cmd/link: clean up pclntab

More minor cleanup:

* Code simplification
* Move variable declaration closer to use
* Add docs
* Refactor loop

Change-Id: I6f662cb65038b6ad927eb83757b241ac1ef58943
Reviewed-on: https://go-review.googlesource.com/c/go/+/172078
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/src/cmd/link/internal/ld/pcln.go b/src/cmd/link/internal/ld/pcln.go
index 9f253f0205d44c962ddc728e8c0db63484c9bf11..96b2028d109bcabc4fa88b6cc40d7075ef0f40b5 100644 (file)
--- a/src/cmd/link/internal/ld/pcln.go
+++ b/src/cmd/link/internal/ld/pcln.go
@@ -201,7 +201,6 @@ func (ctxt *Link) pclntab() {
        //      function table, alternating PC and offset to func struct [each entry thearch.ptrsize bytes]
        //      end PC [thearch.ptrsize bytes]
        //      offset to file table [4 bytes]
-       nfunc := int32(0)
 
        // Find container symbols and mark them as such.
        for _, s := range ctxt.Textp {
@@ -210,9 +209,15 @@ func (ctxt *Link) pclntab() {
                }
        }
 
+       // Gather some basic stats and info.
+       var nfunc int32
        for _, s := range ctxt.Textp {
-               if emitPcln(ctxt, s) {
-                       nfunc++
+               if !emitPcln(ctxt, s) {
+                       continue
+               }
+               nfunc++
+               if pclntabFirstFunc == nil {
+                       pclntabFirstFunc = s
                }
        }
 
@@ -234,10 +239,8 @@ func (ctxt *Link) pclntab() {
                return nameoff
        }
 
-       nfunc = 0
-       var last *sym.Symbol
+       nfunc = 0 // repurpose nfunc as a running index
        for _, s := range ctxt.Textp {
-               last = s
                if !emitPcln(ctxt, s) {
                        continue
                }
@@ -246,10 +249,6 @@ func (ctxt *Link) pclntab() {
                        pcln = &pclntabZpcln
                }
 
-               if pclntabFirstFunc == nil {
-                       pclntabFirstFunc = s
-               }
-
                if len(pcln.InlTree) > 0 {
                        if len(pcln.Pcdata) <= objabi.PCDATA_InlTreeIndex {
                                // Create inlining pcdata table.
@@ -270,7 +269,7 @@ func (ctxt *Link) pclntab() {
                }
 
                funcstart := int32(len(ftab.P))
-               funcstart += int32(-len(ftab.P)) & (int32(ctxt.Arch.PtrSize) - 1)
+               funcstart += int32(-len(ftab.P)) & (int32(ctxt.Arch.PtrSize) - 1) // align to ptrsize
 
                ftab.SetAddr(ctxt.Arch, 8+int64(ctxt.Arch.PtrSize)+int64(nfunc)*2*int64(ctxt.Arch.PtrSize), s)
                ftab.SetUint(ctxt.Arch, 8+int64(ctxt.Arch.PtrSize)+int64(nfunc)*2*int64(ctxt.Arch.PtrSize)+int64(ctxt.Arch.PtrSize), uint64(funcstart))
@@ -402,16 +401,15 @@ func (ctxt *Link) pclntab() {
                                off += 4
                        }
                        for i := range pcln.Funcdata {
+                               dataoff := int64(off) + int64(ctxt.Arch.PtrSize)*int64(i)
                                if pcln.Funcdata[i] == nil {
-                                       ftab.SetUint(ctxt.Arch, int64(off)+int64(ctxt.Arch.PtrSize)*int64(i), uint64(pcln.Funcdataoff[i]))
-                               } else {
-                                       // TODO: Dedup.
-                                       funcdataBytes += pcln.Funcdata[i].Size
-
-                                       ftab.SetAddrPlus(ctxt.Arch, int64(off)+int64(ctxt.Arch.PtrSize)*int64(i), pcln.Funcdata[i], pcln.Funcdataoff[i])
+                                       ftab.SetUint(ctxt.Arch, dataoff, uint64(pcln.Funcdataoff[i]))
+                                       continue
                                }
+                               // TODO: Dedup.
+                               funcdataBytes += pcln.Funcdata[i].Size
+                               ftab.SetAddrPlus(ctxt.Arch, dataoff, pcln.Funcdata[i], pcln.Funcdataoff[i])
                        }
-
                        off += int32(len(pcln.Funcdata)) * int32(ctxt.Arch.PtrSize)
                }
 
@@ -423,6 +421,7 @@ func (ctxt *Link) pclntab() {
                nfunc++
        }
 
+       last := ctxt.Textp[len(ctxt.Textp)-1]
        pclntabLastFunc = last
        // Final entry of table is just end pc.
        ftab.SetAddrPlus(ctxt.Arch, 8+int64(ctxt.Arch.PtrSize)+int64(nfunc)*2*int64(ctxt.Arch.PtrSize), last, last.Size)