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Add support for leaf fn frame pointer elimination

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This PR adds ability for the target specifications to specify frame
pointer emission type that's not just “always” or “whatever cg decides”.

In particular there's a new mode that allows omission of the frame
pointer for leaf functions (those that don't call any other functions).

We then set this new mode for Aarch64-based Apple targets.

Fixes #86196
This commit is contained in:
Simonas Kazlauskas 2021-06-26 23:53:35 +03:00
parent 3ddb78a346
commit 9b67cba4f6
24 changed files with 149 additions and 60 deletions
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30
compiler/rustc_codegen_llvm/src/attributes.rs
View File

@ -12,7 +12,7 @@ use rustc_middle::ty::{self, TyCtxt};
use rustc_session::config::OptLevel;
use rustc_session::Session;
use rustc_target::spec::abi::Abi;
use rustc_target::spec::{SanitizerSet, StackProbeType};
use rustc_target::spec::{FramePointer, SanitizerSet, StackProbeType};
use crate::attributes;
use crate::llvm::AttributePlace::Function;
@ -69,15 +69,25 @@ fn naked(val: &'ll Value, is_naked: bool) {
Attribute::Naked.toggle_llfn(Function, val, is_naked);
}
pub fn set_frame_pointer_elimination(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
if cx.sess().must_not_eliminate_frame_pointers() {
llvm::AddFunctionAttrStringValue(
llfn,
llvm::AttributePlace::Function,
cstr!("frame-pointer"),
cstr!("all"),
);
pub fn set_frame_pointer_type(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
let mut fp = cx.sess().target.frame_pointer;
// "mcount" function relies on stack pointer.
// See <https://sourceware.org/binutils/docs/gprof/Implementation.html>.
if cx.sess().instrument_mcount() || matches!(cx.sess().opts.cg.force_frame_pointers, Some(true))
{
fp = FramePointer::Always;
}
let attr_value = match fp {
FramePointer::Always => cstr!("all"),
FramePointer::NonLeaf => cstr!("non-leaf"),
FramePointer::MayOmit => return,
};
llvm::AddFunctionAttrStringValue(
llfn,
llvm::AttributePlace::Function,
cstr!("frame-pointer"),
attr_value,
);
}
/// Tell LLVM what instrument function to insert.
@ -254,7 +264,7 @@ pub fn from_fn_attrs(cx: &CodegenCx<'ll, 'tcx>, llfn: &'ll Value, instance: ty::
}
// FIXME: none of these three functions interact with source level attributes.
set_frame_pointer_elimination(cx, llfn);
set_frame_pointer_type(cx, llfn);
set_instrument_function(cx, llfn);
set_probestack(cx, llfn);

4
compiler/rustc_codegen_llvm/src/context.rs
View File

@ -410,8 +410,8 @@ impl MiscMethods<'tcx> for CodegenCx<'ll, 'tcx> {
&self.used_statics
}
fn set_frame_pointer_elimination(&self, llfn: &'ll Value) {
attributes::set_frame_pointer_elimination(self, llfn)
fn set_frame_pointer_type(&self, llfn: &'ll Value) {
attributes::set_frame_pointer_type(self, llfn)
}
fn apply_target_cpu_attr(&self, llfn: &'ll Value) {

2
compiler/rustc_codegen_llvm/src/intrinsic.rs
View File

@ -674,7 +674,7 @@ fn gen_fn<'ll, 'tcx>(
) -> &'ll Value {
let fn_abi = FnAbi::of_fn_ptr(cx, rust_fn_sig, &[]);
let llfn = cx.declare_fn(name, &fn_abi);
cx.set_frame_pointer_elimination(llfn);
cx.set_frame_pointer_type(llfn);
cx.apply_target_cpu_attr(llfn);
// FIXME(eddyb) find a nicer way to do this.
unsafe { llvm::LLVMRustSetLinkage(llfn, llvm::Linkage::InternalLinkage) };

