IMHO this makes the code easier to read and should help with linker
scripts.
This is strongly based on D16575. The main differences are:
We record a range of sections, not every section in a program header.
scanHeaders takes case of deciding what goes in every program header,
including PT_GNU_RELRO
We create dummy sections for the start of the file
With this, program header creation has 3 isolated stages:
Map sections to program headers.
Assign addresses to *sections*
Looking at sections find the address and size of each program header.
Thanks to George Rimar for the initial version.
llvm-svn: 260453
The previous names contained "Local" and "Current", but what we
are handling is always local and current, so they were redundant.
TlsIndex comes from "tls_index" struct that Ulrich Drepper is using
in this document to describe this data structure in GOT.
llvm-svn: 259852
Another case where we currently have almost duplicated code is the
creation of dynamic relocations. First to decide if we need one, then to
decide what to write.
This patch fixes it by passing more information from the relocation scan
to the section writing code. This is the same idea used for r258723.
I actually think it should be possible to simplify this further by
reordering things a bit in the writer. For example, we should be able to
represent almost every position in the file with an OutputSeciton and
offset. When writing it out we then just need to add the offset to the
OutputSection VA.
llvm-svn: 259829
Previously, the methods to get symbol addresses were somewhat scattered
in many places. You can use getEntryAddr returns the address of the symbol,
but if you want to get the GOT address for the symbol, you needed to call
Out<ELFT>::Got->getEntryAddr(Sym). This change adds new functions, getVA,
getGotVA, getGotPltVA, and getPltVA to SymbolBody, so that you can use
SymbolBody as the central place to ask about symbols.
http://reviews.llvm.org/D16710
llvm-svn: 259404
This avoids the need to have reserve and addString in sync.
We avoid hashing the global symbols again. This means that we don't
merge a global symbol that has the same name as some other string, but
that doesn't seem very common. The string table size is the same in
clang an scylladb with or without hashing global symbols again.
llvm-svn: 259136
There are a few cases where we have almost duplicated code.
This patches fixes the simplest: the finalize and write of dynamic
section. Right now they have to have exactly the same structure to
decide if a DT_* entry is needed and then to actually write it.
We cannot just write it to a std::vector in the first pass since
addresses have not been computed yet.
llvm-svn: 258723
Summary: It looks like this snuck through in r256143/D15383.
Reviewers: ruiu, grimar
Differential Revision: http://reviews.llvm.org/D16500
llvm-svn: 258599
Some MIPS relocation (for now R_MIPS_GOT16) requires creation of GOT
entries for symbol not included in the dynamic symbol table. They are
local symbols and non-local symbols with 'local' visibility. Local GOT
entries occupy continuous block between GOT header and regular GOT
entries.
The patch adds initial support for handling local GOT entries. The main
problem is allocating local GOT entries for local symbols. Such entries
should be initialized by high 16-bit of the symbol value. In ideal world
there should be no duplicated entries with the same values. But at the
moment of the `Writer::scanRelocs` call we do not know a value of the
symbol. In this patch we create new local GOT entry for each relocation
against local symbol, though we can exhaust GOT quickly. That needs to
be optimized later. When we calculate relocation we know a final symbol
value and request local GOT entry index. To do that we maintain map
between addresses and local GOT entry indexes. If we start to calculate
relocations in parallel we will have to serialize access to this map.
Differential Revision: http://reviews.llvm.org/D16324
llvm-svn: 258388
Added check for terminator CIE/FDE which has zero data size.
void EHOutputSection<ELFT>::addSectionAux(
...
// If CIE/FDE data length is zero then Length is 4, this
// shall be considered a terminator and processing shall end.
if (Length == 4)
break;
...
After this "Bug 25923 - lld/ELF2 linked application crashes if exceptions were used." is fixed for me. Self link of clang also works.
Initial commit message:
[ELF] - implemented --eh-frame-hdr command line option.
--eh-frame-hdr
Request creation of ".eh_frame_hdr" section and ELF "PT_GNU_EH_FRAME" segment header.
