cmd/compile: allow conversion from slice to array ptr

Panic if the slice is too short.

Updates #395

Change-Id: I90f4bff2da5d8f3148ba06d2482084f32b25c29a
Reviewed-on: https://go-review.googlesource.com/c/go/+/301650
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

11 files changed, 49 insertions, 0 deletions

diff --git a/src/runtime/asm_386.s b/src/runtime/asm_386.s
index 5cf6827c21..45f8bf1003 100644
--- a/src/runtime/asm_386.s
+++ b/src/runtime/asm_386.s
@@ -1473,6 +1473,10 @@ TEXT runtime·panicSlice3CU(SB),NOSPLIT,$0-8
 	MOVL	AX, x+0(FP)
 	MOVL	CX, y+4(FP)
 	JMP	runtime·goPanicSlice3CU(SB)
+TEXT runtime·panicSliceConvert(SB),NOSPLIT,$0-8
+	MOVL	DX, x+0(FP)
+	MOVL	BX, y+4(FP)
+	JMP	runtime·goPanicSliceConvert(SB)
 
 // Extended versions for 64-bit indexes.
 TEXT runtime·panicExtendIndex(SB),NOSPLIT,$0-12
diff --git a/src/runtime/asm_amd64.s b/src/runtime/asm_amd64.s
index 1e6d8189c9..d2848e5a45 100644
--- a/src/runtime/asm_amd64.s
+++ b/src/runtime/asm_amd64.s
@@ -2091,6 +2091,14 @@ TEXT runtime·panicSlice3CU<ABIInternal>(SB),NOSPLIT,$0-16
 	MOVQ	CX, y+8(FP)
 #endif
 	JMP	runtime·goPanicSlice3CU<ABIInternal>(SB)
+TEXT runtime·panicSliceConvert<ABIInternal>(SB),NOSPLIT,$0-16
+#ifdef GOEXPERIMENT_regabiargs
+	MOVQ	DX, AX
+#else
+	MOVQ	DX, x+0(FP)
+	MOVQ	BX, y+8(FP)
+#endif
+	JMP	runtime·goPanicSliceConvert<ABIInternal>(SB)
 
 #ifdef GOOS_android
 // Use the free TLS_SLOT_APP slot #2 on Android Q.
diff --git a/src/runtime/asm_arm.s b/src/runtime/asm_arm.s
index 9896ab4383..f468b77ee3 100644
--- a/src/runtime/asm_arm.s
+++ b/src/runtime/asm_arm.s
@@ -992,6 +992,10 @@ TEXT runtime·panicSlice3CU(SB),NOSPLIT,$0-8
 	MOVW	R0, x+0(FP)
 	MOVW	R1, y+4(FP)
 	JMP	runtime·goPanicSlice3CU(SB)
+TEXT runtime·panicSliceConvert(SB),NOSPLIT,$0-8
+	MOVW	R2, x+0(FP)
+	MOVW	R3, y+4(FP)
+	JMP	runtime·goPanicSliceConvert(SB)
 
 // Extended versions for 64-bit indexes.
 TEXT runtime·panicExtendIndex(SB),NOSPLIT,$0-12
diff --git a/src/runtime/asm_arm64.s b/src/runtime/asm_arm64.s
index 2e120dcf1e..2d495397a8 100644
--- a/src/runtime/asm_arm64.s
+++ b/src/runtime/asm_arm64.s
@@ -1314,3 +1314,7 @@ TEXT runtime·panicSlice3CU(SB),NOSPLIT,$0-16
 	MOVD	R0, x+0(FP)
 	MOVD	R1, y+8(FP)
 	JMP	runtime·goPanicSlice3CU(SB)
+TEXT runtime·panicSliceConvert(SB),NOSPLIT,$0-16
+	MOVD	R2, x+0(FP)
+	MOVD	R3, y+8(FP)
+	JMP	runtime·goPanicSliceConvert(SB)
diff --git a/src/runtime/asm_mips64x.s b/src/runtime/asm_mips64x.s
index cee4b528bb..c3b57e472a 100644
--- a/src/runtime/asm_mips64x.s
+++ b/src/runtime/asm_mips64x.s
@@ -805,3 +805,7 @@ TEXT runtime·panicSlice3CU(SB),NOSPLIT,$0-16
 	MOVV	R1, x+0(FP)
 	MOVV	R2, y+8(FP)
 	JMP	runtime·goPanicSlice3CU(SB)
+TEXT runtime·panicSliceConvert(SB),NOSPLIT,$0-16
+	MOVV	R3, x+0(FP)
+	MOVV	R4, y+8(FP)
+	JMP	runtime·goPanicSliceConvert(SB)
diff --git a/src/runtime/asm_mipsx.s b/src/runtime/asm_mipsx.s
index 17fbc902c2..1d828b03cf 100644
--- a/src/runtime/asm_mipsx.s
+++ b/src/runtime/asm_mipsx.s
@@ -801,6 +801,10 @@ TEXT runtime·panicSlice3CU(SB),NOSPLIT,$0-8
 	MOVW	R1, x+0(FP)
 	MOVW	R2, y+4(FP)
 	JMP	runtime·goPanicSlice3CU(SB)
+TEXT runtime·panicSliceConvert(SB),NOSPLIT,$0-8
+	MOVW	R3, x+0(FP)
+	MOVW	R4, y+4(FP)
+	JMP	runtime·goPanicSliceConvert(SB)
 
