cmd/link: don't create __x86.get_pc_thunk symbol if it already exists

On 386, in some build modes we need to create the __x86.get_pc_thunk
symbols, to support PC-relative addressing. In some situation
the thunk symbols may already exist, e.g. loaded from a C object
in internal linking mode. In this case, we should use the exiting
symbol instead of making a new one. The current code updates the
symbol content in place but also adds a duplicated entry to Textp,
which breaks the address sorting order.

Fixes #76815.

Change-Id: Iab11106ce592dc5219b7a0e07cfafcd270661a2f
Reviewed-on: https://go-review.googlesource.com/c/go/+/730161
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

diff --git a/src/cmd/link/internal/x86/asm.go b/src/cmd/link/internal/x86/asm.go
index 036514819a0b0684981dc4f68ef7a8fe381dd4da..2c38473702f646052cb6ca1d1371ee8439b5bfb3 100644 (file)
--- a/src/cmd/link/internal/x86/asm.go
+++ b/src/cmd/link/internal/x86/asm.go
@@ -72,6 +72,9 @@ func gentext(ctxt *ld.Link, ldr *loader.Loader) {
                {"di", 7},
        } {
                thunkfunc := ldr.CreateSymForUpdate("__x86.get_pc_thunk."+r.name, 0)
+               if t := thunkfunc.Type(); t != 0 && t != sym.SXREF && t != sym.SDYNIMPORT && t != sym.SUNDEFEXT {
+                       continue // symbol already exists, probably loaded from a C object
+               }
                thunkfunc.SetType(sym.STEXT)
                ldr.SetAttrLocal(thunkfunc.Sym(), true)
                o := func(op ...uint8) {