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
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 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
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
Kellie Medlin