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Re: [Xen-devel] [PATCH 1/3] x86: use MOV instead of PUSH/POP when saving/restoring register state



On Tue, Oct 02, 2012 at 04:26:23PM +0100, Jan Beulich wrote:
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

What's the reasoning behind it? Just that mov's are faster than
pop/push?

> 
> --- a/xen/arch/x86/x86_64/compat/entry.S
> +++ b/xen/arch/x86/x86_64/compat/entry.S
> @@ -21,8 +21,7 @@ ENTRY(compat_hypercall)
>  UNLIKELY_START(ne, msi_check)
>          movl  $HYPERCALL_VECTOR,%edi
>          call  check_for_unexpected_msi
> -        RESTORE_ALL
> -        SAVE_ALL
> +        LOAD_C_CLOBBERED
>  UNLIKELY_END(msi_check)
>  
>          GET_CURRENT(%rbx)
> @@ -173,8 +172,7 @@ compat_bad_hypercall:
>  /* %rbx: struct vcpu, interrupts disabled */
>  compat_restore_all_guest:
>          ASSERT_INTERRUPTS_DISABLED
> -        RESTORE_ALL
> -        addq  $8,%rsp
> +        RESTORE_ALL adj=8
>  .Lft0:  iretq
>  
>  .section .fixup,"ax"
> --- a/xen/arch/x86/x86_64/entry.S
> +++ b/xen/arch/x86/x86_64/entry.S
> @@ -47,12 +47,10 @@ restore_all_guest:
>          cmpl  $1,%ecx
>          ja    .Lforce_iret
>  
> -        addq  $8,%rsp
> -        popq  %rcx                    # RIP
> -        popq  %r11                    # CS
> -        cmpw  $FLAT_USER_CS32,%r11
> -        popq  %r11                    # RFLAGS
> -        popq  %rsp                    # RSP
> +        cmpw  $FLAT_USER_CS32,16(%rsp)# CS
> +        movq  8(%rsp),%rcx            # RIP
> +        movq  24(%rsp),%r11           # RFLAGS
> +        movq  32(%rsp),%rsp           # RSP
>          je    1f
>          sysretq
>  1:      sysretl
> @@ -101,8 +99,7 @@ failsafe_callback:
>          ALIGN
>  /* No special register assumptions. */
>  restore_all_xen:
> -        RESTORE_ALL
> -        addq  $8,%rsp
> +        RESTORE_ALL adj=8
>          iretq
>  
>  /*
> @@ -311,8 +308,7 @@ ENTRY(int80_direct_trap)
>  UNLIKELY_START(ne, msi_check)
>          movl  $0x80,%edi
>          call  check_for_unexpected_msi
> -        RESTORE_ALL
> -        SAVE_ALL
> +        LOAD_C_CLOBBERED
>  UNLIKELY_END(msi_check)
>  
>          GET_CURRENT(%rbx)
> --- a/xen/include/asm-x86/x86_64/asm_defns.h
> +++ b/xen/include/asm-x86/x86_64/asm_defns.h
> @@ -5,11 +5,11 @@
>  
>  #ifdef CONFIG_FRAME_POINTER
>  /* Indicate special exception stack frame by inverting the frame pointer. */
> -#define SETUP_EXCEPTION_FRAME_POINTER           \
> -        movq  %rsp,%rbp;                        \
> +#define SETUP_EXCEPTION_FRAME_POINTER(offs)     \
> +        leaq  offs(%rsp),%rbp;                  \
>          notq  %rbp
>  #else
> -#define SETUP_EXCEPTION_FRAME_POINTER
> +#define SETUP_EXCEPTION_FRAME_POINTER(off)
>  #endif
>  
>  #ifndef NDEBUG
> @@ -27,40 +27,49 @@
>  #define ASSERT_INTERRUPTS_DISABLED ASSERT_INTERRUPT_STATUS(z)
>  
>  #define SAVE_ALL                                \
> +        addq  $-(UREGS_error_code-UREGS_r15), %rsp; \
>          cld;                                    \
> -        pushq %rdi;                             \
> -        pushq %rsi;                             \
> -        pushq %rdx;                             \
> -        pushq %rcx;                             \
> -        pushq %rax;                             \
> -        pushq %r8;                              \
