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debug/dwarf: factor finding unit containing entry offset

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This factors out the code for finding which unit contains an offset in
the "info" section.  The new code also replaces linear search with a
binary search.  The line table reader will also need this
functionality.

Change-Id: I2076e4fc6719b6f06fd2796cbbc7548ec1876cb3
Reviewed-on: https://go-review.googlesource.com/6733
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
This commit is contained in:
Austin Clements 2015-03-03 20:53:40 -05:00
parent de1693f984
commit 0e31b4ed26
2 changed files with 27 additions and 12 deletions
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17
src/debug/dwarf/entry.go
View File

@ -308,18 +308,13 @@ func (r *Reader) Seek(off Offset) {
return
}
// TODO(rsc): binary search (maybe a new package)
var i int
var u *unit
for i = range d.unit {
u = &d.unit[i]
if u.off <= off && off < u.off+Offset(len(u.data)) {
r.unit = i
r.b = makeBuf(r.d, u, "info", off, u.data[off-u.off:])
return
}
i := d.offsetToUnit(off)
if i == -1 {
r.err = errors.New("offset out of range")
}
r.err = errors.New("offset out of range")
u := &d.unit[i]
r.unit = i
r.b = makeBuf(r.d, u, "info", off, u.data[off-u.off:])
}
// maybeNextUnit advances to the next unit if this one is finished.

22
src/debug/dwarf/unit.go
View File

@ -4,7 +4,10 @@
package dwarf
import "strconv"
import (
"sort"
"strconv"
)
// DWARF debug info is split into a sequence of compilation units.
// Each unit has its own abbreviation table and address size.
@ -88,3 +91,20 @@ func (d *Data) parseUnits() ([]unit, error) {
}
return units, nil
}
// offsetToUnit returns the index of the unit containing offset off.
// It returns -1 if no unit contains this offset.
func (d *Data) offsetToUnit(off Offset) int {
// Find the unit after off
next := sort.Search(len(d.unit), func(i int) bool {
return d.unit[i].off > off
})
if next == 0 {
return -1
}
u := &d.unit[next-1]
if u.off <= off && off < u.off+Offset(len(u.data)) {
return next - 1
}
return -1
}