Both gold and the GNU linker support an option --eh-frame-hdr which tell them to construct a header for all the .eh_frame sections. This header is placed in a section named .eh_frame_hdr and also in a PT_GNU_EH_FRAME segment. At runtime the unwinder can find all the PT_GNU_EH_FRAME segments by calling dl_iterate_phdr.
This section contains a lookup table for quick binary search of FDEs.
Detailed info can be found here:
http://www.airs.com/blog/archives/462
Differential revision: http://reviews.llvm.org/D15712
llvm-svn: 257889
--eh-frame-hdr
Request creation of ".eh_frame_hdr" section and ELF "PT_GNU_EH_FRAME" segment header.
Both gold and the GNU linker support an option --eh-frame-hdr which tell them to construct a header for all the .eh_frame sections. This header is placed in a section named .eh_frame_hdr and also in a PT_GNU_EH_FRAME segment. At runtime the unwinder can find all the PT_GNU_EH_FRAME segments by calling dl_iterate_phdr.
This section contains a lookup table for quick binary search of FDEs.
Detailed info can be found here:
http://www.airs.com/blog/archives/462
Differential revision: http://reviews.llvm.org/D15712
llvm-svn: 257753
String tables in unstripped executable files are fairly large in size.
For example, lld's executable file is about 34.4 MB in my environment,
and of which 3.5 MB is the string table. Efficiency of string table
construction matters.
Previously, the string table was built in an inefficient way. We used
StringTableBuilder to build that and enabled string tail merging,
although tail merging is not effective for the symbol table (you can
only make the string table 0.3% smaller for lld.) Tail merging is
computation intensive task and slow.
This patch eliminates string tail merging.
I changed the way of adding strings to the string table in this patch
too. Previously, strings were added using add() and the same strings
were then passed to getOffset() to get their offsets in the string table.
In this way, getOffset() needs to look up a hash table to get offsets
for given strings. This is a violation of "we look up the symbol table
(or a hash table) only once for each symbol" dogma of the new LLD's
design. Hash table lookup for long C++ mangled names is slow.
I eliminated that lookup in this patch.
In total, this patch improves link time of lld itself about 12%
(3.50 seconds -> 3.08 seconds.)
llvm-svn: 257017
MipsReginfoInputSection is basically just a container of Elf_Mips_Reginfo
struct. This patch makes that struct directly accessible from others.
llvm-svn: 256984
The number of output sections is usually limited, so the cost
of allocating them is not a bottleneck. This patch simplifies
the code by removing the allocators.
llvm-svn: 256437
OutputSectionBase already has virtual member functions.
This patch makes addSection() a virtual function to remove code
from Writer::createSections().
llvm-svn: 256436
I am working on adding LTO support to the new ELF lld.
In order to do that, it will be necessary to represent defined and
undefined symbols that are not from ELF files. One way to do it is to
change the symbol hierarchy to look like
Defined : SymbolBody
Undefined : SymbolBody
DefinedElf<ELFT> : Defined
UndefinedElf<ELFT> : Undefined
Another option would be to use bogus Elf_Sym, but I think that is
getting a bit too hackish.
This patch does the Undefined/UndefinedElf. Split. The next one
will do the Defined/DefinedElf split.
llvm-svn: 256289
This patch changes sequence of applying relocations, moving tls optimized relocation handling code before code for other locals.
Without that change relocation @GOTTPOFF against local symbol caused runtime error ("unrecognized reloc ...").
That change also should fix other tls optimized relocations, but I did not check them, that's a field for another patch.
R_X86_64_GOTTPOFF relocations against locals can be found when linking against libc.a(malloc.o):
000000000036 000600000016 R_X86_64_GOTTPOFF 0000000000000000 libc_tsd_MALLOC - 4
000000000131 000600000016 R_X86_64_GOTTPOFF 0000000000000000 libc_tsd_MALLOC - 4
Differential revision: http://reviews.llvm.org/D15581
llvm-svn: 256145
This relocation is similar to R_*_RELATIVE except that the value used in this relocation is the program address returned by the function, which takes no arguments, at the address of
the result of the corresponding R_*_RELATIVE relocation as specified in the processor-specific ABI. The purpose of this relocation to avoid name lookup for locally defined STT_GNU_IFUNC symbols at load-time.
