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[dev.link] cmd/link: refactor section creation in dodata

Additional cleanups and refactorings in the allocateSections portion
of dodata. Introduce some new helper routines to be used for common
cases in creating sections and assigning symbols, with a goal of
reducing duplicated code blocks and having more readable code.

No change in functionality.

Change-Id: I1b020b3ee993674329b2bebfd7c35995e3a2c043
Reviewed-on: https://go-review.googlesource.com/c/go/+/228883
Reviewed-by: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Jeremy Faller <jeremy@golang.org>
This commit is contained in:
Than McIntosh 2020-04-17 17:23:02 -04:00
parent 47cac82e36
commit 87b43088cd

View File

@ -1436,7 +1436,7 @@ func (ctxt *Link) dodata() {
fixZeroSizedSymbols(ctxt)
// Collect data symbols by type into data.
state := dodataState{}
state := dodataState{ctxt: ctxt}
for _, s := range ctxt.Syms.Allsym {
if !s.Attr.Reachable() || s.Attr.Special() || s.Attr.SubSymbol() {
continue
@ -1507,6 +1507,42 @@ func (ctxt *Link) dodata() {
}
}
// allocateDataSectionForSym creates a new sym.Section into which a a
// single symbol will be placed. Here "seg" is the segment into which
// the section will go, "s" is the symbol to be placed into the new
// section, and "rwx" contains permissions for the section.
func (state *dodataState) allocateDataSectionForSym(seg *sym.Segment, s *sym.Symbol, rwx int) *sym.Section {
sect := addsection(state.ctxt.Arch, seg, s.Name, rwx)
sect.Align = symalign(s)
state.datsize = Rnd(state.datsize, int64(sect.Align))
sect.Vaddr = uint64(state.datsize)
return sect
}
// allocateNamedDataSection creates a new sym.Section for a category
// of data symbols. Here "seg" is the segment into which the section
// will go, "sName" is the name to give to the section, "types" is a
// range of symbol types to be put into the section, and "rwx"
// contains permissions for the section.
func (state *dodataState) allocateNamedDataSection(seg *sym.Segment, sName string, types []sym.SymKind, rwx int) *sym.Section {
sect := addsection(state.ctxt.Arch, seg, sName, rwx)
if len(types) == 0 {
sect.Align = 1
} else if len(types) == 1 {
sect.Align = state.dataMaxAlign[types[0]]
} else {
for _, symn := range types {
align := state.dataMaxAlign[symn]
if sect.Align < align {
sect.Align = align
}
}
}
state.datsize = Rnd(state.datsize, int64(sect.Align))
sect.Vaddr = uint64(state.datsize)
return sect
}
// assignDsymsToSection assigns a collection of data symbols to a
// newly created section. "sect" is the section into which to place
// the symbols, "syms" holds the list of symbols to assign,
@ -1531,6 +1567,38 @@ func (state *dodataState) assignToSection(sect *sym.Section, symn sym.SymKind, f
state.checkdatsize(symn)
}
// allocateSingleSymSections walks through the bucketed data symbols
// with type 'symn', creates a new section for each sym, and assigns
// the sym to a newly created section. Section name is set from the
// symbol name. "Seg" is the segment into which to place the new
// section, "forceType" is the new sym.SymKind to assign to the symbol
// within the section, and "rwx" holds section permissions.
func (state *dodataState) allocateSingleSymSections(seg *sym.Segment, symn sym.SymKind, forceType sym.SymKind, rwx int) {
for _, s := range state.data[symn] {
sect := state.allocateDataSectionForSym(seg, s, rwx)
s.Sect = sect
s.Type = forceType
s.Value = int64(uint64(state.datsize) - sect.Vaddr)
state.datsize += s.Size
sect.Length = uint64(state.datsize) - sect.Vaddr
}
state.checkdatsize(symn)
}
// allocateNamedSectionAndAssignSyms creates a new section with the
// specified name, then walks through the bucketed data symbols with
// type 'symn' and assigns each of them to this new section. "Seg" is
// the segment into which to place the new section, "secName" is the
// name to give to the new section, "forceType" (if non-zero) contains
// a new sym type to apply to each sym during the assignment, and
// "rwx" holds section permissions.
