runtime: make the test addresses for pageAlloc smaller on 32-bit

This change makes the test addresses start at 1 GiB instead of 2 GiB to
support mips and mipsle, which only have 31-bit address spaces.

It also changes some tests to use smaller offsets for the chunk index to
avoid jumping too far ahead in the address space to support 31-bit
address spaces. The tests don't require such large jumps for what
they're testing anyway.

Updates #35112.
Fixes #35440.

Change-Id: Ic68ff2b0a1f10ef37ac00d4bb5b910ddcdc76f2e
Reviewed-on: https://go-review.googlesource.com/c/go/+/205938
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

src/runtime/export_test.go

@@ -830,7 +830,10 @@ func FreePageAlloc(pp *PageAlloc) {
 // BaseChunkIdx is a convenient chunkIdx value which works on both
 // 64 bit and 32 bit platforms, allowing the tests to share code
 // between the two.
-var BaseChunkIdx = ChunkIdx(chunkIndex((0xc000*pageAlloc64Bit + 0x200*pageAlloc32Bit) * pallocChunkBytes))
+//
+// This should not be higher than 0x100*pallocChunkBytes to support
+// mips and mipsle, which only have 31-bit address spaces.
+var BaseChunkIdx = ChunkIdx(chunkIndex((0xc000*pageAlloc64Bit + 0x100*pageAlloc32Bit) * pallocChunkBytes))
 
 // PageBase returns an address given a chunk index and a page index
 // relative to that chunk.

src/runtime/mpagealloc_test.go

@@ -280,23 +280,23 @@ func TestPageAllocAlloc(t *testing.T) {
 		"NotContiguousPallocChunkPages*2": {
 			before: map[ChunkIdx][]BitRange{
 				BaseChunkIdx:        {},
-				BaseChunkIdx + 0x100: {},
-				BaseChunkIdx + 0x101: {},
+				BaseChunkIdx + 0x40: {},
+				BaseChunkIdx + 0x41: {},
 			},
 			scav: map[ChunkIdx][]BitRange{
 				BaseChunkIdx:        {{0, PallocChunkPages}},
-				BaseChunkIdx + 0x100: {},
-				BaseChunkIdx + 0x101: {},
+				BaseChunkIdx + 0x40: {},
+				BaseChunkIdx + 0x41: {},
 			},
 			hits: []hit{
-				{PallocChunkPages * 2, PageBase(BaseChunkIdx+0x100, 0), 0},
+				{PallocChunkPages * 2, PageBase(BaseChunkIdx+0x40, 0), 0},
 				{21, PageBase(BaseChunkIdx, 0), 21 * PageSize},
 				{1, PageBase(BaseChunkIdx, 21), PageSize},
 			},
 			after: map[ChunkIdx][]BitRange{
 				BaseChunkIdx:        {{0, 22}},
-				BaseChunkIdx + 0x100: {{0, PallocChunkPages}},
-				BaseChunkIdx + 0x101: {{0, PallocChunkPages}},
+				BaseChunkIdx + 0x40: {{0, PallocChunkPages}},
+				BaseChunkIdx + 0x41: {{0, PallocChunkPages}},
 			},
 		},
 		"StraddlePallocChunkPages*2": {