More info can be found in ifunc.txt from https://sites.google.com/site/x32abi/documents.
Differential revision: http://reviews.llvm.org/D15235
llvm-svn: 256144
R_386_GOTOFF is calculated as S + A - GOT, where:
S - Represents the value of the symbol whose index resides in the relocation entry.
A - Represents the addend used to compute the value of the relocatable field.
GOT - Represents the address of the global offset table.
Differential revision: http://reviews.llvm.org/D15383
llvm-svn: 256143
MIPS .reginfo section provides information on the registers used by
the code in the object file. Linker should collect this information and
write .reginfo section in the output file. This section contains a union
of used registers masks taken from input .reginfo sections and final
value of the `_gp` symbol.
For details see the "Register Information" section in Chapter 4 in the
following document:
ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
The patch implements .reginfo sections handling with a couple missed
features: a) it does not put output .reginfo section into the separate
REGINFO segment; b) it does not merge `ri_cprmask` masks from input
section. These features will be implemented later.
Differential Revision: http://reviews.llvm.org/D15669
llvm-svn: 256119
Main aim of the patch to introduce basic support for TLS access models for x86 target.
Models using @tlsgd, @tlsldm and @gotntpoff are implemented.
Differential revision: http://reviews.llvm.org/D15060
llvm-svn: 254500
Combination of @tlsgd and @gottpoff at the same time leads to miss of R_X86_64_TPOFF64 dynamic relocation. Patch fixes that.
@tlsgd(%rip) - Allocate two contiguous entries in the GOT to hold a tls index
structure (for passing to tls get addr).
@gottpoff(%rip) - Allocate one GOT entry to hold a variable offset in initial TLS
block (relative to TLS block end, %fs:0).
The same situation can be observed for x86 (probably others too, not sure) with corresponding for that target relocations: @tlsgd, @gotntpoff.
Differential revision: http://reviews.llvm.org/D15105
llvm-svn: 254443
Fix was:
uint32_t getLocalTlsIndexVA() { return getVA() + LocalTlsIndexOff; }
=>
uint32_t getLocalTlsIndexVA() { return Base::getVA() + LocalTlsIndexOff; }
Both works for my MSVS.
Original commit message:
[ELF] - Refactor of tls_index implementation for tls local dynamic model.
Patch contains the next 2 changes:
1) static variable Out<ELFT>::LocalModuleTlsIndexOffset moved to Out<ELFT>::Got. At fact there is no meaning for it to be separated from GOT class because at each place of using it anyways needs to call GOT`s getVA(). Also it is impossible to have that offset and not have GOT.
2) addLocalModuleTlsIndex -> addLocalModelTlsIndex (word "Module" changed to "Model"). Not sure was it a mistype or not but I think that update is closer to Urlich terminology.
Differential revision: http://reviews.llvm.org/D15113
llvm-svn: 254433
It failed buildbot:
http://lab.llvm.org:8011/builders/llvm-clang-lld-x86_64-scei-ps4-ubuntu-fast/builds/3782/steps/build/logs/stdio
Target.cpp
In file included from /home/buildbot/Buildbot/Slave/llvm-clang-lld-x86_64-scei-ps4-ubuntu-fast/llvm.src/tools/lld/ELF/Target.cpp:20:
/home/buildbot/Buildbot/Slave/llvm-clang-lld-x86_64-scei-ps4-ubuntu-fast/llvm.src/tools/lld/ELF/OutputSections.h:136:42: error: use of undeclared identifier 'getVA'
uint32_t getLocalTlsIndexVA() { return getVA() + LocalTlsIndexOff; }
llvm-svn: 254432
Patch contains the next 2 changes:
1) static variable Out<ELFT>::LocalModuleTlsIndexOffset moved to Out<ELFT>::Got. At fact there is no meaning for it to be separated from GOT class because at each place of using it anyways needs to call GOT`s getVA(). Also it is impossible to have that offset and not have GOT.
2) addLocalModuleTlsIndex -> addLocalModelTlsIndex (word "Module" changed to "Model"). Not sure was it a mistype or not but I think that update is closer to Urlich terminology.
