From 80038586ed2814a03dcb95cd6f130766f8d803c3 Mon Sep 17 00:00:00 2001 From: Alessandro Arzilli Date: Mon, 18 Aug 2025 15:49:50 +0200 Subject: [PATCH] cmd/compile: export to DWARF types only referenced through interfaces Delve and viewcore use DWARF type DIEs to display and explore the runtime value of interface variables. This has always been slightly problematic since the runtime type of an interface variable might only be reachable through interfaces and thus be missing from debug_info (see issue #46670). Prior to commit f4de2ecf this was not a severe problem since a struct literal caused the allocation of a struct into an autotemp variable, which was then used by dwarfgen to make sure that the DIE for that type would be generated. After f4de2ecf such autotemps are no longer being generated and go1.25.0 ends up having many more instances of interfaces with unreadable runtime type (https://github.com/go-delve/delve/issues/4080). This commit fixes this problem by scanning the relocation of the function symbol and adding to the function's DIE symbol references to all types used by the function to create interfaces. Fixes go-delve/delve#4080 Updates #46670 Change-Id: I3e9db1c0d1662905373239816a72604ac533b09e Reviewed-on: https://go-review.googlesource.com/c/go/+/696955 Reviewed-by: Michael Pratt LUCI-TryBot-Result: Go LUCI Auto-Submit: Michael Pratt Reviewed-by: Keith Randall Reviewed-by: Than McIntosh Reviewed-by: Florian Lehner --- src/cmd/compile/internal/dwarfgen/dwarf.go | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/src/cmd/compile/internal/dwarfgen/dwarf.go b/src/cmd/compile/internal/dwarfgen/dwarf.go index 6ab39d2aaa..9d975e0bc1 100644 --- a/src/cmd/compile/internal/dwarfgen/dwarf.go +++ b/src/cmd/compile/internal/dwarfgen/dwarf.go @@ -128,14 +128,29 @@ func Info(ctxt *obj.Link, fnsym *obj.LSym, infosym *obj.LSym, curfn obj.Func) (s // already referenced by a dwarf var, attach an R_USETYPE relocation to // the function symbol to insure that the type included in DWARF // processing during linking. + // Do the same with R_USEIFACE relocations from the function symbol for the + // same reason. + // All these R_USETYPE relocations are only looked at if the function + // survives deadcode elimination in the linker. typesyms := []*obj.LSym{} for t := range fnsym.Func().Autot { typesyms = append(typesyms, t) } + for i := range fnsym.R { + if fnsym.R[i].Type == objabi.R_USEIFACE && !strings.HasPrefix(fnsym.R[i].Sym.Name, "go:itab.") { + // Types referenced through itab will be referenced from somewhere else + typesyms = append(typesyms, fnsym.R[i].Sym) + } + } slices.SortFunc(typesyms, func(a, b *obj.LSym) int { return strings.Compare(a.Name, b.Name) }) + var lastsym *obj.LSym for _, sym := range typesyms { + if sym == lastsym { + continue + } + lastsym = sym infosym.AddRel(ctxt, obj.Reloc{Type: objabi.R_USETYPE, Sym: sym}) } fnsym.Func().Autot = nil -- 2.52.0