Pretty straightforward; just emits LC_RPATH for dyld to consume.
Note that lld itself does not yet support dylib lookup via @rpath.
Reviewed By: #lld-macho, compnerd
Differential Revision: https://reviews.llvm.org/D85701
It's similar to lld-ELF's `-whole-archive`, but applied to individual
archives instead of to a series of them.
Reviewed By: #lld-macho, smeenai
Differential Revision: https://reviews.llvm.org/D85550
Do folks care if we don't have a test for this? Creating 16
dylibs to trigger this straightforward code path seems a little tedious
Reviewed By: #lld-macho, smeenai
Differential Revision: https://reviews.llvm.org/D85467
Previously, lld would crash while complaining that `Expected<T>
must be checked before access or destruction`.
Reviewed By: #lld-macho, compnerd
Differential Revision: https://reviews.llvm.org/D85403
DylibFile doesn't store a pointer to its InterfaceFile
parameter, so there's no need to use a shared_ptr.
Reviewed By: #lld-macho, compnerd
Differential Revision: https://reviews.llvm.org/D85402
References to symbols in dylibs work very similarly regardless of
whether the symbol is a TLV. The main difference is that we have a
separate `__thread_ptrs` section that acts as the GOT for these
thread-locals.
We can identify thread-locals in dylibs by a flag in their export trie
entries, and we cross-check it with the relocations that refer to them
to ensure that we are not using a GOT relocation to reference a
thread-local (or vice versa).
Reviewed By: #lld-macho, smeenai
Differential Revision: https://reviews.llvm.org/D85081
This improves the handling of `-platform_version` by addressing the FIXME in the code to process the arguments.
Reviewed By: int3, #lld-macho
Differential Revision: https://reviews.llvm.org/D81413
Handle command-line option `-sectcreate SEG SECT FILE`, which inputs a binary blob from `FILE` into `SEG,SECT`
Reviewed By: int3
Differential Revision: https://reviews.llvm.org/D85501
Required for e.g. linking iOS apps since they don't have a platform-native
SDK
Reviewed By: #lld-macho, compnerd, smeenai
Differential Revision: https://reviews.llvm.org/D85153
Note: What ELF refers to as "TLS", Mach-O seems to refer to as "TLV", i.e.
thread-local variables.
This diff implements support for TLV relocations that reference defined
symbols. On x86_64, TLV relocations are always used with movq opcodes, so for
defined TLVs, we don't need to create a synthetic section to store the
addresses of the symbols -- we can just convert the `movq` to a `leaq`.
One notable quirk of Mach-O's TLVs is that absolute-address relocations
inside TLV-defining sections behave differently -- their addresses are
no longer absolute, but relative to the start of the target section.
(AFAICT, RIP-relative relocations are not allowed in these sections.)
Reviewed By: #lld-macho, compnerd, smeenai
Differential Revision: https://reviews.llvm.org/D85080
This diff makes the behavior in {D80859} and {D81888} apply to
thread-local ZeroFill sections too. I realized this was necessary whie
trying to implement thread-local variables.
Reviewed By: #lld-macho, compnerd, MaskRay
Differential Revision: https://reviews.llvm.org/D85079
This adds support for the `-syslibroot` option. This is required to
make the library search order actually function. With this, it is now
possible to link a test Darwin x86_64 program with lld on Darwin.
Differential Revision: https://reviews.llvm.org/D82252
Reviewed By: Jez Ng
codesign (or more specifically libstuff) checks that each section in
__LINKEDIT ends where the next one starts -- no gaps are permitted. This
diff achieves it by aligning every section's start and end points to
WordSize.
Remarks: ld64 appears to satisfy the constraint by adding padding bytes
when generating the __LINKEDIT data, e.g. by emitting BIND_OPCODE_DONE
(which is a 0x0 byte) repeatedly. I think the approach this diff takes
is a bit more elegant, but I'm not sure if it's too restrictive. In
particular, it assumes padding always uses the zero byte. But we can
revisit this later.
Reviewed By: #lld-macho, compnerd
Differential Revision: https://reviews.llvm.org/D84718
Tools like `install_name_tool` and `codesign` may modify the Mach-O
header and increase its size. The linker has to provide padding to make this
possible. This diff does that, plus sets its default value to 32 bytes (which
is what ld64 does).
