From 27603028eb48c19964722e09ee7e4b1c44b960cc Mon Sep 17 00:00:00 2001 From: Cherry Mui Date: Tue, 14 May 2024 21:40:51 -0400 Subject: [PATCH] cmd/internal/obj/x86: make SEH symbols content-addressable Currently, the SEH symbol is defined as an aux symbol of the function symbol, without adding to ctxt.Data. Each function has its own SEH symbol. As there are a lot of duplications of the SEH symbol contents, currently a Go object file may contain many copies of identical SEH symbols. They are deduplicated at link time. But it does make the linker do redundant work, and make it hard to reason about the SEH symbol writing in the object file writer, and its resolution in the linker. In fact, in the object file writer, the same SEH symbol may be added to the ctxt.defs multiple times (as it is the aux of multiple function symbols), which is not expected. In fact, "aux symbol" is just a mechanism to associate auxiliary data to another symbol. The auxiliary data symbol itself can be an ordinary data symbol, even a content-addressable symbol. Define the SEH symbol as a conntent-addressable symbol and add it to ctxt.Data. This way there is only one definition of each unique SEH symbol, which can be the aux of many functions. While here, add a check to ensure that we add a symbol at most once to the defs list. Change-Id: Ie7a0cf02ca114060423e025931b30de97ca330fe Reviewed-on: https://go-review.googlesource.com/c/go/+/585656 LUCI-TryBot-Result: Go LUCI Reviewed-by: Quim Muntal Reviewed-by: Than McIntosh --- src/cmd/internal/obj/link.go | 4 ++++ src/cmd/internal/obj/objfile.go | 6 +++++- src/cmd/internal/obj/sym.go | 7 +++++++ src/cmd/internal/obj/x86/seh.go | 5 ++--- 4 files changed, 18 insertions(+), 4 deletions(-) diff --git a/src/cmd/internal/obj/link.go b/src/cmd/internal/obj/link.go index dac6e209f1..3ebaa2aa5c 100644 --- a/src/cmd/internal/obj/link.go +++ b/src/cmd/internal/obj/link.go @@ -1058,6 +1058,10 @@ type Link struct { // to Data. constSyms []*LSym + // Windows SEH symbols are also data symbols that can be created + // concurrently. + SEHSyms []*LSym + // pkgIdx maps package path to index. The index is used for // symbol reference in the object file. pkgIdx map[string]int32 diff --git a/src/cmd/internal/obj/objfile.go b/src/cmd/internal/obj/objfile.go index 3da8c30640..648aae4fa2 100644 --- a/src/cmd/internal/obj/objfile.go +++ b/src/cmd/internal/obj/objfile.go @@ -788,14 +788,18 @@ func genFuncInfoSyms(ctxt *Link) { fn.FuncInfoSym = isym b.Reset() - auxsyms := []*LSym{fn.dwarfRangesSym, fn.dwarfLocSym, fn.dwarfDebugLinesSym, fn.dwarfInfoSym, fn.WasmImportSym, fn.sehUnwindInfoSym} + auxsyms := []*LSym{fn.dwarfRangesSym, fn.dwarfLocSym, fn.dwarfDebugLinesSym, fn.dwarfInfoSym, fn.WasmImportSym} for _, s := range auxsyms { if s == nil || s.Size == 0 { continue } + if s.OnList() { + panic("a symbol is added to defs multiple times") + } s.PkgIdx = goobj.PkgIdxSelf s.SymIdx = symidx s.Set(AttrIndexed, true) + s.Set(AttrOnList, true) symidx++ infosyms = append(infosyms, s) } diff --git a/src/cmd/internal/obj/sym.go b/src/cmd/internal/obj/sym.go index f27d4ef4fc..22153050f2 100644 --- a/src/cmd/internal/obj/sym.go +++ b/src/cmd/internal/obj/sym.go @@ -245,6 +245,13 @@ func (ctxt *Link) NumberSyms() { ctxt.Data = append(ctxt.Data, ctxt.constSyms...) ctxt.constSyms = nil + // So are SEH symbols. + sort.Slice(ctxt.SEHSyms, func(i, j int) bool { + return ctxt.SEHSyms[i].Name < ctxt.SEHSyms[j].Name + }) + ctxt.Data = append(ctxt.Data, ctxt.SEHSyms...) + ctxt.SEHSyms = nil + ctxt.pkgIdx = make(map[string]int32) ctxt.defs = []*LSym{} ctxt.hashed64defs = []*LSym{} diff --git a/src/cmd/internal/obj/x86/seh.go b/src/cmd/internal/obj/x86/seh.go index 71cdd36642..11963e53f9 100644 --- a/src/cmd/internal/obj/x86/seh.go +++ b/src/cmd/internal/obj/x86/seh.go @@ -151,6 +151,7 @@ func populateSeh(ctxt *obj.Link, s *obj.LSym) (sehsym *obj.LSym) { s.Type = objabi.SSEHUNWINDINFO s.Set(obj.AttrDuplicateOK, true) s.Set(obj.AttrLocal, true) + s.Set(obj.AttrContentAddressable, true) if exceptionHandler != nil { r := obj.Addrel(s) r.Off = int32(len(buf.data) - 4) @@ -158,8 +159,6 @@ func populateSeh(ctxt *obj.Link, s *obj.LSym) (sehsym *obj.LSym) { r.Sym = exceptionHandler r.Type = objabi.R_PEIMAGEOFF } - // Note: AttrContentAddressable cannot be set here, - // because the content-addressable-handling code - // does not know about aux symbols. + ctxt.SEHSyms = append(ctxt.SEHSyms, s) }) }