU state format, as saved by FXSAVE and + * restored by the FXRSTOR instructions. It's similar to the FSAVE + * format, but differs in some areas, plus has extensions at + * the end for the XMM registers. + */ struct fxregs_state { u16 cwd; /* Control Word */ u16 swd; /* Status Word */ @@ -56,7 +66,8 @@ struct fxregs_state { } __attribute__((aligned(16))); /* - * Software based FPU emulation state: + * Software based FPU emulation state. This is arbitrary really, + * it matches the x87 format to make it easier to understand: */ struct swregs_state { u32 cwd; @@ -140,6 +151,14 @@ struct xstate_header { u64 reserved[6]; } __attribute__((packed)); +/* + * This is our most modern FPU state format, as saved by the XSAVE + * and restored by the XRSTOR instructions. + * + * It consists of a legacy fxregs portion, an xstate header and + * subsequent fixed size areas as defined by the xstate header. + * Not all CPUs support all the extensions. + */ struct xregs_state { struct fxregs_state i387; struct xstate_header header; @@ -150,6 +169,13 @@ struct xregs_state { /* New processor state extensions will go here. */ } __attribute__ ((packed, aligned (64))); +/* + * This is a union of all the possible FPU state formats + * put together, so that we can pick the right one runtime. + * + * The size of the structure is determined by the largest + * member - which is the xsave area: + */ union fpregs_state { struct fregs_state fsave; struct fxregs_state fxsave; @@ -157,6 +183,11 @@ union fpregs_state { struct xregs_state xsave; }; +/* + * Highest level per task FPU state data structure that + * contains the FPU register state plus various FPU + * state fields: + */ struct fpu { /* * @state: -- 2.20.1