cmd/internal/objabi, cmd/link: move linker-only symkind values into linker

Many (most!) of the values of objapi.SymKind are used only in the linker, so
this creates a separate cmd/link/internal/ld.SymKind type, removes most values
from SymKind and maps one to the other when reading object files in the linker.

Two of the remaining objapi.SymKind values are only checked for, never set and
so will never be actually found but I wanted to keep this to the most
mechanical change possible.

Change-Id: I4bbc5aed6713cab3e8de732e6e288eb77be0474c
Reviewed-on: https://go-review.googlesource.com/40985
Run-TryBot: Michael Hudson-Doyle <michael.hudson@canonical.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>

3 files changed, 17 insertions, 91 deletions

diff --git a/src/cmd/internal/objabi/symkind.go b/src/cmd/internal/objabi/symkind.go
index c1e88aabe1..6c2eecf8a5 100644
--- a/src/cmd/internal/objabi/symkind.go
+++ b/src/cmd/internal/objabi/symkind.go
@@ -36,102 +36,28 @@ type SymKind int16
 // Defined SymKind values.
 //
 // TODO(rsc): Give idiomatic Go names.
-// TODO(rsc): Reduce the number of symbol types in the object files.
 //go:generate stringer -type=SymKind
 const (
+	// An otherwise invalid zero value for the type
 	Sxxx SymKind = iota
+	// Executable instructions
 	STEXT
-	SELFRXSECT
-
-	// Read-only sections.
-	STYPE
-	SSTRING
-	SGOSTRING
-	SGOFUNC
-	SGCBITS
+	// Read only static data
 	SRODATA
-	SFUNCTAB
-
-	SELFROSECT
-	SMACHOPLT
-
-	// Read-only sections with relocations.
-	//
-	// Types STYPE-SFUNCTAB above are written to the .rodata section by default.
-	// When linking a shared object, some conceptually "read only" types need to
-	// be written to by relocations and putting them in a section called
-	// ".rodata" interacts poorly with the system linkers. The GNU linkers
-	// support this situation by arranging for sections of the name
-	// ".data.rel.ro.XXX" to be mprotected read only by the dynamic linker after
-	// relocations have applied, so when the Go linker is creating a shared
-	// object it checks all objects of the above types and bumps any object that
-	// has a relocation to it to the corresponding type below, which are then
-	// written to sections with appropriate magic names.
-	STYPERELRO
-	SSTRINGRELRO
-	SGOSTRINGRELRO
-	SGOFUNCRELRO
-	SGCBITSRELRO
-	SRODATARELRO
-	SFUNCTABRELRO
-
-	// Part of .data.rel.ro if it exists, otherwise part of .rodata.
-	STYPELINK
-	SITABLINK
-	SSYMTAB
-	SPCLNTAB
-
-	// Writable sections.
-	SELFSECT
-	SMACHO
-	SMACHOGOT
-	SWINDOWS
-	SELFGOT
+	// Static data that does not contain any pointers
 	SNOPTRDATA
-	SINITARR
+	// Static data
 	SDATA
+	// Statically data that is initially all 0s
 	SBSS
+	// Statically data that is initially all 0s and does not contain pointers
 	SNOPTRBSS
+	// Thread-local data that is initally all 0s
 	STLSBSS
+	// TODO(mwhudson): outside of the linker, these values are
+	// only checked for, not set, so they should be removed.
 	SXREF
-	SMACHOSYMSTR
-	SMACHOSYMTAB
-	SMACHOINDIRECTPLT
-	SMACHOINDIRECTGOT
-	SFILE
-	SFILEPATH
 	SCONST
-	SDYNIMPORT
-	SHOSTOBJ
-	SDWARFSECT
+	// Debugging data
 	SDWARFINFO
-	SSUB       = SymKind(1 << 8)
-	SMASK      = SymKind(SSUB - 1)
-	SHIDDEN    = SymKind(1 << 9)
-	SCONTAINER = SymKind(1 << 10) // has a sub-symbol
 )
-
-// ReadOnly are the symbol kinds that form read-only sections. In some
-// cases, if they will require relocations, they are transformed into
-// rel-ro sections using RelROMap.
-var ReadOnly = []SymKind{
-	STYPE,
-	SSTRING,
-	SGOSTRING,
-	SGOFUNC,
-	SGCBITS,
-	SRODATA,
-	SFUNCTAB,
-}
-
-// RelROMap describes the transformation of read-only symbols to rel-ro
-// symbols.
-var RelROMap = map[SymKind]SymKind{
-	STYPE:     STYPERELRO,
-	SSTRING:   SSTRINGRELRO,
-	SGOSTRING: SGOSTRINGRELRO,
-	SGOFUNC:   SGOFUNCRELRO,
-	SGCBITS:   SGCBITSRELRO,
-	SRODATA:   SRODATARELRO,
-	SFUNCTAB:  SFUNCTABRELRO,
-}
diff --git a/src/cmd/internal/objabi/symkind_string.go b/src/cmd/internal/objabi/symkind_string.go
index d89876093d..365bf17a73 100644
--- a/src/cmd/internal/objabi/symkind_string.go
+++ b/src/cmd/internal/objabi/symkind_string.go
@@ -4,9 +4,9 @@ package objabi
 
