This is an LLD extension to MSVC link.exe command line. MSVC linker
does not write symbol tables for executables. We do unless no /debug
option is given.
There's a situation that we want to enable debug info but don't want
to emit the symbol table. One example is when we are comparing output
file size. With this patch, you can tell the linker to not create
a symbol table by just specifying /nosymtab.
llvm-svn: 248225
std::distance(C->Relocs.end(), C->Relocs.begin()) is the same as NumRelocs
which is already added to the hash value. What we are missing here is the
section size.
llvm-svn: 248202
This patch fixes a regression introduced by r247964. Relocations that
are referring the same symbol should be considered equal, but they
were not if they were pointing to non-section chunks.
llvm-svn: 248132
Previously, InputFile::parse() was run in batch. We construct a list
of all input files and call parse() on each file using parallel_for_each.
That means we cannot start parsing files until we get a complete list
of input files, although InputFile::parse() is safe to call from anywhere.
This patch makes it asynchronous. As soon as we add a file to the symbol
table, we now start parsing the file using std::async().
This change shortens self-hosting time (650 ms) by 28 ms. It's about 4%
improvement.
llvm-svn: 248109
I made the field an atomic pointer in hope that we would be able to
parallelize the symbol resolver soon, but that's not going to happen
soon. This patch reverts that change for the sake of readability.
llvm-svn: 248104
InputFile::parse() can be called in parallel with other calls of
the same function. By doing that, time to self-link improves from
741 ms to 654 ms or 12% faster.
This is probably the last low hanging fruit in terms of parallelism.
Input file parsing and symbol table insertion takes 450 ms in total.
If we want to optimize further, we probably have to parallelize
symbol table insertion using concurrent hashmap or something.
That's doable, but that's not easy, especially if you want to keep
the exact same semantics and linking order. I'm not going to do that
at least soon.
Anyway, compared to r248019 (the change before the first attempt for
parallelism), we achieved 36% performance improvement from 1022 ms
to 654 ms. MSVC linker takes 3.3 seconds to link the same program.
MSVC's ICF feature is very slow for some reason, but even if we
disable the feature, it still takes about 1.2 seconds.
Our number is probably good enough.
llvm-svn: 248078
Self-hosting took 801 ms on my machine. Of which this function took
69 ms. Now it takes 37 ms. That is about 4% overall performance
improvement.
llvm-svn: 248052
The LLD's ICF algorithm is highly parallelizable. This patch does that
using parallel_for_each.
ICF accounted for about one third of total execution time. Previously,
it took 324 ms when self-hosting. Now it takes only 62 ms.
Of course your mileage may vary. My machine is a beefy 24-core Xeon machine,
so you may not see this much speedup. But this optimization should be
effective even for 2-core machine, since I saw speedup (324 ms -> 189 ms)
when setting parallelism parameter to 2.
llvm-svn: 248038
Previously, ICF created a vector for each SectionChunk. The vector
contained pointers to successors, which are namely associative sections
and COMDAT relocation targets. The reason I created vectors is because
I thought that that would make section comparison faster.
It did make the comparison faster. When self-linking, for example, it
saved about 10 ms on each iteration. The time we spent on constructing
the vectors was 124 ms. If we iterate more than 12 times, return from
the investment exceeds the initial cost.
In reality, it usually needs 5 iterations. So we shouldn't construct
the vectors.
llvm-svn: 247963
equalsConstants() is the heaviest function in ICF, and that consumes
more than half of total ICF execution time. Of which, section content
comparison accounts for roughly one third.
Previously, we compared section contents at the beginning of the
function after comparing their checksums. The comparison is very
likely to succeed because when the control reaches that comparison,
their checksums are always equal. And because checksums are 64-bit
CRC, they are unlikely to collide.
We compared relocations and associative sections after that.
If they are different, the time we spent on byte-by-byte comparison
of section contents were wasted.
This patch moves the comparison at the end of function. If the
comparison fails, the time we spent on relocation comparison are
wasted, but as I wrote it's very unlikely to happen.