Differential revision: http://reviews.llvm.org/D15113
llvm-svn: 254428
Splitted writeTo to separate tls relocs handling stuff which is too long for one method now. NFC.
Differential revision: http://reviews.llvm.org/D15012
llvm-svn: 254309
Patch implements lazy relocations for x86.
One of features of x86 is that executable files and shared object files have separate procedure linkage tables. So patch implements both cases.
Detailed information about instructions used can be found in http://docs.oracle.com/cd/E19620-01/805-3050/chapter6-1235/index.html (search: x86: Procedure Linkage Table).
Differential revision: http://reviews.llvm.org/D14955
llvm-svn: 254098
The MIPS target requires specific dynamic section entries to be defined.
* DT_MIPS_RLD_VERSION and DT_MIPS_FLAGS store predefined values.
* DT_MIPS_BASE_ADDRESS holds base VA.
* DT_MIPS_LOCAL_GOTNO holds the number of local GOT entries.
* DT_MIPS_SYMTABNO holds the number of .dynsym entries.
* DT_MIPS_GOTSYM holds the index of the .dynsym entry
which corresponds to the first entry of the global part of GOT.
* DT_MIPS_RLD_MAP holds the address of the reserved space in the data segment.
* DT_MIPS_PLTGOT points to the .got.plt section if it exists.
* DT_PLTGOT holds the address of the GOT section.
See "Dynamic Section" in Chapter 5 in the following document for detailed
description: ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
Differential revision: http://reviews.llvm.org/D14450
llvm-svn: 252857
This adds support for:
* Uniquing CIEs
* Dropping FDEs that point to dropped sections
It drops 657 488 bytes from the .eh_frame of a Release+Asserts clang.
The link time impact is smallish. Linking clang with a Release+Asserts
lld goes from 0.488064805 seconds to 0.504763060 seconds (1.034 X slower).
llvm-svn: 252790
leaq symbol@tlsld(%rip), %rdi
call __tls_get_addr@plt
symbol@tlsld (R_X86_64_TLSLD) instructs the linker to generate a tls_index entry (two GOT slots) in the GOT for the entire module (shared object or executable) with an offset of 0. The symbol for this GOT entry doesn't matter (as long as it's either local to the module or null), and gold doesn't put a symbol in the dynamic R_X86_64_DTPMOD64 relocation for the GOT entry.
All other platforms defined in http://www.akkadia.org/drepper/tls.pdf except for Itanium use a similar model where global and local dynamic GOT entries take up 2 contiguous GOT slots, so we can handle this in a unified manner if we don't care about Itanium.
While scanning relocations we need to identify local dynamic relocations and generate a single tls_index entry in the GOT for the module and store the address of it somewhere so we can later statically resolve the offset for R_X86_64_TLSLD relocations. We also need to generate a R_X86_64_DTPMOD64 relocation in the RelaDyn relocation section.
This implementation is a bit hacky. It side steps the issue of GotSection and RelocationSection only handling SymbolBody entries by relying on a specific relocation type. The alternative to this seemed to be completely rewriting how GotSection and RelocationSection work, or using a different hacky signaling method.
llvm-svn: 252682
This is cleaner than computing relocations as if we had done it.
While at it, keep a single Phdr variable instead of multiple fields of it.
llvm-svn: 252352
This patch implements R_MIPS_GOT16 relocation for global symbols in order to
generate some entries in GOT. Only reserved and global entries are supported
for now. For the detailed description about GOT in MIPS, see "Global Offset
Table" in Chapter 5 in the followin document:
ftp://www.linux-mips.org/pub/linux/mips/doc/ABI/mipsabi.pdf
In addition, the platform specific symbol "_gp" is added, see "Global Data
Symbols" in Chapter 6 in the aforementioned document.
Differential revision: http://reviews.llvm.org/D14211
llvm-svn: 252275
For x86-64 the initial executable TLS block is placed directly before the
thread specific data register so compilers can directly access it via
R_X86_64_TPOFF32. Generate the correct (negative) offset for this case.
llvm-svn: 252131
This does not support TPOFF32 relocations to local symbols as the address calculations are separate. Support for this will be a separate patch.
llvm-svn: 251998
It is the GNU hash table section that should be reaponsible for storing its own
data and applying its requirements for the order to dynamic symbols.
