Remove support for legacy PM
This removes support for optimizing with LLVM's legacy pass manager, as well as the unstable `-Znew-llvm-pass-manager` option. We have been defaulting to the new PM since LLVM 13 (except for s390x that waited for 14), and LLVM 15 removed support altogether. The only place we still use the legacy PM is for writing the output file, just like `llc` does.
cc #74705
r? ``@nikic``
Update the minimum external LLVM to 13
With this change, we'll have stable support for LLVM 13 through 15 (pending release).
For reference, the previous increase to LLVM 12 was #90175.
r? `@nagisa`
This obviates the patch that teaches LLVM internals about
_rust_{re,de}alloc functions by putting annotations directly in the IR
for the optimizer.
The sole test change is required to anchor FileCheck to the body of the
`box_uninitialized` method, so it doesn't see the `allocalign` on
`__rust_alloc` and get mad about the string `alloca` showing up. Since I
was there anyway, I added some checks on the attributes to prove the
right attributes got set.
While we're here, we also emit allocator attributes on
__rust_alloc_zeroed. This should allow LLVM to perform more
optimizations for zeroed blocks, and probably fixes#90032. [This
comment](https://github.com/rust-lang/rust/issues/24194#issuecomment-308791157)
mentions "weird UB-like behaviour with bitvec iterators in
rustc_data_structures" so we may need to back this change out if things
go wrong.
The new test cases require LLVM 15, so we copy them into LLVM
14-supporting versions, which we can delete when we drop LLVM 14.
Remove branch target prologues from `#[naked] fn`
This patch hacks around rust-lang/rust#98768 for now via injecting appropriate attributes into the LLVMIR we emit for naked functions. I intend to pursue this upstream so that these attributes can be removed in general, but it's slow going wading through C++ for me.
This adds the typeid and `vcall_visibility` metadata to vtables when the
-Cvirtual-function-elimination flag is set.
The typeid is generated in the same way as for the
`llvm.type.checked.load` intrinsic from the trait_ref.
The offset that is added to the typeid is always 0. This is because LLVM
assumes that vtables are constructed according to the definition in the
Itanium ABI. This includes an "address point" of the vtable. In C++ this
is the offset in the vtable where information for RTTI is placed. Since
there is no RTTI information in Rust's vtables, this "address point" is
always 0. This "address point" in combination with the offset passed to
the `llvm.type.checked.load` intrinsic determines the final function
that should be loaded from the vtable in the
`WholeProgramDevirtualization` pass in LLVM. That's why the
`llvm.type.checked.load` intrinsics are generated with the typeid of the
trait, rather than with that of the function that is called. This
matches what `clang` does for C++.
The vcall_visibility metadata depends on three factors:
1. LTO level: Currently this is always fat LTO, because LLVM only
supports this optimization with fat LTO.
2. Visibility of the trait: If the trait is publicly visible, VFE
can only act on its vtables after linking.
3. Number of CGUs: if there is more than one CGU, also vtables with
restricted visibility could be seen outside of the CGU, so VFE can
only act on them after linking.
To reflect this, there are three visibility levels: Public, LinkageUnit,
and TranslationUnit.
To apply the optimization the `Virtual Function Elim` module flag has to
be set. To apply this optimization post-link the `LTOPostLink` module
flag has to be set.
In https://reviews.llvm.org/D125556 upstream changed sext() and zext()
to allow some no-op cases, which previously required use of the *OrSelf()
methods, which I assume is what was going on here. The *OrSelf() methods
got removed in https://reviews.llvm.org/D125559 after two weeks of
deprecation because they came with some bonus (probably-undesired)
behavior. Since the behavior of sext() and zext() changed slightly, I
kept the old *OrSelf() calls in LLVM 14 and earlier, and only use the
new version in LLVM 15.
r? @nikic
This new enum entry was introduced in https://reviews.llvm.org/D122268,
and if I'm reading correctly there's no case where we'd ever encounter
it in our uses of LLVM. To preserve the ability to compile this file
with -Werror -Wswitch we add an explicit case for this entry.