LLD took 1198 ms to link itself to produce a 27.11 MB executable.
Of which, ICF accounted for 536 ms. This patch cuts it by 90 ms,
which is 17% speedup of ICF and 7.5% speedup overall. All numbers
are median of ten runs.
llvm-svn: 247961
Basically the concept of "liveness" is for sections (or chunks in LLD
terminology) and not for symbols. Symbols are always available or live,
or otherwise it indicates a link failure.
Previously, we had isLive() and markLive() methods for DefinedSymbol.
They are confusing methods. What they actually did is to act as a proxy
to backing section chunks. We can simplify eliminate these methods
and call section chunk's methods directly.
llvm-svn: 247869
Only live symbols are written to the symbol table. Because isLive()
returned false if dead-stripping was disabled entirely, only
non-COMDAT sections were written to the symbol table. This patch fixes
the issue.
llvm-svn: 247856
This patch defines ICF class and defines ICF-related functions as
members of the class. By doing this we can move code that are
related only to ICF from SectionChunk to the newly-defined class.
This also eliminates a global variable "NextID".
llvm-svn: 247802
This is a patch to make LLD to be on par with MSVC in terms of ICF
effectiveness. MSVC produces a 27.14MB executable when linking LLD.
LLD previously produced a 27.61MB when self-linking. Now the size
is reduced to 27.11MB. Note that without ICF the size is 29.63MB.
In r247387, I implemented an algorithm that handles section graphs
as cyclic graphs and merge them using SCC. The algorithm did not
always work as intended as I demonstrated in r247721. The new
algortihm implemented in this patch is different from the previous
one. If you are interested the details, you want to read the file
comment of ICF.cpp.
llvm-svn: 247770
Previously, LLD's ICF couldn't merge cyclic graphs. That was unfortunate
because, in COFF, cyclic graphs are not exceptional at all. That is
pretty common.
In this patch, sections are grouped by Tarjan's strongly connected
component algorithm to get acyclic graphs. And then we try to merge
SCCs whose outdegree is zero, and remove them from the graph. This
makes other SCCs to have outdegree zero, so we can repeat the
process until all SCCs are removed. When comparing two SCCs, we handle
cycles properly.
This algorithm works better than previous one. Previously, self-linking
produced a 29.0MB executable. It now produces a 27.7MB. There's still some
gap compared to MSVC linker which produces a 27.1MB executable for the
same input. So the gap is narrowed, but still LLD is not on par with MSVC.
I'll investigate that later.
llvm-svn: 247387
Identical COMDAT Folding is a feature to merge COMDAT sections
by contents. Two sections are considered the same if their contents,
relocations, attributes, etc, are all the same.
An interesting fact is that MSVC linker takes "iterations" parameter
for ICF because the algorithm they are using is iterative. Merging
two sections could make more sections to be mergeable because
different relocations could now point to the same section. ICF is
repeated until we get a convergence (until no section can be merged).
This algorithm is not fast. Usually it needs three iterations until a
convergence is obtained.
In the new algorithm implemented in this patch, we consider sections
and relocations as a directed acyclic graph, and we try to merge
sections whose outdegree is zero. Sections with outdegree zero are then
removed from the graph, which makes other sections to have outdegree
zero. We repeat that until all sections are processed. In this
algorithm, we don't iterate over the same sections many times.
There's an apparent issue in the algorithm -- the section graph is
not guaranteed to be acyclic. It's actually pretty often cyclic.
So this algorithm cannot eliminate all possible duplicates.
That's OK for now because the previous algorithm was not able to
eliminate cycles too. I'll address the issue in a follow-up patch.
llvm-svn: 246878
Previously, we calculated our own hash values for section contents.
Of coruse that's slow because we had to access all bytes in sections.
Fortunately, COFF objects usually contain hash values for COMDAT
sections. We can use that to speed up Identical COMDAT Folding.
llvm-svn: 246869
The option is added in MSVC 2015, and there's no documentation about
what the option is. This patch is to ignore the option for now, so that
at least LLD is usable with MSVC 2015.
llvm-svn: 246780
This patch fixes a subtle incompatibility with MSVC linker.
