There are some issues in `llvm-libgcc` before this patch:
Commit c5a20b5182 ([llvm-libgcc] initial
commit)
uses `$<TARGET_OBJECTS:unwind_static>` to get libunwind objects, which
is empty.
The built library is actually a shared version of libclang_rt.builtins.
When configuring with `llvm/CMakeLists.txt`, target `llvm-libgcc`
requires a
corresponding target in `llvm-libgcc/CMakeLists.txt`.
Per target installation is not handled by `llvm-libgcc`, which is not
consistent
with `libunwind`.
This patch fixes those issues by:
Reusing target `unwind_shared` in `libunwind`, linking
`compiler-rt.builtins`
objects into it, and applying version script.
Adding target `llvm-libgcc`, creating symlinks, and utilizing cmake's
dependency
and component mechanism to ensure link targets will be built and
installed along
with symlinks.
Mimicking `libunwind` to handle per target installation.
It is quite hard to set necessary options without further modifying the
order of
runtime projects in `runtimes/CMakeLists.txt`. So though this patch
reveals the
possibility of co-existence of `llvm-libgcc` and
`compiler-rt`/`libunwind` in
`LLVM_ENABLE_RUNTIMES`, we still inhibit it to minimize influence on
other
projects, considering that `llvm-libgcc` is only intended for toolchain
vendors,
and not for casual use.
These symbols are used in the absence of PT_GNU_EH_FRAME, for ld
--no-eh-frame-hdr (gcc -static default).
libunwind defines these empty functions when
`defined(_LIBUNWIND_BUILD_ZERO_COST_APIS) && defined(_LIBUNWIND_SUPPORT_DWARF_UNWIND) && defined(_LIBUNWIND_SUPPORT_FRAME_APIS)`.
They should be perceived as Mac OS X workarounds.
For Linux, GCC crtbeginT.o (for -static) and clang_rt.crtbegin.o contain
weak references to `__{,de}register_frame_info`. Dynamically linked
executables will either not reference `__{,de}register_frame_info` (using
libgcc) or reference them as weak symbols (using compiler-rt).
Therefore, not defining these symbols is backward compatible.
Reviewed By: phosek
Differential Revision: https://reviews.llvm.org/D158241
This reverts commit d763c6e5e2.
Adds the patch by @hans from
https://github.com/llvm/llvm-project/issues/62719
This patch fixes the Windows build.
d763c6e5e2 reverted the reviews
D144509 [CMake] Bumps minimum version to 3.20.0.
This partly undoes D137724.
This change has been discussed on discourse
https://discourse.llvm.org/t/rfc-upgrading-llvms-minimum-required-cmake-version/66193
Note this does not remove work-arounds for older CMake versions, that
will be done in followup patches.
D150532 [OpenMP] Compile assembly files as ASM, not C
Since CMake 3.20, CMake explicitly passes "-x c" (or equivalent)
when compiling a file which has been set as having the language
C. This behaviour change only takes place if "cmake_minimum_required"
is set to 3.20 or newer, or if the policy CMP0119 is set to new.
Attempting to compile assembly files with "-x c" fails, however
this is workarounded in many cases, as OpenMP overrides this with
"-x assembler-with-cpp", however this is only added for non-Windows
targets.
Thus, after increasing cmake_minimum_required to 3.20, this breaks
compiling the GNU assembly for Windows targets; the GNU assembly is
used for ARM and AArch64 Windows targets when building with Clang.
This patch unbreaks that.
D150688 [cmake] Set CMP0091 to fix Windows builds after the cmake_minimum_required bump
The build uses other mechanism to select the runtime.
Fixes#62719
Reviewed By: #libc, Mordante
Differential Revision: https://reviews.llvm.org/D151344
This is an ongoing series of commits that are reformatting our
Python code. This catches the last of the python files to
reformat. Since they where so few I bunched them together.
Reformatting is done with `black`.
