From: Cherry Mui <cherryyz@google.com>
Date: Wed, 19 Nov 2025 22:32:12 +0000 (-0500)
Subject: cmd/internal/obj/x86: handle global reference in From3 in dynlink mode
X-Git-Tag: go1.26rc1~227
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=4b740af56a864eeaf3504d7f873c3d3cb3fcd72e;p=gostls13.git

cmd/internal/obj/x86: handle global reference in From3 in dynlink mode

In dynlink mode, we rewrite reference to a global variable to
a load from the GOT. Currently this code does not handle the case
that the global reference is in From3 of a Prog. Most instructions
don't expect a memory operand in From3, but some do, like
VGF2P8AFFINEQB. Handle this case.

Change-Id: Ibb6773606e6967bcc629d9ef5dac6e050f4008ef
Reviewed-on: https://go-review.googlesource.com/c/go/+/722181
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
---

diff --git a/src/cmd/asm/internal/asm/testdata/amd64dynlinkerror.s b/src/cmd/asm/internal/asm/testdata/amd64dynlinkerror.s
index 4bf58a39a4..8b104307cd 100644
--- a/src/cmd/asm/internal/asm/testdata/amd64dynlinkerror.s
+++ b/src/cmd/asm/internal/asm/testdata/amd64dynlinkerror.s
@@ -169,3 +169,8 @@ TEXT ·a34(SB), 0, $0-0
 	SHLXQ AX, CX, R15
 	ADDQ $1, R15
 	RET
+
+// Ensure from3 get GOT-rewritten without errors.
+TEXT ·a35(SB), 0, $0-0
+	VGF2P8AFFINEQB	$0, runtime·writeBarrier(SB), Z1, Z1
+	RET
diff --git a/src/cmd/internal/obj/x86/obj6.go b/src/cmd/internal/obj/x86/obj6.go
index 48287546b3..b2023ee48f 100644
--- a/src/cmd/internal/obj/x86/obj6.go
+++ b/src/cmd/internal/obj/x86/obj6.go
@@ -423,8 +423,12 @@ func rewriteToUseGot(ctxt *obj.Link, p *obj.Prog, newprog obj.ProgAlloc) {
 			q.From.Reg = reg
 		}
 	}
-	if p.GetFrom3() != nil && p.GetFrom3().Name == obj.NAME_EXTERN {
-		ctxt.Diag("don't know how to handle %v with -dynlink", p)
+	from3 := p.GetFrom3()
+	for i := range p.RestArgs {
+		a := &p.RestArgs[i].Addr
+		if a != from3 && a.Name == obj.NAME_EXTERN && !a.Sym.Local() {
+			ctxt.Diag("don't know how to handle %v with -dynlink", p)
+		}
 	}
 	var source *obj.Addr
 	// MOVx sym, Ry becomes $MOV sym@GOT, R15; MOVx (R15), Ry
@@ -434,9 +438,17 @@ func rewriteToUseGot(ctxt *obj.Link, p *obj.Prog, newprog obj.ProgAlloc) {
 		if p.To.Name == obj.NAME_EXTERN && !p.To.Sym.Local() {
 			ctxt.Diag("cannot handle NAME_EXTERN on both sides in %v with -dynlink", p)
 		}
+		if from3 != nil && from3.Name == obj.NAME_EXTERN && !from3.Sym.Local() {
+			ctxt.Diag("cannot handle NAME_EXTERN on multiple operands in %v with -dynlink", p)
+		}
 		source = &p.From
 	} else if p.To.Name == obj.NAME_EXTERN && !p.To.Sym.Local() {
+		if from3 != nil && from3.Name == obj.NAME_EXTERN && !from3.Sym.Local() {
+			ctxt.Diag("cannot handle NAME_EXTERN on multiple operands in %v with -dynlink", p)
+		}
 		source = &p.To
+	} else if from3 != nil && from3.Name == obj.NAME_EXTERN && !from3.Sym.Local() {
+		source = from3
 	} else {
 		return
 	}
@@ -501,9 +513,7 @@ func rewriteToUseGot(ctxt *obj.Link, p *obj.Prog, newprog obj.ProgAlloc) {
 	p2.As = p.As
 	p2.From = p.From
 	p2.To = p.To
-	if from3 := p.GetFrom3(); from3 != nil {
-		p2.AddRestSource(*from3)
-	}
+	p2.RestArgs = p.RestArgs
 	if p.From.Name == obj.NAME_EXTERN {
 		p2.From.Reg = reg
 		p2.From.Name = obj.NAME_NONE
@@ -512,6 +522,11 @@ func rewriteToUseGot(ctxt *obj.Link, p *obj.Prog, newprog obj.ProgAlloc) {
 		p2.To.Reg = reg
 		p2.To.Name = obj.NAME_NONE
 		p2.To.Sym = nil
+	} else if p.GetFrom3() != nil && p.GetFrom3().Name == obj.NAME_EXTERN {
+		from3 = p2.GetFrom3()
+		from3.Reg = reg
+		from3.Name = obj.NAME_NONE
+		from3.Sym = nil
 	} else {
 		return
 	}