MSVC linker preserves the original spelling of a DLL in the
import descriptor table. LLD previously converted all
characters to lowercase. Usually this difference is benign,
but if a program explicitly checks for DLL file names, the
program could fail.
llvm-svn: 246620
In r246424, I made a change that disables non-DLL to export
symbols. It turned out that the change was not correct. Both
DLLs and executables are able to export symbols (although the
latter is relatively rare). This change restores the feature.
llvm-svn: 246537
I have totally no idea why, but MSVC linker is sensitive about
file names of archive members. If we do not make import library
file names to the same as the DLL name, MSVC link *crashes*
when it is processing the library file. This patch is to set
the same name.
llvm-svn: 246535
The rules for dllexported symbols are overly complicated due to
x86 name decoration, fuzzy symbol resolution, and the fact that
one symbol can be resolved by so many different names. The rules
are probably intended to be "intuitive", so that users don't have
to understand the name mangling schemes, but it seems that it can
lead to unintended symbol exports.
To make it clear what I'm trying to do with this patch, let me
write how the export rules are subtle and complicated.
- x86 name decoration: If machine type is i386 and export name
is given by a command line option, like /export:foo, the
real symbol name the linker has to search for is _foo because
all symbols are decorated with "_" prefixes. This doesn't happen
on non-x86 machines. This automatic name decoration happens only
when the name is not C++ mangled.
However, the symbol name exported from DLLs are ones without "_"
on all platforms.
Moreover, if the option is given via .drectve section, no
symbol decoration is done (the reason being that the .drectve
section is created by a compiler and the compiler should always
know the exact name of the symbol, I guess).
- Fuzzy symbol resolution: In addition to x86 name decoration,
the linker has to look for cdecl or C++ mangled symbols
for a given /export. For example, it searches for not only
_foo but also _foo@<number> or ??foo@... for /export:foo.
Previous implementation didn't get it right. I'm trying to make
it as compatible with MSVC linker as possible with this patch
however the rules are. The new code looks a bit messy to me, but
I don't think it can be simpler due to the ad-hoc-ness of the rules.
llvm-svn: 246424
This is exposed via a new flag /opt:lldltojobs=N, where N is the number of
code generation threads.
Differential Revision: http://reviews.llvm.org/D12309
llvm-svn: 246342
lib.exe has a feature to create import library files (which contain
short import files) from module-definition files. Previously, we were
using that feature, but it turned out that the feature is not complete
for us.
There seems no way to specify "Import Types" in module-definition file.
lib.exe always adds "_" to given symbols and specify IMPORT_NAME_UNDECORATE.
We need more fine-grainded control on that value.
This patch teaches LLD to create short import files itself.
We are still using lib.exe, but the use of the tool is limited to create
empty import library files. We then create short import files and add them
to the empty files as new members.
This patch does not intend to change the functionality. LLD produces
the same import libraries as before. I'll make another change to create
different import libraries in a follow-up patch.
llvm-svn: 246292
__NULL_IMPORT_DESCRIPTOR is a symbol used by MSVC liner to construct
the import descriptor table. We do not use the symbol. Previously,
we had code to skip that symbol. That code does not actually do
anything meaningful because no one is referencing the symbol, the
symbol would naturally be ignored. This patch stops recognizing
the symbol.
llvm-svn: 245280
Previously, weak external symbols could reference only symbols that
appeared before them. Although that covers almost all use cases
of weak externals, there are object files out there which contains
weak externals that have forward references.
This patch supports such weak externals.
llvm-svn: 245258
There are some DLLs whose initializers depends on other DLLs'
initializers. The initialization order matters for them.
MSVC linker uses the order of the libraries from the command line.
LLD used ASCII-betical order. So they were incompatible.
This patch makes LLD compatible with MSVC.
llvm-svn: 245201
This is more convenient than the offset from the start of the file as we
don't have to worry about it changing when we move the output section.
