[ros-dev] [ros-diffs] [ion] 52807: [KERNEL32]: Optimize SwitchToFiber to simply use "ret" to jump between fibers, instead of saving EIP and doing a JMP. Bug #50: SwitchToFiber needs to check if FXSR is *NOT* present in ...

[Timo Kreuzer]

This won't work, since new Fibers, created with CreateFiber(Ex) don't 
push a "return address" on the stack, but set the Eip member to 
BaseFiberStartup.


Am 23.07.2011 14:08, schrieb ion at svn.reactos.org:
> Author: ion
> Date: Sat Jul 23 12:08:36 2011
> New Revision: 52807
>
> URL: http://svn.reactos.org/svn/reactos?rev=52807&view=rev
> Log:
> [KERNEL32]: Optimize SwitchToFiber to simply use "ret" to jump between fibers, instead of saving EIP and doing a JMP.
> Bug #50: SwitchToFiber needs to check if FXSR is *NOT* present in order to skip using ldmxcsr/stmxcsr. Previously, it would check if it's unsupported, and jump past the instruction if it was (resulting in invalid opcode instructions on older systems)
> 50 bugs. Penance has been paid.
>
> Modified:
>      trunk/reactos/dll/win32/kernel32/client/i386/fiber.S
>
> Modified: trunk/reactos/dll/win32/kernel32/client/i386/fiber.S
> URL: http://svn.reactos.org/svn/reactos/trunk/reactos/dll/win32/kernel32/client/i386/fiber.S?rev=52807&r1=52806&r2=52807&view=diff
> ==============================================================================
> --- trunk/reactos/dll/win32/kernel32/client/i386/fiber.S [iso-8859-1] (original)
> +++ trunk/reactos/dll/win32/kernel32/client/i386/fiber.S [iso-8859-1] Sat Jul 23 12:08:36 2011
> @@ -26,20 +26,16 @@
>       mov [eax+FIBER_CONTEXT_EDI], edi
>       mov [eax+FIBER_CONTEXT_EBP], ebp
>
> -    /* Save the return address */
> -    mov ebx, [esp]
> -    mov [eax+FIBER_CONTEXT_EIP], ebx
> -
>       /* Check if we're to save FPU State */
>       cmp dword ptr [eax+FIBER_CONTEXT_FLAGS], CONTEXT_FULL OR CONTEXT_FLOATING_POINT
>       jnz NoFpuStateSave
>
>       /* Save the FPU State (Status and Control)*/
>       fstsw [eax+FIBER_CONTEXT_FLOAT_SAVE_STATUS_WORD]
> -    fstcw [eax+FIBER_CONTEXT_FLOAT_SAVE_CONTROL_WORD]
> +    fnstcw [eax+FIBER_CONTEXT_FLOAT_SAVE_CONTROL_WORD]
>
>       /* Check if the CPU supports SIMD MXCSR State Save */
> -    cmp byte ptr ds:[PROCESSOR_FEATURE_FXSR], 0
> +    cmp byte ptr ds:[PROCESSOR_FEATURE_FXSR], 1
>       jnz NoFpuStateSave
>       stmxcsr [eax+FIBER_CONTEXT_DR6]
>
> @@ -103,7 +99,7 @@
>   ControlWordEqual:
>
>       /* Load the new one */
> -    cmp byte ptr ds:[PROCESSOR_FEATURE_FXSR], 0
> +    cmp byte ptr ds:[PROCESSOR_FEATURE_FXSR], 1
>       jnz NoFpuStateRestore
>       ldmxcsr [ecx+FIBER_CONTEXT_DR6]
>
> @@ -121,7 +117,8 @@
>       mov [edx+TEB_FLS_DATA], eax
>
>       /* Jump to new fiber */
> -    jmp dword ptr [ecx+FIBER_CONTEXT_EIP]
> +    mov esp, [ecx+FIBER_CONTEXT_ESP]
> +    ret 4
> +END
>
> -END
>   /* EOF */
>
>
>