2
compiler/rustc_codegen_ssa/src/base.rs
View File

@ -406,7 +406,7 @@ pub fn maybe_create_entry_wrapper<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
};
// `main` should respect same config for frame pointer elimination as rest of code
cx.set_frame_pointer_elimination(llfn);
cx.set_frame_pointer_type(llfn);
cx.apply_target_cpu_attr(llfn);
let llbb = Bx::append_block(&cx, llfn, "top");

2
compiler/rustc_codegen_ssa/src/traits/misc.rs
View File

@ -16,7 +16,7 @@ pub trait MiscMethods<'tcx>: BackendTypes {
fn sess(&self) -> &Session;
fn codegen_unit(&self) -> &'tcx CodegenUnit<'tcx>;
fn used_statics(&self) -> &RefCell<Vec<Self::Value>>;
fn set_frame_pointer_elimination(&self, llfn: Self::Function);
fn set_frame_pointer_type(&self, llfn: Self::Function);
fn apply_target_cpu_attr(&self, llfn: Self::Function);
fn create_used_variable(&self);
/// Declares the extern "C" main function for the entry point. Returns None if the symbol already exists.

12
compiler/rustc_session/src/session.rs
View File

@ -792,18 +792,6 @@ impl Session {
!self.target.is_like_windows && !self.target.is_like_osx
}
pub fn must_not_eliminate_frame_pointers(&self) -> bool {
// "mcount" function relies on stack pointer.
// See <https://sourceware.org/binutils/docs/gprof/Implementation.html>.
if self.instrument_mcount() {
true
} else if let Some(x) = self.opts.cg.force_frame_pointers {
x
} else {
!self.target.eliminate_frame_pointer
}
}
pub fn must_emit_unwind_tables(&self) -> bool {
// This is used to control the emission of the `uwtable` attribute on
// LLVM functions.

8
compiler/rustc_target/src/spec/aarch64_apple_darwin.rs
View File

@ -1,4 +1,4 @@
use crate::spec::{LinkerFlavor, SanitizerSet, Target, TargetOptions};
use crate::spec::{FramePointer, LinkerFlavor, SanitizerSet, Target, TargetOptions};
pub fn target() -> Target {
let mut base = super::apple_base::opts("macos");
@ -20,6 +20,10 @@ pub fn target() -> Target {
pointer_width: 64,
data_layout: "e-m:o-i64:64-i128:128-n32:64-S128".to_string(),
arch: arch.to_string(),
options: TargetOptions { mcount: "\u{1}mcount".to_string(), ..base },
options: TargetOptions {
mcount: "\u{1}mcount".to_string(),
frame_pointer: FramePointer::NonLeaf,
..base
},
}
}

3
compiler/rustc_target/src/spec/aarch64_apple_ios.rs
View File

@ -1,5 +1,5 @@
use super::apple_sdk_base::{opts, Arch};
use crate::spec::{Target, TargetOptions};
use crate::spec::{FramePointer, Target, TargetOptions};
pub fn target() -> Target {
let base = opts("ios", Arch::Arm64);
@ -13,6 +13,7 @@ pub fn target() -> Target {
max_atomic_width: Some(128),
unsupported_abis: super::arm_base::unsupported_abis(),
forces_embed_bitcode: true,
frame_pointer: FramePointer::NonLeaf,
// Taken from a clang build on Xcode 11.4.1.
// These arguments are not actually invoked - they just have
// to look right to pass App Store validation.

3
compiler/rustc_target/src/spec/aarch64_apple_ios_macabi.rs
View File

@ -1,5 +1,5 @@
use super::apple_sdk_base::{opts, Arch};
use crate::spec::{Target, TargetOptions};
use crate::spec::{FramePointer, Target, TargetOptions};
pub fn target() -> Target {
let base = opts("ios", Arch::Arm64_macabi);
@ -13,6 +13,7 @@ pub fn target() -> Target {
max_atomic_width: Some(128),
unsupported_abis: super::arm_base::unsupported_abis(),
forces_embed_bitcode: true,
frame_pointer: FramePointer::NonLeaf,
// Taken from a clang build on Xcode 11.4.1.
// These arguments are not actually invoked - they just have
// to look right to pass App Store validation.

