From dead03b7947c79112ef6c2a91843d7b10e5ebcfe Mon Sep 17 00:00:00 2001 From: David Chase Date: Tue, 13 Feb 2018 17:39:38 -0500 Subject: cmd/link: process is_stmt data into dwarf line tables To improve debugging, instructions should be annotated with DWARF is_stmt. The DWARF default before was is_stmt=1, and to remove "jumpy" stepping the optimizer was tagging instructions with a no-position position, which interferes with the accuracy of profiling information. This allows that to be corrected, and also allows more "jumpy" positions to be annotated with is_stmt=0 (these changes were not made for 1.10 because of worries about further messing up profiling). The is_stmt values are placed in a pc-encoded table and passed through a symbol derived from the name of the function and processed in the linker alongside its processing of each function's pc/line tables. The only change in binary size is in the .debug_line tables measured with "objdump -h --section=.debug_line go1.test" For go1.test, these are 2614 bytes larger, or 0.72% of the size of .debug_line, or 0.025% of the file size. This will increase in proportion to how much the is_stmt flag is used (toggled). Change-Id: Ic1f1aeccff44591ad0494d29e1a0202a3c506a7a Reviewed-on: https://go-review.googlesource.com/93664 Run-TryBot: David Chase Reviewed-by: Heschi Kreinick --- src/cmd/internal/obj/objfile.go | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'src/cmd/internal/obj/objfile.go') diff --git a/src/cmd/internal/obj/objfile.go b/src/cmd/internal/obj/objfile.go index b5f5790a50..91b48b5e08 100644 --- a/src/cmd/internal/obj/objfile.go +++ b/src/cmd/internal/obj/objfile.go @@ -497,7 +497,7 @@ func (c dwCtxt) Logf(format string, args ...interface{}) { c.Link.Logf(format, args...) } -func (ctxt *Link) dwarfSym(s *LSym) (dwarfInfoSym, dwarfLocSym, dwarfRangesSym, dwarfAbsFnSym *LSym) { +func (ctxt *Link) dwarfSym(s *LSym) (dwarfInfoSym, dwarfLocSym, dwarfRangesSym, dwarfAbsFnSym, dwarfIsStmtSym *LSym) { if s.Type != objabi.STEXT { ctxt.Diag("dwarfSym of non-TEXT %v", s) } @@ -510,9 +510,10 @@ func (ctxt *Link) dwarfSym(s *LSym) (dwarfInfoSym, dwarfLocSym, dwarfRangesSym, if s.WasInlined() { s.Func.dwarfAbsFnSym = ctxt.DwFixups.AbsFuncDwarfSym(s) } + s.Func.dwarfIsStmtSym = ctxt.LookupDerived(s, dwarf.IsStmtPrefix+s.Name) } - return s.Func.dwarfInfoSym, s.Func.dwarfLocSym, s.Func.dwarfRangesSym, s.Func.dwarfAbsFnSym + return s.Func.dwarfInfoSym, s.Func.dwarfLocSym, s.Func.dwarfRangesSym, s.Func.dwarfAbsFnSym, s.Func.dwarfIsStmtSym } func (s *LSym) Len() int64 { @@ -536,13 +537,14 @@ func (ctxt *Link) fileSymbol(fn *LSym) *LSym { // TEXT symbol 's'. The various DWARF symbols must already have been // initialized in InitTextSym. func (ctxt *Link) populateDWARF(curfn interface{}, s *LSym, myimportpath string) { - info, loc, ranges, absfunc := ctxt.dwarfSym(s) + info, loc, ranges, absfunc, _ := ctxt.dwarfSym(s) if info.Size != 0 { ctxt.Diag("makeFuncDebugEntry double process %v", s) } var scopes []dwarf.Scope var inlcalls dwarf.InlCalls if ctxt.DebugInfo != nil { + stmtData(ctxt, s) scopes, inlcalls = ctxt.DebugInfo(s, curfn) } var err error -- cgit v1.3-5-g9baa