> -        pushq %r9;                              \
> -        pushq %r10;                             \
> -        pushq %r11;                             \
> -        pushq %rbx;                             \
> -        pushq %rbp;                             \
> -        SETUP_EXCEPTION_FRAME_POINTER;          \
> -        pushq %r12;                             \
> -        pushq %r13;                             \
> -        pushq %r14;                             \
> -        pushq %r15;
> -
> -#define RESTORE_ALL                             \
> -        popq  %r15;                             \
> -        popq  %r14;                             \
> -        popq  %r13;                             \
> -        popq  %r12;                             \
> -        popq  %rbp;                             \
> -        popq  %rbx;                             \
> -        popq  %r11;                             \
> -        popq  %r10;                             \
> -        popq  %r9;                              \
> -        popq  %r8;                              \
> -        popq  %rax;                             \
> -        popq  %rcx;                             \
> -        popq  %rdx;                             \
> -        popq  %rsi;                             \
> -        popq  %rdi;
> +        movq  %rdi,UREGS_rdi(%rsp);             \
> +        movq  %rsi,UREGS_rsi(%rsp);             \
> +        movq  %rdx,UREGS_rdx(%rsp);             \
> +        movq  %rcx,UREGS_rcx(%rsp);             \
> +        movq  %rax,UREGS_rax(%rsp);             \
> +        movq  %r8,UREGS_r8(%rsp);               \
> +        movq  %r9,UREGS_r9(%rsp);               \
> +        movq  %r10,UREGS_r10(%rsp);             \
> +        movq  %r11,UREGS_r11(%rsp);             \
> +        movq  %rbx,UREGS_rbx(%rsp);             \
> +        movq  %rbp,UREGS_rbp(%rsp);             \
> +        SETUP_EXCEPTION_FRAME_POINTER(UREGS_rbp); \
> +        movq  %r12,UREGS_r12(%rsp);             \
> +        movq  %r13,UREGS_r13(%rsp);             \
> +        movq  %r14,UREGS_r14(%rsp);             \
> +        movq  %r15,UREGS_r15(%rsp);             \
> +
> +#ifdef __ASSEMBLY__
> +.macro LOAD_C_CLOBBERED
> +        movq  UREGS_r11(%rsp),%r11
> +        movq  UREGS_r10(%rsp),%r10
> +        movq  UREGS_r9(%rsp),%r9
> +        movq  UREGS_r8(%rsp),%r8
> +        movq  UREGS_rax(%rsp),%rax
> +        movq  UREGS_rcx(%rsp),%rcx
> +        movq  UREGS_rdx(%rsp),%rdx
> +        movq  UREGS_rsi(%rsp),%rsi
> +        movq  UREGS_rdi(%rsp),%rdi
> +.endm
> +
> +.macro RESTORE_ALL adj=0
> +        movq  UREGS_r15(%rsp),%r15
> +        movq  UREGS_r14(%rsp),%r14
> +        movq  UREGS_r13(%rsp),%r13
> +        movq  UREGS_r12(%rsp),%r12
> +        movq  UREGS_rbp(%rsp),%rbp
> +        movq  UREGS_rbx(%rsp),%rbx
> +        LOAD_C_CLOBBERED
> +        subq  $-(UREGS_error_code-UREGS_r15+\adj), %rsp
> +.endm
> +#endif
>  
>  #ifdef PERF_COUNTERS
>  #define PERFC_INCR(_name,_idx,_cur)             \
> @@ -94,7 +103,7 @@
>  __asm__(                                        \
>      "\n" __ALIGN_STR"\n"                        \
>      "common_interrupt:\n\t"                     \
> -    STR(SAVE_ALL)                               \
> +    STR(SAVE_ALL) "\n\t"                        \
>      "movq %rsp,%rdi\n\t"                        \