3
compiler/rustc_target/src/spec/aarch64_apple_ios_sim.rs
View File

@ -1,5 +1,5 @@
use super::apple_sdk_base::{opts, Arch};
use crate::spec::{Target, TargetOptions};
use crate::spec::{FramePointer, Target, TargetOptions};
pub fn target() -> Target {
let base = opts("ios", Arch::Arm64_sim);
@ -21,6 +21,7 @@ pub fn target() -> Target {
max_atomic_width: Some(128),
unsupported_abis: super::arm_base::unsupported_abis(),
forces_embed_bitcode: true,
frame_pointer: FramePointer::NonLeaf,
// Taken from a clang build on Xcode 11.4.1.
// These arguments are not actually invoked - they just have
// to look right to pass App Store validation.

3
compiler/rustc_target/src/spec/aarch64_apple_tvos.rs
View File

@ -1,5 +1,5 @@
use super::apple_sdk_base::{opts, Arch};
use crate::spec::{Target, TargetOptions};
use crate::spec::{FramePointer, Target, TargetOptions};
pub fn target() -> Target {
let base = opts("tvos", Arch::Arm64);
@ -13,6 +13,7 @@ pub fn target() -> Target {
max_atomic_width: Some(128),
unsupported_abis: super::arm_base::unsupported_abis(),
forces_embed_bitcode: true,
frame_pointer: FramePointer::NonLeaf,
..base
},
}

4
compiler/rustc_target/src/spec/apple_base.rs
View File

@ -1,6 +1,6 @@
use std::env;
use crate::spec::{SplitDebuginfo, TargetOptions};
use crate::spec::{FramePointer, SplitDebuginfo, TargetOptions};
pub fn opts(os: &str) -> TargetOptions {
// ELF TLS is only available in macOS 10.7+. If you try to compile for 10.6
@ -27,7 +27,7 @@ pub fn opts(os: &str) -> TargetOptions {
families: vec!["unix".to_string()],
is_like_osx: true,
dwarf_version: Some(2),
eliminate_frame_pointer: false,
frame_pointer: FramePointer::Always,
has_rpath: true,
dll_suffix: ".dylib".to_string(),
archive_format: "darwin".to_string(),

4
compiler/rustc_target/src/spec/freebsd_base.rs
View File

@ -1,4 +1,4 @@
use crate::spec::{RelroLevel, TargetOptions};
use crate::spec::{FramePointer, RelroLevel, TargetOptions};
pub fn opts() -> TargetOptions {
TargetOptions {
@ -8,7 +8,7 @@ pub fn opts() -> TargetOptions {
families: vec!["unix".to_string()],
has_rpath: true,
position_independent_executables: true,
eliminate_frame_pointer: false, // FIXME 43575
frame_pointer: FramePointer::Always, // FIXME 43575: should be MayOmit...
relro_level: RelroLevel::Full,
abi_return_struct_as_int: true,
dwarf_version: Some(2),

4
compiler/rustc_target/src/spec/i686_apple_darwin.rs
View File

@ -1,4 +1,4 @@
use crate::spec::{LinkerFlavor, StackProbeType, Target, TargetOptions};
use crate::spec::{FramePointer, LinkerFlavor, StackProbeType, Target, TargetOptions};
pub fn target() -> Target {
let mut base = super::apple_base::opts("macos");
@ -8,7 +8,7 @@ pub fn target() -> Target {
base.link_env_remove.extend(super::apple_base::macos_link_env_remove());
// don't use probe-stack=inline-asm until rust#83139 and rust#84667 are resolved
base.stack_probes = StackProbeType::Call;
base.eliminate_frame_pointer = false;
base.frame_pointer = FramePointer::Always;
// Clang automatically chooses a more specific target based on
// MACOSX_DEPLOYMENT_TARGET. To enable cross-language LTO to work

