Auto merge of rust-lang#74576 - myfreeweb:freebsd-sanitizers, r=oli-obk

Add sanitizer support on FreeBSD

Restarting rust-lang#47337. Everything is better now, no more weird llvm problems, well not everything:

Unfortunately, the sanitizers don't have proper support for versioned symbols (google/sanitizers#628), so `libc`'s usage of `stat@FBSD_1.0` and so on explodes, e.g. in calling `std::fs::metadata`.

Building std (now easy thanks to cargo `-Zbuild-std`) and libc with `freebsd12/13` config via the `LIBC_CI=1` env variable is a good workaround…

```
LIBC_CI=1 RUSTFLAGS="-Z sanitizer=address" cargo +san-test -Zbuild-std run --target x86_64-unknown-freebsd --verbose
```

…*except* std won't build because there's no `st_lspare` in the ino64 version of the struct, so an std patch is required:

```diff
--- i/src/libstd/os/freebsd/fs.rs
+++ w/src/libstd/os/freebsd/fs.rs
@@ -66,8 +66,6 @@ pub trait MetadataExt {
     fn st_flags(&self) -> u32;
     #[stable(feature = "metadata_ext2", since = "1.8.0")]
     fn st_gen(&self) -> u32;
-    #[stable(feature = "metadata_ext2", since = "1.8.0")]
-    fn st_lspare(&self) -> u32;
 }

 #[stable(feature = "metadata_ext", since = "1.1.0")]
@@ -136,7 +134,4 @@ impl MetadataExt for Metadata {
     fn st_flags(&self) -> u32 {
         self.as_inner().as_inner().st_flags as u32
     }
-    fn st_lspare(&self) -> u32 {
-        self.as_inner().as_inner().st_lspare as u32
-    }
 }
```

I guess std could like.. detect that `libc` isn't built for the old ABI, and replace the implementation of `st_lspare` with a panic?

Author: bors

std/build.rs

@@ -16,6 +16,9 @@ fn main() {
     } else if target.contains("freebsd") {
         println!("cargo:rustc-link-lib=execinfo");
         println!("cargo:rustc-link-lib=pthread");
+        if env::var("RUST_STD_FREEBSD_12_ABI").is_ok() {
+            println!("cargo:rustc-cfg=freebsd12");
+        }
     } else if target.contains("netbsd") {
         println!("cargo:rustc-link-lib=pthread");
         println!("cargo:rustc-link-lib=rt");

std/src/os/freebsd/fs.rs

@@ -74,7 +74,14 @@ pub trait MetadataExt {
 impl MetadataExt for Metadata {
     #[allow(deprecated)]
     fn as_raw_stat(&self) -> &raw::stat {
-        unsafe { &*(self.as_inner().as_inner() as *const libc::stat as *const raw::stat) }
+        // The methods below use libc::stat, so they work fine when libc is built with FreeBSD 12 ABI.
+        // This method would just return nonsense.
+        #[cfg(freebsd12)]
+        panic!("as_raw_stat not supported with FreeBSD 12 ABI");
+        #[cfg(not(freebsd12))]
+        unsafe {
+            &*(self.as_inner().as_inner() as *const libc::stat as *const raw::stat)
+        }
     }
     fn st_dev(&self) -> u64 {
         self.as_inner().as_inner().st_dev as u64
@@ -136,6 +143,11 @@ impl MetadataExt for Metadata {
     fn st_flags(&self) -> u32 {
         self.as_inner().as_inner().st_flags as u32
     }
+    #[cfg(freebsd12)]
+    fn st_lspare(&self) -> u32 {
+        panic!("st_lspare not supported with FreeBSD 12 ABI");
+    }
+    #[cfg(not(freebsd12))]
     fn st_lspare(&self) -> u32 {
         self.as_inner().as_inner().st_lspare as u32
     }