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cmd/link, runtime: don't store text start in pcHeader

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The textStart field requires a relocation, the only relocation in pclntab.
And nothing uses it. So remove it. Replace it with a zero,
which can itself be removed at some point in coordination with Delve.

For #76038

Change-Id: I35675c0868c5d957bb375e40b804c516ae0300ca
Reviewed-on: https://go-review.googlesource.com/c/go/+/717240
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>
Auto-Submit: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Ian Lance Taylor 2025-11-02 20:04:57 -08:00 • committed by Gopher Robot
parent 7347b54727
commit 0e1bd8b5f1
3 changed files with 17 additions and 19 deletions
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9
src/cmd/link/internal/ld/pcln.go
View file

@ -243,7 +243,6 @@ func makeInlSyms(ctxt *Link, funcs []loader.Sym, nameOffsets map[loader.Sym]uint
// generator to fill in its data later.
func (state *pclntab) generatePCHeader(ctxt *Link) {
ldr := ctxt.loader
textStartOff := int64(8 + 2*ctxt.Arch.PtrSize)
size := int64(8 + 8*ctxt.Arch.PtrSize)
writeHeader := func(ctxt *Link, s loader.Sym) {
header := ctxt.loader.MakeSymbolUpdater(s)
@ -264,10 +263,7 @@ func (state *pclntab) generatePCHeader(ctxt *Link) {
header.SetUint8(ctxt.Arch, 7, uint8(ctxt.Arch.PtrSize))
off := header.SetUint(ctxt.Arch, 8, uint64(state.nfunc))
off = header.SetUint(ctxt.Arch, off, uint64(state.nfiles))
if off != textStartOff {
panic(fmt.Sprintf("pcHeader textStartOff: %d != %d", off, textStartOff))
}
off += int64(ctxt.Arch.PtrSize) // skip runtimeText relocation
off = header.SetUintptr(ctxt.Arch, off, 0) // unused
off = writeSymOffset(off, state.funcnametab)
off = writeSymOffset(off, state.cutab)
off = writeSymOffset(off, state.filetab)
@ -279,9 +275,6 @@ func (state *pclntab) generatePCHeader(ctxt *Link) {
}
state.pcheader = state.addGeneratedSym(ctxt, "runtime.pcheader", size, writeHeader)
// Create the runtimeText relocation.
sb := ldr.MakeSymbolUpdater(state.pcheader)
sb.SetAddr(ctxt.Arch, textStartOff, ldr.Lookup("runtime.text", 0))
}
// walkFuncs iterates over the funcs, calling a function for each unique

2
src/runtime/runtime2.go
View file

@ -1009,7 +1009,7 @@ const (
type _func struct {
sys.NotInHeap // Only in static data
entryOff uint32 // start pc, as offset from moduledata.text/pcHeader.textStart
entryOff uint32 // start pc, as offset from moduledata.text
nameOff int32 // function name, as index into moduledata.funcnametab.
args int32 // in/out args size

25
src/runtime/symtab.go
View file

@ -374,13 +374,19 @@ 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
textStart uintptr // base for function entry PC offsets in this module, equal to moduledata.text
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
// The next field used to be textStart. This is no longer stored
// as it requires a relocation. Code should use the moduledata text
// field instead. This unused field can be removed in coordination
// with Delve.
_ uintptr
funcnameOffset uintptr // offset to the funcnametab variable from pcHeader
cuOffset uintptr // offset to the cutab variable from pcHeader
filetabOffset uintptr // offset to the filetab variable from pcHeader
@ -618,10 +624,9 @@ 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 ||
hdr.minLC != sys.PCQuantum || hdr.ptrSize != goarch.PtrSize || hdr.textStart != datap.text {
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, "pcHeader.textStart=", hex(hdr.textStart),
"text=", hex(datap.text), "pluginpath=", datap.pluginpath)
"minLC=", hdr.minLC, "ptrSize=", hdr.ptrSize, "pluginpath=", datap.pluginpath)
throw("invalid function symbol table")
}