4
compiler/rustc_target/src/spec/i686_pc_windows_gnu.rs
View File

@ -1,4 +1,4 @@
use crate::spec::{LinkerFlavor, LldFlavor, Target};
use crate::spec::{FramePointer, LinkerFlavor, LldFlavor, Target};
pub fn target() -> Target {
let mut base = super::windows_gnu_base::opts();
@ -6,7 +6,7 @@ pub fn target() -> Target {
base.pre_link_args
.insert(LinkerFlavor::Lld(LldFlavor::Ld), vec!["-m".to_string(), "i386pe".to_string()]);
base.max_atomic_width = Some(64);
base.eliminate_frame_pointer = false; // Required for backtraces
base.frame_pointer = FramePointer::Always; // Required for backtraces
base.linker = Some("i686-w64-mingw32-gcc".to_string());
// Mark all dynamic libraries and executables as compatible with the larger 4GiB address

4
compiler/rustc_target/src/spec/i686_unknown_linux_musl.rs
View File

@ -1,4 +1,4 @@
use crate::spec::{LinkerFlavor, StackProbeType, Target};
use crate::spec::{FramePointer, LinkerFlavor, StackProbeType, Target};
pub fn target() -> Target {
let mut base = super::linux_musl_base::opts();
@ -21,7 +21,7 @@ pub fn target() -> Target {
//
// This may or may not be related to this bug:
// https://llvm.org/bugs/show_bug.cgi?id=30879
base.eliminate_frame_pointer = false;
base.frame_pointer = FramePointer::Always;
Target {
llvm_target: "i686-unknown-linux-musl".to_string(),

4
compiler/rustc_target/src/spec/i686_uwp_windows_gnu.rs
View File

@ -1,4 +1,4 @@
use crate::spec::{LinkerFlavor, LldFlavor, Target};
use crate::spec::{FramePointer, LinkerFlavor, LldFlavor, Target};
pub fn target() -> Target {
let mut base = super::windows_uwp_gnu_base::opts();
@ -6,7 +6,7 @@ pub fn target() -> Target {
base.pre_link_args
.insert(LinkerFlavor::Lld(LldFlavor::Ld), vec!["-m".to_string(), "i386pe".to_string()]);
base.max_atomic_width = Some(64);
base.eliminate_frame_pointer = false; // Required for backtraces
base.frame_pointer = FramePointer::Always; // Required for backtraces
// Mark all dynamic libraries and executables as compatible with the larger 4GiB address
// space available to x86 Windows binaries on x86_64.

4
compiler/rustc_target/src/spec/illumos_base.rs
View File

@ -1,4 +1,4 @@
use crate::spec::{LinkArgs, LinkerFlavor, TargetOptions};
use crate::spec::{FramePointer, LinkArgs, LinkerFlavor, TargetOptions};
use std::default::Default;
pub fn opts() -> TargetOptions {
@ -35,7 +35,7 @@ pub fn opts() -> TargetOptions {
is_like_solaris: true,
linker_is_gnu: false,
limit_rdylib_exports: false, // Linker doesn't support this
eliminate_frame_pointer: false,
frame_pointer: FramePointer::Always,
eh_frame_header: false,
late_link_args,

5
compiler/rustc_target/src/spec/linux_kernel_base.rs
View File

@ -1,4 +1,5 @@
use crate::spec::{PanicStrategy, RelocModel, RelroLevel, StackProbeType, TargetOptions};
use crate::spec::TargetOptions;
use crate::spec::{FramePointer, PanicStrategy, RelocModel, RelroLevel, StackProbeType};
pub fn opts() -> TargetOptions {
TargetOptions {
@ -7,7 +8,7 @@ pub fn opts() -> TargetOptions {
panic_strategy: PanicStrategy::Abort,
// don't use probe-stack=inline-asm until rust#83139 and rust#84667 are resolved
stack_probes: StackProbeType::Call,
eliminate_frame_pointer: false,
frame_pointer: FramePointer::Always,
position_independent_executables: true,
needs_plt: true,
relro_level: RelroLevel::Full,

