In the case where either a bitcode file and a regular file or two bitcode
files export a common or comdat symbol with the same name, the linker needs
to pick one of them following COFF semantics. This patch implements a design
for resolving such symbols that pushes most of the work onto either LLD's
regular mechanism for resolving common or comdat symbols or the IR linker's
mechanism for doing the same.
We modify SymbolBody::compare to always prefer non-bitcode symbols, so that
during the initial phase of symbol resolution, the symbol table always contains
a regular symbol in any case where we need to choose between a regular and
a bitcode symbol. In SymbolTable::addCombinedLTOObject, we force export
any bitcode symbols that were initially pre-empted by a regular symbol,
and later use SymbolBody::compare to choose between the regular symbol in
the symbol table and the regular symbol from the combined LTO object file.
This design seems to be sound, so long as the resolution mechanism is defined
to be commutative and associative modulo arbitrary choices between symbols
(which seems to be the case for COFF).
Differential Revision: http://reviews.llvm.org/D10329
llvm-svn: 239563
isRoot, isLive and markLive functions are called very frequently.
Previously, they were virtual functions. This patch make them
non-virtual.
Also this patch checks chunk liveness before calling its mark().
Previously, we did that at beginning of markLive(), so the virtual
function would return immediately if it's live. That was inefficient.
llvm-svn: 239458
The code generator may create references to runtime library symbols such as
__chkstk which were not visible via LTOModule. Handle these cases by loading
the object file from the library, but abort if we end up having loaded any
bitcode objects.
Because loading the object file may have introduced new undefined references,
call reportRemainingUndefines again to detect and report them.
Differential Revision: http://reviews.llvm.org/D10332
llvm-svn: 239386
The LLVM code generator can sometimes synthesize symbols, such as SSE
constants, that are not visible via the LTOModule interface. Allow such
symbols so long as they have definitions.
Differential Revision: http://reviews.llvm.org/D10331
llvm-svn: 239385
This change seems to make the linker about 10% faster.
Reading symbol name is not very cheap because it needs strlen()
on the string table. We were wasting time on reading non-external
symbol names that would never be used by the linker.
llvm-svn: 239332
MSVC profiler reported that this stable_sort takes 7% time
when self-linking. As a result, createSection was taking 10% time.
Now createSection takes 3%. This small change actually makes
the linker a bit but perceptibly faster.
llvm-svn: 239292
We forgot to check for auxiliary symbol's type. So we sometimes read
garbage as associative section definitions.
Associative sections are considered as not live themselves by the
garbage collector because they are live only when associaited sections
are live.
By reading more data (or garbage) as associative section definitions,
we treated more sections as non-GC-roots, that caused the linker to
discard too many sections by mistake. That caused another mysterious
bug (such as some global constructors don't run at all for some reason.)
llvm-svn: 239287
I don't know what the right thing to do here, but at least 1 does
not seem like a correct value. If we do not align common chunks at
all, a small program which calls puts() from global dtors crashes
mysteriously in a kernel32's function.
I believe the crash was caused by symbols overlapping each other,
and my guess is that alignment has something to do with that, but
I am not 100% sure. Needs investigating.
llvm-svn: 239280
Chunk has writeTo function which takes uint8_t *Buf.
writeHeaderTo feels more consistent with that because this member
function also takes uint8_t *Buf.
llvm-svn: 239236
Previously, half of the constructor for .idata contents was in Chunks.cpp
and the rest was in Writer.cpp. This patch moves the latter to Chunks.cpp.
Now IdataContents class manages everything for .idata section.
llvm-svn: 239230
In this design, Chunk is the only thing that knows how to write
its contents to output file as well as how to apply relocations
there. The writer shouldn't know about the details.
llvm-svn: 239216
This test case uses too large addends in relocations. Now the test is correct.
Later we need to implement overflow checking to catch such cases.
llvm-svn: 239177
For some reason llvm's r239045 made lld propagate data_1's size. This indicates
a bug somewhere in lld.
