bjoernager/rust
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Rewrite implementation of #[alloc_error_handler]

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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).
This commit is contained in:
Amanieu d'Antras 2022-10-14 02:24:58 +01:00
parent 2afca78a0b
commit 56074b5231
40 changed files with 441 additions and 166 deletions
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5
compiler/rustc_codegen_llvm/src/allocator.rs
View file

@ -15,7 +15,7 @@ pub(crate) unsafe fn codegen(
module_llvm: &mut ModuleLlvm,
module_name: &str,
kind: AllocatorKind,
has_alloc_error_handler: bool,
alloc_error_handler_kind: AllocatorKind,
) {
let llcx = &*module_llvm.llcx;
let llmod = module_llvm.llmod();
@ -117,8 +117,7 @@ pub(crate) unsafe fn codegen(
attributes::apply_to_llfn(llfn, llvm::AttributePlace::Function, &[uwtable]);
}
let kind = if has_alloc_error_handler { AllocatorKind::Global } else { AllocatorKind::Default };
let callee = kind.fn_name(sym::oom);
let callee = alloc_error_handler_kind.fn_name(sym::oom);
let callee = llvm::LLVMRustGetOrInsertFunction(llmod, callee.as_ptr().cast(), callee.len(), ty);
// -> ! DIFlagNoReturn
attributes::apply_to_llfn(callee, llvm::AttributePlace::Function, &[no_return]);

4
compiler/rustc_codegen_llvm/src/lib.rs
View file

@ -108,11 +108,11 @@ impl ExtraBackendMethods for LlvmCodegenBackend {
tcx: TyCtxt<'tcx>,
module_name: &str,
kind: AllocatorKind,
has_alloc_error_handler: bool,
alloc_error_handler_kind: AllocatorKind,
) -> ModuleLlvm {
let mut module_llvm = ModuleLlvm::new_metadata(tcx, module_name);
unsafe {
allocator::codegen(tcx, &mut module_llvm, module_name, kind, has_alloc_error_handler);
allocator::codegen(tcx, &mut module_llvm, module_name, kind, alloc_error_handler_kind);
}
module_llvm
}