CompactUnwindSplitter splits compact-unwind sections on record boundaries and
adds keep-alive edges from target functions back to their respective records.
In MachO_arm64.cpp, a CompactUnwindSplitter pass is added to the pre-prune pass
list when setting up the standard pipeline.
This patch does not provide runtime support for compact-unwind, but is a first
step towards enabling it.
The C-string section splitting support added in f9649d123d triggered an assert
("Duplicate canonical symbol at address") when multiple symbols were defined at
the the same offset within a C-string block (this triggered on arm64, where we
always add a block start symbol). The bug was caused by a failure to update the
record of the last canonical symbol address. The fix was to maintain this record
correctly, and move the auto-generation of the block-start symbol above the
handling for symbols defined in the object itself so that all symbols
(auto-generated and defined) are processed in address order.
MachO C-string literal sections should be split on null-terminator boundaries,
rather than the usual symbol boundaries. This patch updates
MachOLinkGraphBuilder to do that.
Adds utilities for creating anonymous pointers and jump stubs to x86_64.h. These
are used by the GOT and Stubs builder, but may also be used by pass writers who
want to create pointer stubs for indirection.
This patch also switches the underlying type for LinkGraph content from
StringRef to ArrayRef<char>. This avoids any confusion when working with buffers
that contain null bytes in the middle like, for example, a newly added null
pointer content array. ;)
JITLink now requires section names to be unique. In MachO section names are only
guaranteed to be unique within their containing segment (e.g. a '__const' section
in the '__DATA' segment does not clash with a '__const' section in the '__TEXT'
segment), so we need to use the fully qualified <segment>,<section> section
names (e.g. '__DATA,__const' or '__TEXT,__const') when constructing
jitlink::Sections for MachO objects.
This patch introduces generic x86-64 edge kinds, and refactors the MachO/x86-64
backend to use these edge kinds. This simplifies the implementation of the
MachO/x86-64 backend and makes it possible to write generic x86-64 passes and
utilities.
The new edge kinds are different from the original set used in the MachO/x86-64
backend. Several edge kinds that were not meaningfully distinguished in that
backend (e.g. the PCRelMinusN edges) have been merged into single edge kinds in
the new scheme (these edge kinds can be reintroduced later if we find a use for
them). At the same time, new edge kinds have been introduced to convey extra
information about the state of the graph. E.g. The Request*AndTransformTo**
edges represent GOT/TLVP relocations prior to synthesis of the GOT/TLVP
entries, and the 'Relaxable' suffix distinguishes edges that are candidates for
optimization from edges which should be left as-is (e.g. to enable runtime
redirection).
ELF/x86-64 will be refactored to use these generic edges at some point in the
future, and I anticipate a similar refactor to create a generic arm64 support
header too.
Differential Revision: https://reviews.llvm.org/D98305
Separates link graph creation from linking. This allows raw LinkGraphs to be
created and passed to a link. ObjectLinkingLayer is updated to support emission
of raw LinkGraphs in addition to object buffers.
Raw LinkGraphs can be created by in-memory compilers to bypass object encoding /
decoding (though this prevents caching, as LinkGraphs have do not have an
on-disk representation), and by utility code to add programatically generated
data structures to the JIT target process.
MachOLinkGraphBuilder has been treating these as hidden, but they should be
treated as local.
Symbols with N_PEXT set and N_EXT unset are produced when hidden symbols are
run through 'ld -r' without passing -keep_private_externs. They will show up
under 'nm -m' as "was private extern", hence the name of the test cases.
Testcase commited as relocatable object to ensure that the test suite doesn't
depend on having 'ld -r' available.
Debug sections will not be linked into the final executable and may contain
ambiguous relocations*. Skipping them avoids both some unnecessary processing
cost and the hassle of dealing with the problematic relocations.
* E.g. __debug_ranges contains non-extern relocations to the end of functions
hat begin with named symbols. Under the usual rules for interpreting non-extern
relocations these will be incorrectly associated with the following block, or
no block at all (if there is a gap between one block and the next).
