Target stack-probe support configurable finely

This adds capability to configure the target's stack probe support in a
more precise manner than just on/off. In particular now we allow
choosing between always inline-asm, always call or either one of those
depending on the LLVM version on a per-target basis.

Author: nagisa

compiler/rustc_codegen_llvm/src/attributes.rs

@@ -13,6 +13,7 @@ use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::{self, TyCtxt};
 use rustc_session::config::{OptLevel, SanitizerSet};
 use rustc_session::Session;
+use rustc_target::spec::StackProbeType;
 
 use crate::attributes;
 use crate::llvm::AttributePlace::Function;
@@ -98,12 +99,6 @@ fn set_instrument_function(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
 }
 
 fn set_probestack(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
-    // Only use stack probes if the target specification indicates that we
-    // should be using stack probes
-    if !cx.sess().target.stack_probes {
-        return;
-    }
-
     // Currently stack probes seem somewhat incompatible with the address
     // sanitizer and thread sanitizer. With asan we're already protected from
     // stack overflow anyway so we don't really need stack probes regardless.
@@ -127,19 +122,31 @@ fn set_probestack(cx: &CodegenCx<'ll, '_>, llfn: &'ll Value) {
         return;
     }
 
-    llvm::AddFunctionAttrStringValue(
-        llfn,
-        llvm::AttributePlace::Function,
-        const_cstr!("probe-stack"),
-        if llvm_util::get_version() < (11, 0, 1) {
-            // Flag our internal `__rust_probestack` function as the stack probe symbol.
-            // This is defined in the `compiler-builtins` crate for each architecture.
-            const_cstr!("__rust_probestack")
-        } else {
-            // On LLVM 11+, emit inline asm for stack probes instead of a function call.
-            const_cstr!("inline-asm")
-        },
-    );
+    let attr_value = match cx.sess().target.stack_probes {
+        StackProbeType::None => None,
+        // Request LLVM to generate the probes inline. If the given LLVM version does not support
+        // this, no probe is generated at all (even if the attribute is specified).
+        StackProbeType::Inline => Some(const_cstr!("inline-asm")),
+        // Flag our internal `__rust_probestack` function as the stack probe symbol.
+        // This is defined in the `compiler-builtins` crate for each architecture.
+        StackProbeType::Call => Some(const_cstr!("__rust_probestack")),
+        // Pick from the two above based on the LLVM version.
+        StackProbeType::InlineOrCall { min_llvm_version_for_inline } => {
+            if llvm_util::get_version() < min_llvm_version_for_inline {
+                Some(const_cstr!("__rust_probestack"))
+            } else {
+                Some(const_cstr!("inline-asm"))
+            }
+        }
+    };
+    if let Some(attr_value) = attr_value {
+        llvm::AddFunctionAttrStringValue(
+            llfn,
+            llvm::AttributePlace::Function,
+            const_cstr!("probe-stack"),
+            attr_value,
+        );
+    }
 }
 
 pub fn llvm_target_features(sess: &Session) -> impl Iterator<Item = &str> {

compiler/rustc_target/src/spec/i386_apple_ios.rs

@@ -1,5 +1,5 @@
 use super::apple_sdk_base::{opts, Arch};
-use crate::spec::{Target, TargetOptions};
+use crate::spec::{StackProbeType, Target, TargetOptions};
 
 pub fn target() -> Target {
     let base = opts("ios", Arch::I386);
@@ -10,6 +10,10 @@ pub fn target() -> Target {
             f64:32:64-f80:128-n8:16:32-S128"
             .to_string(),
         arch: "x86".to_string(),
-        options: TargetOptions { max_atomic_width: Some(64), stack_probes: true, ..base },
+        options: TargetOptions {
+            max_atomic_width: Some(64),
+            stack_probes: StackProbeType::InlineOrCall { min_llvm_version_for_inline: (11, 0, 1) },
+            ..base
+        },
     }
 }

compiler/rustc_target/src/spec/i686_apple_darwin.rs

@@ -1,12 +1,12 @@
-use crate::spec::{LinkerFlavor, Target, TargetOptions};
+use crate::spec::{LinkerFlavor, StackProbeType, Target, TargetOptions};
 
 pub fn target() -> Target {
     let mut base = super::apple_base::opts("macos");
     base.cpu = "yonah".to_string();
     base.max_atomic_width = Some(64);
     base.pre_link_args.insert(LinkerFlavor::Gcc, vec!["-m32".to_string()]);
     base.link_env_remove.extend(super::apple_base::macos_link_env_remove());
-    base.stack_probes = true;
+    base.stack_probes = StackProbeType::InlineOrCall { min_llvm_version_for_inline: (11, 0, 1) };
     base.eliminate_frame_pointer = false;
 
     // Clang automatically chooses a more specific target based on

compiler/rustc_target/src/spec/i686_linux_android.rs

@@ -1,4 +1,4 @@
-use crate::spec::Target;
+use crate::spec::{StackProbeType, Target};
 
