runtime: negate errno value for mips pipe/pipe2

The callers expect negative errno values, so negate them when necessary.

No test because there is no reasonable way to make pipe/pipe2 fail.
This was reported on a system on which pipe2 returned ENOSYS.

Fixes #37997

Change-Id: I3ad6cbbc2521cf495f8df6ec991a3f781122b508
Reviewed-on: https://go-review.googlesource.com/c/go/+/224592
Run-TryBot: Ian Lance Taylor <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>
Reviewed-by: Tobias Klauser <[email protected]>

Author: ianlancetaylor

src/runtime/sys_linux_mips64x.s

@@ -117,6 +117,8 @@ TEXT runtime·pipe(SB),NOSPLIT|NOFRAME,$0-12
 	MOVV	R0, R5
 	MOVV	$SYS_pipe2, R2
 	SYSCALL
+	BEQ	R7, 2(PC)
+	SUBVU	R2, R0, R2	// caller expects negative errno
 	MOVW	R2, errno+8(FP)
 	RET
 
@@ -126,6 +128,8 @@ TEXT runtime·pipe2(SB),NOSPLIT|NOFRAME,$0-20
 	MOVW	flags+0(FP), R5
 	MOVV	$SYS_pipe2, R2
 	SYSCALL
+	BEQ	R7, 2(PC)
+	SUBVU	R2, R0, R2	// caller expects negative errno
 	MOVW	R2, errno+16(FP)
 	RET
 

src/runtime/sys_linux_mipsx.s

@@ -118,6 +118,7 @@ TEXT runtime·pipe(SB),NOSPLIT,$0-12
 	MOVW	$-1, R1
 	MOVW	R1, r+0(FP)
 	MOVW	R1, w+4(FP)
+	SUBU	R2, R0, R2	// caller expects negative errno
 	MOVW	R2, errno+8(FP)
 	RET
 pipeok:
@@ -132,6 +133,8 @@ TEXT runtime·pipe2(SB),NOSPLIT,$0-16
 	MOVW	flags+0(FP), R5
 	MOVW	$SYS_pipe2, R2
 	SYSCALL
+	BEQ	R7, 2(PC)
+	SUBU	R2, R0, R2	// caller expects negative errno
 	MOVW	R2, errno+12(FP)
 	RET