Correctly sign extend the addend, and fix implicit shift operand decoding
(it incorrectly returned 0 for some cases), and check that the initial
encoded immediate is 0.
Identify relocations by (section name, offset) pairs, rather than plain
vmaddrs. This makes it easier to cross-reference debugging output for
relocations with output from standard object inspection tools (otool,
readelf, objdump, etc.).
When processing a MachO SUBTRACTOR/UNSIGNED pair, if the UNSIGNED target
is non-extern then check the r_symbolnum field of the relocation to find
the targeted section and use the section's address to find 'ToSymbol'.
Previously 'ToSymbol' was found by loading the initial value stored at
the fixup location and treating this as an address to search for. This
is incorrect, however: the initial value includes the addend and will
point to the wrong block if the addend is less than zero or greater than
the block size.
rdar://65756694
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).
This removes the conditional layout of relocation_info bitfields that was
introduced in 3ccd677bf (svn r358839). The platform relocation_info
struct (defined in usr/include/mach-o/reloc.h) does not define the layout of
this struct differently on big-endian platforms and we want to keep the LLVM
and platform definitions in sync.
To fix the bug that 3ccd677bf addressed this patch modifies JITLink to construct
its relocation_info structs from the raw relocation words using shift and mask
operations.
Global symbols with linker-private prefixes should be resolvable across object
boundaries, but internal symbols with linker-private prefixes should not.
Some targets (E.g. MachO/arm64) use relocations to fix some CFI record fields
in the eh-frame section. When relocations are used the initial (pre-relocation)
content of the eh-frame section can no longer be interpreted by following the
eh-frame specification. This causes errors in the existing eh-frame parser.
This patch moves eh-frame handling into two LinkGraph passes that are run after
relocations have been parsed (but before they are applied). The first] pass
breaks up blocks in the eh-frame section into per-CFI-record blocks, and the
second parses blocks of (potentially multiple) CFI records and adds the
appropriate edges to any CFI fields that do not have existing relocations.
These passes can be run independently of one another. By handling eh-frame
splitting/fixing with LinkGraph passes we can both re-use existing relocations
for CFI record fields and avoid applying eh-frame fixups before parsing the
section (which would complicate the linker and require extra temporary
allocations of working memory).
This implementation has support for all relocation types except TLV.
Compact unwind sections are not yet supported, so exceptions/unwinding will not
work.
llvm-svn: 374476
Lang Hames