cmd/link: fix off-by-one in ftabaddstring

ftabaddstring adds a string to the pclntab.
The pclntab uses C strings, so the code added 1 to the length.
However, it also added an extraneous 1 in the Grow call. Remove that.

While we're here, simplify, document, remove an unnecessary parameter,
and remove some unnecessary conversions.

Shaves off a few bytes here and there, and thus updates #6853.

file      before    after     Δ       %
go        14671316  14659028  -12288  -0.084%
addr2line 4280552   4276456   -4096   -0.096%
api       6058936   6050744   -8192   -0.135%
buildid   2861040   2856944   -4096   -0.143%
cgo       4867912   4863816   -4096   -0.084%
compile   25770104  25753720  -16384  -0.064%
cover     5286888   5282792   -4096   -0.077%
dist      3634048   3629952   -4096   -0.113%
doc       4691000   4686904   -4096   -0.087%
fix       3393736   3389640   -4096   -0.121%
link      6109280   6105184   -4096   -0.067%
nm        4225960   4221864   -4096   -0.097%
objdump   4636520   4632424   -4096   -0.088%
pack      2285200   2281104   -4096   -0.179%
pprof     14657508  14645220  -12288  -0.084%
test2json 2818568   2814472   -4096   -0.145%
trace     11618524  11610332  -8192   -0.071%
vet       8403544   8395352   -8192   -0.097%

Change-Id: I20b1f541de5d3ed326dd937aad6a43801862df51
Reviewed-on: https://go-review.googlesource.com/c/go/+/171820
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

diff --git a/src/cmd/link/internal/ld/pcln.go b/src/cmd/link/internal/ld/pcln.go
index 5c590608e301c50ef32b2d8e65721567a6272e66..5924acc0b08591fe50a0e8236a3b9c95cbad3c0c 100644 (file)
--- a/src/cmd/link/internal/ld/pcln.go
+++ b/src/cmd/link/internal/ld/pcln.go
@@ -104,12 +104,11 @@ func addpctab(ctxt *Link, ftab *sym.Symbol, off int32, d *sym.Pcdata) int32 {
        return int32(ftab.SetUint32(ctxt.Arch, int64(off), uint32(start)))
 }
 
-func ftabaddstring(ctxt *Link, ftab *sym.Symbol, s string) int32 {
-       n := int32(len(s)) + 1
-       start := int32(len(ftab.P))
-       ftab.Grow(int64(start) + int64(n) + 1)
+func ftabaddstring(ftab *sym.Symbol, s string) int32 {
+       start := len(ftab.P)
+       ftab.Grow(int64(start + len(s) + 1)) // make room for s plus trailing NUL
        copy(ftab.P[start:], s)
-       return start
+       return int32(start)
 }
 
 // numberfile assigns a file number to the file if it hasn't been assigned already.
@@ -236,7 +235,7 @@ func (ctxt *Link) pclntab() {
        nameToOffset := func(name string) int32 {
                nameoff, ok := funcnameoff[name]
                if !ok {
-                       nameoff = ftabaddstring(ctxt, ftab, name)
+                       nameoff = ftabaddstring(ftab, name)
                        funcnameoff[name] = nameoff
                }
                return nameoff
@@ -446,7 +445,7 @@ func (ctxt *Link) pclntab() {
        ftab.SetUint32(ctxt.Arch, int64(start), uint32(len(ctxt.Filesyms)+1))
        for i := len(ctxt.Filesyms) - 1; i >= 0; i-- {
                s := ctxt.Filesyms[i]
-               ftab.SetUint32(ctxt.Arch, int64(start)+s.Value*4, uint32(ftabaddstring(ctxt, ftab, s.Name)))
+               ftab.SetUint32(ctxt.Arch, int64(start)+s.Value*4, uint32(ftabaddstring(ftab, s.Name)))
        }
 
        ftab.Size = int64(len(ftab.P))