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[dev.link] cmd/link: refactor some of dodata
This is a non-functional change, just moving things around, making dodata a more approachable piece of code. Change-Id: I06fa047cbef2313040a31998fa8d242ccb2fedea Reviewed-on: https://go-review.googlesource.com/c/go/+/222662 Run-TryBot: Jeremy Faller <jeremy@golang.org> TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Than McIntosh <thanm@google.com>
This commit is contained in:
Jeremy Faller
parent
d44c9a046b
commit
4d5fdd74ab
@ -1155,71 +1155,135 @@ func checkdatsize(ctxt *Link, datsize int64, symn sym.SymKind) {
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}
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}
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// fixZeroSizedSymbols gives a few special symbols with zero size some space.
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func fixZeroSizedSymbols(ctxt *Link) {
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// The values in moduledata are filled out by relocations
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// pointing to the addresses of these special symbols.
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// Typically these symbols have no size and are not laid
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// out with their matching section.
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//
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// However on darwin, dyld will find the special symbol
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// in the first loaded module, even though it is local.
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//
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// (An hypothesis, formed without looking in the dyld sources:
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// these special symbols have no size, so their address
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// matches a real symbol. The dynamic linker assumes we
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// want the normal symbol with the same address and finds
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// it in the other module.)
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//
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// To work around this we lay out the symbls whose
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// addresses are vital for multi-module programs to work
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// as normal symbols, and give them a little size.
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//
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// On AIX, as all DATA sections are merged together, ld might not put
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// these symbols at the beginning of their respective section if there
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// aren't real symbols, their alignment might not match the
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// first symbol alignment. Therefore, there are explicitly put at the
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// beginning of their section with the same alignment.
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if !(ctxt.DynlinkingGo() && ctxt.HeadType == objabi.Hdarwin) && !(ctxt.HeadType == objabi.Haix && ctxt.LinkMode == LinkExternal) {
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return
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}
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bss := ctxt.Syms.Lookup("runtime.bss", 0)
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bss.Size = 8
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bss.Attr.Set(sym.AttrSpecial, false)
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ctxt.Syms.Lookup("runtime.ebss", 0).Attr.Set(sym.AttrSpecial, false)
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data := ctxt.Syms.Lookup("runtime.data", 0)
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data.Size = 8
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data.Attr.Set(sym.AttrSpecial, false)
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edata := ctxt.Syms.Lookup("runtime.edata", 0)
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edata.Attr.Set(sym.AttrSpecial, false)
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if ctxt.HeadType == objabi.Haix {
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// XCOFFTOC symbols are part of .data section.
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edata.Type = sym.SXCOFFTOC
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}
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types := ctxt.Syms.Lookup("runtime.types", 0)
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types.Type = sym.STYPE
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types.Size = 8
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types.Attr.Set(sym.AttrSpecial, false)
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etypes := ctxt.Syms.Lookup("runtime.etypes", 0)
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etypes.Type = sym.SFUNCTAB
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etypes.Attr.Set(sym.AttrSpecial, false)
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if ctxt.HeadType == objabi.Haix {
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rodata := ctxt.Syms.Lookup("runtime.rodata", 0)
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rodata.Type = sym.SSTRING
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rodata.Size = 8
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rodata.Attr.Set(sym.AttrSpecial, false)
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ctxt.Syms.Lookup("runtime.erodata", 0).Attr.Set(sym.AttrSpecial, false)
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}
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}
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// makeRelroForSharedLib creates a section of readonly data if necessary.
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func makeRelroForSharedLib(target *Link, data *[sym.SXREF][]*sym.Symbol) {
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if !target.UseRelro() {
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return
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}
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// "read only" data with relocations needs to go in its own section
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// when building a shared library. We do this by boosting objects of
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// type SXXX with relocations to type SXXXRELRO.