Unlike ld64, however, we lay out our sections *exactly* `-headerpad` bytes from
the header, whereas ld64 just treats the padding requirement as a lower bound.
ld64 actually starts laying out the non-header sections in the __TEXT segment
from the end of the (page-aligned) segment rather than the front, so its
binaries typically have more than `-headerpad` bytes of actual padding.
We should consider implementing the same alignment behavior.
Reviewed By: #lld-macho, compnerd
Differential Revision: https://reviews.llvm.org/D84714
The C++ ABI requires dylibs to pass a pointer to __cxa_atexit which does
e.g. cleanup of static global variables. The C++ spec says that the pointer
can point to any address in one of the dylib's segments, but in practice
ld64 seems to set it to point to the header, so that's what's implemented
here.
Reviewed By: #lld-macho, smeenai
Differential Revision: https://reviews.llvm.org/D83603
The previous approach of adding up the file sizes of the
component sections ignored the fact that the sections did not have to be
contiguous in the file. As such, it was underestimating the true size.
I discovered this issue because `codesign` checks whether `__LINKEDIT`
extends to the end of the file. Since we were underestimating segment
sizes, this check failed.
Reviewed By: #lld-macho, compnerd
Differential Revision: https://reviews.llvm.org/D84574
Needed for testing Objective-C programs (since e.g. Core
Foundation is a framework)
Reviewed By: #lld-macho, compnerd
Differential Revision: https://reviews.llvm.org/D83925
XCode passes in this flag, which we do not yet implement. Skip
over the argument for now so we can at least successfully parse the
linker invocation.
Reviewed By: #lld-macho, compnerd
Differential Revision: https://reviews.llvm.org/D84485
This diff adds support for weak definitions, though it doesn't handle weak
symbols in dylibs quite correctly -- we need to emit binding opcodes for them
in the weak binding section rather than the lazy binding section.
What *is* covered in this diff:
1. Reading the weak flag from symbol table / export trie, and writing it to the
export trie
2. Refining the symbol table's rules for choosing one symbol definition over
another. Wrote a few dozen test cases to make sure we were matching ld64's
behavior.
We can now link basic C++ programs.
Reviewed By: #lld-macho, compnerd
Differential Revision: https://reviews.llvm.org/D83532
Previously, we only supported binding dysyms to the GOT. This
diff adds support for binding them to any arbitrary section. C++
programs appear to use this, I believe for vtables and type_info.
This diff also makes our bind opcode encoding a bit smarter -- we now
encode just the differences between bindings, which will make things
more compact.
I was initially concerned about the performance overhead of iterating
over these relocations, but it turns out that the number of such
relocations is small. A quick analysis of my llvm-project build
directory showed that < 1.3% out of ~7M relocations are RELOC_UNSIGNED
bindings to symbols (including both dynamic and static symbols).
Reviewed By: #lld-macho, smeenai
Differential Revision: https://reviews.llvm.org/D83103
Summary:
ld64 does this, and references an internal rdar:// number as an explanation. No
idea what that rdar issue is, but in practice, it seems that not putting a BSS
section at the end can cause subsequent sections in the same segment to be
overwritten with zeroes.
Reviewers: #lld-macho
Subscribers: llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D81888
Summary:
There were a few issues with the previous setup:
1. The section sorting comparator used a declarative map of section names to
determine the correct order, but it turns out we need to match on more than
just names -- in particular, an upcoming diff will sort based on whether the
S_ZERO_FILL flag is set. This diff changes the sorter to a more imperative but
flexible form.
2. We were sorting OutputSections stored in a MapVector, which left the
MapVector in an inconsistent state -- the wrong keys map to the wrong values!
In practice, we weren't doing key lookups (only container iteration) after the
sort, so this was fine, but it was still a dubious state of affairs. This diff
copies the OutputSections to a vector before sorting them.
3. We were adding unneeded OutputSections to OutputSegments and then filtering
them out later, which meant that we had to remember whether an OutputSegment
was in a pre- or post-filtered state. This diff only adds the sections to the
segments if they are needed.
In addition to those major changes, two minor ones worth noting:
1. I renamed all OutputSection variable names to `osec`, to parallel `isec`.
Previously we were using some inconsistent combination of `osec`, `os`, and
`section`.
2. I added a check (and a test) for InputSections with names that clashed with
those of our synthetic OutputSections.
