runtime: make the GC bitmap a byte array
Half the code in the garbage collector accesses the bitmap
as an array of bytes instead of as an array of uintptrs.
This is tricky to do correctly in a portable fashion,
it breaks on big-endian systems.
Make the bitmap a byte array.
Simplifies markallocated, scanblock and span sweep along the way,
as we don't need to recalculate bitmap position for each word.
LGTM=khr
R=golang-codereviews, khr
CC=golang-codereviews, rlh, rsc
https://golang.org/cl/125250043
diff --git a/src/pkg/runtime/asm_amd64.s b/src/pkg/runtime/asm_amd64.s
index d94df0b..6446b5d 100644
--- a/src/pkg/runtime/asm_amd64.s
+++ b/src/pkg/runtime/asm_amd64.s
@@ -702,6 +702,14 @@
XCHGQ AX, 0(BX)
RET
+// void runtime·atomicor8(byte volatile*, byte);
+TEXT runtime·atomicor8(SB), NOSPLIT, $0-16
+ MOVQ ptr+0(FP), AX
+ MOVB val+8(FP), BX
+ LOCK
+ ORB BX, (AX)
+ RET
+
// void jmpdefer(fn, sp);
// called from deferreturn.
// 1. pop the caller
