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_passes/src/dead.rs
View file

@ -470,11 +470,6 @@ fn has_allow_dead_code_or_lang_attr_helper(
return true;
}
// (To be) stable attribute for #[lang = "oom"]
if tcx.sess.contains_name(attrs, sym::alloc_error_handler) {
return true;
}
let def_id = tcx.hir().local_def_id(id);
if tcx.def_kind(def_id).has_codegen_attrs() {
let cg_attrs = tcx.codegen_fn_attrs(def_id);

8
compiler/rustc_passes/src/errors.rs
View file

@ -701,14 +701,6 @@ pub struct UnknownExternLangItem {
#[diag(passes_missing_panic_handler)]
pub struct MissingPanicHandler;
#[derive(Diagnostic)]
#[diag(passes_alloc_func_required)]
pub struct AllocFuncRequired;
#[derive(Diagnostic)]
#[diag(passes_missing_alloc_error_handler)]
pub struct MissingAllocErrorHandler;
#[derive(Diagnostic)]
#[diag(passes_missing_lang_item)]
#[note]

10
compiler/rustc_passes/src/weak_lang_items.rs
View file

@ -7,10 +7,7 @@ use rustc_middle::middle::lang_items::required;
use rustc_middle::ty::TyCtxt;
use rustc_session::config::CrateType;
use crate::errors::{
AllocFuncRequired, MissingAllocErrorHandler, MissingLangItem, MissingPanicHandler,
UnknownExternLangItem,
};
use crate::errors::{MissingLangItem, MissingPanicHandler, UnknownExternLangItem};
/// Checks the crate for usage of weak lang items, returning a vector of all the
/// language items required by this crate, but not defined yet.
@ -69,11 +66,6 @@ fn verify<'tcx>(tcx: TyCtxt<'tcx>, items: &lang_items::LanguageItems) {
if missing.contains(&item) && required(tcx, item) && items.get(item).is_none() {
if item == LangItem::PanicImpl {
tcx.sess.emit_err(MissingPanicHandler);
} else if item == LangItem::Oom {
if !tcx.features().default_alloc_error_handler {
tcx.sess.emit_err(AllocFuncRequired);
tcx.sess.emit_note(MissingAllocErrorHandler);
}
} else {
tcx.sess.emit_err(MissingLangItem { name: item.name() });
}