MinGW configurations don't use associative comdats, as GNU ld doesn't
support that. Instead they produce normal comdats named .text$sym,
.xdata$sym and .pdata$sym.
GNU ld doesn't discard any comdats starting with .xdata or .pdata,
even if --gc-sections is used (while it does discard other unreferenced
comdats), regardless of what symbol name is used after the $ separator.
For LLD, treat any such comdat as implicitly associative to the base
symbol. This requires maintaining a map from symbol name to section
number, but that is only maintained when the MinGW flag has been
enabled.
Differential Revision: https://reviews.llvm.org/D49700
llvm-svn: 339058
Future symbol insertions can potentially change the type of these
symbols - keep pointers to the base class to reflect this, and
use dynamic casts to inspect them before using as the subclass
type.
This fixes crashes that were possible before, by touching these
symbols that now are populated as e.g. a DefinedRegular, via
the old pointers with DefinedImportThunk type.
Differential Revision: https://reviews.llvm.org/D48953
llvm-svn: 336652
In COFF, duplicate string literals are merged by placing them in a
comdat whose leader symbol name contains a specific prefix followed
by the hash and partial contents of the string literal. This gives
us an easy way to identify sections containing string literals in
the linker: check for leader symbol names with the given prefix.
Any sections that are identified in this way as containing string
literals may be tail merged. We do so using the StringTableBuilder
class, which is also used to tail merge string literals in the ELF
linker. Tail merging is enabled only if ICF is enabled, as this
provides a signal as to whether the user cares about binary size.
Differential Revision: https://reviews.llvm.org/D44504
llvm-svn: 327668
Summary:
This protects calls to longjmp from transferring control to arbitrary
program points. Instead, longjmp calls are limited to the set of
registered setjmp return addresses.
This also implements /guard:nolongjmp to allow users to link in object
files that call setjmp that weren't compiled with /guard:cf. In this
case, the linker will approximate the set of address taken functions,
but it will leave longjmp unprotected.
I used the following program to test, compiling it with different -guard
flags:
$ cl -c t.c -guard:cf
$ lld-link t.obj -guard:cf
#include <setjmp.h>
#include <stdio.h>
jmp_buf buf;
void g() {
printf("before longjmp\n");
fflush(stdout);
longjmp(buf, 1);
}
void f() {
if (setjmp(buf)) {
printf("setjmp returned non-zero\n");
return;
}
g();
}
int main() {
f();
printf("hello world\n");
}
In particular, the program aborts when the code is compiled *without*
-guard:cf and linked with -guard:cf. That indicates that longjmps are
protected.
Reviewers: ruiu, inglorion, amccarth
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D43217
llvm-svn: 325047
Summary:
This patch adds some initial support for Windows control flow guard. At
the end of the day, the linker needs to synthesize a table of RVAs very
similar to the structured exception handler table (/safeseh).
Both /safeseh and /guard:cf take sections of symbol table indices
(.sxdata and .gfids$y) and turn them into RVA tables referenced by the
load config struct in the CRT through special symbols.
Reviewers: ruiu, amccarth
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D42592
llvm-svn: 324306
Instead of building intermediate sets of exception handlers for each
object file, just create one for the final output file.
Differential Revision: https://reviews.llvm.org/D40581
llvm-svn: 319244
If /debug was not specified, readSection will return a null
pointer for debug sections. If the debug section is associative with
another section, we need to make sure that the section returned from
readSection is not a null pointer before adding it as an associative
section.
Differential Revision: https://reviews.llvm.org/D40533
llvm-svn: 319133
With this change, instead of creating a SectionChunk for each section
in the object file, we only create them when we encounter a prevailing
comdat section.
Also change how symbol resolution occurs between comdat symbols. Now
only the comdat leader participates in comdat resolution, and not any
other external associated symbols. This is more in line with how COFF
semantics are defined, and should allow for a more straightforward
implementation of non-ANY comdat types.
On my machine, this change reduces our runtime linking a release
build of chrome_child.dll with /nopdb from 5.65s to 4.54s (median of
50 runs).
Differential Revision: https://reviews.llvm.org/D40238
llvm-svn: 319090
Now that we have only SymbolBody as the symbol class. So, "SymbolBody"
is a bit strange name now. This is a mechanical change generated by
perl -i -pe s/SymbolBody/Symbol/g $(git grep -l SymbolBody lld/ELF lld/COFF)
nd clang-format-diff.
Differential Revision: https://reviews.llvm.org/D39459
llvm-svn: 317370
New lld's files are spread under lib subdirectory, and it isn't easy
to find which files are actually maintained. This patch moves maintained
files to Common subdirectory.
Differential Revision: https://reviews.llvm.org/D37645
llvm-svn: 314719
Apply the simplification suggestions that Peter Collingbourne made
during the review at D37368. The returned thunk is cast to the
appropriate type in the SymbolTable, and the constant symbol's body is
not needed directly, so avoid the assignment. NFC
llvm-svn: 312391
Summary:
Expose the module descriptor index and fill it in for section
contributions.
