Add CFI information to __rust_probestack

In order for GDB to correctly backtrace a stack overflow, it needs
CFI information in __rust_probestack.

This turns the following backtrace,

```
>> bt
 #0  0x0000555555576f73 in __rust_probestack () at /cargo/registry/src/github.com-1ecc6299db9ec823/compiler_builtins-0.1.14/src/probestack.rs:55
Backtrace stopped: Cannot access memory at address 0x7fffff7fedf0
```

To this:

```
>>> bt
 #0  0x0000555555574e47 in __rust_probestack ()
 #1  0x00005555555595ba in test::main ()
 #2  0x00005555555594f3 in std::rt::lang_start::{{closure}} ()
 #3  0x0000555555561ae3 in std::panicking::try::do_call ()
 #4  0x000055555556595a in __rust_maybe_catch_panic ()
 #5  0x000055555555af9b in std::rt::lang_start_internal ()
 #6  0x00005555555594d5 in std::rt::lang_start ()
 #7  0x000055555555977b in main ()
```

Cargo.toml

@@ -32,7 +32,7 @@ test = false
 core = { version = "1.0.0", optional = true, package = 'rustc-std-workspace-core' }
 
 [build-dependencies]
-cc = { optional = true, version = "1.0" }
+cc = { version = "1.0" }
 
 [dev-dependencies]
 panic-handler = { path = 'crates/panic-handler' }
@@ -42,7 +42,7 @@ default = ["compiler-builtins"]
 
 # Enable compilation of C code in compiler-rt, filling in some more optimized
 # implementations and also filling in unimplemented intrinsics
-c = ["cc"]
+c = []
 
 # Flag this library as the unstable compiler-builtins lib
 compiler-builtins = []

build.rs

@@ -28,6 +28,19 @@ fn main() {
         println!("cargo:rustc-cfg=feature=\"mem\"");
     }
 
+    let target_arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap();
+    if target_arch == "x86_64" {
+        let cfg = &mut cc::Build::new();
+        cfg.file(&"src/probestack_x86_64.S");
+        cfg.compile("libcompiler-probestack.a");
+    }
+
+    if target_arch == "x86" {
+        let cfg = &mut cc::Build::new();
+        cfg.file(&"src/probestack_x86.S");
+        cfg.compile("libcompiler-probestack.a");
+    }
+
     // NOTE we are going to assume that llvm-target, what determines our codegen option, matches the
     // target triple. This is usually correct for our built-in targets but can break in presence of
     // custom targets, which can have arbitrary names.

src/probestack.rs

@@ -41,88 +41,4 @@
 //! probes on any other architecture like ARM or PowerPC64. LLVM I'm sure would
 //! be more than welcome to accept such a change!
 
-#![cfg(not(windows))] // Windows already has builtins to do this
-
-#[naked]
-#[no_mangle]
-#[cfg(all(target_arch = "x86_64", not(feature = "mangled-names")))]
-pub unsafe extern "C" fn __rust_probestack() {
-    // Our goal here is to touch each page between %rsp+8 and %rsp+8-%rax,
-    // ensuring that if any pages are unmapped we'll make a page fault.
-    //
-    // The ABI here is that the stack frame size is located in `%eax`. Upon
-    // return we're not supposed to modify `%esp` or `%eax`.
-    asm!("
-        mov    %rax,%r11        // duplicate %rax as we're clobbering %r11
-
-        // Main loop, taken in one page increments. We're decrementing rsp by
-        // a page each time until there's less than a page remaining. We're
-        // guaranteed that this function isn't called unless there's more than a
-        // page needed.
-        //
-        // Note that we're also testing against `8(%rsp)` to account for the 8
-        // bytes pushed on the stack orginally with our return address. Using
-        // `8(%rsp)` simulates us testing the stack pointer in the caller's
-        // context.
-
-        // It's usually called when %rax >= 0x1000, but that's not always true.
-        // Dynamic stack allocation, which is needed to implement unsized
-        // rvalues, triggers stackprobe even if %rax < 0x1000.
-        // Thus we have to check %r11 first to avoid segfault.
-        cmp    $$0x1000,%r11
-        jna    3f
-    2:
-        sub    $$0x1000,%rsp
-        test   %rsp,8(%rsp)
-        sub    $$0x1000,%r11
-        cmp    $$0x1000,%r11
-        ja     2b
-
-    3:
-        // Finish up the last remaining stack space requested, getting the last
-        // bits out of r11
-        sub    %r11,%rsp
-        test   %rsp,8(%rsp)
-
-        // Restore the stack pointer to what it previously was when entering
-        // this function. The caller will readjust the stack pointer after we
-        // return.
-        add    %rax,%rsp
-
-        ret
-    " ::: "memory" : "volatile");
-    ::core::intrinsics::unreachable();
-}
-
-#[naked]
-#[no_mangle]
-#[cfg(all(target_arch = "x86", not(feature = "mangled-names")))]
-pub unsafe extern "C" fn __rust_probestack() {
-    // This is the same as x86_64 above, only translated for 32-bit sizes. Note
-    // that on Unix we're expected to restore everything as it was, this
-    // function basically can't tamper with anything.
-    //
-    // The ABI here is the same as x86_64, except everything is 32-bits large.
-    asm!("
-        push   %ecx
-        mov    %eax,%ecx
-
-        cmp    $$0x1000,%ecx
-        jna    3f
-    2:
-        sub    $$0x1000,%esp
-        test   %esp,8(%esp)
-        sub    $$0x1000,%ecx
-        cmp    $$0x1000,%ecx
-        ja     2b
-
-    3:
-        sub    %ecx,%esp
-        test   %esp,8(%esp)
-
-        add    %eax,%esp
-        pop    %ecx
-        ret
-    " ::: "memory" : "volatile");
-    ::core::intrinsics::unreachable();
-}
+// The code here moved to probestack_*.S, to support debugger frame information.