>      "callq " STR(do_IRQ) "\n\t"                 \
>      "jmp ret_from_intr\n");
> 
> 

> x86: use MOV instead of PUSH/POP when saving/restoring register state
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> --- a/xen/arch/x86/x86_64/compat/entry.S
> +++ b/xen/arch/x86/x86_64/compat/entry.S
> @@ -21,8 +21,7 @@ ENTRY(compat_hypercall)
>  UNLIKELY_START(ne, msi_check)
>          movl  $HYPERCALL_VECTOR,%edi
>          call  check_for_unexpected_msi
> -        RESTORE_ALL
> -        SAVE_ALL
> +        LOAD_C_CLOBBERED
>  UNLIKELY_END(msi_check)
>  
>          GET_CURRENT(%rbx)
> @@ -173,8 +172,7 @@ compat_bad_hypercall:
>  /* %rbx: struct vcpu, interrupts disabled */
>  compat_restore_all_guest:
>          ASSERT_INTERRUPTS_DISABLED
> -        RESTORE_ALL
> -        addq  $8,%rsp
> +        RESTORE_ALL adj=8
>  .Lft0:  iretq
>  
>  .section .fixup,"ax"
> --- a/xen/arch/x86/x86_64/entry.S
> +++ b/xen/arch/x86/x86_64/entry.S
> @@ -47,12 +47,10 @@ restore_all_guest:
>          cmpl  $1,%ecx
>          ja    .Lforce_iret
>  
> -        addq  $8,%rsp
> -        popq  %rcx                    # RIP
> -        popq  %r11                    # CS
> -        cmpw  $FLAT_USER_CS32,%r11
> -        popq  %r11                    # RFLAGS
> -        popq  %rsp                    # RSP
> +        cmpw  $FLAT_USER_CS32,16(%rsp)# CS
> +        movq  8(%rsp),%rcx            # RIP
> +        movq  24(%rsp),%r11           # RFLAGS
> +        movq  32(%rsp),%rsp           # RSP
>          je    1f
>          sysretq
>  1:      sysretl
> @@ -101,8 +99,7 @@ failsafe_callback:
>          ALIGN
>  /* No special register assumptions. */
>  restore_all_xen:
> -        RESTORE_ALL
> -        addq  $8,%rsp
> +        RESTORE_ALL adj=8
>          iretq
>  
>  /*
> @@ -311,8 +308,7 @@ ENTRY(int80_direct_trap)
>  UNLIKELY_START(ne, msi_check)
>          movl  $0x80,%edi
>          call  check_for_unexpected_msi
> -        RESTORE_ALL
> -        SAVE_ALL
> +        LOAD_C_CLOBBERED
>  UNLIKELY_END(msi_check)
>  
>          GET_CURRENT(%rbx)
> --- a/xen/include/asm-x86/x86_64/asm_defns.h
> +++ b/xen/include/asm-x86/x86_64/asm_defns.h
> @@ -5,11 +5,11 @@
>  
>  #ifdef CONFIG_FRAME_POINTER
>  /* Indicate special exception stack frame by inverting the frame pointer. */
> -#define SETUP_EXCEPTION_FRAME_POINTER           \
> -        movq  %rsp,%rbp;                        \
> +#define SETUP_EXCEPTION_FRAME_POINTER(offs)     \
> +        leaq  offs(%rsp),%rbp;                  \
>          notq  %rbp
>  #else
> -#define SETUP_EXCEPTION_FRAME_POINTER
> +#define SETUP_EXCEPTION_FRAME_POINTER(off)
>  #endif
>  
>  #ifndef NDEBUG
> @@ -27,40 +27,49 @@
>  #define ASSERT_INTERRUPTS_DISABLED ASSERT_INTERRUPT_STATUS(z)
>  
>  #define SAVE_ALL                                \
> +        addq  $-(UREGS_error_code-UREGS_r15), %rsp; \
>          cld;                                    \
> -        pushq %rdi;                             \
> -        pushq %rsi;                             \
> -        pushq %rdx;                             \
> -        pushq %rcx;                             \
> -        pushq %rax;                             \
> -        pushq %r8;                              \
> -        pushq %r9;                              \
> -        pushq %r10;                             \
> -        pushq %r11;                             \