Differential Revision: http://reviews.llvm.org/D14084
llvm-svn: 251502
getFileOff functions defined for other classes return an offset
from beginning of the file. StringTableSection's getFileOff however
returned an offset from beginning of the section. That was confusing.
llvm-svn: 251192
This patch implements --hash-style command line switch.
* By default, or with "sysv" or "both" parameters, the linker generates
a standard ELF hash section.
* With "gnu" or "both", it produces a GNU-style hash section.
That section requires the symbols in the dynamic symbol table section, which
are referenced in the GNU hash section, to be placed after not hashed ones and
to be sorted to correspond the order of hash buckets in the GNU Hash section.
The division function, as well as estimations for the section's parameters,
are just the first rough attempt and the subjects for further adjustments.
Differential Revision: http://reviews.llvm.org/D13815
llvm-svn: 251000
* Move the responsibility to call SymbolBody::setDynamicSymbolTableIndex()
from the hash table to the dynamic symbol table.
* Hash table is not longer responsible for filling the dynamic symbol table.
* The final order of symbols of both symbol tables is set before writing
phase starts.
* Remove repeaded scan of the symbol table during writting SymbolTableSection.
Differential Revision: http://reviews.llvm.org/D13911
llvm-svn: 250864
The section header table index of the entry that is associated with the section name string table.
Differential Revision: http://reviews.llvm.org/D13904
llvm-svn: 250836
Target has supportsLazyRelocations() method which can switch lazy relocations on/off (currently all targets are OFF except x64 which is ON). So no any other targets are affected now.
Differential Revision: http://reviews.llvm.org/D13856?id=37726
llvm-svn: 250808
Given the name, it is natural for this function to compute the full target.
This will simplify SHF_MERGE handling by allowing getLocalRelTarget to
centralize the addend logic.
llvm-svn: 250731
R_PPC64_TOC does not have an associated symbol, but does have a non-zero VA
that target-specific code must compute using some non-trivial rule. We
handled this as a special case in PPC64TargetInfo::relocateOne, where
we knew to write this special address, but that did not work when creating shared
libraries. The special TOC address needs to be the subject of a
R_PPC64_RELATIVE relocation, and so we also need to know how to encode this
special address in the addend of that relocation.
Thus, some target-specific logic is necessary when creating R_PPC64_RELATIVE as
well. To solve this problem, we teach getLocalRelTarget to handle R_PPC64_TOC
as a special case. This allows us to remove the special case in
PPC64TargetInfo::relocateOne (simplifying code there), and naturally allows the
existing logic to do the right thing when creating associated R_PPC64_RELATIVE
relocations for shared libraries.
llvm-svn: 250555
This patch is to use ELFT instead of Is64Bits to template OutputSection
and its subclasses. This increases code size slightly because it creates
two identical functions for some classes, but that's only 20 KB out of
33 MB, so it's negligible.
This is as per discussion with Rafael. He's not fan of the idea but OK
with this. We'll revisit later to this topic.
llvm-svn: 250466
What was done:
1) .got.plt section is created for functions that requires PLT. .got.plt has 3 predefined empty entries now that are required for dynamic linker.
Also other new items created are configured to have correct jump to PLT[N].
2) PLT section now has PLT[0] entry, also others ones are configured to support PLT->GOT(.got.plt) calls.
3) Implemented .rel[a].plt sections (based on patch http://reviews.llvm.org/D13569).
4) Fixed plt relocations types (based on patch http://reviews.llvm.org/D13589).
NOTES:
The .plt.got zero entry is still empty now. According to ELF specification it should hold the address of the dynamic structure, referenced with the symbol
_DYNAMIC. The _DYNAMIC entry points to the .dynamic section which contains information used by the ELF interpreter to setup the binary.
