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[2a00:1098:0:86:1000:23:0:2]) by smtp.gmail.com with ESMTPSA id g1sm19950764wjy.5.2016.08.26.05.54.41 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 26 Aug 2016 05:54:41 -0700 (PDT) Date: Fri, 26 Aug 2016 13:54:39 +0100 From: Leif Lindholm To: Ard Biesheuvel Cc: edk2-devel@lists.01.org, jbrasen@codeaurora.org, feng.tian@intel.com, star.zeng@intel.com, daniil.egranov@arm.com Message-ID: <20160826125439.GF4715@bivouac.eciton.net> References: <1471445945-19239-1-git-send-email-ard.biesheuvel@linaro.org> <1471445945-19239-4-git-send-email-ard.biesheuvel@linaro.org> MIME-Version: 1.0 In-Reply-To: <1471445945-19239-4-git-send-email-ard.biesheuvel@linaro.org> User-Agent: Mutt/1.5.23 (2014-03-12) Subject: Re: [PATCH v3 3/4] MdeModulePkg/EbxDxe AARCH64: use tail call for EBC to native thunk X-BeenThere: edk2-devel@lists.01.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: EDK II Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 26 Aug 2016 12:54:44 -0000 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Wed, Aug 17, 2016 at 04:59:04PM +0200, 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 Should this say "does not"? > 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 > --- > MdeModulePkg/Universal/EbcDxe/AArch64/EbcLowLevel.S | 73 +++++++++++++++----- > 1 file changed, 55 insertions(+), 18 deletions(-) > > diff --git a/MdeModulePkg/Universal/EbcDxe/AArch64/EbcLowLevel.S b/MdeModulePkg/Universal/EbcDxe/AArch64/EbcLowLevel.S > index cb7a70b5a4f8..d95713e82b0f 100644 > --- a/MdeModulePkg/Universal/EbcDxe/AArch64/EbcLowLevel.S > +++ b/MdeModulePkg/Universal/EbcDxe/AArch64/EbcLowLevel.S > @@ -35,30 +35,67 @@ 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 > + // > + // 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 > > - bl CopyMem // Sp, NewStackPointer, Length > + adr x0, 0f > + sub x0, x0, x3, lsr #1 > + br x0 > > - ldp x0, x1, [sp], #16 > - ldp x2, x3, [sp], #16 > - ldp x4, x5, [sp], #16 > - ldp x6, x7, [sp], #16 > + ldr x7, [x9, #56] > + ldr x6, [x9, #48] > + ldr x5, [x9, #40] > + ldr x4, [x9, #32] > + ldr x3, [x9, #24] > + ldr x2, [x9, #16] > + ldr x1, [x9, #8] > + ldr x0, [x9] Why not keep using ldp, but with x9? > > - blr x19 > +0: br x8 > > - 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 >