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Slit the relocation scan in two parts. 

The first part handles whatever has to be written to the r_offset
position.

The second part handles creating got and plt entries.

llvm-svn: 269375
This commit is contained in:
Rafael Espindola 2016-05-12 22:51:22 +00:00
parent 0e85b97307
commit 686ffc6f4c
1 changed files with 43 additions and 53 deletions
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96
lld/ELF/Writer.cpp
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@ -672,15 +672,51 @@ void Writer<ELFT>::scanRelocs(InputSectionBase<ELFT> &C, ArrayRef<RelTy> Rels) {
continue;
}
if (Expr == R_GOT && !isStaticLinkTimeConstant<ELFT>(Expr, Type, Body) &&
Config->Shared)
AddDyn({Target->RelativeRel, C.OutSec, Offset, true, &Body, Addend});
// If a relocation needs PLT, we create a PLT and a GOT slot
// for the symbol.
if (needsPlt(Expr)) {
if (needsPlt(Expr) || Expr == R_THUNK || refersToGotEntry(Expr) ||
!Body.isPreemptible()) {
// If the relocation points to something in the file, remember it so that
// we can apply it when writting the section.
C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
// If the output being produced is position independent, the final value
// is still not known. In that case we still need some help from the
// dynamic linker. We can however do better than just copying the incoming
// relocation. We can process some of it and and just ask the dynamic
// linker to add the load address.
if (!isStaticLinkTimeConstant<ELFT>(Expr, Type, Body))
AddDyn({Target->RelativeRel, C.OutSec, Offset, true, &Body, Addend});
} else {
// We don't know anything about the finaly symbol. Just ask the dynamic
// linker to handle the relocation for us.
AddDyn({Target->getDynRel(Type), C.OutSec, Offset, false, &Body, Addend});
// MIPS ABI turns using of GOT and dynamic relocations inside out.
// While regular ABI uses dynamic relocations to fill up GOT entries
// MIPS ABI requires dynamic linker to fills up GOT entries using
// specially sorted dynamic symbol table. This affects even dynamic
// relocations against symbols which do not require GOT entries
// creation explicitly, i.e. do not have any GOT-relocations. So if
// a preemptible symbol has a dynamic relocation we anyway have
// to create a GOT entry for it.
// If a non-preemptible symbol has a dynamic relocation against it,
// dynamic linker takes it st_value, adds offset and writes down
// result of the dynamic relocation. In case of preemptible symbol
// dynamic linker performs symbol resolution, writes the symbol value
// to the GOT entry and reads the GOT entry when it needs to perform
// a dynamic relocation.
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf p.4-19
if (Config->EMachine == EM_MIPS && !Body.isInGot())
Out<ELFT>::Got->addEntry(Body);
continue;
}
if (Expr == R_THUNK)
continue;
// At this point we are done with the relocated position. Some relocations
// also require us to create a got or plt entry.
// If a relocation needs PLT, we create a PLT and a GOT slot for the symbol.
if (needsPlt(Expr)) {
if (Body.isInPlt())
continue;
Out<ELFT>::Plt->addEntry(Body);
@ -706,14 +742,7 @@ void Writer<ELFT>::scanRelocs(InputSectionBase<ELFT> &C, ArrayRef<RelTy> Rels) {
continue;
}
if (Expr == R_THUNK) {
C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
continue;
}
// If a relocation needs GOT, we create a GOT slot for the symbol.
if (refersToGotEntry(Expr)) {
C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
if (Body.isInGot())
continue;
Out<ELFT>::Got->addEntry(Body);
@ -739,45 +768,6 @@ void Writer<ELFT>::scanRelocs(InputSectionBase<ELFT> &C, ArrayRef<RelTy> Rels) {
}
continue;
}
if (Body.isPreemptible()) {
// We don't know anything about the finaly symbol. Just ask the dynamic
// linker to handle the relocation for us.
AddDyn({Target->getDynRel(Type), C.OutSec, Offset, false, &Body, Addend});
// MIPS ABI turns using of GOT and dynamic relocations inside out.
// While regular ABI uses dynamic relocations to fill up GOT entries
// MIPS ABI requires dynamic linker to fills up GOT entries using
// specially sorted dynamic symbol table. This affects even dynamic
// relocations against symbols which do not require GOT entries
// creation explicitly, i.e. do not have any GOT-relocations. So if
// a preemptible symbol has a dynamic relocation we anyway have
// to create a GOT entry for it.
// If a non-preemptible symbol has a dynamic relocation against it,
// dynamic linker takes it st_value, adds offset and writes down
// result of the dynamic relocation. In case of preemptible symbol
// dynamic linker performs symbol resolution, writes the symbol value
// to the GOT entry and reads the GOT entry when it needs to perform
// a dynamic relocation.
// ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf p.4-19
if (Config->EMachine == EM_MIPS && !Body.isInGot())
Out<ELFT>::Got->addEntry(Body);
continue;
}
// We know that this is the final symbol. If the program being produced
// is position independent, the final value is still not known.
// If the relocation depends on the symbol value (not the size or distances
// in the output), we still need some help from the dynamic linker.
// We can however do better than just copying the incoming relocation. We
// can process some of it and and just ask the dynamic linker to add the
// load address.
if (!Config->Pic || isStaticLinkTimeConstant<ELFT>(Expr, Type, Body)) {
C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
continue;
}
AddDyn({Target->RelativeRel, C.OutSec, Offset, true, &Body, Addend});
C.Relocations.push_back({Expr, Type, Offset, Addend, &Body});
}
// Scan relocations for necessary thunks.