Remove LLVM attribute removal
This was necessary before, because `declare_raw_fn` would always apply
the default optimization attributes to every declared function.
Then `attributes::from_fn_attrs` would have to remove the default
attributes in the case of, e.g. `#[optimize(speed)]` in a `-Os` build.
(see [`src/test/codegen/optimize-attr-1.rs`](03a8cc7df1/src/test/codegen/optimize-attr-1.rs (L33)))
However, every relevant callsite of `declare_raw_fn` (i.e. where we
actually generate code for the function, and not e.g. a call to an
intrinsic, where optimization attributes don't [?] matter)
calls `from_fn_attrs`, so we can remove the attribute setting
from `declare_raw_fn`, and rely on `from_fn_attrs` to apply the correct
attributes all at once.
r? `@ghost` (blocked on #94221)
`@rustbot` label S-blocked
This was necessary before, because `declare_raw_fn` would always apply
the default optimization attributes to every declared function,
and then `attributes::from_fn_attrs` would have to remove the default
attributes in the case of, e.g. `#[optimize(speed)]` in a `-Os` build.
However, every relevant callsite of `declare_raw_fn` (i.e. where we
actually generate code for the function, and not e.g. a call to an
intrinsic, where optimization attributes don't [?] matter)
calls `from_fn_attrs`, so we can simply remove the attribute setting
from `declare_raw_fn`, and rely on `from_fn_attrs` to apply the correct
attributes all at once.
Add MemTagSanitizer Support
Add support for the LLVM [MemTagSanitizer](https://llvm.org/docs/MemTagSanitizer.html).
On hardware which supports it (see caveats below), the MemTagSanitizer can catch bugs similar to AddressSanitizer and HardwareAddressSanitizer, but with lower overhead.
On a tag mismatch, a SIGSEGV is signaled with code SEGV_MTESERR / SEGV_MTEAERR.
# Usage
`-Zsanitizer=memtag -C target-feature="+mte"`
# Comments/Caveats
* MemTagSanitizer is only supported on AArch64 targets with hardware support
* Requires `-C target-feature="+mte"`
* LLVM MemTagSanitizer currently only performs stack tagging.
# TODO
* Tests
* Example
In https://reviews.llvm.org/D114543 the uwtable attribute gained a flag
so that we can ask for sync uwtables instead of async, as the former are
much cheaper. The default is async, so that's what I've done here, but I
left a TODO that we might be able to do better.
While in here I went ahead and dropped support for removing uwtable
attributes in rustc: we never did it, so I didn't write the extra C++
bridge code to make it work. Maybe I should have done the same thing
with the `sync|async` parameter but we'll see.
This doesn't handle `char` because it's a bit awkward to distinguish it
from u32 at this point in codegen.
Note that for some types (like `&Struct` and `&mut Struct`),
we already apply `dereferenceable`, which implies `noundef`,
so the IR does not change.
This agrees with Clang, and avoids an error when using LTO with mixed
C/Rust. LLVM considers different behaviour flags to be a mismatch,
even when the flag value itself is the same.
This also makes the flag setting explicit for all uses of
LLVMRustAddModuleFlag.
RustWrapper: adapt to new AttributeMask API
Upstream LLVM change 9290ccc3c1a1 migrated attribute removal to use
AttributeMask instead of AttrBuilder, so we need to follow suit here.
r? ``@nagisa`` cc ``@nikic``
No functional changes intended.
The LLVM commit
ec501f15a8
removed the signed version of `createExpression`. This adapts the Rust
LLVM wrappers accordingly.
Emit LLVM optimization remarks when enabled with `-Cremark`
The default diagnostic handler considers all remarks to be disabled by
default unless configured otherwise through LLVM internal flags:
`-pass-remarks`, `-pass-remarks-missed`, and `-pass-remarks-analysis`.
This behaviour makes `-Cremark` ineffective on its own.
