cmd/link, runtime, debug/gosym: move pclntab magic to internal/abi

Change-Id: I2d3c41b0e61b994d7b04bd16a791fd226dc45269
Reviewed-on: https://go-review.googlesource.com/c/go/+/720302
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

4 files changed, 54 insertions, 25 deletions

diff --git a/src/cmd/link/internal/ld/pcln.go b/src/cmd/link/internal/ld/pcln.go
index 472fa715c7..1eb7112e64 100644
--- a/src/cmd/link/internal/ld/pcln.go
+++ b/src/cmd/link/internal/ld/pcln.go
@@ -261,7 +261,7 @@ func (state *pclntab) generatePCHeader(ctxt *Link) {
 
 		// Write header.
 		// Keep in sync with runtime/symtab.go:pcHeader and package debug/gosym.
-		header.SetUint32(ctxt.Arch, 0, 0xfffffff1)
+		header.SetUint32(ctxt.Arch, 0, uint32(abi.CurrentPCLnTabMagic))
 		header.SetUint8(ctxt.Arch, 6, uint8(ctxt.Arch.MinLC))
 		header.SetUint8(ctxt.Arch, 7, uint8(ctxt.Arch.PtrSize))
 		off := header.SetUint(ctxt.Arch, 8, uint64(state.nfunc))
diff --git a/src/debug/gosym/pclntab.go b/src/debug/gosym/pclntab.go
index 1d5498e037..da80c8460d 100644
--- a/src/debug/gosym/pclntab.go
+++ b/src/debug/gosym/pclntab.go
@@ -11,6 +11,7 @@ package gosym
 import (
 	"bytes"
 	"encoding/binary"
+	"internal/abi"
 	"sort"
 	"sync"
 )
@@ -174,13 +175,6 @@ func (t *LineTable) isGo12() bool {
 	return t.version >= ver12
 }
 
-const (
-	go12magic  = 0xfffffffb
-	go116magic = 0xfffffffa
-	go118magic = 0xfffffff0
-	go120magic = 0xfffffff1
-)
-
 // uintptr returns the pointer-sized value encoded at b.
 // The pointer size is dictated by the table being read.
 func (t *LineTable) uintptr(b []byte) uint64 {
@@ -220,24 +214,29 @@ func (t *LineTable) parsePclnTab() {
 	}
 
 	var possibleVersion version
-	leMagic := binary.LittleEndian.Uint32(t.Data)
-	beMagic := binary.BigEndian.Uint32(t.Data)
+
+	// The magic numbers are chosen such that reading the value with
+	// a different endianness does not result in the same value.
+	// That lets us the magic number to determine the endianness.
+	leMagic := abi.PCLnTabMagic(binary.LittleEndian.Uint32(t.Data))
+	beMagic := abi.PCLnTabMagic(binary.BigEndian.Uint32(t.Data))
+
 	switch {
-	case leMagic == go12magic:
+	case leMagic == abi.Go12PCLnTabMagic:
 		t.binary, possibleVersion = binary.LittleEndian, ver12
-	case beMagic == go12magic:
+	case beMagic == abi.Go12PCLnTabMagic:
 		t.binary, possibleVersion = binary.BigEndian, ver12
-	case leMagic == go116magic:
+	case leMagic == abi.Go116PCLnTabMagic:
 		t.binary, possibleVersion = binary.LittleEndian, ver116
-	case beMagic == go116magic:
+	case beMagic == abi.Go116PCLnTabMagic:
 		t.binary, possibleVersion = binary.BigEndian, ver116
-	case leMagic == go118magic:
+	case leMagic == abi.Go118PCLnTabMagic:
 		t.binary, possibleVersion = binary.LittleEndian, ver118
-	case beMagic == go118magic:
+	case beMagic == abi.Go118PCLnTabMagic:
 		t.binary, possibleVersion = binary.BigEndian, ver118
-	case leMagic == go120magic:
+	case leMagic == abi.Go120PCLnTabMagic:
 		t.binary, possibleVersion = binary.LittleEndian, ver120
-	case beMagic == go120magic:
+	case beMagic == abi.Go120PCLnTabMagic:
 		t.binary, possibleVersion = binary.BigEndian, ver120
 	default:
 		return
diff --git a/src/internal/abi/symtab.go b/src/internal/abi/symtab.go
index 86d6700388..10033e7277 100644
--- a/src/internal/abi/symtab.go
+++ b/src/internal/abi/symtab.go
@@ -4,6 +4,36 @@
 
