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
method to get a SymbolBody and into the callers, and kill now dead
includes.
This removes the need to have the SymbolBody definition when we're
defining the inline method and makes it a better inline method. That was
the only reason for a lot of header includes here. Removing these and
using forward declarations actually uncovers a bunch of cross-header
dependencies that I've fixed while I'm here, and will allow me to
introduce some *important* inline code into Chunks.h that requires the
definition of ObjectFile.
No functionality changed at this point.
Differential Revision: http://reviews.llvm.org/D10789
llvm-svn: 240982
The previous logic to find default entry name or subsystem does not
seem correct (i.e. was not compatible with MSVC linker). Previously,
default entry name was inferred from CRT functions and user-defined
entry functions. Subsystem was inferred from CRT functions.
Default entry name and subsystem are now inferred based on the
following table. Note that we no longer use CRT functions to infer
them.
Entry name Subsystem
main mainCRTStartup console
wmain wmainCRTStartup console
WinMain WinMainCRTStartup windows
wWinMain wWinMainCRTStartup windows
llvm-svn: 240922
Usually dllexported symbols are defined with 'extern "C"',
so identifying them is easy. We can just do hash table lookup
to look up exported symbols.
However, C++ non-member functions are also allowed to be exported,
and they can be specified with unmangled name. So, if /export:foo
is given, we need to look up not only "foo" but also its all
mangled names. In MSVC mangling scheme, that means that we need to
look up any symbol which starts with "?foo@@Y".
In this patch, we scan the entire symbol table to search for
a mangled symbol. The symbol table is a DenseMap, and that doesn't
support table lookup by string prefix. This is of course very
inefficient. But that should be probably OK because the user
should always add 'extern "C"' to dllexported symbols.
llvm-svn: 240919
This option is to ignore remaining undefined symbols and force
the linker to create an output file anyways.
The existing code assumes that there's no undefined symbol after
reportRemainingUndefines(). That assumption is legitimate.
I also don't want to mess up the existing code for this minor feature.
In order to keep it as is, remaining undefined symbols are replaced
with dummy defined symbols.
llvm-svn: 240913
This flag can be used to produce a map file, which is essentially a list
of objects linked into the final output file together with the RVAs of
their symbols. Because our format differs from MSVC's we expose it as a
separate flag.
Differential Revision: http://reviews.llvm.org/D10773
llvm-svn: 240812
We were resolving entry symbols and /include'd symbols after all other
symbols are resolved. But looks like it's too late. I found that it
causes some program to fail to link.
Let's say we have an object file A which defines symbols X and Y in an
archive. We also have another file B after A which defines X, Y and
_DLLMainCRTStartup in another archive. They conflict each other, so
either A or B can be linked.
If we have _DLLMainCRTStartup as an undefined symbol, file B is always
chosen. If not, there's a chance that A is chosen. If the linker
find it needs _DllMainCRTStartup after that, it's too late.
This patch adds undefined symbols to the symbol table as soon as
possible to fix the issue.
llvm-svn: 240757
The change I made in r240620 was not correct. If a symbol foo is
defined, and if you use __imp_foo, __imp_foo symbol is automatically
defined as a pointer (not just an alias) to foo.
Now that we need to create a chunk for automatically-created symbols.
I defined LocalImportChunk class for them.
llvm-svn: 240622
MSVC linker is able to link an object file created from the following code.
Note that __imp_hello is not defined anywhere.
void hello() { printf("Hello\n"); }
extern void (*__imp_hello)();
int main() { __imp_hello(); }
Function symbols exported from DLLs are automatically mangled by appending
__imp_ prefix, so they have two names (original one and with the prefix).
This "feature" seems to simulate that behavior even for non-DLL symbols.
This is in my opnion very odd feature. Even MSVC linker warns if you use this.
I'm adding that anyway for the sake of compatibiltiy.
llvm-svn: 240620
Previously, we added files in directive sections to the symbol
table as we read the sections, so the link order was depth-first.
That's not compatible with MSVC link.exe nor the old LLD.
This patch is to queue files so that new files are added to the
end of the queue and processed last. Now addFile() doesn't parse
files nor resolve symbols. You need to call run() to process
queued files.
llvm-svn: 240483
In this linker model, adding an undefined symbol may trigger chain
reactions. It may trigger a Lazy symbol to read a new file.
A new file may contain a directive section, which may contain various
command line options.
Previously, we didn't handle chain reactions well. We visited /include'd
symbols only once, so newly-added /include symbols were ignored.
This patch fixes that bug.
Now, the symbol table is versioned; every time the symbol table is
updated, the version number is incremented. We repeat adding undefined
symbols until the version number does not change. It is guaranteed to
converge -- the number of undefined symbol in the system is finite,
and adding the same undefined symbol more than once is basically no-op.
llvm-svn: 240177
Alternatename option is in the form of /alternatename:<from>=<to>.
It's effect is to resolve <from> as <to> if <from> is still undefined
at end of name resolution.
If <from> is not undefined but completely a new symbol, alternatename
shouldn't do anything. Previously, it introduced a new undefined
symbol for <from>, which resulted in undefined symbol error.
llvm-svn: 240161
DLL files are in the same format as executables but they have export tables.
The format of the export table is described in PE/COFF spec section 5.3.
A new class, EdataContents, takes care of creating chunks for export tables.
What we need to do is to parse command line flags for dllexports, and then
instantiate the class to create chunks. For the writer, export table chunks
are opaque data -- it just add chunks to .edata section.
llvm-svn: 239869
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
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
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
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
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
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
Rui Ueyama