Auto merge of #80838 - nagisa:nagisa/stack-probe-type, r=cuviper

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.

Note that this removes the ability to turn off the generation of the
stack-probe attribute. This is valid to replace it with inline-asm for all targets because
`probe-stack="inline-asm"` will not generate any machine code on targets
that do not currently support stack probes. This makes support for stack
probes on targets that don't have any right now automatic with LLVM
upgrades in the future.

(This is valid to do based on the fact that clang unconditionally sets
this attribute when `-fstack-clash-protection` is used, AFAICT)

cc #77885
r? `@cuviper`

1 files changed, 26 insertions, 19 deletions

diff --git a/compiler/rustc_codegen_llvm/src/attributes.rs b/compiler/rustc_codegen_llvm/src/attributes.rs
index 700f32e15b9..a78d692aaa7 100644
--- a/compiler/rustc_codegen_llvm/src/attributes.rs
+++ b/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> {