Reviewers: zturner
Subscribers: llvm-commits, ruiu, hiraditya
Differential Revision: https://reviews.llvm.org/D34126
llvm-svn: 305296
This is a different implementation than r303225 (which was reverted
in r303270, re-submitted in r303304 and then re-reverted in r303527).
In the previous patch, I tried to add Live bit to each dllimported
symbol. It turned out that it didn't work with "oldnames.lib" which
contains a lot of weak aliases to dllimported symbols.
The way we handle weak aliases is to check if undefined symbols
can be resolved using weak aliases, and if so, memcpy the Defined
symbols to weak Undefined symbols, so that any references to weak
aliases automatically see defined symbols instead of undefined ones.
This memcpy happens before MarkLive kicks in.
That means we may have multiple copies of dllimported symbols. So
turning on one instance's Live bit is not enough.
This patch moves the Live bit to dllimport file. Since multiple
copies of dllsymbols still point to the same file, we can use it as the
central repository to keep track of liveness.
Differential Revision: https://reviews.llvm.org/D33520
llvm-svn: 303814
We've been using make<> to allocate new objects in ELF. We have
the same function in COFF, but we didn't use it widely due to
negligence. This patch uses the function in COFF to close the gap
between ELF and COFF.
llvm-svn: 303357
CONSTANT imports expect both the `_imp_` prefixed and non-prefixed
symbols should be added to the symbol table. This allows for linking
symbols like _NSConcreteGlobalBlock in WinObjC. The previous change
would generate the import library properly by handling the option but
would not consume the generated entry properly.
llvm-svn: 301657
Summary: When using /msvclto, lld and MSVC's linker both do their own symbol resolution. This can cause them to select different archive members, which can result in undefined references. This change avoids that situation by extracting archive members that are selected by lld and passing those to link.exe before any archives, so that MSVC's uses those objects for symbol resolution instead of different archive members.
Reviewers: pcc, rnk, ruiu
Reviewed By: pcc
Subscribers: llvm-commits, mehdi_amini
Differential Revision: https://reviews.llvm.org/D32317
llvm-svn: 301045
Summary: The COFF linker previously implemented link-time optimization using an API which has now been marked as legacy. This change refactors the COFF linker to use the new LTO API, which is also used by the ELF linker.
Reviewers: pcc, ruiu
Reviewed By: pcc
Subscribers: mgorny, mehdi_amini
Differential Revision: https://reviews.llvm.org/D29059
llvm-svn: 293967
Profiling revealed that the majority of lld's execution time on Windows was
spent opening and mapping input files. We can reduce this cost significantly
by performing these operations asynchronously.
This change introduces a queue for all operations on input file data. When
we discover that we need to load a file (for example, when we find a lazy
archive for an undefined symbol, or when we read a linker directive to
load a file from disk), the file operation is launched using a future and
the symbol resolution operation is enqueued. This implies another change
to symbol resolution semantics, but it seems to be harmless ("ninja All"
in Chromium still succeeds).
To measure the perf impact of this change I linked Chromium's chrome_child.dll
with both thin and fat archives.
Thin archives:
Before (median of 5 runs): 19.50s
After: 10.93s
Fat archives:
Before: 12.00s
After: 9.90s
On Linux I found that doing this asynchronously had a negative effect on
performance, probably because the cost of mapping a file is small enough that
it becomes outweighed by the cost of managing the futures. So on non-Windows
platforms I use the deferred execution strategy.
Differential Revision: https://reviews.llvm.org/D27768
llvm-svn: 289760
This ports the ELF linker's symbol table design, introduced in r268178,
to the COFF linker.
Differential Revision: http://reviews.llvm.org/D21166
llvm-svn: 289280
Previously, we had different way to stringize SymbolBody and InputFile
to construct error messages. This patch defines overloaded function
toString() so that we don't need to memorize all these different
function names.
With that change, it is now easy to include demangled names in error
messages. Now, if there is a symbol name conflict, we'll print out
both mangled and demangled names.
llvm-svn: 288992
Previously, we discarded .debug$ sections. This patch adds them to
files so that PDB.cpp can access them.
This patch also adds a debug option, /dumppdb, to dump debug info
fed to createPDB so that we can verify that valid data has been passed.
llvm-svn: 287555
LLD type-punned an integral type and a pointer type using a pointer
field. This is problematic because the pointer type has alignment
greater than some of the integral values.
This would be less problematic if a union was used but it turns out the
integral values are only present for a short, transient, amount of time.
Let's remove this undefined behavior by skipping the punning altogether
by storing the state in a separate memory location: a vector which
informs us which symbols to process for weak externs.
llvm-svn: 263918
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
Peter Collingbourne