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for _, symnro := range sym.ReadOnly {
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symnrelro := sym.RelROMap[symnro]
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ro := []*sym.Symbol{}
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relro := data[symnrelro]
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for _, s := range data[symnro] {
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isRelro := len(s.R) > 0
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switch s.Type {
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case sym.STYPE, sym.STYPERELRO, sym.SGOFUNCRELRO:
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// Symbols are not sorted yet, so it is possible
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// that an Outer symbol has been changed to a
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// relro Type before it reaches here.
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isRelro = true
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case sym.SFUNCTAB:
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if target.IsAIX() && s.Name == "runtime.etypes" {
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// runtime.etypes must be at the end of
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// the relro datas.
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isRelro = true
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}
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}
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if isRelro {
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s.Type = symnrelro
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if s.Outer != nil {
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s.Outer.Type = s.Type
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}
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relro = append(relro, s)
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} else {
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ro = append(ro, s)
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}
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}
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// Check that we haven't made two symbols with the same .Outer into
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// different types (because references two symbols with non-nil Outer
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// become references to the outer symbol + offset it's vital that the
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// symbol and the outer end up in the same section).
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for _, s := range relro {
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if s.Outer != nil && s.Outer.Type != s.Type {
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Errorf(s, "inconsistent types for symbol and its Outer %s (%v != %v)",
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s.Outer.Name, s.Type, s.Outer.Type)
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}
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}
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data[symnro] = ro
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data[symnrelro] = relro
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}
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}
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// datap is a collection of reachable data symbols in address order.
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// Generated by dodata.
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var datap []*sym.Symbol
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func (ctxt *Link) dodata() {
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if (ctxt.DynlinkingGo() && ctxt.HeadType == objabi.Hdarwin) || (ctxt.HeadType == objabi.Haix && ctxt.LinkMode == LinkExternal) {
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// The values in moduledata are filled out by relocations
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// pointing to the addresses of these special symbols.
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// Typically these symbols have no size and are not laid
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// out with their matching section.
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//
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// However on darwin, dyld will find the special symbol
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// in the first loaded module, even though it is local.
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//
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// (An hypothesis, formed without looking in the dyld sources:
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// these special symbols have no size, so their address
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// matches a real symbol. The dynamic linker assumes we
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// want the normal symbol with the same address and finds
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// it in the other module.)
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//
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// To work around this we lay out the symbls whose
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// addresses are vital for multi-module programs to work
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// as normal symbols, and give them a little size.
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//
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// On AIX, as all DATA sections are merged together, ld might not put
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// these symbols at the beginning of their respective section if there
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// aren't real symbols, their alignment might not match the
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// first symbol alignment. Therefore, there are explicitly put at the
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// beginning of their section with the same alignment.
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bss := ctxt.Syms.Lookup("runtime.bss", 0)
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bss.Size = 8
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bss.Attr.Set(sym.AttrSpecial, false)
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ctxt.Syms.Lookup("runtime.ebss", 0).Attr.Set(sym.AttrSpecial, false)
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data := ctxt.Syms.Lookup("runtime.data", 0)
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data.Size = 8
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data.Attr.Set(sym.AttrSpecial, false)
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edata := ctxt.Syms.Lookup("runtime.edata", 0)
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edata.Attr.Set(sym.AttrSpecial, false)
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if ctxt.HeadType == objabi.Haix {
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// XCOFFTOC symbols are part of .data section.
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edata.Type = sym.SXCOFFTOC
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}
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types := ctxt.Syms.Lookup("runtime.types", 0)
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types.Type = sym.STYPE
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types.Size = 8
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types.Attr.Set(sym.AttrSpecial, false)
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etypes := ctxt.Syms.Lookup("runtime.etypes", 0)
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etypes.Type = sym.SFUNCTAB
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etypes.Attr.Set(sym.AttrSpecial, false)
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if ctxt.HeadType == objabi.Haix {
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rodata := ctxt.Syms.Lookup("runtime.rodata", 0)
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rodata.Type = sym.SSTRING
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rodata.Size = 8
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rodata.Attr.Set(sym.AttrSpecial, false)
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ctxt.Syms.Lookup("runtime.erodata", 0).Attr.Set(sym.AttrSpecial, false)
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}
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}
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// Give zeros sized symbols space if necessary.
