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[dev.link] cmd/link/internal/loader: change storage mechanism for sym alignment

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Switch the storage mechanism for symbol alignment away from a map and
to a slice of uint8 values per symbol, where value K indicates
alignment 2^K. Intended to help speed up alignment get/set in dodata.

Change-Id: I26416e455c808f697dd0d7f6d2582247ee5c5b40
Reviewed-on: https://go-review.googlesource.com/c/go/+/231220
Run-TryBot: Than McIntosh <thanm@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
This commit is contained in:
Than McIntosh 2020-04-30 16:01:03 -04:00
parent cdfff4d25a
commit 2f83d68926
1 changed files with 19 additions and 21 deletions
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36
src/cmd/link/internal/loader/loader.go
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@ -223,6 +223,8 @@ type Loader struct {
sects []*sym.Section // sections
symSects []uint16 // symbol's section, index to sects array
align []uint8 // symbol 2^N alignment, indexed by global index
outdata [][]byte // symbol's data in the output buffer
extRelocs [][]ExtReloc // symbol's external relocations
@ -263,8 +265,6 @@ type Loader struct {
outer map[Sym]Sym
sub map[Sym]Sym
align map[Sym]int32 // stores alignment for symbols
dynimplib map[Sym]string // stores Dynimplib symbol attribute
dynimpvers map[Sym]string // stores Dynimpvers symbol attribute
localentry map[Sym]uint8 // stores Localentry symbol attribute
@ -336,7 +336,6 @@ func NewLoader(flags uint32, elfsetstring elfsetstringFunc, reporter *ErrorRepor
objByPkg: make(map[string]*oReader),
outer: make(map[Sym]Sym),
sub: make(map[Sym]Sym),
align: make(map[Sym]int32),
dynimplib: make(map[Sym]string),
dynimpvers: make(map[Sym]string),
localentry: make(map[Sym]uint8),
@ -1128,36 +1127,35 @@ func (l *Loader) InitExtRelocs() {
// SymAlign returns the alignment for a symbol.
func (l *Loader) SymAlign(i Sym) int32 {
// If an alignment has been recorded, return that.
if align, ok := l.align[i]; ok {
return align
if int(i) >= len(l.align) {
// align is extended lazily -- it the sym in question is
// outside the range of the existing slice, then we assume its
// alignment has not yet been set.
return 0
}
// TODO: would it make sense to return an arch-specific
// alignment depending on section type? E.g. STEXT => 32,
// SDATA => 1, etc?
abits := l.align[i]
if abits == 0 {
return 0
}
return int32(1 << (abits - 1))
}
// SetSymAlign sets the alignment for a symbol.
func (l *Loader) SetSymAlign(i Sym, align int32) {
// reject bad synbols
if i >= Sym(len(l.objSyms)) || i == 0 {
panic("bad symbol index in SetSymAlign")
}
// Reject nonsense alignments.
// TODO: do we need this?
if align < 0 {
if align < 0 || align&(align-1) != 0 {
panic("bad alignment value")
}
if int(i) >= len(l.align) {
l.align = append(l.align, make([]uint8, l.NSym()-len(l.align))...)
}
if align == 0 {
delete(l.align, i)
} else {
// Alignment should be a power of 2.
if bits.OnesCount32(uint32(align)) != 1 {
panic("bad alignment value")
}
l.align[i] = align
l.align[i] = 0
}
l.align[i] = uint8(bits.Len32(uint32(align)))
}
// SymValue returns the section of the i-th symbol. i is global index.