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Merge pull request rust-lang#1074 from bjorn3/fix_weak_linkage
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Fix weak linkage
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@bjorn3
bjorn3 authored Aug 20, 2020
2 parents 02b7cdc + ca9fc10 commit a80d642
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Showing 4 changed files with 60 additions and 90 deletions.
17 changes: 10 additions & 7 deletions example/mini_core_hello_world.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -241,19 +241,22 @@ fn main() {

assert_eq!(((|()| 42u8) as fn(()) -> u8)(()), 42);

extern {
#[linkage = "extern_weak"]
static ABC: *const u8;
}

#[cfg(not(jit))]
{
extern {
#[linkage = "extern_weak"]
static ABC: *const u8;
}
}

unsafe { assert_eq!(ABC as usize, 0); }
{
extern {
#[linkage = "extern_weak"]
static ABC: *const u8;
}
}

unsafe { assert_eq!(ABC as usize, 0); }
}

&mut (|| Some(0 as *const ())) as &mut dyn FnMut() -> Option<*const ()>;

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45 changes: 0 additions & 45 deletions patches/0025-Remove-usage-of-extern_weak-in-thread_local_dtor.patch
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This file was deleted.

80 changes: 44 additions & 36 deletions src/constant.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -43,8 +43,7 @@ pub(crate) fn codegen_tls_ref<'tcx>(
def_id: DefId,
layout: TyAndLayout<'tcx>,
) -> CValue<'tcx> {
let linkage = crate::linkage::get_static_ref_linkage(fx.tcx, def_id);
let data_id = data_id_for_static(fx.tcx, fx.module, def_id, linkage);
let data_id = data_id_for_static(fx.tcx, fx.module, def_id, false);
let local_data_id = fx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
#[cfg(debug_assertions)]
fx.add_comment(local_data_id, format!("tls {:?}", def_id));
Expand All @@ -57,8 +56,7 @@ fn codegen_static_ref<'tcx>(
def_id: DefId,
layout: TyAndLayout<'tcx>,
) -> CPlace<'tcx> {
let linkage = crate::linkage::get_static_ref_linkage(fx.tcx, def_id);
let data_id = data_id_for_static(fx.tcx, fx.module, def_id, linkage);
let data_id = data_id_for_static(fx.tcx, fx.module, def_id, false);
let local_data_id = fx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
#[cfg(debug_assertions)]
fx.add_comment(local_data_id, format!("{:?}", def_id));
Expand Down Expand Up @@ -159,8 +157,7 @@ pub(crate) fn trans_const_value<'tcx>(
}
Some(GlobalAlloc::Static(def_id)) => {
assert!(fx.tcx.is_static(def_id));
let linkage = crate::linkage::get_static_ref_linkage(fx.tcx, def_id);
let data_id = data_id_for_static(fx.tcx, fx.module, def_id, linkage);
let data_id = data_id_for_static(fx.tcx, fx.module, def_id, false);
let local_data_id = fx.module.declare_data_in_func(data_id, &mut fx.bcx.func);
#[cfg(debug_assertions)]
fx.add_comment(local_data_id, format!("{:?}", def_id));
Expand Down Expand Up @@ -226,8 +223,20 @@ fn data_id_for_static(
tcx: TyCtxt<'_>,
module: &mut Module<impl Backend>,
def_id: DefId,
linkage: Linkage,
definition: bool,
) -> DataId {
let rlinkage = tcx.codegen_fn_attrs(def_id).linkage;
let linkage = if definition {
crate::linkage::get_static_linkage(tcx, def_id)
} else {
if rlinkage == Some(rustc_middle::mir::mono::Linkage::ExternalWeak)
|| rlinkage == Some(rustc_middle::mir::mono::Linkage::WeakAny) {
Linkage::Preemptible
} else {
Linkage::Import
}
};

let instance = Instance::mono(tcx, def_id).polymorphize(tcx);
let symbol_name = tcx.symbol_name(instance).name;
let ty = instance.ty(tcx, ParamEnv::reveal_all());
Expand Down Expand Up @@ -255,26 +264,39 @@ fn data_id_for_static(
)
.unwrap();