> -        pushq %rbx;                             \
> -        pushq %rbp;                             \
> -        SETUP_EXCEPTION_FRAME_POINTER;          \
> -        pushq %r12;                             \
> -        pushq %r13;                             \
> -        pushq %r14;                             \
> -        pushq %r15;
> -
> -#define RESTORE_ALL                             \
> -        popq  %r15;                             \
> -        popq  %r14;                             \
> -        popq  %r13;                             \
> -        popq  %r12;                             \
> -        popq  %rbp;                             \
> -        popq  %rbx;                             \
> -        popq  %r11;                             \
> -        popq  %r10;                             \
> -        popq  %r9;                              \
> -        popq  %r8;                              \
> -        popq  %rax;                             \
> -        popq  %rcx;                             \
> -        popq  %rdx;                             \
> -        popq  %rsi;                             \
> -        popq  %rdi;
> +        movq  %rdi,UREGS_rdi(%rsp);             \
> +        movq  %rsi,UREGS_rsi(%rsp);             \
> +        movq  %rdx,UREGS_rdx(%rsp);             \
> +        movq  %rcx,UREGS_rcx(%rsp);             \
> +        movq  %rax,UREGS_rax(%rsp);             \
> +        movq  %r8,UREGS_r8(%rsp);               \
> +        movq  %r9,UREGS_r9(%rsp);               \
> +        movq  %r10,UREGS_r10(%rsp);             \
> +        movq  %r11,UREGS_r11(%rsp);             \
> +        movq  %rbx,UREGS_rbx(%rsp);             \
> +        movq  %rbp,UREGS_rbp(%rsp);             \
> +        SETUP_EXCEPTION_FRAME_POINTER(UREGS_rbp); \
> +        movq  %r12,UREGS_r12(%rsp);             \
> +        movq  %r13,UREGS_r13(%rsp);             \
> +        movq  %r14,UREGS_r14(%rsp);             \
> +        movq  %r15,UREGS_r15(%rsp);             \
> +
> +#ifdef __ASSEMBLY__
> +.macro LOAD_C_CLOBBERED
> +        movq  UREGS_r11(%rsp),%r11
> +        movq  UREGS_r10(%rsp),%r10
> +        movq  UREGS_r9(%rsp),%r9
> +        movq  UREGS_r8(%rsp),%r8
> +        movq  UREGS_rax(%rsp),%rax
> +        movq  UREGS_rcx(%rsp),%rcx
> +        movq  UREGS_rdx(%rsp),%rdx
> +        movq  UREGS_rsi(%rsp),%rsi
> +        movq  UREGS_rdi(%rsp),%rdi
> +.endm
> +
> +.macro RESTORE_ALL adj=0
> +        movq  UREGS_r15(%rsp),%r15
> +        movq  UREGS_r14(%rsp),%r14
> +        movq  UREGS_r13(%rsp),%r13
> +        movq  UREGS_r12(%rsp),%r12
> +        movq  UREGS_rbp(%rsp),%rbp
> +        movq  UREGS_rbx(%rsp),%rbx
> +        LOAD_C_CLOBBERED
> +        subq  $-(UREGS_error_code-UREGS_r15+\adj), %rsp
> +.endm
> +#endif
>  
>  #ifdef PERF_COUNTERS
>  #define PERFC_INCR(_name,_idx,_cur)             \
> @@ -94,7 +103,7 @@
>  __asm__(                                        \
>      "\n" __ALIGN_STR"\n"                        \
>      "common_interrupt:\n\t"                     \
> -    STR(SAVE_ALL)                               \
> +    STR(SAVE_ALL) "\n\t"                        \
>      "movq %rsp,%rdi\n\t"                        \
>      "callq " STR(do_IRQ) "\n\t"                 \
>      "jmp ret_from_intr\n");

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