Reviewers: #lld-macho
Subscribers: llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D81887
Summary:
llvm-mc emits `__bss` sections with an offset of zero, but we weren't expecting
that in our input, so we were copying non-zero data from the start of the file and
putting it in `__bss`, with obviously undesirable runtime results. (It appears that
the kernel will copy those nonzero bytes as long as the offset is nonzero, regardless
of whether S_ZERO_FILL is set.)
I debated on whether to make a special ZeroFillSection -- separate from a
regular InputSection -- but it seemed like too much work for now. But I'm happy
to refactor if anyone feels strongly about having it as a separate class.
Depends on D80857.
Reviewers: ruiu, pcc, MaskRay, smeenai, alexshap, gkm, Ktwu, christylee
Reviewed By: smeenai
Subscribers: llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D80859
Summary:
Turns out this case is actually really common -- it happens whenever there's
a reference to an `extern` variable that ends up statically linked.
Depends on D80856.
Reviewers: ruiu, pcc, MaskRay, smeenai, alexshap, gkm, Ktwu, christylee
Reviewed By: smeenai
Subscribers: llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D80857
Summary:
As far as I can tell, it's identical to _GOT_LOAD. llvm-mc has the following
comment explaining why _GOT exists:
```
// x86_64 distinguishes movq foo@GOTPCREL so that the linker can
// rewrite the movq to an leaq at link time if the symbol ends up in
// the same linkage unit.
```
Depends on D80855.
Reviewers: ruiu, pcc, MaskRay, smeenai, alexshap, gkm, Ktwu, christylee
Reviewed By: MaskRay, smeenai
Subscribers: llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D80856
Summary:
As mentioned in https://reviews.llvm.org/D81326#2093931, I'm not sure it
makes sense to use the default target triple to determine -arch.
Long-term we should probably detect it from the input object files, but
in the meantime it would be nice not to have to add it to all our tests
by using a convenient default.
Reviewers: #lld-macho
Subscribers: arphaman, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D81983
Summary:
So things work on 32-bit machines. (@vzakhari reported the
breakage starting from D80177).
Reviewers: #lld-macho, vzakhari
Subscribers: llvm-commits, vzakhari
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D81982
This removes the stub library that lld injected to satisfy the
dependency on the libSystem. Now with TBD support, we can provide the
stub library to permit the tests to function properly as they would on a
real system.
Reviewed By: smeenai
Differential Revision: https://reviews.llvm.org/D81418
This is a complete Options.td compiled from ld(1) dated 2018-03-07 and
cross checked with ld64 source code version 512.4 dated 2018-03-18.
This is the first in a series of diffs for argument handling. Follow-ups
will include switch cases for all the new instances of `OPT_foo`, and
parsing/validation of arguments attached to options, e.g., more code
akin to `OPT_platform_version` and associated `parsePlatformVersion()`.
Reviewed By: smeenai
Differential Revision: https://reviews.llvm.org/D80582
Summary:
We should be reading / writing our addends / relocated addresses based on
r_length, and not just based on the type of the relocation. But since only
some r_length values are valid for a given reloc type, I've also added some
validation.
ld64 has code to allow for r_length = 0 in X86_64_RELOC_BRANCH relocs, but I'm
not sure how to create such a relocation...
Reviewed By: smeenai
Differential Revision: https://reviews.llvm.org/D80854
Summary: After {D81326} landed, some tests started failing if they did
not have `-arch` specified. I think one of the reasons happened was due
to the fact that we were taking a reference to a temporary value that
was freed too early. Fixing that got the error to go away on my local
Linux machine.
Reviewed By: MaskRay
Differential Revision: https://reviews.llvm.org/D81802
Add support to lld to use Text Based API stubs for linking. This is
support is incomplete not filtering out platforms. It also does not
account for architecture specific API handling and potentially does not
correctly handle trees of re-exports with inlined libraries being
treated as direct children of the top level library.
Use the default target triple configured by the user to determine the
default architecture for `ld64.lld`. Stash the architecture in the
configuration as when linking against TBDs, we will need to filter out
the symbols based upon the architecture. Treat the Haswell slice as it
is equivalent to `x86_64` but with the extra Haswell extensions (e.g.
AVX2, FMA3, BMI1, etc). This will make it easier to add new
architectures in the future.
This change also changes the failure mode where an invalid `-arch`
parameter will result in the linker exiting without further processing.