func (state *dodataState) allocateNamedSectionAndAssignSyms(seg *sym.Segment, secName string, symn sym.SymKind, forceType sym.SymKind, rwx int) *sym.Section {
sect := state.allocateNamedDataSection(seg, secName, []sym.SymKind{symn}, rwx)
state.assignDsymsToSection(sect, state.data[symn], forceType, aligndatsize)
return sect
}
// allocateSections allocates sym.Section objects for data sections
// of interest and assigns symbols into the sections.
func (state *dodataState) allocateSections(ctxt *Link) {
@ -1548,27 +1616,12 @@ func (state *dodataState) allocateSections(ctxt *Link) {
sym.SWINDOWS,
}
for _, symn := range writable {
for _, s := range state.data[symn] {
sect := addsection(ctxt.Arch, &Segdata, s.Name, 06)
sect.Align = symalign(s)
state.datsize = Rnd(state.datsize, int64(sect.Align))
sect.Vaddr = uint64(state.datsize)
s.Sect = sect
s.Type = sym.SDATA
s.Value = int64(uint64(state.datsize) - sect.Vaddr)
state.datsize += s.Size
sect.Length = uint64(state.datsize) - sect.Vaddr
}
state.checkdatsize(symn)
state.allocateSingleSymSections(&Segdata, symn, sym.SDATA, 06)
}
// .got (and .toc on ppc64)
if len(state.data[sym.SELFGOT]) > 0 {
sect := addsection(ctxt.Arch, &Segdata, ".got", 06)
sect.Align = state.dataMaxAlign[sym.SELFGOT]
state.datsize = Rnd(state.datsize, int64(sect.Align))
sect.Vaddr = uint64(state.datsize)
state.assignToSection(sect, sym.SELFGOT, sym.SDATA)
sect := state.allocateNamedSectionAndAssignSyms(&Segdata, ".got", sym.SELFGOT, sym.SDATA, 06)
if ctxt.IsPPC64() {
for _, s := range state.data[sym.SELFGOT] {
// Resolve .TOC. symbol for this object file (ppc64)
@ -1586,13 +1639,9 @@ func (state *dodataState) allocateSections(ctxt *Link) {
}
/* pointer-free data */
sect := addsection(ctxt.Arch, &Segdata, ".noptrdata", 06)
sect.Align = state.dataMaxAlign[sym.SNOPTRDATA]
state.datsize = Rnd(state.datsize, int64(sect.Align))
sect.Vaddr = uint64(state.datsize)
sect := state.allocateNamedSectionAndAssignSyms(&Segdata, ".noptrdata", sym.SNOPTRDATA, sym.SDATA, 06)
ctxt.Syms.Lookup("runtime.noptrdata", 0).Sect = sect
ctxt.Syms.Lookup("runtime.enoptrdata", 0).Sect = sect
state.assignToSection(sect, sym.SNOPTRDATA, sym.SDATA)
hasinitarr := ctxt.linkShared
@ -1609,21 +1658,13 @@ func (state *dodataState) allocateSections(ctxt *Link) {
}
if hasinitarr && len(state.data[sym.SINITARR]) > 0 {
sect := addsection(ctxt.Arch, &Segdata, ".init_array", 06)
sect.Align = state.dataMaxAlign[sym.SINITARR]
state.datsize = Rnd(state.datsize, int64(sect.Align))
sect.Vaddr = uint64(state.datsize)
state.assignToSection(sect, sym.SINITARR, sym.Sxxx)
state.allocateNamedSectionAndAssignSyms(&Segdata, ".init_array", sym.SINITARR, sym.Sxxx, 06)
}
/* data */
sect = addsection(ctxt.Arch, &Segdata, ".data", 06)
sect.Align = state.dataMaxAlign[sym.SDATA]
state.datsize = Rnd(state.datsize, int64(sect.Align))
sect.Vaddr = uint64(state.datsize)
sect = state.allocateNamedSectionAndAssignSyms(&Segdata, ".data", sym.SDATA, sym.SDATA, 06)
ctxt.Syms.Lookup("runtime.data", 0).Sect = sect
ctxt.Syms.Lookup("runtime.edata", 0).Sect = sect
state.assignToSection(sect, sym.SDATA, sym.SDATA)
dataGcEnd := state.datsize - int64(sect.Vaddr)
// On AIX, TOC entries must be the last of .data
@ -1633,13 +1674,9 @@ func (state *dodataState) allocateSections(ctxt *Link) {
sect.Length = uint64(state.datsize) - sect.Vaddr
/* bss */
sect = addsection(ctxt.Arch, &Segdata, ".bss", 06)
sect.Align = state.dataMaxAlign[sym.SBSS]
state.datsize = Rnd(state.datsize, int64(sect.Align))
sect.Vaddr = uint64(state.datsize)
sect = state.allocateNamedSectionAndAssignSyms(&Segdata, ".bss", sym.SBSS, sym.Sxxx, 06)
ctxt.Syms.Lookup("runtime.bss", 0).Sect = sect
ctxt.Syms.Lookup("runtime.ebss", 0).Sect = sect
state.assignToSection(sect, sym.SBSS, sym.Sxxx)
bssGcEnd := state.datsize - int64(sect.Vaddr)
// Emit gcdata for bcc symbols now that symbol values have been assigned.