if linkage == Linkage::Preemptible {
if let ty::RawPtr(_) = ty.kind {
} else {
tcx.sess.span_fatal(
tcx.def_span(def_id),
"must have type `*const T` or `*mut T` due to `#[linkage]` attribute",
if rlinkage.is_some() {
// Comment copied from https://github.com/rust-lang/rust/blob/45060c2a66dfd667f88bd8b94261b28a58d85bd5/src/librustc_codegen_llvm/consts.rs#L141
// Declare an internal global `extern_with_linkage_foo` which
// is initialized with the address of `foo`. If `foo` is
// discarded during linking (for example, if `foo` has weak
// linkage and there are no definitions), then
// `extern_with_linkage_foo` will instead be initialized to
// zero.

let ref_name = format!("_rust_extern_with_linkage_{}", symbol_name);
let ref_data_id = module
.declare_data(
&ref_name,
Linkage::Local,
true,
false,
Some(align.try_into().unwrap()),
)
}

.unwrap();
let mut data_ctx = DataContext::new();
data_ctx.define_zeroinit(pointer_ty(tcx).bytes() as usize);
match module.define_data(data_id, &data_ctx) {
// Everytime a weak static is referenced, there will be a zero pointer definition,
let data = module.declare_data_in_data(data_id, &mut data_ctx);
data_ctx.define(std::iter::repeat(0).take(pointer_ty(tcx).bytes() as usize).collect());
data_ctx.write_data_addr(0, data, 0);
match module.define_data(ref_data_id, &data_ctx) {
// Every time the static is referenced there will be another definition of this global,
// so duplicate definitions are expected and allowed.
Err(ModuleError::DuplicateDefinition(_)) => {}
res => res.unwrap(),
}
ref_data_id
} else {
data_id
}

data_id
}

fn define_all_allocs(tcx: TyCtxt<'_>, module: &mut Module<impl Backend>, cx: &mut ConstantCx) {
Expand All @@ -301,16 +323,7 @@ fn define_all_allocs(tcx: TyCtxt<'_>, module: &mut Module<impl Backend>, cx: &mu
_ => bug!("static const eval returned {:#?}", const_),
};

let data_id = data_id_for_static(
tcx,
module,
def_id,
if tcx.is_reachable_non_generic(def_id) {
Linkage::Export
} else {
Linkage::Export // FIXME Set hidden visibility
},
);
let data_id = data_id_for_static(tcx, module, def_id, true);
(data_id, alloc, section_name)
}
};
Expand Down Expand Up @@ -360,12 +373,7 @@ fn define_all_allocs(tcx: TyCtxt<'_>, module: &mut Module<impl Backend>, cx: &mu
// Don't push a `TodoItem::Static` here, as it will cause statics used by
// multiple crates to be duplicated between them. It isn't necessary anyway,
// as it will get pushed by `codegen_static` when necessary.
data_id_for_static(
tcx,
module,
def_id,
crate::linkage::get_static_ref_linkage(tcx, def_id),
)
data_id_for_static(tcx, module, def_id, false)
}
};

Expand Down
8 changes: 6 additions & 2 deletions src/linkage.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -11,7 +11,7 @@ pub(crate) fn get_clif_linkage(mono_item: MonoItem<'_>, linkage: RLinkage, visib
}
}

pub(crate) fn get_static_ref_linkage(tcx: TyCtxt<'_>, def_id: DefId) -> Linkage {
pub(crate) fn get_static_linkage(tcx: TyCtxt<'_>, def_id: DefId) -> Linkage {
let fn_attrs = tcx.codegen_fn_attrs(def_id);

if let Some(linkage) = fn_attrs.linkage {
Expand All @@ -22,6 +22,10 @@ pub(crate) fn get_static_ref_linkage(tcx: TyCtxt<'_>, def_id: DefId) -> Linkage
_ => panic!("{:?}", linkage),
}
} else {
Linkage::Import
if tcx.is_reachable_non_generic(def_id) {
Linkage::Export
} else {
Linkage::Export // FIXME use Linkage::Hidden
}
}
}

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