runtime: change amd64 startup convention
Now the default startup is that the program begins at _rt0_amd64_$GOOS,
which sets DI = argc, SI = argv and jumps to _rt0_amd64.
This makes the _rt0_amd64 entry match the expected semantics for
the standard C "main" function, which we can now provide for use when
linking against a standard C library.
R=golang-dev, devon.odell, minux.ma
CC=golang-dev
https://golang.org/cl/7525043
diff --git a/src/pkg/runtime/asm_amd64.s b/src/pkg/runtime/asm_amd64.s
index 696befd..a671f39 100644
--- a/src/pkg/runtime/asm_amd64.s
+++ b/src/pkg/runtime/asm_amd64.s
@@ -6,8 +6,8 @@
TEXT _rt0_amd64(SB),7,$-8
// copy arguments forward on an even stack
- MOVQ 0(DI), AX // argc
- LEAQ 8(DI), BX // argv
+ MOVQ DI, AX // argc
+ MOVQ SI, BX // argv
SUBQ $(4*8+7), SP // 2args 2auto
ANDQ $~15, SP
MOVQ AX, 16(SP)