 package abi
 
+// PCLnTabMagic is the version at the start of the PC/line table.
+// This is the start of the .pclntab section, and is also runtime.pcHeader.
+// The magic numbers are chosen such that reading the value with
+// a different endianness does not result in the same value.
+// That lets us the magic number to determine the endianness.
+type PCLnTabMagic uint32
+
+const (
+	// Initial PCLnTabMagic value used in Go 1.2 through Go 1.15.
+	Go12PCLnTabMagic PCLnTabMagic = 0xfffffffb
+	// PCLnTabMagic value used in Go 1.16 through Go 1.17.
+	// Several fields added to header (CL 241598).
+	Go116PCLnTabMagic PCLnTabMagic = 0xfffffffa
+	// PCLnTabMagic value used in Go 1.18 through Go 1.19.
+	// Entry PC of func data changed from address to offset (CL 351463).
+	Go118PCLnTabMagic PCLnTabMagic = 0xfffffff0
+	// PCLnTabMagic value used in Go 1.20 and later.
+	// A ":" was added to generated symbol names (#37762).
+	Go120PCLnTabMagic PCLnTabMagic = 0xfffffff1
+
+	// CurrentPCLnTabMagic is the value emitted by the current toolchain.
+	// This is written by the linker to the pcHeader and read by the
+	// runtime and debug/gosym (and external tools like Delve).
+	//
+	// Change this value when updating the pclntab version.
+	// Changing this exported value is OK because is an
+	// internal package.
+	CurrentPCLnTabMagic = Go120PCLnTabMagic
+)
+
 // A FuncFlag records bits about a function, passed to the runtime.
 type FuncFlag uint8
 
diff --git a/src/runtime/symtab.go b/src/runtime/symtab.go
index 3a814cd203..c1643c1b39 100644
--- a/src/runtime/symtab.go
+++ b/src/runtime/symtab.go
@@ -374,12 +374,12 @@ func (f *_func) funcInfo() funcInfo {
 
 // pcHeader holds data used by the pclntab lookups.
 type pcHeader struct {
-	magic      uint32 // 0xFFFFFFF1
-	pad1, pad2 uint8  // 0,0
-	minLC      uint8  // min instruction size
-	ptrSize    uint8  // size of a ptr in bytes
-	nfunc      int    // number of functions in the module
-	nfiles     uint   // number of entries in the file tab
+	magic      abi.PCLnTabMagic // abi.Go1NNPcLnTabMagic
+	pad1, pad2 uint8            // 0,0
+	minLC      uint8            // min instruction size
+	ptrSize    uint8            // size of a ptr in bytes
+	nfunc      int              // number of functions in the module
+	nfiles     uint             // number of entries in the file tab
 
 	// The next field used to be textStart. This is no longer stored
 	// as it requires a relocation. Code should use the moduledata text
@@ -623,7 +623,7 @@ const debugPcln = false
 func moduledataverify1(datap *moduledata) {
 	// Check that the pclntab's format is valid.
 	hdr := datap.pcHeader
-	if hdr.magic != 0xfffffff1 || hdr.pad1 != 0 || hdr.pad2 != 0 ||
+	if hdr.magic != abi.CurrentPCLnTabMagic || hdr.pad1 != 0 || hdr.pad2 != 0 ||
 		hdr.minLC != sys.PCQuantum || hdr.ptrSize != goarch.PtrSize {
 		println("runtime: pcHeader: magic=", hex(hdr.magic), "pad1=", hdr.pad1, "pad2=", hdr.pad2,
 			"minLC=", hdr.minLC, "ptrSize=", hdr.ptrSize, "pluginpath=", datap.pluginpath)