@ -1661,29 +1698,23 @@ func (state *dodataState) allocateSections(ctxt *Link) {
}
/* pointer-free bss */
sect = addsection(ctxt.Arch, &Segdata, ".noptrbss", 06)
sect.Align = state.dataMaxAlign[sym.SNOPTRBSS]
state.datsize = Rnd(state.datsize, int64(sect.Align))
sect.Vaddr = uint64(state.datsize)
sect = state.allocateNamedSectionAndAssignSyms(&Segdata, ".noptrbss", sym.SNOPTRBSS, sym.Sxxx, 06)
ctxt.Syms.Lookup("runtime.noptrbss", 0).Sect = sect
ctxt.Syms.Lookup("runtime.enoptrbss", 0).Sect = sect
ctxt.Syms.Lookup("runtime.end", 0).Sect = sect
state.assignToSection(sect, sym.SNOPTRBSS, sym.Sxxx)
// Coverage instrumentation counters for libfuzzer.
if len(state.data[sym.SLIBFUZZER_EXTRA_COUNTER]) > 0 {
sect := addsection(ctxt.Arch, &Segdata, "__libfuzzer_extra_counters", 06)
sect.Align = state.dataMaxAlign[sym.SLIBFUZZER_EXTRA_COUNTER]
state.datsize = Rnd(state.datsize, int64(sect.Align))
sect.Vaddr = uint64(state.datsize)
state.assignToSection(sect, sym.SLIBFUZZER_EXTRA_COUNTER, sym.Sxxx)
state.allocateNamedSectionAndAssignSyms(&Segdata, "__libfuzzer_extra_counters", sym.SLIBFUZZER_EXTRA_COUNTER, sym.Sxxx, 06)
}
if len(state.data[sym.STLSBSS]) > 0 {
var sect *sym.Section
// FIXME: not clear why it is sometimes necessary to suppress .tbss section creation.
if (ctxt.IsELF || ctxt.HeadType == objabi.Haix) && (ctxt.LinkMode == LinkExternal || !*FlagD) {
sect = addsection(ctxt.Arch, &Segdata, ".tbss", 06)
sect.Align = int32(ctxt.Arch.PtrSize)
// FIXME: why does this need to be set to zero?
