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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 e6d1a0ed95
1 changed files with 46 additions and 35 deletions
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21
src/allocator.rs
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@ -3,10 +3,12 @@
use crate::prelude::*;
use rustc_ast::expand::allocator::{AllocatorKind, AllocatorTy, ALLOCATOR_METHODS};
use rustc_ast::expand::allocator::{
alloc_error_handler_name, default_fn_name, global_fn_name, AllocatorKind, AllocatorTy,
ALLOCATOR_METHODS, NO_ALLOC_SHIM_IS_UNSTABLE,
};
use rustc_codegen_ssa::base::allocator_kind_for_codegen;
use rustc_session::config::OomStrategy;
use rustc_span::symbol::sym;
/// Returns whether an allocator shim was created
pub(crate) fn codegen(
@ -34,6 +36,7 @@ fn codegen_inner(
) {
let usize_ty = module.target_config().pointer_type();
if kind == AllocatorKind::Default {
for method in ALLOCATOR_METHODS {
let mut arg_tys = Vec::with_capacity(method.inputs.len());
for ty in method.inputs.iter() {
@ -66,10 +69,11 @@ fn codegen_inner(
module,
unwind_context,
sig,
&format!("__rust_{}", method.name),
&kind.fn_name(method.name),
&global_fn_name(method.name),
&default_fn_name(method.name),
);
}
}
let sig = Signature {
call_conv: module.target_config().default_call_conv,
@ -81,7 +85,7 @@ fn codegen_inner(
unwind_context,
sig,
"__rust_alloc_error_handler",
&alloc_error_handler_kind.fn_name(sym::oom),
&alloc_error_handler_name(alloc_error_handler_kind),
);
let data_id = module.declare_data(OomStrategy::SYMBOL, Linkage::Export, false, false).unwrap();
@ -90,4 +94,11 @@ fn codegen_inner(
let val = oom_strategy.should_panic();
data_ctx.define(Box::new([val]));
module.define_data(data_id, &data_ctx).unwrap();
let data_id =
module.declare_data(NO_ALLOC_SHIM_IS_UNSTABLE, Linkage::Export, false, false).unwrap();
let mut data_ctx = DataContext::new();
data_ctx.set_align(1);
data_ctx.define(Box::new([0]));
module.define_data(data_id, &data_ctx).unwrap();
}