If you end up having problems merging this commit because you
have made changes to a python file, the best way to handle that
is to run git checkout --ours <yourfile> and then reformat it
with black.
If you run into any problems, post to discourse about it and
we will try to help.
RFC Thread below:
https://discourse.llvm.org/t/rfc-document-and-standardize-python-code-style
Reviewed By: jhenderson, #libc, Mordante, sivachandra
Differential Revision: https://reviews.llvm.org/D150784
This reverts commit 65429b9af6.
Broke several projects, see https://reviews.llvm.org/D144509#4347562 onwards.
Also reverts follow-up commit "[OpenMP] Compile assembly files as ASM, not C"
This reverts commit 4072c8aee4.
Also reverts fix attempt "[cmake] Set CMP0091 to fix Windows builds after the cmake_minimum_required bump"
This reverts commit 7d47dac5f8.
Some build bots have not been updated to the new minimal CMake version.
Reverting for now and ping the buildbot owners.
This reverts commit 44c6b905f8.
This partly undoes D137724.
This change has been discussed on discourse
https://discourse.llvm.org/t/rfc-upgrading-llvms-minimum-required-cmake-version/66193
Note this does not remove work-arounds for older CMake versions, that
will be done in followup patches.
Reviewed By: mehdi_amini, MaskRay, ChuanqiXu, to268, thieta, tschuett, phosek, #libunwind, #libc_vendors, #libc, #libc_abi, sivachandra, philnik, zibi
Differential Revision: https://reviews.llvm.org/D144509
Note: the term "libgcc" refers to the all of `libgcc.a`, `libgcc_eh.a`,
and `libgcc_s.so`.
Enabling libunwind as a replacement for libgcc on Linux has proven to be
challenging since libgcc_s.so is a required dependency in the [Linux
standard base][5]. Some software is transitively dependent on libgcc
because glibc makes hardcoded calls to functions in libgcc_s. For example,
the function `__GI___backtrace` eventually makes its way to a [hardcoded
dlopen to libgcc_s' _Unwind_Backtrace][1]. Since libgcc_{eh.a,s.so} and
libunwind have the same ABI, but different implementations, the two
libraries end up [cross-talking, which ultimately results in a
segfault][2].
To solve this problem, libunwind needs to build a “libgcc”. That is, link
the necessary functions from compiler-rt and libunwind into an archive
and shared object that advertise themselves as `libgcc.a`, `libgcc_eh.a`,
and `libgcc_s.so`, so that glibc’s baked calls are diverted to the
correct objects in memory. Fortunately for us, compiler-rt and libunwind
use the same ABI as the libgcc family, so the problem is solvable at the
llvm-project configuration level: no program source needs to be edited.
Thus, the end result is for a user to configure their LLVM build with a
flag that indicates they want to archive compiler-rt/unwind as libgcc.
We achieve this by compiling libunwind with all the symbols necessary
for compiler-rt to emulate the libgcc family, and then generate symlinks
named for our "libgcc" that point to their corresponding libunwind
counterparts.
We alternatively considered patching glibc so that the source doesn't
directly refer to libgcc, but rather _defaults_ to libgcc, so that a
system preferring compiler-rt/libunwind can point to these libraries
at the config stage instead. Even if we modified the Linux standard
base, this alternative won't work because binaries that are built using
libgcc will still end up having crosstalk between the differing
implementations.
This problem has been solved in this manner for [FreeBSD][3], and this
CL has been tested against [Chrome OS][4].
[1]: https://github.com/bminor/glibc/blob/master/sysdeps/arm/backtrace.c#L68
[2]: https://bugs.chromium.org/p/chromium/issues/detail?id=1162190#c16
[3]: https://github.com/freebsd/freebsd-src/tree/main/lib/libgcc_s
[4]: https://chromium-review.googlesource.com/c/chromiumos/overlays/chromiumos-overlay/+/2945947
[5]: https://refspecs.linuxbase.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/libgcc-s.html
Differential Revision: https://reviews.llvm.org/D108416