This is a port of r245008 from ELF.
llvm-svn: 245018
Sections must start at page boundaries in memory, but they
can be aligned to sector boundaries (512-bytes) on disk.
We aligned them to 4096-byte boundaries even on disk, so we
wasted disk space a bit.
llvm-svn: 244691
MSVC 2015's load configuration object (__load_config_used) contains
references to these symbols. I don't fully understand how it works,
but looks like these symbols are linker-defined ones. So I define them
here in the Driver. With this patch, LLD can self-host with MSVC 2015.
This patch is to link MSVC 2015-produced object files. It does not
implement Control Flow Protection. If I understand correctly, the
linker has to create a bitmap of function entry point addresses for
the CFG runtime. We don't do that yet. Produced executables will not
be protected by CFG.
llvm-svn: 244425
SymbolTable::find(mangle(X)) is equivalent to SymbolTable::findUnderscore(X)
except that the latter is slightly efficient as that doesn't allocate a new
string.
llvm-svn: 244377
This has a few advantages
* Less C++ code (about 300 lines less).
* Less machine code (about 14 KB of text on a linux x86_64 build).
* It is more debugger friendly. Just set a breakpoint on the exit function and
you get the complete lld stack trace of when the error was found.
* It is a more robust API. The errors are handled early and we don't get a
std::error_code hot potato being passed around.
* In most cases the error function in a better position to print diagnostics
(it has more context).
llvm-svn: 244215
Various parameters are passed implicitly using Config global variable
already. Output file path is no different from others, so there was no
special reason to handle that differnetly.
This patch changes the signature of writeResult(SymbolTable *, StringRef)
to writeResult(SymbolTable *).
llvm-svn: 244180
We were printing an error but exiting with 0.
Not sure how to test this. We could add a no-winlib feature,
but that is probably not worth it.
llvm-svn: 244109
I don't remember why I thought that only functions are subject
of garbage collection, but the comment here said so, which is
not correct. Moreover, the code just below the comment does not
do what the comment says -- it handles non-COMDAT, non-function
sections as GC root. As a result, it just handles non-COMDAT
sections as GC root.
This patch cleans that up by removing SectionChunk::isRoot and
use isCOMDAT instead.
llvm-svn: 243700
We want to convince the NT loader not to map these sections into memory.
A good first step is to move them to the end of the executable.
Differential Revision: http://reviews.llvm.org/D11655
llvm-svn: 243680
We create a module-definition file and give that to lib.exe to
create an import library file. A module-definition has to be
syntactically and semantically correct, of course.
There was a case that we created a module-definition file that
lib.exe would complain for duplicate entries. If a user gives
an unmangled and mangled name for the same symbol, we would end
up having two duplicate lines for the mangled name in a module-
definition file.
This patch fixes that issue by uniquefying entries by mangled
symbol name.
llvm-svn: 243587
Windows ARM is the thumb ARM environment, and pointers to thumb code
needs to have its LSB set. When we apply relocations, we need to
adjust the LSB if it points to an executable section.
llvm-svn: 243560
SECREL should sets the 32-bit offset of the target from the beginning
of *target's* output section. Previously, the offset from the beginning
of source's output section was used instead.
SECTION means the target section's index, and not the source section's
index. This patch fixes that issue too.
llvm-svn: 243535
I don't fully understand the rationale behind the name mangling
scheme used for the DLL export table and the import library.
Why only leading "_" is dropped for the import library while
both "_" and "@" are dropped from DLL symbol table? But this seems
to be what MSVC linker does.
llvm-svn: 243490
The linker is now able to link not only LLVM/Clang/LLD for x86 but
even larger programs. I confirmed that it successsfully linked Chrome
for x86. Because the browser is a pretty large program, I think I can
say that the linker is now mostly feature complete. (I'm pretty sure
that there are hidden bugs somewhere, but they shouldn't be significant.)
llvm-svn: 243377
Previously, we ignore /merge option if /debug is specified
because I thought that was MSVC linker did. This was wrong.
