runtime: reduce stack usage for asmcgocall on PPC64

Define it as ABIInternal, so the result does not take space on
stack.

Also use R10 as a temporary register for arithmetics on SP, so it
is hidden from the assembler's SP delta calculation, which is
irrelevant anyway as we are on the system stack.

Change-Id: I8fed467601c19cad2d7afab26978246d15ce3147
Reviewed-on: https://go-review.googlesource.com/c/go/+/580918
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Cherry Mui <cherryyz@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>

diff --git a/src/runtime/asm_ppc64x.s b/src/runtime/asm_ppc64x.s
index ff9b736430cc2fa3930b868d4574bcec8192b7ec..97c2a370bdd8c19d511d0b0a12cb4466fb4e0537 100644 (file)
--- a/src/runtime/asm_ppc64x.s
+++ b/src/runtime/asm_ppc64x.s
@@ -615,9 +615,9 @@ TEXT ·asmcgocall_no_g(SB),NOSPLIT,$0-16
 // Call fn(arg) on the scheduler stack,
 // aligned appropriately for the gcc ABI.
 // See cgocall.go for more details.
-TEXT ·asmcgocall(SB),NOSPLIT,$0-20
-       MOVD    fn+0(FP), R3
-       MOVD    arg+8(FP), R4
+TEXT ·asmcgocall<ABIInternal>(SB),NOSPLIT,$0-20
+       // R3 = fn
+       // R4 = arg
 
        MOVD    R1, R7          // save original stack pointer
        CMP     $0, g
@@ -651,8 +651,11 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-20
 #endif
        // Save room for two of our pointers, plus the callee
        // save area that lives on the caller stack.
-       SUB     $(asmcgocallSaveOffset+16), R1
-       RLDCR   $0, R1, $~15, R1        // 16-byte alignment for gcc ABI
+       // Do arithmetics in R10 to hide from the assembler
+       // counting it as SP delta, which is irrelevant as we are
+       // on the system stack.
+       SUB     $(asmcgocallSaveOffset+16), R1, R10
+       RLDCR   $0, R10, $~15, R1       // 16-byte alignment for gcc ABI
        MOVD    R5, (asmcgocallSaveOffset+8)(R1)        // save old g on stack
        MOVD    (g_stack+stack_hi)(R5), R5
        SUB     R7, R5
@@ -689,7 +692,7 @@ TEXT ·asmcgocall(SB),NOSPLIT,$0-20
        MOVD    R5, R1
        BL      runtime·save_g(SB)
 
-       MOVW    R3, ret+16(FP)
+       // ret = R3
        RET
 
 nosave:
@@ -703,8 +706,8 @@ nosave:
        // Using this code for all "already on system stack" calls exercises it more,
        // which should help keep it correct.
 
-       SUB     $(asmcgocallSaveOffset+8), R1
-       RLDCR   $0, R1, $~15, R1                // 16-byte alignment for gcc ABI
+       SUB     $(asmcgocallSaveOffset+8), R1, R10
+       RLDCR   $0, R10, $~15, R1               // 16-byte alignment for gcc ABI
        MOVD    R7, asmcgocallSaveOffset(R1)    // Save original stack pointer.
 
        MOVD    R3, R12         // fn
@@ -724,7 +727,7 @@ nosave:
 #ifndef GOOS_aix
        MOVD    24(R1), R2
 #endif
-       MOVW    R3, ret+16(FP)
+       // ret = R3
        RET
 
 // func cgocallback(fn, frame unsafe.Pointer, ctxt uintptr)