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Auto merge of #86844 - bjorn3:global_alloc_improvements, r=pnkfelix

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Support #[global_allocator] without the allocator shim

This makes it possible to use liballoc/libstd in combination with `--emit obj` if you use `#[global_allocator]`. This is what rust-for-linux uses right now and systemd may use in the future. Currently they have to depend on the exact implementation of the allocator shim to create one themself as `--emit obj` doesn't create an allocator shim.

Note that currently the allocator shim also defines the oom error handler, which is normally required too. Once `#![feature(default_alloc_error_handler)]` becomes the only option, this can be avoided. In addition when using only fallible allocator methods and either `--cfg no_global_oom_handling` for liballoc (like rust-for-linux) or `--gc-sections` no references to the oom error handler will exist.

To avoid this feature being insta-stable, you will have to define `__rust_no_alloc_shim_is_unstable` to avoid linker errors.

(Labeling this with both T-compiler and T-lang as it originally involved both an implementation detail and had an insta-stable user facing change. As noted above, the `__rust_no_alloc_shim_is_unstable` symbol requirement should prevent unintended dependence on this unstable feature.)
This commit is contained in:
bors 2023-05-25 16:59:57 +00:00
commit a2b1646c59
19 changed files with 357 additions and 216 deletions
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8
compiler/rustc_builtin_macros/src/global_allocator.rs
View file

@ -1,7 +1,7 @@
use crate::util::check_builtin_macro_attribute;
use rustc_ast::expand::allocator::{
AllocatorKind, AllocatorMethod, AllocatorTy, ALLOCATOR_METHODS,
global_fn_name, AllocatorMethod, AllocatorTy, ALLOCATOR_METHODS,
};
use rustc_ast::ptr::P;
use rustc_ast::{self as ast, AttrVec, Expr, FnHeader, FnSig, Generics, Param, StmtKind};
@ -40,8 +40,7 @@ pub fn expand(
// Generate a bunch of new items using the AllocFnFactory
let span = ecx.with_def_site_ctxt(item.span);
let f =
AllocFnFactory { span, ty_span, kind: AllocatorKind::Global, global: item.ident, cx: ecx };
let f = AllocFnFactory { span, ty_span, global: item.ident, cx: ecx };
// Generate item statements for the allocator methods.
let stmts = ALLOCATOR_METHODS.iter().map(|method| f.allocator_fn(method)).collect();
@ -63,7 +62,6 @@ pub fn expand(
struct AllocFnFactory<'a, 'b> {
span: Span,
ty_span: Span,
kind: AllocatorKind,
global: Ident,
cx: &'b ExtCtxt<'a>,
}
@ -92,7 +90,7 @@ impl AllocFnFactory<'_, '_> {
}));
let item = self.cx.item(
self.span,
Ident::from_str_and_span(&self.kind.fn_name(method.name), self.span),
Ident::from_str_and_span(&global_fn_name(method.name), self.span),
self.attrs(),
kind,
);