 // See https://developer.android.com/ndk/guides/abis.html#x86
 // for target ABI requirements.
@@ -11,7 +11,7 @@ pub fn target() -> Target {
     // http://developer.android.com/ndk/guides/abis.html#x86
     base.cpu = "pentiumpro".to_string();
     base.features = "+mmx,+sse,+sse2,+sse3,+ssse3".to_string();
-    base.stack_probes = true;
+    base.stack_probes = StackProbeType::InlineOrCall { min_llvm_version_for_inline: (11, 0, 1) };
 
     Target {
         llvm_target: "i686-linux-android".to_string(),

compiler/rustc_target/src/spec/i686_unknown_freebsd.rs

@@ -1,4 +1,4 @@
-use crate::spec::{LinkerFlavor, Target};
+use crate::spec::{LinkerFlavor, StackProbeType, Target};
 
 pub fn target() -> Target {
     let mut base = super::freebsd_base::opts();
@@ -7,7 +7,7 @@ pub fn target() -> Target {
     let pre_link_args = base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap();
     pre_link_args.push("-m32".to_string());
     pre_link_args.push("-Wl,-znotext".to_string());
-    base.stack_probes = true;
+    base.stack_probes = StackProbeType::InlineOrCall { min_llvm_version_for_inline: (11, 0, 1) };
 
     Target {
         llvm_target: "i686-unknown-freebsd".to_string(),

compiler/rustc_target/src/spec/i686_unknown_haiku.rs

@@ -1,11 +1,11 @@
-use crate::spec::{LinkerFlavor, Target};
+use crate::spec::{LinkerFlavor, StackProbeType, Target};
 
 pub fn target() -> Target {
     let mut base = super::haiku_base::opts();
     base.cpu = "pentium4".to_string();
     base.max_atomic_width = Some(64);
     base.pre_link_args.insert(LinkerFlavor::Gcc, vec!["-m32".to_string()]);
-    base.stack_probes = true;
+    base.stack_probes = StackProbeType::InlineOrCall { min_llvm_version_for_inline: (11, 0, 1) };
 
     Target {
         llvm_target: "i686-unknown-haiku".to_string(),

compiler/rustc_target/src/spec/i686_unknown_linux_gnu.rs

@@ -1,11 +1,11 @@
-use crate::spec::{LinkerFlavor, Target};
+use crate::spec::{LinkerFlavor, StackProbeType, Target};
 
 pub fn target() -> Target {
     let mut base = super::linux_gnu_base::opts();
     base.cpu = "pentium4".to_string();
     base.max_atomic_width = Some(64);
     base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-m32".to_string());
-    base.stack_probes = true;
+    base.stack_probes = StackProbeType::InlineOrCall { min_llvm_version_for_inline: (11, 0, 1) };
 
     Target {
         llvm_target: "i686-unknown-linux-gnu".to_string(),

compiler/rustc_target/src/spec/i686_unknown_linux_musl.rs

@@ -1,12 +1,12 @@
-use crate::spec::{LinkerFlavor, Target};
+use crate::spec::{LinkerFlavor, StackProbeType, Target};
 
 pub fn target() -> Target {
     let mut base = super::linux_musl_base::opts();
     base.cpu = "pentium4".to_string();
     base.max_atomic_width = Some(64);
     base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-m32".to_string());
     base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-Wl,-melf_i386".to_string());
-    base.stack_probes = true;
+    base.stack_probes = StackProbeType::InlineOrCall { min_llvm_version_for_inline: (11, 0, 1) };
 
     // The unwinder used by i686-unknown-linux-musl, the LLVM libunwind
     // implementation, apparently relies on frame pointers existing... somehow.

compiler/rustc_target/src/spec/i686_unknown_netbsd.rs

@@ -1,11 +1,11 @@
-use crate::spec::{LinkerFlavor, Target, TargetOptions};
+use crate::spec::{LinkerFlavor, StackProbeType, Target, TargetOptions};
 
 pub fn target() -> Target {
     let mut base = super::netbsd_base::opts();
     base.cpu = "pentium4".to_string();
     base.max_atomic_width = Some(64);
     base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-m32".to_string());
-    base.stack_probes = true;
+    base.stack_probes = StackProbeType::InlineOrCall { min_llvm_version_for_inline: (11, 0, 1) };
 
     Target {
         llvm_target: "i686-unknown-netbsdelf".to_string(),

compiler/rustc_target/src/spec/i686_unknown_openbsd.rs

@@ -1,12 +1,12 @@
-use crate::spec::{LinkerFlavor, Target};
+use crate::spec::{LinkerFlavor, StackProbeType, Target};
 
 pub fn target() -> Target {
     let mut base = super::openbsd_base::opts();
     base.cpu = "pentium4".to_string();
     base.max_atomic_width = Some(64);
     base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-m32".to_string());
     base.pre_link_args.get_mut(&LinkerFlavor::Gcc).unwrap().push("-fuse-ld=lld".to_string());
-    base.stack_probes = true;
+    base.stack_probes = StackProbeType::InlineOrCall { min_llvm_version_for_inline: (11, 0, 1) };
 
     Target {
         llvm_target: "i686-unknown-openbsd".to_string(),