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[dev.link] cmd/link: remove implicit reachability setting from SymbolBuilder

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The loader's SymbolBuilder Add*/Set* methods include a call to mark
the underlying symbol as reachable (as a convenience, so that callers
would not have to set it explicitly). This code was carried over from
the corresponding sym.Symbol methods; back in the sym.Symbol world
unreachable symbols were never removed from the AllSyms slice, hence
setting and checking reachability was a good deal more important.

With the advent of the loader and the new deadcode implementation,
there is less of a need for this sort of fallback, and in addition the
implicit attr setting introduces data races in the the loader if there
are SymbolBuilder Add*/Set* method calls in parallel threads, as well
as adding overhead to the methods.

This patch gets rid of the implicit reachability setting, and instead
marks reachability in CreateSymForUpdate, as well as adding a few
explicit SetAttrReachable calls where needed.

Change-Id: I029a0c5a4a24237826a7831f9cbe5180d44cbc40
Reviewed-on: https://go-review.googlesource.com/c/go/+/237678
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
This commit is contained in:
Than McIntosh 2020-06-12 09:35:42 -04:00
parent 27144d166b
commit 0fb1517b3f
13 changed files with 41 additions and 115 deletions
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19
src/cmd/link/internal/loader/symbolbuilder.go
View file

@ -54,7 +54,9 @@ func (l *Loader) MakeSymbolUpdater(symIdx Sym) *SymbolBuilder {
// returns a CreateSymForUpdate for update. If the symbol already
// exists, it will update in-place.
func (l *Loader) CreateSymForUpdate(name string, version int) *SymbolBuilder {
return l.MakeSymbolUpdater(l.LookupOrCreateSym(name, version))
s := l.LookupOrCreateSym(name, version)
l.SetAttrReachable(s, true)
return l.MakeSymbolUpdater(s)
}
// Getters for properties of the symbol we're working on.
@ -105,7 +107,6 @@ func (sb *SymbolBuilder) SetNotInSymbolTable(value bool) {
func (sb *SymbolBuilder) SetSect(sect *sym.Section) { sb.l.SetSymSect(sb.symIdx, sect) }
func (sb *SymbolBuilder) AddBytes(data []byte) {
sb.setReachable()
if sb.kind == 0 {
sb.kind = sym.SDATA
}
@ -248,7 +249,6 @@ func (sb *SymbolBuilder) AddUint8(v uint8) int64 {
if sb.kind == 0 {
sb.kind = sym.SDATA
}
sb.setReachable()
sb.size++
sb.data = append(sb.data, v)
return off
@ -256,7 +256,6 @@ func (sb *SymbolBuilder) AddUint8(v uint8) int64 {
func (sb *SymbolBuilder) AddUintXX(arch *sys.Arch, v uint64, wid int) int64 {
off := sb.size
sb.setReachable()
sb.setUintXX(arch, off, v, int64(wid))
return off
}
@ -301,22 +300,18 @@ func (sb *SymbolBuilder) AddUint(arch *sys.Arch, v uint64) int64 {
}
func (sb *SymbolBuilder) SetUint8(arch *sys.Arch, r int64, v uint8) int64 {
sb.setReachable()
return sb.setUintXX(arch, r, uint64(v), 1)
}
func (sb *SymbolBuilder) SetUint16(arch *sys.Arch, r int64, v uint16) int64 {
sb.setReachable()
return sb.setUintXX(arch, r, uint64(v), 2)
}
func (sb *SymbolBuilder) SetUint32(arch *sys.Arch, r int64, v uint32) int64 {
sb.setReachable()
return sb.setUintXX(arch, r, uint64(v), 4)
}
func (sb *SymbolBuilder) SetUint(arch *sys.Arch, r int64, v uint64) int64 {
sb.setReachable()
return sb.setUintXX(arch, r, v, int64(arch.PtrSize))
}
@ -324,7 +319,6 @@ func (sb *SymbolBuilder) SetAddrPlus(arch *sys.Arch, off int64, tgt Sym, add int
if sb.Type() == 0 {
sb.SetType(sym.SDATA)
}
sb.setReachable()
if off+int64(arch.PtrSize) > sb.size {
sb.size = off + int64(arch.PtrSize)
sb.Grow(sb.size)
@ -344,7 +338,6 @@ func (sb *SymbolBuilder) SetAddr(arch *sys.Arch, off int64, tgt Sym) int64 {
}
func (sb *SymbolBuilder) Addstring(str string) int64 {
sb.setReachable()
if sb.kind == 0 {
sb.kind = sym.SNOPTRDATA
}
@ -382,17 +375,14 @@ func (sb *SymbolBuilder) addSymRef(tgt Sym, add int64, typ objabi.RelocType, rsi
// Add a symbol reference (relocation) with given type, addend, and size
// (the most generic form).
func (sb *SymbolBuilder) AddSymRef(arch *sys.Arch, tgt Sym, add int64, typ objabi.RelocType, rsize int) int64 {
sb.setReachable()
return sb.addSymRef(tgt, add, typ, rsize)
}
func (sb *SymbolBuilder) AddAddrPlus(arch *sys.Arch, tgt Sym, add int64) int64 {
sb.setReachable()
return sb.addSymRef(tgt, add, objabi.R_ADDR, arch.PtrSize)
}
func (sb *SymbolBuilder) AddAddrPlus4(arch *sys.Arch, tgt Sym, add int64) int64 {
sb.setReachable()
return sb.addSymRef(tgt, add, objabi.R_ADDR, 4)
}
@ -401,17 +391,14 @@ func (sb *SymbolBuilder) AddAddr(arch *sys.Arch, tgt Sym) int64 {
}
func (sb *SymbolBuilder) AddPCRelPlus(arch *sys.Arch, tgt Sym, add int64) int64 {
sb.setReachable()
return sb.addSymRef(tgt, add, objabi.R_PCREL, 4)
}
func (sb *SymbolBuilder) AddCURelativeAddrPlus(arch *sys.Arch, tgt Sym, add int64) int64 {
sb.setReachable()
return sb.addSymRef(tgt, add, objabi.R_ADDRCUOFF, arch.PtrSize)
}
func (sb *SymbolBuilder) AddSize(arch *sys.Arch, tgt Sym) int64 {
sb.setReachable()
return sb.addSymRef(tgt, 0, objabi.R_SIZE, arch.PtrSize)
}