On Tue, Aug 30, 2016 at 03:27:23PM +0100, Ard Biesheuvel wrote: > Instead of pessimistically copying at least 64 bytes from the VM stack > to the native stack, and popping off the register arguments again > before doing the native call, try to avoid touching the stack completely > if the VM stack frame is <= 64 bytes. Also, if the stack frame does exceed > 64 bytes, there is no need to copy the first 64 bytes, since we are passing > those in registers anyway. > > Contributed-under: TianoCore Contribution Agreement 1.0 > Signed-off-by: Ard Biesheuvel <[email protected]>
Reviewed-by: Leif Lindholm <[email protected]> > --- > MdeModulePkg/Universal/EbcDxe/AArch64/EbcLowLevel.S | 85 +++++++++++++++----- > 1 file changed, 65 insertions(+), 20 deletions(-) > > diff --git a/MdeModulePkg/Universal/EbcDxe/AArch64/EbcLowLevel.S > b/MdeModulePkg/Universal/EbcDxe/AArch64/EbcLowLevel.S > index b4b8531f1a01..34794c06a644 100644 > --- a/MdeModulePkg/Universal/EbcDxe/AArch64/EbcLowLevel.S > +++ b/MdeModulePkg/Universal/EbcDxe/AArch64/EbcLowLevel.S > @@ -35,30 +35,75 @@ ASM_GLOBAL ASM_PFX(mEbcInstructionBufferTemplate) > > //**************************************************************************** > // UINTN EbcLLCALLEXNative(UINTN FuncAddr, UINTN NewStackPointer, VOID > *FramePtr) > ASM_PFX(EbcLLCALLEXNative): > - stp x19, x20, [sp, #-16]! > - stp x29, x30, [sp, #-16]! > + mov x8, x0 // Preserve x0 > + mov x9, x1 // Preserve x1 > > - mov x19, x0 > - mov x20, sp > - sub x2, x2, x1 // Length = NewStackPointer-FramePtr > - sub sp, sp, x2 > - sub sp, sp, #64 // Make sure there is room for at least 8 args in > the new stack > - mov x0, sp > - > - bl CopyMem // Sp, NewStackPointer, Length > - > - ldp x0, x1, [sp], #16 > - ldp x2, x3, [sp], #16 > - ldp x4, x5, [sp], #16 > - ldp x6, x7, [sp], #16 > + // > + // If the EBC stack frame is smaller than or equal to 64 bytes, we know > there > + // are no stacked arguments #9 and beyond that we need to copy to the > native > + // stack. In this case, we can perform a tail call which is much more > + // efficient, since there is no need to touch the native stack at all. > + // > + sub x3, x2, x1 // Length = NewStackPointer - FramePtr > + cmp x3, #64 > + b.gt 1f > > - blr x19 > + // > + // While probably harmless in practice, we should not access the VM stack > + // outside of the interval [NewStackPointer, FramePtr), which means we > + // should not blindly fill all 8 argument registers with VM stack data. > + // So instead, calculate how many argument registers we can fill based on > + // the size of the VM stack frame, and skip the remaining ones. > + // > + adr x0, 0f // Take address of 'br' instruction below > + bic x3, x3, #7 // Ensure correct alignment > + sub x0, x0, x3, lsr #1 // Subtract 4 bytes for each arg to > unstack > + br x0 // Skip remaining argument registers > + > + ldr x7, [x9, #56] // Call with 8 arguments > + ldr x6, [x9, #48] // | > + ldr x5, [x9, #40] // | > + ldr x4, [x9, #32] // | > + ldr x3, [x9, #24] // | > + ldr x2, [x9, #16] // | > + ldr x1, [x9, #8] // V > + ldr x0, [x9] // Call with 1 argument > + > +0: br x8 // Call with no arguments > > - mov sp, x20 > - ldp x29, x30, [sp], #16 > - ldp x19, x20, [sp], #16 > + // > + // More than 64 bytes: we need to build the full native stack frame and > copy > + // the part of the VM stack exceeding 64 bytes (which may contain stacked > + // arguments) to the native stack > + // > +1: stp x29, x30, [sp, #-16]! > + mov x29, sp > > - ret > + // > + // Ensure that the stack pointer remains 16 byte aligned, > + // even if the size of the VM stack frame is not a multiple of 16 > + // > + add x1, x1, #64 // Skip over [potential] reg params > + tbz x3, #3, 2f // Multiple of 16? > + ldr x4, [x2, #-8]! // No? Then push one word > + str x4, [sp, #-16]! // ... but use two slots > + b 3f > + > +2: ldp x4, x5, [x2, #-16]! > + stp x4, x5, [sp, #-16]! > +3: cmp x2, x1 > + b.gt 2b > + > + ldp x0, x1, [x9] > + ldp x2, x3, [x9, #16] > + ldp x4, x5, [x9, #32] > + ldp x6, x7, [x9, #48] > + > + blr x8 > + > + mov sp, x29 > + ldp x29, x30, [sp], #16 > + ret > > > //**************************************************************************** > // EbcLLEbcInterpret > -- > 2.7.4 > _______________________________________________ edk2-devel mailing list [email protected] https://lists.01.org/mailman/listinfo/edk2-devel
