Commit Graph

18 Commits

Author SHA1 Message Date
Jez Ng 62a3f0c984 [lld-macho] Support absolute symbols
They operate like Defined symbols but with no associated InputSection.

Note that `ld64` seems to treat the weak definition flag like a no-op for
absolute symbols, so I have replicated that behavior.

Reviewed By: #lld-macho, smeenai

Differential Revision: https://reviews.llvm.org/D87909
2020-09-25 11:28:35 -07:00
Jez Ng 5213576fa2 [lld-macho][re-land] Implement and test resolution of common symbols
Earlier build break fixed in c32e69b2ce.

This reverts commit c367f93e85.
2020-09-24 15:00:56 -07:00
Jez Ng c32e69b2ce [lld-macho][re-land] Initial support for common symbols
Fix earlier build break via a static_cast.

This reverts commit 8112d494d3.

Differential Revision: https://reviews.llvm.org/D86909
2020-09-24 15:00:20 -07:00
Muhammad Omair Javaid 8112d494d3 Revert "[lld-macho] Initial support for common symbols"
This reverts commit 63ace77962.

Breaks LLDB Arm build:
http://lab.llvm.org:8011/builders/lldb-arm-ubuntu/builds/4409
2020-09-24 12:26:40 +05:00
Muhammad Omair Javaid c367f93e85 Revert "[lld-macho] Implement and test resolution of common symbols"
This reverts commit cd7cb0c303.
Break lldb Arm build:
http://lab.llvm.org:8011/builders/lldb-arm-ubuntu/builds/4409
2020-09-24 12:25:47 +05:00
Jez Ng cd7cb0c303 [lld-macho] Implement and test resolution of common symbols
Handle the case where there are both common and non-common definitions
of the same symbol. Add a bunch of tests to ensure compatibility with ld64.

Reviewed By: #lld-macho, gkm

Differential Revision: https://reviews.llvm.org/D86910
2020-09-23 19:26:40 -07:00
Jez Ng 63ace77962 [lld-macho] Initial support for common symbols
On Unix, it is traditionally allowed to write variable definitions without
initialization expressions (such as "int foo;") to header files. These are
called tentative definitions.

The compiler creates common symbols when it sees tentative definitions. When
linking the final binary, if there are remaining common symbols after name
resolution is complete, the linker converts them to regular defined symbols in
a `__common` section.

This diff implements most of that functionality, though we do not yet handle
the case where there are both common and non-common definitions of the same
symbol.

Reviewed By: #lld-macho, gkm

Differential Revision: https://reviews.llvm.org/D86909
2020-09-23 19:26:40 -07:00
Jez Ng 2a38dba7dd [lld-macho] Emit binding opcodes for defined symbols that override weak dysyms
These opcodes tell dyld to coalesce the overridden weak dysyms to this
particular symbol definition.

Reviewed By: #lld-macho, smeenai

Differential Revision: https://reviews.llvm.org/D86575
2020-08-27 17:44:16 -07:00
Jez Ng cbe27316ef [lld-macho] Implement weak bindings for GOT/TLV
Previously, we were only emitting regular bindings to weak
dynamic symbols; this diff adds support for the weak bindings too, which
can overwrite the regular bindings at runtime. We also treat weak
defined global symbols similarly -- since they can also be interposed at
runtime, they need to be treated as potentially dynamic symbols.

Note that weak bindings differ from regular bindings in that they do not
specify the dylib to do the lookup in (i.e. weak symbol lookup happens
in a flat namespace.)

Differential Revision: https://reviews.llvm.org/D86572
2020-08-26 19:21:09 -07:00
Jez Ng 3c9100fb78 [lld-macho] Support dynamic linking of thread-locals
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
2020-08-12 19:50:09 -07:00
Jez Ng 3587de2281 [lld-macho] Support __dso_handle for C++
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
2020-07-30 14:28:41 -07:00
Jez Ng 31d5885842 [lld-macho] Partial support for weak definitions
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
2020-07-24 15:55:25 -07:00
Kellie Medlin 2b920ae78c [lld] Add archive file support to Mach-O backend
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
2020-05-14 12:58:35 -07:00
Jez Ng 5d3feefa0d [lld-macho] Dylib symbols should always replace undefined symbols
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
2020-05-09 20:56:22 -07:00
Jez Ng 060efd24c7 [lld-macho] Add basic support for linking against dylibs
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
2020-04-21 13:43:19 -07:00
Fangrui Song 6acd300375 Reland D75382 "[lld] Initial commit for new Mach-O backend"
With a fix for http://lab.llvm.org:8011/builders/clang-cmake-armv8-lld/builds/3636

Also trims some unneeded dependencies.
2020-04-02 12:03:43 -07:00
Oliver Stannard af39151f3c Revert "[lld] Initial commit for new Mach-O backend"
This is causing buildbot failures on 32-bit hosts, for example:
http://lab.llvm.org:8011/builders/clang-cmake-armv8-lld/builds/3636

This reverts commit 03f43b3aca.
2020-04-02 13:23:30 +01:00
Jez Ng 03f43b3aca [lld] Initial commit for new Mach-O backend
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
2020-03-31 11:58:47 -07:00