 import "fmt"
 
-const _SymKind_name = "SxxxSTEXTSELFRXSECTSTYPESSTRINGSGOSTRINGSGOFUNCSGCBITSSRODATASFUNCTABSELFROSECTSMACHOPLTSTYPERELROSSTRINGRELROSGOSTRINGRELROSGOFUNCRELROSGCBITSRELROSRODATARELROSFUNCTABRELROSTYPELINKSITABLINKSSYMTABSPCLNTABSELFSECTSMACHOSMACHOGOTSWINDOWSSELFGOTSNOPTRDATASINITARRSDATASBSSSNOPTRBSSSTLSBSSSXREFSMACHOSYMSTRSMACHOSYMTABSMACHOINDIRECTPLTSMACHOINDIRECTGOTSFILESFILEPATHSCONSTSDYNIMPORTSHOSTOBJSDWARFSECTSDWARFINFO"
+const _SymKind_name = "SxxxSTEXTSRODATASNOPTRDATASDATASBSSSNOPTRBSSSTLSBSSSXREFSCONSTSDWARFINFO"
 
-var _SymKind_index = [...]uint16{0, 4, 9, 19, 24, 31, 40, 47, 54, 61, 69, 79, 88, 98, 110, 124, 136, 148, 160, 173, 182, 191, 198, 206, 214, 220, 229, 237, 244, 254, 262, 267, 271, 280, 287, 292, 304, 316, 333, 350, 355, 364, 370, 380, 388, 398, 408}
+var _SymKind_index = [...]uint8{0, 4, 9, 16, 26, 31, 35, 44, 51, 56, 62, 72}
 
 func (i SymKind) String() string {
 	if i < 0 || i >= SymKind(len(_SymKind_index)-1) {
diff --git a/src/cmd/internal/objfile/goobj.go b/src/cmd/internal/objfile/goobj.go
index 847861d822..63c66a8dc2 100644
--- a/src/cmd/internal/objfile/goobj.go
+++ b/src/cmd/internal/objfile/goobj.go
@@ -45,15 +45,15 @@ func (f *goobjFile) symbols() ([]Sym, error) {
 		seen[s.SymID] = true
 		sym := Sym{Addr: uint64(s.Data.Offset), Name: goobjName(s.SymID), Size: int64(s.Size), Type: s.Type.Name, Code: '?'}
 		switch s.Kind {
-		case objabi.STEXT, objabi.SELFRXSECT:
+		case objabi.STEXT:
 			sym.Code = 'T'
-		case objabi.STYPE, objabi.SSTRING, objabi.SGOSTRING, objabi.SGOFUNC, objabi.SRODATA, objabi.SFUNCTAB, objabi.STYPELINK, objabi.SITABLINK, objabi.SSYMTAB, objabi.SPCLNTAB, objabi.SELFROSECT:
+		case objabi.SRODATA:
 			sym.Code = 'R'
-		case objabi.SMACHOPLT, objabi.SELFSECT, objabi.SMACHO, objabi.SMACHOGOT, objabi.SNOPTRDATA, objabi.SINITARR, objabi.SDATA, objabi.SWINDOWS:
+		case objabi.SDATA:
 			sym.Code = 'D'
 		case objabi.SBSS, objabi.SNOPTRBSS, objabi.STLSBSS:
 			sym.Code = 'B'
-		case objabi.SXREF, objabi.SMACHOSYMSTR, objabi.SMACHOSYMTAB, objabi.SMACHOINDIRECTPLT, objabi.SMACHOINDIRECTGOT, objabi.SFILE, objabi.SFILEPATH, objabi.SCONST, objabi.SDYNIMPORT, objabi.SHOSTOBJ:
+		case objabi.SXREF, objabi.SCONST:
 			sym.Code = 'X' // should not see
 		}
 		if s.Version != 0 {