55
compiler/rustc_target/src/spec/mod.rs
View File

@ -671,6 +671,42 @@ impl ToJson for SanitizerSet {
}
}
#[derive(Clone, Copy, PartialEq, Hash, Debug)]
pub enum FramePointer {
/// Forces the machine code generator to always preserve the frame pointers.
Always,
/// Forces the machine code generator to preserve the frame pointers except for the leaf
/// functions (i.e. those that don't call other functions).
NonLeaf,
/// Allows the machine code generator to omit the frame pointers.
///
/// This option does not guarantee that the frame pointers will be omitted.
MayOmit,
}
impl FromStr for FramePointer {
type Err = ();
fn from_str(s: &str) -> Result<Self, ()> {
Ok(match s {
"always" => Self::Always,
"non-leaf" => Self::NonLeaf,
"may-omit" => Self::MayOmit,
_ => return Err(()),
})
}
}
impl ToJson for FramePointer {
fn to_json(&self) -> Json {
match *self {
Self::Always => "always",
Self::NonLeaf => "non-leaf",
Self::MayOmit => "may-omit",
}
.to_json()
}
}
macro_rules! supported_targets {
( $(($( $triple:literal, )+ $module:ident ),)+ ) => {
$(mod $module;)+
@ -1068,8 +1104,8 @@ pub struct TargetOptions {
pub tls_model: TlsModel,
/// Do not emit code that uses the "red zone", if the ABI has one. Defaults to false.
pub disable_redzone: bool,
/// Eliminate frame pointers from stack frames if possible. Defaults to true.
pub eliminate_frame_pointer: bool,
/// Frame pointer mode for this target. Defaults to `MayOmit`.
pub frame_pointer: FramePointer,
/// Emit each function in its own section. Defaults to true.
pub function_sections: bool,
/// String to prepend to the name of every dynamic library. Defaults to "lib".
@ -1330,7 +1366,7 @@ impl Default for TargetOptions {
code_model: None,
tls_model: TlsModel::GeneralDynamic,
disable_redzone: false,
eliminate_frame_pointer: true,
frame_pointer: FramePointer::MayOmit,
function_sections: true,
dll_prefix: "lib".to_string(),
dll_suffix: ".so".to_string(),
@ -1833,6 +1869,16 @@ impl Target {
}
}
if let Some(fp) = obj.remove_key("frame-pointer") {
if let Some(s) = Json::as_string(&fp) {
base.frame_pointer = s
.parse()
.map_err(|()| format!("'{}' is not a valid value for frame-pointer", s))?;
} else {
incorrect_type.push("frame-pointer".to_string())
}
}
key!(is_builtin, bool);
key!(c_int_width = "target-c-int-width");
key!(os);
@ -1864,7 +1910,6 @@ impl Target {
key!(code_model, CodeModel)?;
key!(tls_model, TlsModel)?;
key!(disable_redzone, bool);
key!(eliminate_frame_pointer, bool);
key!(function_sections, bool);
key!(dll_prefix);
key!(dll_suffix);
@ -2128,7 +2173,7 @@ impl ToJson for Target {
target_option_val!(code_model);
target_option_val!(tls_model);
target_option_val!(disable_redzone);
target_option_val!(eliminate_frame_pointer);
target_option_val!(frame_pointer);
target_option_val!(function_sections);
target_option_val!(dll_prefix);
target_option_val!(dll_suffix);