src/probestack_x86.S

@@ -0,0 +1,38 @@
+// This is the same as x86_64, only translated for 32-bit sizes. Note that on
+// Unix we're expected to restore everything as it was, this function basically
+// can't tamper with anything.
+//
+// The ABI here is the same as x86_64, except everything is 32-bits large.
+
+.text
+.globl  __rust_probestack
+.type   __rust_probestack, @function
+__rust_probestack:
+    .cfi_startproc
+    pushq  %ebp
+    .cfi_def_cfa_offset 8
+    .cfi_offset 6, -8
+    movq   %esp, %ebp
+    .cfi_def_cfa_register 6
+    push   %ecx
+    mov    %eax,%ecx
+
+    cmp    $0x1000,%ecx
+    jna    3f
+2:
+    sub    $0x1000,%esp
+    test   %esp,8(%esp)
+    sub    $0x1000,%ecx
+    cmp    $0x1000,%ecx
+    ja     2b
+
+3:
+    sub    %ecx,%esp
+    test   %esp,8(%esp)
+
+    add    %eax,%esp
+    pop    %ecx
+    leave
+    .cfi_def_cfa 7, 8
+    ret
+    .cfi_endproc

src/probestack_x86_64.S

@@ -0,0 +1,57 @@
+// Our goal here is to touch each page between %rsp+8 and %rsp+8-%rax,
+// ensuring that if any pages are unmapped we'll make a page fault.
+//
+// The ABI here is that the stack frame size is located in `%eax`. Upon
+// return we're not supposed to modify `%esp` or `%eax`.
+
+.text
+.p2align 4,,15
+.globl  __rust_probestack
+.type   __rust_probestack, @function
+__rust_probestack:
+    .cfi_startproc
+    pushq   %rbp
+    .cfi_def_cfa_offset 16
+    .cfi_offset 6, -16
+    movq    %rsp, %rbp
+    .cfi_def_cfa_register 6
+    mov    %rax,%r11
+    // duplicate %rax as we're clobbering %r11
+
+    // Main loop, taken in one page increments. We're decrementing rsp by
+    // a page each time until there's less than a page remaining. We're
+    // guaranteed that this function isn't called unless there's more than a
+    // page needed.
+    //
+    // Note that we're also testing against `8(%rsp)` to account for the 8
+    // bytes pushed on the stack orginally with our return address. Using
+    // `8(%rsp)` simulates us testing the stack pointer in the caller's
+    // context.
+
+    // It's usually called when %rax >= 0x1000, but that's not always true.
+    // Dynamic stack allocation, which is needed to implement unsized
+    // rvalues, triggers stackprobe even if %rax < 0x1000.
+    // Thus we have to check %r11 first to avoid segfault.
+    cmp    $0x1000,%r11
+    jna    3f
+2:
+    sub    $0x1000,%rsp
+    test   %rsp,8(%rsp)
+    sub    $0x1000,%r11
+    cmp    $0x1000,%r11
+    ja     2b
+
+3:
+    // Finish up the last remaining stack space requested, getting the last
+    // bits out of r11
+    sub    %r11,%rsp
+    test   %rsp,8(%rsp)
+
+    // Restore the stack pointer to what it previously was when entering
+    // this function. The caller will readjust the stack pointer after we
+    // return.
+    add    %rax,%rsp
+    leave
+    .cfi_def_cfa 7, 8
+    ret
+    .cfi_endproc