Mangle personality symbol

Previously, std-internal symbols (like `__rust_alloc` or `rust_panic`)
were changed to now be mangled via a v0 scheme with the compiler version
hash (`_RNvCs4CIB29Id3dw_7___rustc10rust_panic`) to make it possible to
have multiple staticlibs (as long as they have different version hashes)
in the same program without symbol conflicts. But the personality
function remained unmangled, because LLVM hardcodes that name.

I made a change in LLVM that makes LLVM now check the suffix instead of
an exact match, so we can mangle the personality function with this
scheme.

This removes the last completely unmangled symbol from Rust staticlibs!
(though the mangling is still quite weak, so it's still not as nice as
it would ideally be).

Before, on a trivial staticlib:

```
readelf -s liblib.a | rg GLOBAL | rg -v " UND | HIDDEN " | rg -v ' _ZN'
     8: 0000000000000000     5 FUNC    GLOBAL DEFAULT     3 _RNvCseCSg29WUqSe_7___rustc12___rust_alloc
    10: 0000000000000000     5 FUNC    GLOBAL DEFAULT     5 _RNvCseCSg29WUqSe_7___rustc14___rust_dealloc
    12: 0000000000000000     5 FUNC    GLOBAL DEFAULT     7 _RNvCseCSg29WUqSe_7___rustc14___rust_realloc
    14: 0000000000000000     5 FUNC    GLOBAL DEFAULT     9 _RNvCseCSg29WUqSe_7___rustc19___rust_alloc_zeroed
    16: 0000000000000000     3 FUNC    GLOBAL DEFAULT    11 _RNvCseCSg29WUqSe_7___rustc42___rust_alloc_error_handler_should_panic_v2
    17: 0000000000000000     1 FUNC    GLOBAL DEFAULT    12 _RNvCseCSg29WUqSe_7___rustc35___rust_no_alloc_shim_is_unstable_v2
  3383: 0000000000000000   111 FUNC    GLOBAL DEFAULT     5 _RNvCseCSg29WUqSe_7___rustc10rust_panic
  3387: 0000000000000000    93 FUNC    GLOBAL DEFAULT     7 _RNvCseCSg29WUqSe_7___rustc11___rdl_alloc
  3390: 0000000000000000    10 FUNC    GLOBAL DEFAULT     9 _RNvCseCSg29WUqSe_7___rustc12___rust_abort
  3391: 0000000000000000     6 FUNC    GLOBAL DEFAULT    11 _RNvCseCSg29WUqSe_7___rustc13___rdl_dealloc
  3393: 0000000000000000   167 FUNC    GLOBAL DEFAULT    13 _RNvCseCSg29WUqSe_7___rustc13___rdl_realloc
  3396: 0000000000000000   203 FUNC    GLOBAL DEFAULT    15 _RNvCseCSg29WUqSe_7___rustc17___rust_drop_panic
  3399: 0000000000000000    29 FUNC    GLOBAL DEFAULT    18 _RNvCseCSg29WUqSe_7___rustc17rust_begin_unwind
  3401: 0000000000000000   140 FUNC    GLOBAL DEFAULT    20 _RNvCseCSg29WUqSe_7___rustc18___rdl_alloc_zeroed
  3404: 0000000000000000   203 FUNC    GLOBAL DEFAULT    22 _RNvCseCSg29WUqSe_7___rustc24___rust_foreign_exception
  3405: 0000000000000000    19 FUNC    GLOBAL DEFAULT    25 _RNvCseCSg29WUqSe_7___rustc26___rust_alloc_error_handler
  4410: 0000000000000000  1471 FUNC    GLOBAL DEFAULT   2752 rust_eh_personality
    25: 0000000000000000   161 FUNC    GLOBAL DEFAULT     5 _RNvCseCSg29WUqSe_7___rustc18___rust_start_panic
    32: 0000000000000000    82 FUNC    GLOBAL DEFAULT     8 _RNvCseCSg29WUqSe_7___rustc20___rust_panic_cleanup
   249: 0000000000000000   182 FUNC    GLOBAL DEFAULT     5 _RNvCseCSg29WUqSe_7___rustc25___rdl_alloc_error_handler
     3: 0000000000000000    57 FUNC    GLOBAL DEFAULT     3 _RNvCseCSg29WUqSe_7___rustc17___rust_probestack
```

