`.debug_pubnames` and `.debug_pubtypes` are poorly designed and people
seldom use them. However, they take a considerable portion of size in
the final binary. This tells LLVM stop emitting those sections on
DWARFv4 or lower. DWARFv5 use `.debug_names` which is more concise
in size and performant for name lookup.
This is intended to be used for Linux kernel RETHUNK builds.
With this commit (optionally backported to Rust 1.73.0), plus a
patched Linux kernel to pass the flag, I get a RETHUNK build with
Rust enabled that is `objtool`-warning-free and is able to boot in
QEMU and load a sample Rust kernel module.
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
llvm-wrapper: Pass newly added param to DIBuilder::createStaticMemberType()
This was added in https://github.com/llvm/llvm-project/pull/72234.
DW_TAG_member was the implicit default before.
The LLVM change is quite sinister since due to weakly typed ints and default params, this was still successfully compiling against LLVM but was passing the wrong parameters.
LLVM already supports emitting compressed debuginfo. In debuginfo=full
builds, the debug section is often a large amount of data, and it
typically compresses very well (3x is not unreasonable.) We add a new
knob to allow debuginfo to be compressed when the matching LLVM
functionality is present. Like clang, if a known-but-disabled
compression mechanism is requested, we disable compression and emit
uncompressed debuginfo sections.
The API is different enough on older LLVMs we just pretend the support
is missing on LLVM older than 16.
CFI: Fix error compiling core with LLVM CFI enabled
Fix#90546 by filtering out global value function pointer types from the type tests, and adding the LowerTypeTests pass to the rustc LTO optimization pipelines.
Fix#90546 by filtering out global value function pointer types from the
type tests, and adding the LowerTypeTests pass to the rustc LTO
optimization pipelines.
Filter out short-lived LLVM diagnostics before they reach the rustc handler
During profiling I saw remark passes being unconditionally enabled: for example `Machine Optimization Remark Emitter`.
The diagnostic remarks enabled by default are [from missed optimizations and opt analyses](https://github.com/rust-lang/rust/pull/113339#discussion_r1259480303). They are created by LLVM, passed to the diagnostic handler on the C++ side, emitted to rust, where they are unpacked, C++ strings are converted to rust, etc.
Then they are discarded in the vast majority of the time (i.e. unless some kind of `-Cremark` has enabled some of these passes' output to be printed).
These unneeded allocations are very short-lived, basically only lasting between the LLVM pass emitting them and the rust handler where they are discarded. So it doesn't hugely impact max-rss, and is only a slight reduction in instruction count (cachegrind reports a reduction between 0.3% and 0.5%) _on linux_. It's possible that targets without `jemalloc` or with a worse allocator, may optimize these less.
It is however significant in the aggregate, looking at the total number of allocated bytes:
- it's the biggest source of allocations according to dhat, on the benchmarks I've tried e.g. `syn` or `cargo`
- allocations on `syn` are reduced by 440MB, 17% (from 2440722647 bytes total, to 2030461328 bytes)
- allocations on `cargo` are reduced by 6.6GB, 19% (from 35371886402 bytes total, to 28723987743 bytes)
Some of these diagnostics objects [are allocated in LLVM](https://github.com/rust-lang/rust/pull/113339#discussion_r1252387484) *before* they're emitted to our diagnostic handler, where they'll be filtered out. So we could remove those in the future, but that will require changing a few LLVM call-sites upstream, so I left a FIXME.
this will eliminate many short-lived allocations (e.g. 20% of the memory used
building cargo) when unpacking the diagnostic and converting its various
C++ strings into rust strings, just to be filtered out most of the time.
LLVM has a neat [statistics] feature that tracks how often optimizations kick
in. It's very handy for optimization work. Since we expose the LLVM pass
timings, I thought it made sense to expose the LLVM statistics too.
[statistics]: https://llvm.org/docs/ProgrammersManual.html#the-statistic-class-stats-option
Adds support for LLVM [SafeStack] which provides backward edge control
flow protection by separating the stack into two parts: data which is
only accessed in provable safe ways is allocated on the normal stack
(the "safe stack") and all other data is placed in a separate allocation
(the "unsafe stack").
SafeStack support is enabled by passing `-Zsanitizer=safestack`.
[SafeStack]: https://clang.llvm.org/docs/SafeStack.html
When we're adding a method to a type DIE, we only want a DW_AT_declaration
there, because LLVM LTO can't unify type definitions when a child DIE is a
full subprogram definition. Now the subprogram definition gets added at the
CU level with a specification link back to the abstract declaration.
`-Cdebuginfo=1` was never line tables only and
can't be due to backwards compatibility issues.
This was clarified and an option for line tables only
was added. Additionally an option for line info
directives only was added, which is well needed for
some targets. The debug info options should now
behave the same as clang's debug info options.
llvm-wrapper: adapt for LLVM API change
No functional changes intended.
The LLVM commit e6b02214c6 added `TargetExtTyID` to the `TypeID` enum. This adapts `RustWrapper` accordingly.
Add LLVM KCFI support to the Rust compiler
This PR adds LLVM Kernel Control Flow Integrity (KCFI) support to the Rust compiler. It initially provides forward-edge control flow protection for operating systems kernels for Rust-compiled code only by aggregating function pointers in groups identified by their return and parameter types. (See llvm/llvm-project@cff5bef.)
Forward-edge control flow protection for C or C++ and Rust -compiled code "mixed binaries" (i.e., for when C or C++ and Rust -compiled code share the same virtual address space) will be provided in later work as part of this project by identifying C char and integer type uses at the time types are encoded (see Type metadata in the design document in the tracking issue #89653).
LLVM KCFI can be enabled with -Zsanitizer=kcfi.
Thank you again, `@bjorn3,` `@eddyb,` `@nagisa,` and `@ojeda,` for all the help!
This commit adds LLVM Kernel Control Flow Integrity (KCFI) support to
the Rust compiler. It initially provides forward-edge control flow
protection for operating systems kernels for Rust-compiled code only by
aggregating function pointers in groups identified by their return and
parameter types. (See llvm/llvm-project@cff5bef.)
Forward-edge control flow protection for C or C++ and Rust -compiled
code "mixed binaries" (i.e., for when C or C++ and Rust -compiled code
share the same virtual address space) will be provided in later work as
part of this project by identifying C char and integer type uses at the
time types are encoded (see Type metadata in the design document in the
tracking issue #89653).
LLVM KCFI can be enabled with -Zsanitizer=kcfi.
Co-authored-by: bjorn3 <17426603+bjorn3@users.noreply.github.com>
Pass 128-bit C-style enum enumerator values to LLVM
Pass the full 128 bits of C-style enum enumerators through to LLVM. This means that debuginfo for C-style repr128 enums is now emitted correctly for DWARF platforms (as compared to not being correctly emitted on any platform).
Tracking issue: #56071