sect.Vaddr = 0
}
state.datsize = 0
@ -1725,36 +1756,16 @@ func (state *dodataState) allocateSections(ctxt *Link) {
if len(state.data[sym.STEXT]) != 0 {
Errorf(nil, "dodata found an sym.STEXT symbol: %s", state.data[sym.STEXT][0].Name)
}
for _, s := range state.data[sym.SELFRXSECT] {
sect := addsection(ctxt.Arch, &Segtext, s.Name, 04)
sect.Align = symalign(s)
state.datsize = Rnd(state.datsize, int64(sect.Align))
sect.Vaddr = uint64(state.datsize)
s.Sect = sect
s.Type = sym.SRODATA
s.Value = int64(uint64(state.datsize) - sect.Vaddr)
state.datsize += s.Size
sect.Length = uint64(state.datsize) - sect.Vaddr
state.checkdatsize(sym.SELFRXSECT)
}
state.allocateSingleSymSections(&Segtext, sym.SELFRXSECT, sym.SRODATA, 04)
/* read-only data */
sect = addsection(ctxt.Arch, segro, ".rodata", 04)
sect.Vaddr = 0
sect = state.allocateNamedDataSection(segro, ".rodata", sym.ReadOnly, 04)
ctxt.Syms.Lookup("runtime.rodata", 0).Sect = sect
ctxt.Syms.Lookup("runtime.erodata", 0).Sect = sect
if !ctxt.UseRelro() {
ctxt.Syms.Lookup("runtime.types", 0).Sect = sect
ctxt.Syms.Lookup("runtime.etypes", 0).Sect = sect
}
for _, symn := range sym.ReadOnly {
align := state.dataMaxAlign[symn]
if sect.Align < align {
sect.Align = align
}
}
state.datsize = Rnd(state.datsize, int64(sect.Align))
for _, symn := range sym.ReadOnly {
symnStartValue := state.datsize
state.assignToSection(sect, symn, sym.SRODATA)
@ -1768,31 +1779,8 @@ func (state *dodataState) allocateSections(ctxt *Link) {
}
/* read-only ELF, Mach-O sections */
for _, s := range state.data[sym.SELFROSECT] {
sect = addsection(ctxt.Arch, segro, s.Name, 04)
sect.Align = symalign(s)
state.datsize = Rnd(state.datsize, int64(sect.Align))
sect.Vaddr = uint64(state.datsize)
s.Sect = sect
s.Type = sym.SRODATA
s.Value = int64(uint64(state.datsize) - sect.Vaddr)
state.datsize += s.Size
sect.Length = uint64(state.datsize) - sect.Vaddr
}
state.checkdatsize(sym.SELFROSECT)
for _, s := range state.data[sym.SMACHOPLT] {
sect = addsection(ctxt.Arch, segro, s.Name, 04)
sect.Align = symalign(s)
state.datsize = Rnd(state.datsize, int64(sect.Align))
sect.Vaddr = uint64(state.datsize)
s.Sect = sect
s.Type = sym.SRODATA
s.Value = int64(uint64(state.datsize) - sect.Vaddr)
state.datsize += s.Size
sect.Length = uint64(state.datsize) - sect.Vaddr
}
state.checkdatsize(sym.SMACHOPLT)
state.allocateSingleSymSections(segro, sym.SELFROSECT, sym.SRODATA, 04)
state.allocateSingleSymSections(segro, sym.SMACHOPLT, sym.SRODATA, 04)
// There is some data that are conceptually read-only but are written to by
// relocations. On GNU systems, we can arrange for the dynamic linker to
@ -1804,9 +1792,13 @@ func (state *dodataState) allocateSections(ctxt *Link) {
// situation.
// TODO(mwhudson): It would make sense to do this more widely, but it makes
// the system linker segfault on darwin.
addrelrosection := func(suffix string) *sym.Section {
return addsection(ctxt.Arch, segro, suffix, 04)
const relroPerm = 06
const fallbackPerm = 04
relroSecPerm := fallbackPerm
genrelrosecname := func(suffix string) string {
return suffix
}
seg := segro
if ctxt.UseRelro() {
segrelro := &Segrelrodata
@ -1823,26 +1815,23 @@ func (state *dodataState) allocateSections(ctxt *Link) {
state.datsize = 0
}
addrelrosection = func(suffix string) *sym.Section {
return addsection(ctxt.Arch, segrelro, ".data.rel.ro"+suffix, 06)
genrelrosecname = func(suffix string) string {
return ".data.rel.ro" + suffix
}
relroReadOnly := []sym.SymKind{}
for _, symnro := range sym.ReadOnly {
symn := sym.RelROMap[symnro]
relroReadOnly = append(relroReadOnly, symn)