This merges the static and shared library and behaves as if
`-search_paths_first` was specified which is also the default behaviour
on ld64 (and now lld). Unify the paths, and use `llvm::sys::path` to
deal with the path to be truly agnostic to the host.
This is a very basic static library search addition. This is the pre-Xcode4
behaviour of searching all paths for the shared version before searching for
the static version of the library. This behaviour is supposed to be inverted
with `-search_paths_first` being the default. This adds the library search
with the intention of providing the setup to merge the paths into one path
and making it controllable by `OPT_search_paths_first`.
ld64 provides the `-search_path_firsts` which will search each path in
the library search path order for both `lib[name].dylib`, `lib[name].a`
before moving on (searching all paths for the dylib and then falling
back to the static library if a shared library was not found).
This option has been the default for a long time, but the command line
flag still exists. Ignore it for compatibility.
My test refactoring in D80217 seems to have caused yaml2obj to emit
unaligned nlist_64 structs, causing ASAN'd lld to be unhappy. I don't
think this is an issue with yaml2obj though -- llvm-mc also seems to
emit unaligned nlist_64s. This diff makes lld able to safely do aligned
reads under ASAN builds while hopefully creating no overhead for regular
builds on architectures that support unaligned reads.
Reviewed By: thakis
Differential Revision: https://reviews.llvm.org/D80414
That's what ld64 uses for 64-bit targets. I figured it's best to make
this change sooner rather than later since a bunch of our tests are
relying on hardcoded addresses that depend on this value.
Reviewed By: smeenai
Differential Revision: https://reviews.llvm.org/D80177
I considered making a `Target::validate()` method, but I wasn't sure how
I felt about the overhead of doing yet another switch-dispatch on the
relocation type, so I put the validation in `relocateOne` instead...
might be a bit of a micro-optimization, but `relocateOne` does assume
certain things about the relocations it gets, and this error handling
makes that explicit, so it's not a totally unreasonable code
organization.
Reviewed By: smeenai
Differential Revision: https://reviews.llvm.org/D80049
Summary:
This diff restores and builds upon @pcc and @ruiu's initial work on
subsections.
The .subsections_via_symbols directive indicates we can split each
section along symbol boundaries, unless those symbols have been marked
with `.alt_entry`.
We exercise this functionality in our tests by using order files that
rearrange those symbols.
Depends on D79668.
Reviewers: ruiu, pcc, MaskRay, smeenai, alexshap, gkm, Ktwu, christylee
Reviewed By: smeenai
Subscribers: thakis, llvm-commits, pcc, ruiu
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D79926
This diff restores and builds upon @pcc and @ruiu's initial work on
subsections.
The .subsections_via_symbols directive indicates we can split each
section along symbol boundaries, unless those symbols have been marked
with `.alt_entry`.
We exercise this functionality in our tests by using order files that
rearrange those symbols.
Reviewed By: smeenai
Differential Revision: https://reviews.llvm.org/D79926
The order file indicates how input sections should be sorted within each
output section, based on the symbols contained within those sections.
This diff sets the stage for implementing and testing
`.subsections_via_symbols`, where we will break up InputSections by each
symbol and sort them more granularly.
Reviewed By: smeenai
Differential Revision: https://reviews.llvm.org/D79668
With this change, basic archive files can be linked together. Input
section discovery has been refactored into a function since archive
files lazily resolve their symbols / the object files containing those
symbols.
Reviewed By: int3, smeenai
Differential Revision: https://reviews.llvm.org/D78342
clang passes these flags; this makes it easier to try `clang -v`
output with `ld -flavor darwinnew`.
Differential Revision: https://reviews.llvm.org/D79797
This unblocks the linking of real programs, since many core system
functions are only available as sub-libraries of libSystem.
Differential Revision: https://reviews.llvm.org/D79228
Summary:
This allows us to link against stripped dylibs. Moreover, it's simply
more correct: The symbol table includes symbols that the dylib uses but
doesn't export.
This temporarily regresses our ability to do lazy symbol binding because
dyld_stub_binder isn't in libSystem's export trie. Rather, it is in one
of the sub-libraries libSystem re-exports. (This doesn't affect our
tests since we are mocking out dyld_stub_binder there.) A follow-up diff
will address this by adding support for sub-libraries.
Depends on D79114.
