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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 committed by Antoni Boucher
parent 4c0a6e610e
commit dd930a3b5c
2 changed files with 4 additions and 11 deletions
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11
src/allocator.rs
View File

@ -9,7 +9,7 @@ use rustc_span::symbol::sym;
use crate::GccContext;
pub(crate) unsafe fn codegen(tcx: TyCtxt<'_>, mods: &mut GccContext, _module_name: &str, kind: AllocatorKind, has_alloc_error_handler: bool) {
pub(crate) unsafe fn codegen(tcx: TyCtxt<'_>, mods: &mut GccContext, _module_name: &str, kind: AllocatorKind, alloc_error_handler_kind: AllocatorKind) {
let context = &mods.context;
let usize =
match tcx.sess.target.pointer_width {
@ -99,14 +99,7 @@ pub(crate) unsafe fn codegen(tcx: TyCtxt<'_>, mods: &mut GccContext, _module_nam
func.add_attribute(FnAttribute::Visibility(gccjit::Visibility::Hidden));
}
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 args: Vec<_> = types.iter().enumerate()
.map(|(index, typ)| context.new_parameter(None, *typ, &format!("param{}", index)))
.collect();

4
src/lib.rs
View File

@ -155,11 +155,11 @@ impl CodegenBackend for GccCodegenBackend {
}
impl ExtraBackendMethods for GccCodegenBackend {
fn codegen_allocator<'tcx>(&self, tcx: TyCtxt<'tcx>, module_name: &str, kind: AllocatorKind, has_alloc_error_handler: bool) -> Self::Module {
fn codegen_allocator<'tcx>(&self, tcx: TyCtxt<'tcx>, module_name: &str, kind: AllocatorKind, alloc_error_handler_kind: AllocatorKind) -> Self::Module {
let mut mods = GccContext {
context: Context::default(),
};
unsafe { allocator::codegen(tcx, &mut mods, module_name, kind, has_alloc_error_handler); }
unsafe { allocator::codegen(tcx, &mut mods, module_name, kind, alloc_error_handler_kind); }
mods
}