/merge shouldn't be ignored even in debug mode.
llvm-svn: 243375
Leaving them in an executable is basically harmless but wastes disk space.
Because no one is using non-DWARF debug info linked by LLD, we can just
remove them.
llvm-svn: 243364
On x64 and x86, we use only one base relocation type, so we handled
base relocations just as a list of RVAs. That doesn't work well for
ARM becuase we have to handle two types of base relocations on ARM.
This patch changes the type of base relocation from uint32_t to
{reltype, uint32_t} to make it easy to port this code to ARM.
llvm-svn: 243197
In many places we assumed that is64() means AMD64 and i386 otherwise.
This assumption is not sound because Windows also supports ARM.
The linker doesn't support ARM yet, but this is a first step.
llvm-svn: 243188
An object file compatible with Safe SEH contains a .sxdata section.
The section contains a list of symbol table indices, each of which
is an exception handler function. A safe SEH-enabled executable
contains a list of exception handler RVAs. So, what the linker has
to do to support Safe SEH is basically to read the .sxdata section,
interpret the contents as a list of symbol indices, unique-fy and
sort their RVAs, and then emit that list to .rdata. This patch
implements that feature.
llvm-svn: 243182
__ImageBase is a special symbol whose value is the image base address.
Previously, we handled __ImageBase symbol as an absolute symbol.
Absolute symbols point to specific locations in memory and the locations
never change even if an image is base-relocated. That means that we
don't have base relocation entries for absolute symbols.
This is not a case for __ImageBase. If an image is base-relocated, its
base address changes, and __ImageBase needs to be shifted as well.
So we have to have base relocations for __ImageBase. That means that
__ImageBase is not really an absolute symbol but a different kind of
symbol.
In this patch, I introduced a new type of symbol -- DefinedRelative.
DefinedRelative is similar to DefinedAbsolute, but it has not a VA but RVA
and is a subject of base relocation. Currently only __ImageBase is of
the new symbol type.
llvm-svn: 243176
Load Configuration field points to a structure containing information
for SEH. That data strucutre is not created by the linker but provided
by an external file. What we have to do is just to set __load_config_used
address to the header.
llvm-svn: 242427
If a symbol is exported as /export:foo, and foo is resolved as a
mangled name (_foo@<number> or ?foo@@Y...), that mangled name should
be written to the export table. Previously, we wrote the original
name to the export table.
llvm-svn: 242342
Because thunks for dllimported symbols contain absolute addresses on x86,
they need to be relocated at load-time. This bug was a cause of crashes
in DLL initialization routines.
llvm-svn: 242259
I am adding support for thin archives. On those, getting the buffer
involves reading another file.
Since we only need an id in here, use the member offset in the archive.
llvm-svn: 242205
Entry name selection rule is already complicated on x64, but it's more
complicated on x86 because of the underscore name mangling scheme.
If one of _main, _main@<number> (a C function) or ?main@@... (a C++ function)
is defined, entry name is _mainCRTStartup. If _wmain, _wmain@<number or
?wmain@@... is defined, entry name is _wmainCRTStartup. And so on.
llvm-svn: 242110
If /delayload option is given, we have to resolve __delayLoadHelper2
since the function is the dynamic loader to delay-load DLLs.
The function name is mangled in x86 as ___delayLoadHelper2@8.
llvm-svn: 242078
clang-cl doesn't compile std::atomic_flag correctly (PR24101). Since the COFF
linker doesn't use threads yet, just revert r241420 and r241481 for now to
work around this clang-cl bug.
llvm-svn: 242006
Symbol foo is mangled as _foo in C and ?foo@@... in C++ on x86.
findMangle has to remove prefix underscore before mangle a given name
as a C++ symbol.
llvm-svn: 241874
Symbol names are usually mangled by appending "_" prefix on x86.
