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// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Loading of code and data fragments from package files into final image.
package main
import (
"cmd/internal/obj"
"os"
)
// load allocates segment images, populates them with data
// read from package files, and applies relocations to the data.
func (p *Prog) load() {
// TODO(rsc): mmap the output file and store the data directly.
// That will make writing the output file more efficient.
for _, seg := range p.Segments {
seg.Data = make([]byte, seg.FileSize)
}
for _, pkg := range p.Packages {
p.loadPackage(pkg)
}
}
// loadPackage loads and relocates data for all the
// symbols needed in the given package.
func (p *Prog) loadPackage(pkg *Package) {
if pkg.File == "" {
// This "package" contains internally generated symbols only.
// All such symbols have a sym.Bytes field holding the actual data
// (if any), plus relocations.
for _, sym := range pkg.Syms {
if sym.Bytes == nil {
continue
}
seg := sym.Section.Segment
off := sym.Addr - seg.VirtAddr
data := seg.Data[off : off+Addr(sym.Size)]
copy(data, sym.Bytes)
p.relocateSym(sym, data)
}
return
}
// Package stored in file.
f, err := os.Open(pkg.File)
if err != nil {
p.errorf("%v", err)
return
}
defer f.Close()
// TODO(rsc): Mmap file into memory.
for _, sym := range pkg.Syms {
if sym.Data.Size == 0 {
continue
}
// TODO(rsc): If not using mmap, at least coalesce nearby reads.
if sym.Section == nil {
p.errorf("internal error: missing section for %s", sym.Name)
}
seg := sym.Section.Segment
off := sym.Addr - seg.VirtAddr
if off >= Addr(len(seg.Data)) || off+Addr(sym.Data.Size) > Addr(len(seg.Data)) {
p.errorf("internal error: allocated space for %s too small: %d bytes for %d+%d (%d)", sym, len(seg.Data), off, sym.Data.Size, sym.Size)
}
data := seg.Data[off : off+Addr(sym.Data.Size)]
_, err := f.ReadAt(data, sym.Data.Offset)
if err != nil {
p.errorf("reading %v: %v", sym.SymID, err)
}
p.relocateSym(sym, data)
}
}
// relocateSym applies relocations to sym's data.
func (p *Prog) relocateSym(sym *Sym, data []byte) {
for i := range sym.Reloc {
r := &sym.Reloc[i]
targ := p.Syms[r.Sym]
if targ == nil {
p.errorf("%v: reference to undefined symbol %v", sym, r.Sym)
continue
}
val := targ.Addr + Addr(r.Add)
switch r.Type {
default:
p.errorf("%v: unknown relocation type %d", sym, r.Type)
case obj.R_ADDR, obj.R_CALLIND:
// ok
case obj.R_PCREL, obj.R_CALL:
val -= sym.Addr + Addr(r.Offset+r.Size)
}
frag := data[r.Offset : r.Offset+r.Size]
switch r.Size {
default:
p.errorf("%v: unknown relocation size %d", sym, r.Size)
case 4:
// TODO(rsc): Check for overflow?
p.byteorder.PutUint32(frag, uint32(val))
case 8:
p.byteorder.PutUint64(frag, uint64(val))
}
}
}
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