Reviewers: ruiu, pcc, MaskRay, smeenai, alexshap, gkm, Ktwu, christylee
Subscribers: mgorny, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D79226
Summary:
Otherwise we get undefined symbol errors depending on the order of
arguments on the command line.
Depends on D78270.
Reviewers: ruiu, pcc, MaskRay, smeenai, alexshap, gkm, Ktwu, christylee
Subscribers: llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D79114
Summary:
This diff implements lazy symbol binding -- very similar to the PLT
mechanism in ELF.
ELF's .plt section is broken up into two sections in Mach-O:
StubsSection and StubHelperSection. Calls to functions in dylibs will
end up calling into StubsSection, which contains indirect jumps to
addresses stored in the LazyPointerSection (the counterpart to ELF's
.plt.got).
Initially, the LazyPointerSection contains addresses that point into one
of the entry points in the middle of the StubHelperSection. The code in
StubHelperSection will push on the stack an offset into the
LazyBindingSection. The push is followed by a jump to the beginning of
the StubHelperSection (similar to PLT0), which then calls into
dyld_stub_binder. dyld_stub_binder is a non-lazily bound symbol, so this
call looks it up in the GOT.
The stub binder will look up the bind opcodes in the LazyBindingSection
at the given offset. The bind opcodes will tell the binder to update the
address in the LazyPointerSection to point to the symbol, so that
subsequent calls don't have to redo the symbol resolution. The binder
will then jump to the resolved symbol.
Depends on D78269.
Reviewers: ruiu, pcc, MaskRay, smeenai, alexshap, gkm, Ktwu, christylee
Subscribers: llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D78270
Summary:
1. Don't have isHidden() depend on isNeeded(). Whether a section is
hidden is orthogonal from whether it is needed: hidden sections will
never have a header regardless of whether they have a body. (I know we
override this method with return false for synthetic sections, but
regardless I think it's confusing to write it this way for non-synthetic
sections.)
2. Don't call writeTo() on unneeded sections. D78270 assumes that this
is true when implementing the stub helper section.
3. Filter out the unneeded sections early on to avoid having to deal
with them in multiple places.
4. Remove assumption in test that the referenced file has no other symbols.
(We should create separate input files for future tests to avoid such
issues.)
Reviewers: ruiu, pcc, MaskRay, smeenai, alexshap, gkm, Ktwu, christylee
Subscribers: llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D79460
We currently only support extern relocations.
`X86_64_RELOC_SIGNED_{1,2,4}` are like X86_64_RELOC_SIGNED, but with the
implicit addend fixed to 1, 2, and 4, respectively.
See the comment in `lib/Target/X86/MCTargetDesc/X86MachObjectWriter.cpp RecordX86_64Relocation`.
Reviewed By: int3
Differential Revision: https://reviews.llvm.org/D79311
Summary: Similar to other formats, input sections in the MachO
implementation are now grouped under output sections. This is primarily
a refactor, although there's some new logic (like resolving the output
section's flags based on its inputs).
Differential Revision: https://reviews.llvm.org/D77893
Currently, getVA() returns a virtual address with the assumption that
the ImageBase is zero. As I understand, this is what lld-ELF is doing.
However, under our current design, it seems like an awkward setup --
I'm finding that I have to add and subtract ImageBase in several places
to make things work out.
As such, I think it's simpler to have getVA() return a non-relative VA,
but I'm not sure if I'm missing something. Would love to hear more from
folks familiar with lld-ELF.
Differential Revision: https://reviews.llvm.org/D78168
Build the trie by performing a three-way radix quicksort: We start by
sorting the strings by their first characters, then sort the strings
with the same first characters by their second characters, and so on
recursively. Each time the prefixes diverge, we add a node to the trie.
Thanks to @ruiu for the idea.
I used llvm-mc's radix quicksort implementation as a starting point. The
trie offset fixpoint code was taken from
MachONormalizedFileBinaryWriter.cpp.
Differential Revision: https://reviews.llvm.org/D76977
This diff implements basic support for writing a symbol table.
Attributes are loosely supported for extern symbols and not at all for
other types.