But the mangled name is not used in DLL export table. The export
table contains unmangled names.
llvm-svn: 241872
With this patch, LLD is now able to self-link an .exe file for x86
that runs correctly, although I don't think some headers (particularly
SEH) are not correct. DLL support is coming soon.
llvm-svn: 241857
Previously, we infer machine type at the very end of linking after
all symbols are resolved. That's actually too late because machine
type affects how we mangle symbols (whether or not we need to
add "_").
For example, /entry:foo adds "_foo" to the symbol table if x86 but
"foo" if x64.
This patch moves the code to infer machine type, so that machine
type is inferred based on input files given via the command line
(but not based on .directives files).
llvm-svn: 241843
Symbols exported by DLLs are listed in import library files.
Exported names may be mangled by "Import Name Type" field as
described in PE/COFF spec 7.3. This patch implements that
mangling scheme.
llvm-svn: 241719
Providing a symbol table in the executable is quite useful when
debugging a fully-linked executable without having to reconstruct one
from DWARF.
Differential Revision: http://reviews.llvm.org/D11023
llvm-svn: 241689
Previously we were unnecessarily loading lazy symbols if they appeared in an
archive multiple times, as can happen with comdat symbols. This change fixes
the bug by only loading symbols from archives at load time if the original
symbol was undefined.
Differential Revision: http://reviews.llvm.org/D10980
llvm-svn: 241538
The previous code was not even safe with MSVC 2013 because the compiler
doesn't guarantee that static variables (in this case, a mutex) are
initialized in a thread-safe manner.
llvm-svn: 241481
TLS table header field is supposed to have address and size of TLS table.
The linker doesn't have to understand what TLS table is. TLS table's name
is always "_tls_used", so if there's that symbol, the linker simply sets
that symbol's RVA to the header. The size of the TLS table is always 40 bytes.
llvm-svn: 241426
This function is called SymbolTable::readObjects, so in order to
parallelize that function, we have to make this function thread-safe.
llvm-svn: 241420
In the new design, mutation of Symbol pointers is the name resolution
operation. This patch makes them atomic pointers so that they can
be mutated by multiple threads safely. I'm going to use atomic
compare-exchange on these pointers.
dyn_cast<> doesn't recognize atomic pointers as pointers,
so we need to call load(). This is unfortunate, but in other places
automatic type conversion works fine.
llvm-svn: 241416
We were previously hitting assertion failures in the writer in cases where
a regular object file defined a weak external symbol that was defined by
a bitcode file. Because /export and /entry name mangling were implemented
using weak externals, the same problem affected mangled symbol names in
bitcode files.
The underlying cause of the problem was that weak external symbols were
being resolved before doing LTO, so the symbol table may have contained stale
references to bitcode symbols. The fix here is to defer weak external symbol
resolution until after LTO.
Also implement support for weak external symbols in bitcode files
by modelling them as replaceable DefinedBitcode symbols.
Differential Revision: http://reviews.llvm.org/D10940
llvm-svn: 241391
Looks like clang-cl sets a bogus value to the field, which makes
getSectionContents() to truncate section contents. This patch directly
uses SizeOfRawData field instead of VirtualSize to see if this can
make buildbot green.
llvm-svn: 241386
This worked before, but only by accident, and only with assertions disabled.
We ended up storing a DefinedRegular symbol in the WeakAlias field,
and never using it as an Undefined.
Differential Revision: http://reviews.llvm.org/D10934
llvm-svn: 241376
This change cut the link time of chrome.dll from 24 seconds
to 22 seconds (5% gain). When the control reaches end of link(),
all output files have already been written. All in-memory
objects can just vanish. There is no use to call their dtors.
llvm-svn: 241320
DLLs can export symbols only by ordinal, and DLLs are also able to be
delay-loaded. The combination of the two is valid. I didn't expect
that combination. This patch implements that feature.
With this patch, LLD is now able to link a working executable of Chrome
for 64-bit debug build. The browser seemed to be working fine. Chrome is
good for testing because of its variety and size. It contains various
open-source libraries written by various people. The largest file in
Chrome is chrome.dll whose size is 496MB. LLD can link it in 24 seconds.