Global symbols with linker-private prefixes should be resolvable across object
boundaries, but internal symbols with linker-private prefixes should not.
This is how it should've been and brings it more in line with
std::string_view. There should be no functional change here.
This is mostly mechanical from a custom clang-tidy check, with a lot of
manual fixups. It uncovers a lot of minor inefficiencies.
This doesn't actually modify StringRef yet, I'll do that in a follow-up.
libraries.
This patch substantially updates ORCv2's lookup API in order to support weak
references, and to better support static archives. Key changes:
-- Each symbol being looked for is now associated with a SymbolLookupFlags
value. If the associated value is SymbolLookupFlags::RequiredSymbol then
the symbol must be defined in one of the JITDylibs being searched (or be
able to be generated in one of these JITDylibs via an attached definition
generator) or the lookup will fail with an error. If the associated value is
SymbolLookupFlags::WeaklyReferencedSymbol then the symbol is permitted to be
undefined, in which case it will simply not appear in the resulting
SymbolMap if the rest of the lookup succeeds.
Since lookup now requires these flags for each symbol, the lookup method now
takes an instance of a new SymbolLookupSet type rather than a SymbolNameSet.
SymbolLookupSet is a vector-backed set of (name, flags) pairs. Clients are
responsible for ensuring that the set property (i.e. unique elements) holds,
though this is usually simple and SymbolLookupSet provides convenience
methods to support this.
-- Lookups now have an associated LookupKind value, which is either
LookupKind::Static or LookupKind::DLSym. Definition generators can inspect
the lookup kind when determining whether or not to generate new definitions.
The StaticLibraryDefinitionGenerator is updated to only pull in new objects
from the archive if the lookup kind is Static. This allows lookup to be
re-used to emulate dlsym for JIT'd symbols without pulling in new objects
from archives (which would not happen in a normal dlsym call).
-- JITLink is updated to allow externals to be assigned weak linkage, and
weak externals now use the SymbolLookupFlags::WeaklyReferencedSymbol value
for lookups. Unresolved weak references will be assigned the default value of
zero.
Since this patch was modifying the lookup API anyway, it alo replaces all of the
"MatchNonExported" boolean arguments with a "JITDylibLookupFlags" enum for
readability. If a JITDylib's associated value is
JITDylibLookupFlags::MatchExportedSymbolsOnly then the lookup will only
match against exported (non-hidden) symbols in that JITDylib. If a JITDylib's
associated value is JITDylibLookupFlags::MatchAllSymbols then the lookup will
match against any symbol defined in the JITDylib.
Sections may have zero size and zero-sized sections may share a start address
with other zero-sized sections. For the section overlap test to function
correctly zero-sized sections must be ordered before any non-zero sized ones.
This should fix the intermittent failures in the
test/ExecutionEngine/JITLink/X86/MachO_zero_fill_alignment.s test case that
have been observed on some builders.
In the Atom model the symbols, content and relocations of a relocatable object
file are represented as a graph of atoms, where each Atom represents a
contiguous block of content with a single name (or no name at all if the
content is anonymous), and where edges between Atoms represent relocations.
If more than one symbol is associated with a contiguous block of content then
the content is broken into multiple atoms and layout constraints (represented by
edges) are introduced to ensure that the content remains effectively contiguous.
These layout constraints must be kept in mind when examining the content
associated with a symbol (it may be spread over multiple atoms) or when applying
certain relocation types (e.g. MachO subtractors).
This patch replaces the Atom model in JITLink with a blocks-and-symbols model.
The blocks-and-symbols model represents relocatable object files as bipartite
graphs, with one set of nodes representing contiguous content (Blocks) and
another representing named or anonymous locations (Symbols) within a Block.
Relocations are represented as edges from Blocks to Symbols. This scheme
removes layout constraints (simplifying handling of MachO alt-entry symbols,
and hopefully ELF sections at some point in the future) and simplifies some
relocation logic.
llvm-svn: 373689
Lang Hames