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cmd/compile: plumb prologueEnd into DWARF

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This marks the first instruction after the prologue for
consumption by debuggers, specifically Delve, who asked
for it.  gdb appears to ignore it, lldb appears to use it.

The bits for end-of-prologue and beginning-of-epilogue
are added to Pos (reducing maximum line number by 4x, to
1048575).  They're added in cmd/internal/obj/<ARCH>.go
(currently x86 only), so the compiler-proper need not
deal with them.

The linker currently does nothing with beginning-of-epilogue,
but the plumbing exists to make it easier in the future.

This also upgrades the line number table to DWARF version 3.

This CL includes a regression in the coverage for
testdata/i22558.gdb-dbg.nexts, this appears to be a gdb
artifact but the fix would be in the preceding CL in the
stack.

Change-Id: I3bda5f46a0ed232d137ad48f65a14835c742c506
Reviewed-on: https://go-review.googlesource.com/110416
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
This commit is contained in:
David Chase 2018-04-30 23:52:14 -04:00
parent c2c1822b12
commit 7bac2a95f6
6 changed files with 127 additions and 16 deletions
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21
src/cmd/link/internal/ld/dwarf.go
View file

@ -15,6 +15,7 @@ package ld
import (
"cmd/internal/dwarf"
"cmd/internal/obj"
"cmd/internal/objabi"
"cmd/internal/sys"
"cmd/link/internal/sym"
@ -953,7 +954,7 @@ const (
LINE_BASE = -4
LINE_RANGE = 10
PC_RANGE = (255 - OPCODE_BASE) / LINE_RANGE
OPCODE_BASE = 10
OPCODE_BASE = 11
)
func putpclcdelta(linkctxt *Link, ctxt dwarf.Context, s *sym.Symbol, deltaPC uint64, deltaLC int64) {
@ -1157,7 +1158,7 @@ func writelines(ctxt *Link, lib *sym.Library, textp []*sym.Symbol, ls *sym.Symbo
unitLengthOffset := ls.Size
ls.AddUint32(ctxt.Arch, 0) // unit_length (*), filled in at end.
unitstart = ls.Size
ls.AddUint16(ctxt.Arch, 2) // dwarf version (appendix F)
ls.AddUint16(ctxt.Arch, 3) // dwarf version (appendix F)
headerLengthOffset := ls.Size
ls.AddUint32(ctxt.Arch, 0) // header_length (*), filled in at end.
headerstart = ls.Size
@ -1177,6 +1178,7 @@ func writelines(ctxt *Link, lib *sym.Library, textp []*sym.Symbol, ls *sym.Symbo
ls.AddUint8(0) // standard_opcode_lengths[7]
ls.AddUint8(0) // standard_opcode_lengths[8]
ls.AddUint8(1) // standard_opcode_lengths[9]
ls.AddUint8(0) // standard_opcode_lengths[10]
ls.AddUint8(0) // include_directories (empty)
// Create the file table. fileNums maps from global file
@ -1271,8 +1273,19 @@ func writelines(ctxt *Link, lib *sym.Library, textp []*sym.Symbol, ls *sym.Symbo
// Only changed if it advanced
if is_stmt != uint8(pcstmt.value) {
is_stmt = uint8(pcstmt.value)
ls.AddUint8(uint8(dwarf.DW_LNS_negate_stmt))
new_stmt := uint8(pcstmt.value)
switch new_stmt &^ 1 {
case obj.PrologueEnd:
ls.AddUint8(uint8(dwarf.DW_LNS_set_prologue_end))
case obj.EpilogueBegin:
// TODO if there is a use for this, add it.
// Don't forget to increase OPCODE_BASE by 1 and add entry for standard_opcode_lengths[11]
}
new_stmt &= 1
if is_stmt != new_stmt {
is_stmt = new_stmt
ls.AddUint8(uint8(dwarf.DW_LNS_negate_stmt))
}
}
// putpcldelta makes a row in the DWARF matrix, always, even if line is unchanged.