There are major questions remaining about the reentrancy that this
allows. It doesn't have any users on github outside of a single project
that uses it in a panic=abort project to show backtraces. It
can still be emulated through #[alloc_error_handler] or
set_alloc_error_hook depending on if you use the standard library or
not. And finally it makes it harder to do various improvements to the
allocator shim.
In the future this should make it easier to use weak symbols for the
allocator shim on platforms that properly support weak symbols. And it
would allow reusing the allocator shim code for handling default
implementations of the upcoming externally implementable items feature
on platforms that don't properly support weak symbols.
Currently it is possible to avoid linking the allocator shim when
__rust_no_alloc_shim_is_unstable_v2 is defined when linking rlibs
directly as some build systems need. However this requires liballoc to
be compiled with --cfg no_global_oom_handling, which places huge
restrictions on what functions you can call and makes it impossible to
use libstd. Or alternatively you have to define
__rust_alloc_error_handler and (when using libstd)
__rust_alloc_error_handler_should_panic
using #[rustc_std_internal_symbol]. With this commit you can either use
libstd and define __rust_alloc_error_handler_should_panic or not use
libstd and use #[alloc_error_handler] instead. Both options are still
unstable though.
Eventually the alloc_error_handler may either be removed entirely
(though the PR for that has been stale for years now) or we may start
using weak symbols for it instead. For the latter case this commit is a
prerequisite anyway.
This emits the same attributes we place on allocator declarations
(and allocator definitions using `#[global_allocator]`) on the
definitions in the allocator shim as well, making sure that the
attributes are not lost if the allocator shim participates in LTO.
Use llfn_attrs_from_instance() to generate the attributes for the
allocator shim. This ensures that we generate all the usual
attributes (and don't get to find out one-by-one that a certain
attribute is important for a certain target). Additionally this
will enable emitting the allocator-specific attributes (not
included here).
This change is quite awkward because the allocator shim uses
SimpleCx, while llfn_attrs_from_instance uses CodegenCx. I've
switched it to use SimpleCx plus tcx/sess arguments where necessary.
If there's a simpler way to do this, I'd love to know about it...
Extract a create_wrapper_function for use in allocator shim writing
This deduplicates some logic and makes it easier to follow what wrappers are produced. In the future it may allow moving the code to determine which wrappers to create to cg_ssa.
This deduplicates some logic and makes it easier to follow what wrappers
are produced. In the future it may allow moving the code to determine
which wrappers to create to cg_ssa.
You will need to add the following as replacement for the old __rust_*
definitions when not using the alloc shim.
#[no_mangle]
static __rust_no_alloc_shim_is_unstable: u8 = 0;
This makes it possible to use liballoc/libstd in combination with
`--emit obj` if you use `#[global_allocator]`. Making it work for the
default libstd allocator would require weak functions, which are not
well supported on all systems.
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>
The new implementation doesn't use weak lang items and instead changes
`#[alloc_error_handler]` to an attribute macro just like
`#[global_allocator]`.
The attribute will generate the `__rg_oom` function which is called by
the compiler-generated `__rust_alloc_error_handler`. If no `__rg_oom`
function is defined in any crate then the compiler shim will call
`__rdl_oom` in the alloc crate which will simply panic.
This also fixes link errors with `-C link-dead-code` with
`default_alloc_error_handler`: `__rg_oom` was previously defined in the
alloc crate and would attempt to reference the `oom` lang item, even if
it didn't exist. This worked as long as `__rg_oom` was excluded from
linking since it was not called.
This is a prerequisite for the stabilization of
`default_alloc_error_handler` (#102318).
Implement -Z oom=panic
This PR removes the `#[rustc_allocator_nounwind]` attribute on `alloc_error_handler` which allows it to unwind with a panic instead of always aborting. This is then used to implement `-Z oom=panic` as per RFC 2116 (tracking issue #43596).
Perf and binary size tests show negligible impact.
This commit
- changes names to use di_node instead of metadata
- uniformly names all functions that build new debuginfo nodes build_xyz_di_node
- renames CrateDebugContext to CodegenUnitDebugContext (which is more accurate)
- moves TypeMap and functions that work directly work with it to a new type_map module
- moves and reimplements enum related builder functions to a new enums module
- splits enum debuginfo building for the native and cpp-like cases, since they are mostly separate
- uses SmallVec instead of Vec in many places
- removes the old infrastructure for dealing with recursion cycles (create_and_register_recursive_type_forward_declaration(), RecursiveTypeDescription, set_members_of_composite_type(), MemberDescription, MemberDescriptionFactory, prepare_xyz_metadata(), etc)
- adds type_map::build_type_with_children() as a replacement for dealing with recursion cycles
- adds many (doc-)comments explaining what's going on
- changes cpp-like naming for C-Style enums so they don't get a enum$<...> name (because the NatVis visualizer does not apply to them)
- fixes detection of what is a C-style enum because some enums where classified as C-style even though they have fields
- changes the position of discriminant debuginfo node so it is consistently nested inside the top-level union instead of, sometimes, next to it
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.
Issue Details:
In some cases it is necessary to generate an "allocator shim" to forward various Rust allocation functions (e.g., `__rust_alloc`) to an underlying function (e.g., `malloc`). However, since this allocator shim is a manually created LLVM module it is not processed via the normal module processing code and so no debug info is generated for it (if debugging info is enabled).
Fix Details:
* Modify the `debuginfo` code to allow creating debug info for a module without a `CodegenCx` (since it is difficult, and expensive, to create one just to emit some debug info).
* After creating the allocator shim add in basic debug info.
Rather than relying on `getPointerElementType()` from LLVM function
pointers, we now pass the function type explicitly when building `call`
or `invoke` instructions.
bjorn3