4
compiler/rustc_target/src/spec/openbsd_base.rs
View File

@ -1,4 +1,4 @@
use crate::spec::{RelroLevel, TargetOptions};
use crate::spec::{FramePointer, RelroLevel, TargetOptions};
pub fn opts() -> TargetOptions {
TargetOptions {
@ -9,7 +9,7 @@ pub fn opts() -> TargetOptions {
has_rpath: true,
abi_return_struct_as_int: true,
position_independent_executables: true,
eliminate_frame_pointer: false, // FIXME 43575
frame_pointer: FramePointer::Always, // FIXME 43575: should be MayOmit...
relro_level: RelroLevel::Full,
dwarf_version: Some(2),
..Default::default()

5
compiler/rustc_target/src/spec/thumb_base.rs
View File

@ -27,7 +27,8 @@
// differentiate these targets from our other `arm(v7)-*-*-gnueabi(hf)` targets in the context of
// build scripts / gcc flags.
use crate::spec::{LinkerFlavor, LldFlavor, PanicStrategy, RelocModel, TargetOptions};
use crate::spec::TargetOptions;
use crate::spec::{FramePointer, LinkerFlavor, LldFlavor, PanicStrategy, RelocModel};
pub fn opts() -> TargetOptions {
// See rust-lang/rfcs#1645 for a discussion about these defaults
@ -52,7 +53,7 @@ pub fn opts() -> TargetOptions {
emit_debug_gdb_scripts: false,
// LLVM is eager to trash the link register when calling `noreturn` functions, which
// breaks debugging. Preserve LR by default to prevent that from happening.
eliminate_frame_pointer: false,
frame_pointer: FramePointer::Always,
..Default::default()
}
}

5
compiler/rustc_target/src/spec/x86_64_apple_darwin.rs
View File

@ -1,10 +1,11 @@
use crate::spec::{LinkerFlavor, SanitizerSet, StackProbeType, Target, TargetOptions};
use crate::spec::TargetOptions;
use crate::spec::{FramePointer, LinkerFlavor, SanitizerSet, StackProbeType, Target};
pub fn target() -> Target {
let mut base = super::apple_base::opts("macos");
base.cpu = "core2".to_string();
base.max_atomic_width = Some(128); // core2 support cmpxchg16b
base.eliminate_frame_pointer = false;
base.frame_pointer = FramePointer::Always;
base.pre_link_args.insert(
LinkerFlavor::Gcc,
vec!["-m64".to_string(), "-arch".to_string(), "x86_64".to_string()],

35
src/test/codegen/frame-pointer.rs Normal file
View File

@ -0,0 +1,35 @@
// compile-flags: --crate-type=rlib
// revisions: aarch64-apple aarch64-linux force x64-apple x64-linux
// [aarch64-apple] needs-llvm-components: aarch64
// [aarch64-apple] compile-flags: --target=aarch64-apple-darwin
// [aarch64-linux] needs-llvm-components: aarch64
// [aarch64-linux] compile-flags: --target=aarch64-unknown-linux-gnu
// [force] needs-llvm-components: x86
// [force] compile-flags: --target=x86_64-unknown-linux-gnu -Cforce-frame-pointers=yes
// [x64-apple] needs-llvm-components: x86
// [x64-apple] compile-flags: --target=x86_64-apple-darwin
// [x64-linux] needs-llvm-components: x86
// [x64-linux] compile-flags: --target=x86_64-unknown-linux-gnu
#![feature(no_core, lang_items)]
#![no_core]
#[lang="sized"]
trait Sized { }
#[lang="copy"]
trait Copy { }
// CHECK: define i32 @peach{{.*}}[[PEACH_ATTRS:\#[0-9]+]] {
#[no_mangle]
pub fn peach(x: u32) -> u32 {
x
}
// CHECK: attributes [[PEACH_ATTRS]] = {
// x64-linux-NOT: {{.*}}"frame-pointer"{{.*}}
// aarch64-linux-NOT: {{.*}}"frame-pointer"{{.*}}
// x64-apple-SAME: {{.*}}"frame-pointer"="all"
// force-SAME: {{.*}}"frame-pointer"="all"
// aarch64-apple-SAME: {{.*}}"frame-pointer"="non-leaf"
// CHECK-SAME: }