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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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2
compiler/rustc_builtin_macros/src/lib.rs
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@ -25,6 +25,7 @@ use rustc_expand::base::{MacroExpanderFn, ResolverExpand, SyntaxExtensionKind};
use rustc_expand::proc_macro::BangProcMacro;
use rustc_span::symbol::sym;
mod alloc_error_handler;
mod assert;
mod cfg;
mod cfg_accessible;
@ -94,6 +95,7 @@ pub fn register_builtin_macros(resolver: &mut dyn ResolverExpand) {
}
register_attr! {
alloc_error_handler: alloc_error_handler::expand,
bench: test::expand_bench,
cfg_accessible: cfg_accessible::Expander,
cfg_eval: cfg_eval::expand,