Re-enables compact-unwind support in JITLink, which was reverted in b04847b427d
due to buildbot failures.
The underlying cause for the failures on the buildbots was the lack of
compact-unwind registration support on older Darwin OSes. Since the
CompactUnwindManager pass now removes eh-frames by default we were left with
unwind-info that could not be registered. On x86-64, where eh-frame info is
produced by default the solution is to fall back to using eh-frames. On arm64
we simply can't support exceptions on older OSes.
This patch updates the EHFrameRegistrationPlugin to remove the compact-unwind
section (__LD,__compact_unwind) when installed, forcing use of eh-frames when
the EHFrameRegistrationPlugin is used. In LLJIT, the EHFrameRegistrationPlugin
continues to be used for all non-Darwin platform, and will be added on Darwin
platforms when the a CompactUnwindRegistrationPlugin instance can't be created
(e.g. due to missing support for compact-unwind info registration).
The lit.cfg.py script is updated to check whether the host OSes default unwind
info supports JIT registration, allowing tests to be disabled for older Darwin
OSes on arm64.
a1ff2d18466 should have disambiguated MachOCompactUnwindInfoSectionName to
MachOUnwindInfoSectionName, given how it's used in MachOPlatform and its
value.
A MachOCompactUnwindSectionName variable with an appropriate value will be
added in an upcoming patch to re-enable compact-unwind support in JITLink.
Rename MachOCompactUnwindInfoSectionName to MachOCompactUnwindSectionName.
Background:
There are two related sections used for compact-unwind info processing:
__LD,__compact_unwind -- the input table stored in relocatable object formats,
and __TEXT,__unwind_info -- the compressed table produced by the linker and
consumed by libunwind. To keep the distinction clear we'll use *CompactUnwind*
for names that refer to the __LD,__compact_unwind input tables and *UnwindInfo*
for names that refer to the __TEXT,__unwind_info output tables. Dropping 'Info'
from the variable above clarifies which section it refers to.
The getMachODefaultTextSection and getMachODefaultRWDataSection functions
return the "__TEXT,__text" and "__DATA,__data" sections respectively, creating
empty sections if the default sections are not already present in the graph.
These functions can be used by utilities that want to add code or data to these
standard sections (e.g. these functions can be used to supply the section
argument to the createAnonymousPointerJumpStub and
createPointerJumpStubBlock functions in the various targets).