Fix this by configuring a custom diagnostic handler that enables
optimization remarks based on the value of `-Cremark` option. With
`-Cremark=all` enabling all remarks.
Fixes#90924.
r? `@nikic`
LLVM has built-in heuristics for adding stack canaries to functions. These
heuristics can be selected with LLVM function attributes. This patch adds a
rustc option `-Z stack-protector={none,basic,strong,all}` which controls the use
of these attributes. This gives rustc the same stack smash protection support as
clang offers through options `-fno-stack-protector`, `-fstack-protector`,
`-fstack-protector-strong`, and `-fstack-protector-all`. The protection this can
offer is demonstrated in test/ui/abi/stack-protector.rs. This fills a gap in the
current list of rustc exploit
mitigations (https://doc.rust-lang.org/rustc/exploit-mitigations.html),
originally discussed in #15179.
Stack smash protection adds runtime overhead and is therefore still off by
default, but now users have the option to trade performance for security as they
see fit. An example use case is adding Rust code in an existing C/C++ code base
compiled with stack smash protection. Without the ability to add stack smash
protection to the Rust code, the code base artifacts could be exploitable in
ways not possible if the code base remained pure C/C++.
Stack smash protection support is present in LLVM for almost all the current
tier 1/tier 2 targets: see
test/assembly/stack-protector/stack-protector-target-support.rs. The one
exception is nvptx64-nvidia-cuda. This patch follows clang's example, and adds a
warning message printed if stack smash protection is used with this target (see
test/ui/stack-protector/warn-stack-protector-unsupported.rs). Support for tier 3
targets has not been checked.
Since the heuristics are applied at the LLVM level, the heuristics are expected
to add stack smash protection to a fraction of functions comparable to C/C++.
Some experiments demonstrating how Rust code is affected by the different
heuristics can be found in
test/assembly/stack-protector/stack-protector-heuristics-effect.rs. There is
potential for better heuristics using Rust-specific safety information. For
example it might be reasonable to skip stack smash protection in functions which
transitively only use safe Rust code, or which uses only a subset of functions
the user declares safe (such as anything under `std.*`). Such alternative
heuristics could be added at a later point.
LLVM also offers a "safestack" sanitizer as an alternative way to guard against
stack smashing (see #26612). This could possibly also be included as a
stack-protection heuristic. An alternative is to add it as a sanitizer (#39699).
This is what clang does: safestack is exposed with option
`-fsanitize=safe-stack`.
The options are only supported by the LLVM backend, but as with other codegen
options it is visible in the main codegen option help menu. The heuristic names
"basic", "strong", and "all" are hopefully sufficiently generic to be usable in
other backends as well.
Reviewed-by: Nikita Popov <nikic@php.net>
Extra commits during review:
- [address-review] make the stack-protector option unstable
- [address-review] reduce detail level of stack-protector option help text
- [address-review] correct grammar in comment
- [address-review] use compiler flag to avoid merging functions in test
- [address-review] specify min LLVM version in fortanix stack-protector test
Only for Fortanix test, since this target specifically requests the
`--x86-experimental-lvi-inline-asm-hardening` flag.
- [address-review] specify required LLVM components in stack-protector tests
- move stack protector option enum closer to other similar option enums
- rustc_interface/tests: sort debug option list in tracking hash test
- add an explicit `none` stack-protector option
Revert "set LLVM requirements for all stack protector support test revisions"
This reverts commit a49b74f92a4e7d701d6f6cf63d207a8aff2e0f68.
`Module::getOrInsertGlobal` returns a `Constant*`, which is a super
class of `GlobalVariable`, but if the given type doesn't match an
existing declaration, it returns a bitcast of that global instead.
This causes UB when we pass that to `LLVMGetVisibility` which
unconditionally casts the opaque argument to a `GlobalValue*`.
Instead, we can do our own get-or-insert without worrying whether
existing types match exactly. It's not relevant when we're just trying
to get/set the linkage and visibility, and if types are needed we can
bitcast or error nicely from `rustc_codegen_llvm` instead.
