runtime: emit more specific errors from checkptr

Update error messages for pointer alignment checks and pointer
arithmetic checks so that each type of error has a unique error
message.

Fixes #37488

Change-Id: Ida2c2fa3f041a3307d665879a463f9e8f2c1fd03
Reviewed-on: https://go-review.googlesource.com/c/go/+/223037
Reviewed-by: Matthew Dempsky <[email protected]>
Run-TryBot: Matthew Dempsky <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: jupj

src/runtime/checkptr.go

@@ -10,18 +10,18 @@ func checkptrAlignment(p unsafe.Pointer, elem *_type, n uintptr) {
 	// Check that (*[n]elem)(p) is appropriately aligned.
 	// TODO(mdempsky): What about fieldAlign?
 	if uintptr(p)&(uintptr(elem.align)-1) != 0 {
-		throw("checkptr: unsafe pointer conversion")
+		throw("checkptr: misaligned pointer conversion")
 	}
 
 	// Check that (*[n]elem)(p) doesn't straddle multiple heap objects.
 	if size := n * elem.size; size > 1 && checkptrBase(p) != checkptrBase(add(p, size-1)) {
-		throw("checkptr: unsafe pointer conversion")
+		throw("checkptr: converted pointer straddles multiple allocations")
 	}
 }
 
 func checkptrArithmetic(p unsafe.Pointer, originals []unsafe.Pointer) {
 	if 0 < uintptr(p) && uintptr(p) < minLegalPointer {
-		throw("checkptr: unsafe pointer arithmetic")
+		throw("checkptr: pointer arithmetic computed bad pointer value")
 	}
 
 	// Check that if the computed pointer p points into a heap
@@ -38,7 +38,7 @@ func checkptrArithmetic(p unsafe.Pointer, originals []unsafe.Pointer) {
 		}
 	}
 
-	throw("checkptr: unsafe pointer arithmetic")
+	throw("checkptr: pointer arithmetic result points to invalid allocation")
 }
 
 // checkptrBase returns the base address for the allocation containing

src/runtime/checkptr_test.go

@@ -24,10 +24,10 @@ func TestCheckPtr(t *testing.T) {
 		cmd  string
 		want string
 	}{
-		{"CheckPtrAlignment", "fatal error: checkptr: unsafe pointer conversion\n"},
-		{"CheckPtrArithmetic", "fatal error: checkptr: unsafe pointer arithmetic\n"},
-		{"CheckPtrSize", "fatal error: checkptr: unsafe pointer conversion\n"},
-		{"CheckPtrSmall", "fatal error: checkptr: unsafe pointer arithmetic\n"},
+		{"CheckPtrAlignment", "fatal error: checkptr: misaligned pointer conversion\n"},
+		{"CheckPtrArithmetic", "fatal error: checkptr: pointer arithmetic result points to invalid allocation\n"},
+		{"CheckPtrSize", "fatal error: checkptr: converted pointer straddles multiple allocations\n"},
+		{"CheckPtrSmall", "fatal error: checkptr: pointer arithmetic computed bad pointer value\n"},
 	}
 
 	for _, tc := range testCases {