MSVC linker takes 48 seconds. So it is exactly 2x faster. (I measured
that with debug info and ICF being turned off.)
With this achievement, I think I can say that the new COFF linker is
now mostly feature complete for x86-64 Windows. I believe there are
still many lingering bugs, though.
llvm-svn: 241318
Previously, __ImageBase symbol got a different value than the one
specified by /base:<number> because the symbol was created in the
SymbolTable's constructor. When the constructor is called,
no command line options are processed yet, so the symbol was
created always with the initial value. This caused wrong relocations
and thus caused mysterious crashes of some executables linked by LLD.
llvm-svn: 241313
Previously, pointers pointed by locally-imported symbols were broken.
It has only 4 bytes although the correct size is 8 byte. This patch
fixes that bug.
llvm-svn: 241295
Previously, SymbolBody::compare(A, B) didn't satisfy weak ordering.
There was a case that A < B and B < A could have been true.
This is because we just pick LHS if A and B are consisdered equivalent.
This patch is to make symbols being weakly ordered. If A and B are
not tie, one of A < B && B > A or A > B && B < A is true.
This is not an improtant property for a single-threaded environment
because everything is deterministic anyways. However, in a multi-
threaded environment, this property becomes important.
If a symbol is defined or lazy, ties are resolved by its file index.
For simple types that we don't really care about their identities,
symbols are compared by their addresses.
llvm-svn: 241294
On Windows, we have four different main functions, {w,}{main,WinMain}.
The linker has to choose a corresponding entry point function among
{w,}{main,WinMain}CRTStartup. These entry point functions are defined
in the standard library. The linker resolves one of them by looking at
which main function is defined and adding a corresponding undefined
symbol to the symbol table.
Object files containing entry point functions conflicts each other.
For example, we cannot resolve both mainCRTStartup and WinMainCRTStartup
because other symbols defined in the files conflict.
Previously, we inferred CRT function name at the very end of name
resolution. I found that that is sometimes too late. If the linker
already linked one of these four archive member objects, it's too late
to change the decision.
The right thing to do here is to infer entry point name after adding
all symbols from command line files and before adding any other files
(which are specified by directive sections). This patch does that.
llvm-svn: 241236
Previously, we use SymbolTable::rename to resolve AlternateName symbols.
This patch is to merge that mechanism with weak aliases, so that we
remove that function.
llvm-svn: 241230
I think Undefined symbols are a bit more convenient than StringRefs
since SymbolBodies are handles for symbols. You can get resolved
symbols for undefined symbols just by calling getReplacmenet without
looking up the symbol table.
llvm-svn: 241214
Occasionally we have to resolve an undefined symbol to its
mangled symbol. Previously, we did that on calling side of
findMangle by explicitly updating SymbolBody.
In this patch, mangled symbols are handled as weak aliases
for undefined symbols.
llvm-svn: 241213
Previously, the order of adding symbols to the symbol table was simple.
We have a list of all input files. We read each file from beginning of
the list and add all symbols in it to the symbol table.
This patch changes that order. Now all archive files are added to the
symbol table first, and then all the other object files are added.
This shouldn't change the behavior in single-threading, and make room
to parallelize in multi-threading.
In the first step, only lazy symbols are added to the symbol table
because archives contain only Lazy symbols. Member object files
found to be necessary are queued. In the second step, defined and
undefined symbols are added from object files. Adding an undefined
symbol to the symbol table may cause more member files to be added
to the queue. We simply continue reading all object files until the
queue is empty.
Finally, new archive or object files may be added to the queues by
object files' directive sections (which contain new command line
options).
The above process is repeated until we get no new files.
Symbols defined both in object files and in archives can make results
undeterministic. If an archive is read before an object, a new member
file gets linked, while in the other way, no new file would be added.
That is the most popular cause of an undeterministic result or linking
failure as I observed. Separating phases of adding lazy symbols and
undefined symbols makes that deterministic. Adding symbols in each
phase should be parallelizable.
llvm-svn: 241107
Rui Ueyama