cmd/compile: use exact constant in go_asm.h

Fixes #50523

Change-Id: Idab1b44d106250e9301d90ee6571f0ea51242dd9
Reviewed-on: https://go-review.googlesource.com/c/go/+/377074
Trust: Ian Lance Taylor <[email protected]>
Run-TryBot: Ian Lance Taylor <[email protected]>
Reviewed-by: Liz Fong-Jones <[email protected]>
Reviewed-by: Emmanuel Odeke <[email protected]>
Trust: Emmanuel Odeke <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Robert Griesemer <[email protected]>
Reviewed-by: Robert Findley <[email protected]>

Author: ianlancetaylor

src/cmd/compile/internal/gc/export.go

@@ -31,7 +31,7 @@ func dumpasmhdr() {
 			if t == constant.Float || t == constant.Complex {
 				break
 			}
-			fmt.Fprintf(b, "#define const_%s %v\n", n.Sym().Name, n.Val())
+			fmt.Fprintf(b, "#define const_%s %v\n", n.Sym().Name, n.Val().ExactString())
 
 		case ir.OTYPE:
 			t := n.Type()

test/asmhdr.dir/main.go

@@ -16,12 +16,15 @@ const (
 	bigInt = 0xffffffffffffffff
 
 	stringVal = "test"
+
+	longStringVal = "this_is_a_string_constant_longer_than_seventy_characters_which_used_to_fail_see_issue_50253"
 )
 
 var (
-	smallIntAsm int64
-	bigIntAsm   uint64
-	stringAsm   [len(stringVal)]byte
+	smallIntAsm   int64
+	bigIntAsm     uint64
+	stringAsm     [len(stringVal)]byte
+	longStringAsm [len(longStringVal)]byte
 )
 
 type typ struct {
@@ -46,6 +49,9 @@ func main() {
 	if stringVal != string(stringAsm[:]) {
 		println("stringVal", stringVal, "!=", string(stringAsm[:]))
 	}
+	if longStringVal != string(longStringAsm[:]) {
+		println("longStringVal", longStringVal, "!=", string(longStringAsm[:]))
+	}
 
 	// We also include boolean consts in go_asm.h, but they're
 	// defined to be "true" or "false", and it's not clear how to

test/asmhdr.dir/main.s

@@ -14,6 +14,9 @@ GLOBL ·bigIntAsm(SB),RODATA,$8
 DATA ·stringAsm(SB)/4, $const_stringVal
 GLOBL ·stringAsm(SB),RODATA,$4
 
+DATA ·longStringAsm(SB)/91, $const_longStringVal
+GLOBL ·longStringAsm(SB),RODATA,$91
+
 DATA ·typSize(SB)/8, $typ__size
 GLOBL ·typSize(SB),RODATA,$8