Initial version by Kellie Medlin <kelliem@fb.com>
Originally committed in a3d95a50ee and reverted in fbae153ca5 due to
UBSAN erroring over unaligned writes. That has been fixed in the
current diff with the following changes:
```
diff --git a/lld/MachO/SyntheticSections.cpp b/lld/MachO/SyntheticSections.cpp
--- a/lld/MachO/SyntheticSections.cpp
+++ b/lld/MachO/SyntheticSections.cpp
@@ -133,6 +133,9 @@ SymtabSection::SymtabSection(StringTableSection &stringTableSection)
: stringTableSection(stringTableSection) {
segname = segment_names::linkEdit;
name = section_names::symbolTable;
+ // TODO: When we introduce the SyntheticSections superclass, we should make
+ // all synthetic sections aligned to WordSize by default.
+ align = WordSize;
}
size_t SymtabSection::getSize() const {
diff --git a/lld/MachO/Writer.cpp b/lld/MachO/Writer.cpp
--- a/lld/MachO/Writer.cpp
+++ b/lld/MachO/Writer.cpp
@@ -371,6 +371,7 @@ void Writer::assignAddresses(OutputSegment *seg) {
ArrayRef<InputSection *> sections = p.second;
for (InputSection *isec : sections) {
addr = alignTo(addr, isec->align);
+ // We must align the file offsets too to avoid misaligned writes of
+ // structs.
+ fileOff = alignTo(fileOff, isec->align);
isec->addr = addr;
addr += isec->getSize();
fileOff += isec->getFileSize();
@@ -396,6 +397,7 @@ void Writer::writeSections() {
uint64_t fileOff = seg->fileOff;
for (auto § : seg->getSections()) {
for (InputSection *isec : sect.second) {
+ fileOff = alignTo(fileOff, isec->align);
isec->writeTo(buf + fileOff);
fileOff += isec->getFileSize();
}
```
I don't think it's easy to write a test for alignment (that doesn't
involve brittly hard-coding file offsets), so there isn't one... but
UBSAN builds pass now.
Differential Revision: https://reviews.llvm.org/D79050
Summary:
Add logic for emitting the correct set of load commands and segments
when `-dylib` is passed.
I haven't gotten to implementing a real export trie yet, so we can only
emit a single symbol, but it's enough to replace the YAML test files
introduced in D76252.
Differential Revision: https://reviews.llvm.org/D76908
This diff implements basic support for writing a symbol table.
- Attributes are loosely supported for extern symbols and not at all for
other types
Immediate future work will involve implementing section merging.
Initial version by Kellie Medlin <kelliem@fb.com>
Differential Revision: https://reviews.llvm.org/D76742
Previously, the special segments `__PAGEZERO` and `__LINKEDIT` were
implemented as special LoadCommands. This diff implements them using
special sections instead which have an `isHidden()` attribute. We do not
emit section headers for hidden sections, but we use their addresses and
file offsets to determine that of their containing segments. In addition
to allowing us to share more segment-related code, this refactor is also
important for the next step of emitting dylibs:
1) dylibs don't have segments like __PAGEZERO, so we need an easy way of
omitting them w/o messing up segment indices
2) Unlike the kernel, which is happy to run an executable with
out-of-order segments, dyld requires dylibs to have their segment
load commands arranged in increasing address order. The refactor
makes it easier to implement sorting of sections and segments.
Differential Revision: https://reviews.llvm.org/D76839
This diff implements:
* dylib loading (much of which is being restored from @pcc and @ruiu's
original work)
* The GOT_LOAD relocation, which allows us to load non-lazy dylib
symbols
* Basic bind opcode emission, which tells `dyld` how to populate the GOT
Differential Revision: https://reviews.llvm.org/D76252
Summary:
This is the first commit for the new Mach-O backend, designed to roughly
follow the architecture of the existing ELF and COFF backends, and
building off work that @ruiu and @pcc did in a branch a while back. Note
that this is a very stripped-down commit with the bare minimum of
functionality for ease of review. We'll be following up with more diffs
soon.
Currently, we're able to generate a simple "Hello World!" executable
that runs on OS X Catalina (and possibly on earlier OS X versions; I
haven't tested them). (This executable can be obtained by compiling
`test/MachO/relocations.s`.) We're mocking out a few load commands to
achieve this -- for example, we can't load dynamic libraries, but
Catalina requires binaries to be linked against `dyld`, so we hardcode
the emission of a `LC_LOAD_DYLIB` command. Other mocked out load
commands include LC_SYMTAB and LC_DYSYMTAB.
Differential Revision: https://reviews.llvm.org/D75382
Jez Ng