We would create a MergeInputSection for the synthetic .comment and
crash trying to add it to a regular output section.

With this we just don't add the synthetic section with -r. That is
consistent with gold that doesn't create .note.gnu.gold-version with
-r.

llvm-svn: 286635

Differential revision: https://reviews.llvm.org/D26498

llvm-svn: 286580

Summary:
This patch adds a ".comment" section to an output. The comment
section contains the linker's version string. You can now
find out whether a binary is created by LLD or not using objdump
command like this.

  $ objdump -s -j .comment foo

  foo:     file format elf64-x86-64

  Contents of section .comment:
   0000 00474343 3a202855 62756e74 7520342e  .GCC: (Ubuntu 4.
   0010 382e342d 32756275 6e747531 7e31342e  8.4-2ubuntu1~14.
   ...
   00c0 766d2f74 72756e6b 20323835 38343629  vm/trunk 285846)
   00d0 004c696e 6b65723a 204c4c44 20342e30  .Linker: LLD 4.0
   00e0 2e302028 7472756e 6b203238 36343036  .0 (trunk 286406
   00f0 2900                                 ).

Compilers emits .comment section as well, so the output contains
both compiler and linker information.

Alternative considered:

I first tried to add a SHT_NOTE section because GNU gold does that.
A NOTE section starts with a header which contains content type.
It turned out that ld.gold sets type NT_GNU_GOLD_VERSION to their
NOTE section. So the NOTE type is only for GNU gold (surprise!)

Next, I tried to create ".linker-version" section. However, it seems
that reusing the existing ".comment" section is better because 1)
other tools already know about .comment section and is able to strip
it and 2) the result contans not only linker info but also compiler
info.

Differential Revision: https://reviews.llvm.org/D26487

llvm-svn: 286496

Relocations are the last thing that we wore storing a raw section
pointer to and parsing on demand.

With this patch we parse it only once and store a pointer to the
actual data.

The patch also changes where we store it. It is now in
InputSectionBase. Not all sections have relocations, but most do and
this simplifies the logic. It also means that we now only support one
relocation section per section. Given that that constraint is
maintained even with -r with gold bfd and lld, I think it is OK.

llvm-svn: 286459

Differential revision: https://reviews.llvm.org/D26349

llvm-svn: 286443

Patch allows to pass a symbols file to linker.
LLD will map symbols to sections and sort sections
in output according to symbol ordering file.

That can help to reduce the startup time and/or
amount of pagefaults during startup.

Also, interesting benchmark result was produced by Rafael Espíndola. 
After applying the symbols file for clang he timed compiling 
X86MCTargetDesc.ii to an object file.  

The page faults went from just
56,988 to 56,946 since most faults are not in the binary.
Running time went from 4.403053515 to 4.178112244. 
The speedup seems to be because of better cache
locality.

Differential revision: https://reviews.llvm.org/D26130

llvm-svn: 286440

The disadvantage is that we use uint64_t instad of uint32_t for some
value in 32 bit files. The advantage is a substantially simpler code,
faster builds and less code duplication.

llvm-svn: 286414

Previously, we have both input and output section for .MIPS.abiflags.
Now we have only one class for .MIPS.abiflags, which is MipsAbiFlagsSection.
This class is a synthetic input section.

.MIPS.abiflags sections are handled as regular sections until
the control reaches Writer. Writer then aggregates all sections
whose type is SHT_MIPS_ABIFLAGS to create a single synthesized
input section. The synthesized section is then processed normally
as if it came from an input file.

llvm-svn: 286398

Previously, we have both input and output sections for .reginfo and
.MIPS.options. Now for each such sections we have one synthetic input
sections: MipsReginfoSection and MipsOptionsSection respectively.

Both sections are handled as regular sections until the control reaches
Writer. Writer then aggregates all sections whose type is SHT_MIPS_REGINFO
or SHT_MIPS_OPTIONS to create a single synthesized input section. In that
moment Writer also save GP0 value to the MipsGp0 field of the corresponding
ObjectFile. This value required for R_MIPS_GPREL16 and R_MIPS_GPREL32
relocations calculation.

Differential revision: https://reviews.llvm.org/D26444

llvm-svn: 286397

This is similar to what was done for InputSection.

With this the various fields are stored in host order and only
converted to target order when writing.

llvm-svn: 286327

Avoids having to skip them multiple times.

llvm-svn: 286261

We can just use a regular InputSection.

llvm-svn: 286237

With the current infrastructure it can be just an ordinary
InputSection like the real .bss sections.

llvm-svn: 286234

Differential revision: https://reviews.llvm.org/D25325

llvm-svn: 286225

A CommonInputSection is a section containing all common symbols.
That was an input section but was abstracted in a different way
than the synthetic input sections because it was written before
the synthetic input section was invented.

This patch rewrites CommonInputSection as a synthetic input section
so that it behaves better with other sections.

llvm-svn: 286053

Previously, we do this piece of code to iterate over all input sections.

  for (elf::ObjectFile<ELFT> *F : Symtab.getObjectFiles())
    for (InputSectionBase<ELFT> *S : F->getSections())

It turned out that this mechanisms doesn't work well with synthetic
input sections because synthetic input sections don't belong to any
input file.