I hesitated between changing the test or just checking in a .o produced with
the old llvm-mc. Since the size is now correct, it seemed better to update the
test.
llvm-svn: 239067
Not only entry point symbol but also symbols specified by /include
option must be preserved, as they will never be dead-stripped.
http://reviews.llvm.org/D10220
llvm-svn: 239005
This patch fixes the TLS initial executable for AArch64. Current
implementation have two issues: 1. does not generate dynamic
R_AARCH64_TLS_TPREL64 relocation for the external module symbols,
and 2. does not export the TLS initial executable symbol in dynamic
symbol table.
The fix follows the MIPS strategy to add a arch-specific GOTSection
class to keep track of TLS symbols required to be place in dynamic
symbol table. It also overrides the buildDynamicSymbolTable for
ExecutableWrite class to add the symbols.
It also adds some refactoring on AArch64RelocationPass.cpp based on ARM
backend.
llvm-svn: 238981
This patch fixes the TLS local relocations alignment done by @238258.
As pointed out, the TLS size should not be considered, but rather the
TCB size based on maximum output segment alignment. Although it has
not shown in the TLS simple cases for test-suite, more comprehensible
tests with more local TLS variable showed wrong relocations values
being generated.
The local TLS testcase is expanded to add more tls variable (both
exported and static) initialized or not.
llvm-svn: 238960
Avoid saying this is based on sections because it's not very accurate.
That we don't split section into smaller chunks of data does not mean
that the linker is built on top of that.
In reality, most part of the code do not care about underlying data,
so they are neither based on "atoms" nor sections.
The symbol table only cares about symbol names and their types.
The writer handles list of chunks, which look like just blobs,
and the writer doesn't care what those chunks are backed by.
The only thing that interact with sections is SectionChunk, which is
abstracted away as one type of Chunk.
llvm-svn: 238902
In r238690, I made all files have only MemoryBufferRefs. This change
is to do the same thing for the bitcode file reader. Also updated
a few variable names to match with other code.
llvm-svn: 238782
Symbols exported by DLLs can be imported not by name but by
small number or ordinal. Usually, symbols have both ordinals
and names, and in that case ordinals are called "hints" and
used by the loader as hints.
However, symbols can have only ordinals. They are called
import-by-ordinal symbols. You need to manage ordinals by hand
so that they will never change if you choose to use the feature.
But it's supposed to make dynamic linking faster because
it needs no string comparison. Not sure if that claim still
stands in year 2015, though. Anyways, the feature exists,
and this patch implements that.
llvm-svn: 238780
I'm adding ordinal-only (nameless) imports to the import table.
The chunk for that type is going to be different from LookupChunk.
Without this change, we cannot add objects of the new type to the
vectors.
llvm-svn: 238779
Instead of returning non-categorized errors, return categorized errors.
All uses of make_dynamic_error_code are removed.
Because we don't have error reporting mechanism, I just chose to print out
error messages to stderr, and then return an error object. Not sure if
that's the right thing to do, but at least it seems practical.
http://reviews.llvm.org/D10129
llvm-svn: 238714
Previously, this feature was implemented using a special type of
undefined symbol, in addition to an intricate way to make the resolver
read a virtual file containing that renaming symbols.
Now the feature is directly handled by the symbol table.
The symbol table has a function, rename(), to rename symbols, whose
definition is 4 lines long. Symbol renaming is naturally modeled using
Symbol and SymbolBody.
llvm-svn: 238696
Previously, a MemoryBuffer of a file was owned by each InputFile object.
This patch makes the Driver own all of them. InputFiles now have only
MemoryBufferRefs. This change simplifies ownership managment
(particularly for ObjectFile -- the object owned a MemoryBuffer only when
it's not created from an archive file, because in that case a parent
archive file owned the entire buffer. Now it owns nothing unconditionally.)
llvm-svn: 238690
New MipsAbiInfoHandler merges and hold both ELF header flags
and registries usage masks. In the future commits it will manage some
additional information.
llvm-svn: 238684
It does not involve notions of virtual archives or virtual files,
nor store a list of undefined symbols somewhere else to consume them later.