Differential Revision: http://reviews.llvm.org/D13651
llvm-svn: 250169
Under PPC64 ELF v1 ABI, the symbols associated with each function name don't
point directly to the code in the .text section (or similar), but rather to a
function descriptor structure in a special data section named .opd. The
elements in the .opd structure include a pointer to the actual code, and a the
relevant TOC base value. Both of these are themselves set by relocations.
When we have a local call, we need the relevant relocation to refer directly to
the target code, not to the function-descriptor in the .opd section. Only when
we have a .plt stub do we care about the address of the .opd function
descriptor itself.
So we make a few changes here:
1. Always write .opd first, so that its relocated data values are available
for later use when writing the text sections. Record a pointer to the .opd
structure, and its corresponding buffer.
2. When processing a relative branch relocation under ppc64, if the
destination points into the .opd section, read the code pointer out of the
function descriptor structure and use that instead.
This this, I can link, and run, a dynamically-compiled "hello world"
application on big-Endian PPC64/Linux (ELF v1 ABI) using lld.
llvm-svn: 250122
SymbolTable was not a template class. Instead we had switch-case-based
type dispatch to call desired functions. We had to do that because
SymbolTable was created before we know what ELF type objects had been
passed.
Every time I tried to add a new function to the symbol table, I had to
define a dispatcher which consist of a single switch statement.
It also brought an restriction what the driver can do. For example,
we cannot add undefined symbols before any files are added to the symbol
table. That's because no symbols can be added until the symbol table
knows the ELF type, but when it knows about that, it's too late.
In this patch, the driver makes a decision on what ELF type objects
are being handled. Then the driver creates a SymbolTable object for
an appropriate ELF type.
http://reviews.llvm.org/D13544
llvm-svn: 249902
This reverts commit r249816.
It broke building llvm with lld:
$ ./bin/FileCheck
./bin/FileCheck: error while loading shared libraries: unexpected PLT reloc type 0x06
I think the only thing that is wrong with this patch is that it is too soon.
The plt we create (and its relocs) don't support lazy loading, so they have
to be relocated as ordinary dynamic relocations.
llvm-svn: 249835
.rela.plt contains list of elements in the PLT, which are liable to the relocation during the dynamic linking.
Differential Revision: http://reviews.llvm.org/D13569
llvm-svn: 249816
The size of a .plt entry is different on different targets (it is,
specifically, much larger than 8 on all PPC ABIs). There is no functional
change here (later patches to create .plt entries for PPC64 will depend on this
change).
llvm-svn: 249756
Previously, output sections that are handled specially by the linker
(e.g. PLT or GOT) were created by Writer and passed to other classes
that need them. The problem was that because these special sections
are required by so many classes, the plumbing work became too much
burden.
This patch is to simply make them accessible from anywhere in the
linker to eliminate the plumbing work once and for all.
http://reviews.llvm.org/D13486
llvm-svn: 249590
This is a case that requires --start-group --end-group with regular ELF
linkers. Fortunately it is still possible to handle it with lazy symbols without
taking a second look at archives.
Thanks to Michael Spencer for the bug report.
llvm-svn: 249406
The entries are added if there are "_init" or "_fini" entries in
the symbol table respectively. According to the behavior of ld,
entries are inserted even for undefined symbols.
Symbol names can be overridden by using -init and -fini command
line switches. If used, these switches neither add new symbol table
entries nor require those symbols to be resolved.
Differential Revision: http://reviews.llvm.org/D13385
llvm-svn: 249297
Using the "raw" Elf64_Dyn or Elf32_Dyn structures in
DynamicSection<ELFT>::writeTo does not correctly handle mixed-Endian
situations. Instead, use the corresponding llvm::object::* structures which
have Endian-converting members (like the rest of the code).
This fixes all currently-failing elf2 tests when running on big-Endian
PPC64/Linux (I've added a big-Endian test case which should fail on
little-Endian machines in the same way that test/elf2/shared.s failed on
big-Endian machines prior to this change).
llvm-svn: 249150
This is just enough to get PLT working on 32 bit x86.
The idea behind using a virtual interface is that it should be easy to
convert any of the functions to template parameters if any turns out to be
performance critical.
llvm-svn: 248308
Rui Ueyama