 // Extended versions for 64-bit indexes.
 TEXT runtime·panicExtendIndex(SB),NOSPLIT,$0-12
diff --git a/src/runtime/asm_ppc64x.s b/src/runtime/asm_ppc64x.s
index 6544048497..2c39b38912 100644
--- a/src/runtime/asm_ppc64x.s
+++ b/src/runtime/asm_ppc64x.s
@@ -1022,3 +1022,7 @@ TEXT runtime·panicSlice3CU(SB),NOSPLIT,$0-16
 	MOVD	R3, x+0(FP)
 	MOVD	R4, y+8(FP)
 	JMP	runtime·goPanicSlice3CU(SB)
+TEXT runtime·panicSliceConvert(SB),NOSPLIT,$0-16
+	MOVD	R5, x+0(FP)
+	MOVD	R6, y+8(FP)
+	JMP	runtime·goPanicSliceConvert(SB)
diff --git a/src/runtime/asm_riscv64.s b/src/runtime/asm_riscv64.s
index d8d5252ed5..ef7af4e10d 100644
--- a/src/runtime/asm_riscv64.s
+++ b/src/runtime/asm_riscv64.s
@@ -806,6 +806,10 @@ TEXT runtime·panicSlice3CU(SB),NOSPLIT,$0-16
 	MOV	T0, x+0(FP)
 	MOV	T1, y+8(FP)
 	JMP	runtime·goPanicSlice3CU(SB)
+TEXT runtime·panicSliceConvert(SB),NOSPLIT,$0-16
+	MOV	T2, x+0(FP)
+	MOV	T3, y+8(FP)
+	JMP	runtime·goPanicSliceConvert(SB)
 
 DATA	runtime·mainPC+0(SB)/8,$runtime·main(SB)
 GLOBL	runtime·mainPC(SB),RODATA,$8
diff --git a/src/runtime/asm_s390x.s b/src/runtime/asm_s390x.s
index 4748e00aa8..fb38271630 100644
--- a/src/runtime/asm_s390x.s
+++ b/src/runtime/asm_s390x.s
@@ -906,3 +906,7 @@ TEXT runtime·panicSlice3CU(SB),NOSPLIT,$0-16
 	MOVD	R0, x+0(FP)
 	MOVD	R1, y+8(FP)
 	JMP	runtime·goPanicSlice3CU(SB)
+TEXT runtime·panicSliceConvert(SB),NOSPLIT,$0-16
+	MOVD	R2, x+0(FP)
+	MOVD	R3, y+8(FP)
+	JMP	runtime·goPanicSliceConvert(SB)
diff --git a/src/runtime/error.go b/src/runtime/error.go
index 9e6cdf35dd..91f83ae126 100644
--- a/src/runtime/error.go
+++ b/src/runtime/error.go
@@ -134,6 +134,7 @@ const (
 	boundsSlice3B    // s[?:x:y], 0 <= x <= y failed (but boundsSlice3A didn't happen)
 	boundsSlice3C    // s[x:y:?], 0 <= x <= y failed (but boundsSlice3A/B didn't happen)
 
+	boundsConvert // (*[x]T)(s), 0 <= x <= len(s) failed
 	// Note: in the above, len(s) and cap(s) are stored in y
 )
 
@@ -149,6 +150,7 @@ var boundsErrorFmts = [...]string{
 	boundsSlice3Acap: "slice bounds out of range [::%x] with capacity %y",
 	boundsSlice3B:    "slice bounds out of range [:%x:%y]",
 	boundsSlice3C:    "slice bounds out of range [%x:%y:]",
+	boundsConvert:    "cannot convert slice with length %y to pointer to array with length %x",
 }
 
 // boundsNegErrorFmts are overriding formats if x is negative. In this case there's no need to report y.
diff --git a/src/runtime/panic.go b/src/runtime/panic.go
index f8f2f39dbb..f6c38aafcc 100644
--- a/src/runtime/panic.go
+++ b/src/runtime/panic.go
@@ -160,6 +160,12 @@ func goPanicSlice3CU(x uint, y int) {
 	panic(boundsError{x: int64(x), signed: false, y: y, code: boundsSlice3C})
 }
 
+// failures in the conversion (*[x]T)s, 0 <= x <= y, x == cap(s)
+func goPanicSliceConvert(x int, y int) {
+	panicCheck1(getcallerpc(), "slice length too short to convert to pointer to array")
+	panic(boundsError{x: int64(x), signed: true, y: y, code: boundsConvert})
+}
+
 // Implemented in assembly, as they take arguments in registers.
 // Declared here to mark them as ABIInternal.
 func panicIndex(x int, y int)
@@ -178,6 +184,7 @@ func panicSlice3B(x int, y int)
 func panicSlice3BU(x uint, y int)
 func panicSlice3C(x int, y int)
 func panicSlice3CU(x uint, y int)
+func panicSliceConvert(x int, y int)
 
 var shiftError = error(errorString("negative shift amount"))