This patch defines a vector that contains all input sections including
synthetic ones.

llvm-svn: 286051

llvm-svn: 285996

Differential Revision: https://reviews.llvm.org/D26225

llvm-svn: 285851

Previously, we added strings from DynamicSection::finalize().
It was a bit tricky because finalize() is supposed to fix the final
size of the section, but adding new strings would change the size of
.dynstr section. So there was a dependency between finalize functions
of .dynamic and .dynstr.

However, I noticed that we can elimiante the dependency by simply
add strings early; we don't have to do that in finalize() but can do
from DynamicSection's ctor.

This patch defines a new function, DynamicSection::addEntries, to
add .dynamic entries that doesn't depend on other sections.

llvm-svn: 285784

llvm-svn: 285767

This is now doable because this code doesn't have to be in the
dynamic scope of Writer::run().

llvm-svn: 285766

llvm-svn: 285764

llvm-svn: 285763

We are going to have many more classes for linker-synthesized
input sections, so it's worth to be added to a separate file
than to the file for regular input sections.

llvm-svn: 285740

Differential revision: https://reviews.llvm.org/D25627

llvm-svn: 285682

Previously, we have a lot of BumpPtrAllocators, but all these
allocators virtually have the same lifetime because they are
not freed until the linker finishes its job. This patch aggregates
them into a single allocator.

Differential revision: https://reviews.llvm.org/D26042

llvm-svn: 285452

Now that it is easy to create input section and symbols, this is
simple.

llvm-svn: 285322

This allows us to set a value for it based on -m.

llvm-svn: 285294

Instead of having 3 section allocators per file, have 3 for all files.

This is a substantial performance improvement for some cases. Linking
chromium without gc speeds up by 1.065x.

This requires using _exit in fatal since we have to avoid destructing
an InputSection if fatal is called from the constructor.

Thanks to Rui for the suggestion.

llvm-svn: 285290

    
When static linking in ARM (like Mips) __tls_get_addr is defined by
the library so we should not define it as a synthetic.
    
We also need to add __exidx_start and __exidx_end for the .ARM.exidx
section as the static libc library startup code is expecting them to
be defined by the default linker script for static linking on ARM.

Differential revision: https://reviews.llvm.org/D25978

llvm-svn: 285279

llvm-svn: 285235

As the state of lld gets more complicated, shutting down gets more
expensive.

In a normal lld run we can just call _exit immediately after renaming
the temporary output file. We still want the ability to run a full
shutdown since that is useful for detecting memory leaks.

This patch adds a --full-shutdown flag and changes lit to use it.

llvm-svn: 285224

llvm-svn: 285190

Instead of storing a pointer, store the members we need.

The reason for doing this is that it makes it far easier to create
synthetic sections. It also avoids reading data from files multiple
times., which might help with cross endian linking and host
architectures with slow unaligned access.

There are obvious compacting opportunities, but this already has mixed
results even on native x86_64 linking.

There is also the possibility of better refactoring the code for
handling common symbols, but this already shows that a custom class is
not necessary.

llvm-svn: 285148

We were fairly inconsistent as to what information should be accessed
with getSectionHdr and what information (like alignment) was stored
elsewhere.

Now all section info has a dedicated getter. The code is also a bit
more compact.

llvm-svn: 285079

We were previously using the (static) addSynthetic function to create
*_start/*_end symbols. This function was doing almost the same thing as
addOptionalSynthetic, except that it would also create the symbol in the
case where it is unreferenced. Because the symbol has hidden visibility,
creating it in that case would have no effect other than adding another
entry to the static symbol table. Remove addSynthetic and change callers to
use addOptionalSynthetic instead.

Differential Revision: https://reviews.llvm.org/D25545

llvm-svn: 285021

In this patch partial gdb_index section is created. 
For costructing the .gdb_index section 6 steps should be performed (details are in
SplitDebugInfo.cpp file header), this patch do first 3:

Creates proper section header.
Fills list of compilation units.
Types CU list area is not supposed to be supported, so it is ignored and therefore
can be treated as implemented either.

Differential revision: https://reviews.llvm.org/D24706

llvm-svn: 284708

llvm-svn: 284705

Previously, we were checking the existence of an entry symbol
too early. It was done before the linker script processor creates
symbols defined in scripts. Fixes bug 30743.

llvm-svn: 284676

This is 30646.

PT_OPENBSD_RANDOMIZE
The array element specifies the location and size of a part of the memory image of the program that must be filled with random data before any code in the object is executed. The memory region specified by a segment of this type may overlap the region specified by a PT_GNU_RELRO segment, in which case the intersection will be filled with random data before being marked read-only.

Reference links:
http://man.openbsd.org/OpenBSD-current/man5/elf.5
https://github.com/openbsd/src/commit/c494713c450d98da3f2e1451ee8c7fb675a7c461

Differential revision: https://reviews.llvm.org/D25469

llvm-svn: 284234