From: Keith Randall <khr@golang.org>
Date: Thu, 2 Mar 2023 06:32:46 +0000 (-0800)
Subject: cmd/asm: don't panic on bad GATHER x86 instructions
X-Git-Tag: go1.21rc1~1390
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=b958d4a597a599e22c78d25d83d803ab2a1f2c52;p=gostls13.git

cmd/asm: don't panic on bad GATHER x86 instructions

Fixes #58822

Change-Id: I9c44c57dac72884ec3209d87ddb25e7e1675a737
Reviewed-on: https://go-review.googlesource.com/c/go/+/472795
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Rob Pike <r@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Keith Randall <khr@google.com>
---

diff --git a/src/cmd/internal/obj/x86/asm6.go b/src/cmd/internal/obj/x86/asm6.go
index b441964492..0e8670c8e5 100644
--- a/src/cmd/internal/obj/x86/asm6.go
+++ b/src/cmd/internal/obj/x86/asm6.go
@@ -4242,6 +4242,11 @@ func (ab *AsmBuf) doasm(ctxt *obj.Link, cursym *obj.LSym, p *obj.Prog) {
 		AVPGATHERQD,
 		AVPGATHERDQ,
 		AVPGATHERQQ:
+		if p.GetFrom3() == nil {
+			// gathers need a 3rd arg. See issue 58822.
+			ctxt.Diag("need a third arg for gather instruction: %v", p)
+			return
+		}
 		// AVX512 gather requires explicit K mask.
 		if p.GetFrom3().Reg >= REG_K0 && p.GetFrom3().Reg <= REG_K7 {
 			if !avx512gatherValid(ctxt, p) {