[dev.link] cmd/link: use function address directly in pclntab generation

If we are internal linking a static executable, in pclntab
generation, the function addresses are known, so we can just use
them directly instead of emitting relocations.

For external linking or other build modes,  we are generating a
relocatable binary so we still need to emit relocations.

Reduce some allocations: for linking cmd/compile,

name           old alloc/op   new alloc/op   delta
Pclntab_GC       38.8MB ± 0%    36.4MB ± 0%   -6.19%  (p=0.008 n=5+5)

TODO: can we also do this in DWARF generation?

Change-Id: I43920d930ab1da97c205871027e01844a07a5e60
Reviewed-on: https://go-review.googlesource.com/c/go/+/228478
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Than McIntosh <thanm@google.com>

diff --git a/src/cmd/link/internal/ld/pcln.go b/src/cmd/link/internal/ld/pcln.go
index b275d208566dabc69611d6784bf244018185dd20..7d5a756a62e62f31c37d48211269c4a72a892684 100644 (file)
--- a/src/cmd/link/internal/ld/pcln.go
+++ b/src/cmd/link/internal/ld/pcln.go
@@ -325,6 +325,21 @@ func (ctxt *Link) pclntab() loader.Bitmap {
                return newoff
        }
 
+       setAddr := (*loader.SymbolBuilder).SetAddrPlus
+       if ctxt.IsExe() && ctxt.IsInternal() {
+               // Internal linking static executable. At this point the function
+               // addresses are known, so we can just use them instead of emitting
+               // relocations.
+               // For other cases we are generating a relocatable binary so we
+               // still need to emit relocations.
+               setAddr = func(s *loader.SymbolBuilder, arch *sys.Arch, off int64, tgt loader.Sym, add int64) int64 {
+                       if v := ldr.SymValue(tgt); v != 0 {
+                               return s.SetUint(arch, off, uint64(v+add))
+                       }
+                       return s.SetAddrPlus(arch, off, tgt, add)
+               }
+       }
+
        pcsp := sym.Pcdata{}
        pcfile := sym.Pcdata{}
        pcline := sym.Pcdata{}
@@ -347,7 +362,7 @@ func (ctxt *Link) pclntab() loader.Bitmap {
                        // invalid funcoff value to mark the hole. See also
                        // runtime/symtab.go:findfunc
                        prevFuncSize := int64(ldr.SymSize(prevFunc))
-                       ftab.SetAddrPlus(ctxt.Arch, 8+int64(ctxt.Arch.PtrSize)+int64(nfunc)*2*int64(ctxt.Arch.PtrSize), prevFunc, prevFuncSize)
+                       setAddr(ftab, ctxt.Arch, 8+int64(ctxt.Arch.PtrSize)+int64(nfunc)*2*int64(ctxt.Arch.PtrSize), prevFunc, prevFuncSize)
                        ftab.SetUint(ctxt.Arch, 8+int64(ctxt.Arch.PtrSize)+int64(nfunc)*2*int64(ctxt.Arch.PtrSize)+int64(ctxt.Arch.PtrSize), ^uint64(0))
                        nfunc++
                }
@@ -397,10 +412,7 @@ func (ctxt *Link) pclntab() loader.Bitmap {
                funcstart := int32(dSize)
                funcstart += int32(-dSize) & (int32(ctxt.Arch.PtrSize) - 1) // align to ptrsize
 
-               // NB: for the static binary internal-link case, we could just
-               // emit the symbol value instead of creating a relocation here
-               // (might speed things up for that case).
-               ftab.SetAddrPlus(ctxt.Arch, 8+int64(ctxt.Arch.PtrSize)+int64(nfunc)*2*int64(ctxt.Arch.PtrSize), s, 0)
+               setAddr(ftab, ctxt.Arch, 8+int64(ctxt.Arch.PtrSize)+int64(nfunc)*2*int64(ctxt.Arch.PtrSize), s, 0)
                ftab.SetUint(ctxt.Arch, 8+int64(ctxt.Arch.PtrSize)+int64(nfunc)*2*int64(ctxt.Arch.PtrSize)+int64(ctxt.Arch.PtrSize), uint64(funcstart))
 
                // Write runtime._func. Keep in sync with ../../../../runtime/runtime2.go:/_func
@@ -416,7 +428,7 @@ func (ctxt *Link) pclntab() loader.Bitmap {
                ftab.Grow(int64(end))
 
                // entry uintptr
-               off = int32(ftab.SetAddrPlus(ctxt.Arch, int64(off), s, 0))
+               off = int32(setAddr(ftab, ctxt.Arch, int64(off), s, 0))
 
                // name int32
                sn := ldr.SymName(s)
@@ -497,7 +509,7 @@ func (ctxt *Link) pclntab() loader.Bitmap {
                                }
                                // TODO: Dedup.
                                funcdataBytes += int64(len(ldr.Data(funcdata[i])))
-                               ftab.SetAddrPlus(ctxt.Arch, dataoff, funcdata[i], funcdataoff[i])
+                               setAddr(ftab, ctxt.Arch, dataoff, funcdata[i], funcdataoff[i])
                        }
                        off += int32(len(funcdata)) * int32(ctxt.Arch.PtrSize)
                }
@@ -513,7 +525,7 @@ func (ctxt *Link) pclntab() loader.Bitmap {
        last := ctxt.Textp2[len(ctxt.Textp2)-1]
        pclntabLastFunc2 = 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, ldr.SymSize(last))
+       setAddr(ftab, ctxt.Arch, 8+int64(ctxt.Arch.PtrSize)+int64(nfunc)*2*int64(ctxt.Arch.PtrSize), last, ldr.SymSize(last))
 
        // Start file table.
        dSize := len(ftab.Data())

diff --git a/src/cmd/link/internal/ld/target.go b/src/cmd/link/internal/ld/target.go
index 09a67365d0805e66b765bfe2a265d40a0224ea3f..7aa2c1ccd0c873359e1711ae9b3d9a0f0b33fa4f 100644 (file)
--- a/src/cmd/link/internal/ld/target.go
+++ b/src/cmd/link/internal/ld/target.go
@@ -28,6 +28,10 @@ type Target struct {
 // Target type functions
 //
 
+func (t *Target) IsExe() bool {
+       return t.BuildMode == BuildModeExe
+}
+
 func (t *Target) IsShared() bool {
        return t.BuildMode == BuildModeShared
 }