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Disable unused variable lint for naked functions

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In most calling conventions, accessing function parameters may require
stack access. However, naked functions have no assembly prelude to set
up stack access.  This is why naked functions may only contain a single
`asm!()` block. All parameter access is done inside the `asm!()` block,
so we cannot validate the liveness of the input parameters. Therefore,
we should disable the lint for naked functions.

rust-lang/rfcs#2774
rust-lang/rfcs#2972
This commit is contained in:
Nathaniel McCallum 2021-08-03 16:45:55 -04:00
parent 7ac0cb0ec1
commit 9c0147c02d
3 changed files with 6 additions and 71 deletions
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5
compiler/rustc_passes/src/liveness.rs
View file

@ -332,6 +332,11 @@ impl<'tcx> Visitor<'tcx> for IrMaps<'tcx> {
}
}
// Don't run unused pass for #[naked]
if self.tcx.has_attr(def_id, sym::naked) {
return;
}
if let Some(captures) = maps.tcx.typeck(local_def_id).closure_min_captures.get(&def_id) {
for &var_hir_id in captures.keys() {
let var_name = maps.tcx.hir().name(var_hir_id);

10
src/test/ui/asm/naked-functions-unused.rs
View file

@ -50,8 +50,6 @@ pub mod normal {
pub mod naked {
#[naked]
pub extern "sysv64" fn function(a: usize, b: usize) -> usize {
//~^ ERROR unused variable: `a`
//~| ERROR unused variable: `b`
unsafe { asm!("", options(noreturn)); }
}
@ -60,15 +58,11 @@ pub mod naked {
impl Naked {
#[naked]
pub extern "sysv64" fn associated(a: usize, b: usize) -> usize {
//~^ ERROR unused variable: `a`
//~| ERROR unused variable: `b`
unsafe { asm!("", options(noreturn)); }
}
#[naked]
pub extern "sysv64" fn method(&self, a: usize, b: usize) -> usize {
//~^ ERROR unused variable: `a`
//~| ERROR unused variable: `b`
unsafe { asm!("", options(noreturn)); }
}
}
@ -76,15 +70,11 @@ pub mod naked {
impl super::Trait for Naked {
#[naked]
extern "sysv64" fn trait_associated(a: usize, b: usize) -> usize {
//~^ ERROR unused variable: `a`
//~| ERROR unused variable: `b`
unsafe { asm!("", options(noreturn)); }
}
#[naked]
extern "sysv64" fn trait_method(&self, a: usize, b: usize) -> usize {
//~^ ERROR unused variable: `a`
//~| ERROR unused variable: `b`
unsafe { asm!("", options(noreturn)); }
}
}

62
src/test/ui/asm/naked-functions-unused.stderr
View file

@ -65,65 +65,5 @@ error: unused variable: `b`
LL | extern "sysv64" fn trait_method(&self, a: usize, b: usize) -> usize {
| ^ help: if this is intentional, prefix it with an underscore: `_b`
error: unused variable: `a`
--> $DIR/naked-functions-unused.rs:52:37
|
LL | pub extern "sysv64" fn function(a: usize, b: usize) -> usize {
| ^ help: if this is intentional, prefix it with an underscore: `_a`
error: unused variable: `b`
--> $DIR/naked-functions-unused.rs:52:47
|
LL | pub extern "sysv64" fn function(a: usize, b: usize) -> usize {
| ^ help: if this is intentional, prefix it with an underscore: `_b`
error: unused variable: `a`
--> $DIR/naked-functions-unused.rs:62:43
|
LL | pub extern "sysv64" fn associated(a: usize, b: usize) -> usize {
| ^ help: if this is intentional, prefix it with an underscore: `_a`
error: unused variable: `b`
--> $DIR/naked-functions-unused.rs:62:53
|
LL | pub extern "sysv64" fn associated(a: usize, b: usize) -> usize {
| ^ help: if this is intentional, prefix it with an underscore: `_b`
error: unused variable: `a`
--> $DIR/naked-functions-unused.rs:69:46
|
LL | pub extern "sysv64" fn method(&self, a: usize, b: usize) -> usize {
| ^ help: if this is intentional, prefix it with an underscore: `_a`
error: unused variable: `b`
--> $DIR/naked-functions-unused.rs:69:56
|
LL | pub extern "sysv64" fn method(&self, a: usize, b: usize) -> usize {
| ^ help: if this is intentional, prefix it with an underscore: `_b`
error: unused variable: `a`
--> $DIR/naked-functions-unused.rs:78:45
|
LL | extern "sysv64" fn trait_associated(a: usize, b: usize) -> usize {
| ^ help: if this is intentional, prefix it with an underscore: `_a`
error: unused variable: `b`
--> $DIR/naked-functions-unused.rs:78:55
|
LL | extern "sysv64" fn trait_associated(a: usize, b: usize) -> usize {
| ^ help: if this is intentional, prefix it with an underscore: `_b`
error: unused variable: `a`
--> $DIR/naked-functions-unused.rs:85:48
|
LL | extern "sysv64" fn trait_method(&self, a: usize, b: usize) -> usize {
| ^ help: if this is intentional, prefix it with an underscore: `_a`
error: unused variable: `b`
--> $DIR/naked-functions-unused.rs:85:58
|
LL | extern "sysv64" fn trait_method(&self, a: usize, b: usize) -> usize {
| ^ help: if this is intentional, prefix it with an underscore: `_b`
error: aborting due to 20 previous errors
error: aborting due to 10 previous errors