We did that before. In this patch, undefined symbols are just added to
the symbol table, which now can be done in very few lines of code.
llvm-svn: 238681
Previously the main linker routine is just a non-member function.
We store some context information to the Config object.
This patch makes it belong to Driver.
llvm-svn: 238677
`main` is not the only main function in Windows. You can choose one
from these four -- {w,}{WinMain,main}. There are four different entry
point functions for them, {w,}{WinMain,main}CRTStartup, respectively.
The linker needs to choose the right one depending on which `main`
function is defined.
llvm-svn: 238667
Section names were truncated to 8 bytes because the section table's
name field is 8 byte long. This patch creates the string table to
store long names.
llvm-svn: 238661
The new mechanism is less code, and fixes the case where all inputs
are archives.
Differential Revision: http://reviews.llvm.org/D10136
llvm-svn: 238618
Currently we set the field to zero, but as per the spec, we should
set numbers we read from import library files. The loader uses the
values as starting offsets for binary search when looking up imported
symbols from DLL.
llvm-svn: 238562
The previous implementation's driver file is cluttered by lots of
small functions, and it was hard to find important functions.
Make a separate file to prevent that issue.
llvm-svn: 238482
Previously Writer directly handles writes to a file.
Chunks needed to give Writer a continuous chunk of memory.
That was inefficent if you construct data in chunks because
it would require two memory copies (one to construct a chunk
and the other is to write that to a file).
This patch teaches chunk to write directly to a file.
From readability point of view, this is also good because
you no longer have to call hasData() before calling getData().
llvm-svn: 238464
This is an initial patch for a section-based COFF linker.
The patch has 2300 lines of code including comments and blank lines.
Before diving into details, you want to start from reading README
because it should give you an overview of the design.
All important things are written in the README file, so I write
summary here.
- The linker is already able to self-link on Windows.
- It's significantly faster than the existing implementation.
The existing one takes 5 seconds to link LLD on my machine,
while the new one only takes 1.2 seconds, even though the new
one is not multi-threaded yet. (And a proof-of-concept multi-
threaded version was able to link it in 0.5 seconds.)
- It uses much less memory (250MB vs. 2GB virtual memory space
to self-host).
- IMHO the new code is much simpler and easier to read than
the existing PE/COFF port.
http://reviews.llvm.org/D10036
llvm-svn: 238458
We do not need to merge ELF flags from DSO. But `isCompatible` is called
for all input files. So this change move ELF flags merging into the
MipsELFFile class.
llvm-svn: 238304
This patch fixes the R_AARCH64_TLSLE_ADD_TPREL_HI12 and R_AARCH64_TLSLE_ADD_TPREL_LO12_NC
handling by using the correct offset by using the target layout along with
aarch64 alignments requirements.
It fixes the TLS test-suite SingleSource failures for aarch64:
* SingleSource/UnitTests/Threads/2010-12-08-tls.execution_time
* SingleSource/UnitTests/Threads/tls.execution_time
llvm-svn: 238258
Original patch of Shankar Easwaran with additional test case.
The yaml2obj does not allow to create an object file with non-unique
sections names so the fix uses a binary input object file in the test
case.
llvm-svn: 238115
These two serve different purpose:
PLTGOT entries are (usually) lazily resolved and serve as trampolines
to correctly call dynamically linked functions. They often have
R_*_JUMP_SLOT dynamic relocation type used.
Simple GOT entries hold other things, one of them may be
R_*_GLOB_DAT to correctly reference global and static data. This
is also used to hold dynamically linked function's address.
To properly handle cases when shared object's function is called
and at the same time its address is taken, we need to be able to have
both GOT and PLTGOT entries bearing different dynamic relocation types
for the same symbol.
llvm-svn: 238015
This is used when referencing global or static data in shared
objects. This is also used when function's address is taken and
function call is made indirectly.
llvm-svn: 238014
Simon Atanasyan