}
seg = segrelro
relroSecPerm = relroPerm
/* data only written by relocations */
sect = addrelrosection("")
sect = state.allocateNamedDataSection(segrelro, genrelrosecname(""), relroReadOnly, relroSecPerm)
ctxt.Syms.Lookup("runtime.types", 0).Sect = sect
ctxt.Syms.Lookup("runtime.etypes", 0).Sect = sect
for _, symnro := range sym.ReadOnly {
symn := sym.RelROMap[symnro]
align := state.dataMaxAlign[symn]
if sect.Align < align {
sect.Align = align
}
}
state.datsize = Rnd(state.datsize, int64(sect.Align))
sect.Vaddr = uint64(state.datsize)
for i, symnro := range sym.ReadOnly {
if i == 0 && symnro == sym.STYPE && ctxt.HeadType != objabi.Haix {
// Skip forward so that no type
@ -1874,10 +1863,7 @@ func (state *dodataState) allocateSections(ctxt *Link) {
}
/* typelink */
sect = addrelrosection(".typelink")
sect.Align = state.dataMaxAlign[sym.STYPELINK]
state.datsize = Rnd(state.datsize, int64(sect.Align))
sect.Vaddr = uint64(state.datsize)
sect = state.allocateNamedDataSection(seg, genrelrosecname(".typelink"), []sym.SymKind{sym.STYPELINK}, relroSecPerm)
typelink := ctxt.Syms.Lookup("runtime.typelink", 0)
typelink.Sect = sect
typelink.Type = sym.SRODATA
@ -1886,13 +1872,9 @@ func (state *dodataState) allocateSections(ctxt *Link) {
sect.Length = uint64(state.datsize) - sect.Vaddr
/* itablink */
sect = addrelrosection(".itablink")
sect.Align = state.dataMaxAlign[sym.SITABLINK]
state.datsize = Rnd(state.datsize, int64(sect.Align))
sect.Vaddr = uint64(state.datsize)
sect = state.allocateNamedSectionAndAssignSyms(seg, genrelrosecname(".itablink"), sym.SITABLINK, sym.Sxxx, relroSecPerm)
ctxt.Syms.Lookup("runtime.itablink", 0).Sect = sect
ctxt.Syms.Lookup("runtime.eitablink", 0).Sect = sect
state.assignToSection(sect, sym.SITABLINK, sym.SRODATA)
if ctxt.HeadType == objabi.Haix {
// Store .itablink size because its symbols are wrapped
// under an outer symbol: runtime.itablink.
@ -1900,22 +1882,14 @@ func (state *dodataState) allocateSections(ctxt *Link) {
}
/* gosymtab */
sect = addrelrosection(".gosymtab")
sect.Align = state.dataMaxAlign[sym.SSYMTAB]
state.datsize = Rnd(state.datsize, int64(sect.Align))
sect.Vaddr = uint64(state.datsize)
sect = state.allocateNamedSectionAndAssignSyms(seg, genrelrosecname(".gosymtab"), sym.SSYMTAB, sym.SRODATA, relroSecPerm)
ctxt.Syms.Lookup("runtime.symtab", 0).Sect = sect
ctxt.Syms.Lookup("runtime.esymtab", 0).Sect = sect
state.assignToSection(sect, sym.SSYMTAB, sym.SRODATA)
/* gopclntab */
sect = addrelrosection(".gopclntab")
sect.Align = state.dataMaxAlign[sym.SPCLNTAB]
state.datsize = Rnd(state.datsize, int64(sect.Align))
sect.Vaddr = uint64(state.datsize)
sect = state.allocateNamedSectionAndAssignSyms(seg, genrelrosecname(".gopclntab"), sym.SPCLNTAB, sym.SRODATA, relroSecPerm)
ctxt.Syms.Lookup("runtime.pclntab", 0).Sect = sect
ctxt.Syms.Lookup("runtime.epclntab", 0).Sect = sect
state.assignToSection(sect, sym.SPCLNTAB, sym.SRODATA)
// 6g uses 4-byte relocation offsets, so the entire segment must fit in 32 bits.
if state.datsize != int64(uint32(state.datsize)) {
@ -1931,11 +1905,8 @@ func (state *dodataState) allocateSections(ctxt *Link) {
for i := 0; i < len(dwarfp); i++ {
// First the section symbol.
s := dwarfp[i].secSym()
sect = addsection(ctxt.Arch, &Segdwarf, s.Name, 04)
sect := state.allocateNamedDataSection(&Segdwarf, s.Name, []sym.SymKind{}, 04)
sect.Sym = s
sect.Align = 1
state.datsize = Rnd(state.datsize, int64(sect.Align))
sect.Vaddr = uint64(state.datsize)
s.Sect = sect
s.Type = sym.SRODATA
s.Value = int64(uint64(state.datsize) - sect.Vaddr)