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fixZeroSizedSymbols(ctxt)
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// Collect data symbols by type into data.
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var data [sym.SXREF][]*sym.Symbol
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@ -1244,57 +1308,8 @@ func (ctxt *Link) dodata() {
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}
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dynreloc(ctxt, &data)
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if ctxt.UseRelro() {
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// "read only" data with relocations needs to go in its own section
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// when building a shared library. We do this by boosting objects of
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// type SXXX with relocations to type SXXXRELRO.
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for _, symnro := range sym.ReadOnly {
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symnrelro := sym.RelROMap[symnro]
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ro := []*sym.Symbol{}
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relro := data[symnrelro]
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for _, s := range data[symnro] {
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isRelro := len(s.R) > 0
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switch s.Type {
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case sym.STYPE, sym.STYPERELRO, sym.SGOFUNCRELRO:
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// Symbols are not sorted yet, so it is possible
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// that an Outer symbol has been changed to a
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// relro Type before it reaches here.
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isRelro = true
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case sym.SFUNCTAB:
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if ctxt.HeadType == objabi.Haix && s.Name == "runtime.etypes" {
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// runtime.etypes must be at the end of
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// the relro datas.
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isRelro = true
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}
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}
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if isRelro {
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s.Type = symnrelro
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if s.Outer != nil {
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s.Outer.Type = s.Type
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}
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relro = append(relro, s)
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} else {
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ro = append(ro, s)
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}
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}
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// Check that we haven't made two symbols with the same .Outer into
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// different types (because references two symbols with non-nil Outer
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// become references to the outer symbol + offset it's vital that the
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// symbol and the outer end up in the same section).
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for _, s := range relro {
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if s.Outer != nil && s.Outer.Type != s.Type {
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Errorf(s, "inconsistent types for symbol and its Outer %s (%v != %v)",
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s.Outer.Name, s.Type, s.Outer.Type)
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}
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}
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data[symnro] = ro
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data[symnrelro] = relro
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}
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}
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// Move any RO data with relocations to a separate section.
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makeRelroForSharedLib(ctxt, &data)
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// Sort symbols.
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var dataMaxAlign [sym.SXREF]int32
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@ -251,17 +251,6 @@ func (ctxt *Link) CanUsePlugins() bool {
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return ctxt.canUsePlugins
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}
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// UseRelro reports whether to make use of "read only relocations" aka
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// relro.
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func (ctxt *Link) UseRelro() bool {
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switch ctxt.BuildMode {
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case BuildModeCArchive, BuildModeCShared, BuildModeShared, BuildModePIE, BuildModePlugin:
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return ctxt.IsELF || ctxt.HeadType == objabi.Haix
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default:
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return ctxt.linkShared || (ctxt.HeadType == objabi.Haix && ctxt.LinkMode == LinkExternal)
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}
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}
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var (
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dynexp []*sym.Symbol
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dynlib []string
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@ -64,6 +64,17 @@ func (t *Target) IsDynlinkingGo() bool {
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return t.IsShared() || t.IsSharedGoLink() || t.IsPlugin() || t.CanUsePlugins()
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}
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// UseRelro reports whether to make use of "read only relocations" aka
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// relro.
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func (t *Target) UseRelro() bool {
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switch t.BuildMode {
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case BuildModeCArchive, BuildModeCShared, BuildModeShared, BuildModePIE, BuildModePlugin:
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return t.IsELF || t.HeadType == objabi.Haix
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default:
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return t.linkShared || (t.HeadType == objabi.Haix && t.LinkMode == LinkExternal)
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}
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}
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//
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// Processor functions
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//
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