After:

```
     8: 0000000000000000     5 FUNC    GLOBAL DEFAULT     3 _RNvCs4CIB29Id3dw_7___rustc12___rust_alloc
    10: 0000000000000000     5 FUNC    GLOBAL DEFAULT     5 _RNvCs4CIB29Id3dw_7___rustc14___rust_dealloc
    12: 0000000000000000     5 FUNC    GLOBAL DEFAULT     7 _RNvCs4CIB29Id3dw_7___rustc14___rust_realloc
    14: 0000000000000000     5 FUNC    GLOBAL DEFAULT     9 _RNvCs4CIB29Id3dw_7___rustc19___rust_alloc_zeroed
    16: 0000000000000000     3 FUNC    GLOBAL DEFAULT    11 _RNvCs4CIB29Id3dw_7___rustc42___rust_alloc_error_handler_should_panic_v2
    17: 0000000000000000     1 FUNC    GLOBAL DEFAULT    12 _RNvCs4CIB29Id3dw_7___rustc35___rust_no_alloc_shim_is_unstable_v2
   422: 0000000000000000    19 FUNC    GLOBAL DEFAULT     5 _RNvCs4CIB29Id3dw_7___rustc26___rust_alloc_error_handler
   429: 0000000000000000   308 FUNC    GLOBAL DEFAULT     5 _RNvCs4CIB29Id3dw_7___rustc19rust_eh_personality
   349: 0000000000000000    10 FUNC    GLOBAL DEFAULT     5 _RNvCs4CIB29Id3dw_7___rustc12___rust_abort
   164: 0000000000000000    93 FUNC    GLOBAL DEFAULT     5 _RNvCs4CIB29Id3dw_7___rustc11___rdl_alloc
   167: 0000000000000000    11 FUNC    GLOBAL DEFAULT     7 _RNvCs4CIB29Id3dw_7___rustc13___rdl_dealloc
   169: 0000000000000000   167 FUNC    GLOBAL DEFAULT     9 _RNvCs4CIB29Id3dw_7___rustc13___rdl_realloc
   172: 0000000000000000   140 FUNC    GLOBAL DEFAULT    11 _RNvCs4CIB29Id3dw_7___rustc18___rdl_alloc_zeroed
   688: 0000000000000000   106 FUNC    GLOBAL DEFAULT     5 _RNvCs4CIB29Id3dw_7___rustc10rust_panic
   693: 0000000000000000   207 FUNC    GLOBAL DEFAULT     7 _RNvCs4CIB29Id3dw_7___rustc17___rust_drop_panic
   696: 0000000000000000    29 FUNC    GLOBAL DEFAULT    10 _RNvCs4CIB29Id3dw_7___rustc17rust_begin_unwind
   698: 0000000000000000   207 FUNC    GLOBAL DEFAULT    12 _RNvCs4CIB29Id3dw_7___rustc24___rust_foreign_exception
    26: 0000000000000000   161 FUNC    GLOBAL DEFAULT     5 _RNvCs4CIB29Id3dw_7___rustc18___rust_start_panic
    33: 0000000000000000    82 FUNC    GLOBAL DEFAULT     8 _RNvCs4CIB29Id3dw_7___rustc20___rust_panic_cleanup
    88: 0000000000000000   182 FUNC    GLOBAL DEFAULT     5 _RNvCs4CIB29Id3dw_7___rustc25___rdl_alloc_error_handler
     3: 0000000000000000    57 FUNC    GLOBAL DEFAULT     3 _RNvCs4CIB29Id3dw_7___rustc17___rust_probestack
```

Author: Noratrieb

compiler/rustc_codegen_llvm/src/context.rs

@@ -862,7 +862,17 @@ impl<'ll, 'tcx> MiscCodegenMethods<'tcx> for CodegenCx<'ll, 'tcx> {
                 DUMMY_SP,
             )),
             _ => {
-                let name = name.unwrap_or("rust_eh_personality");
+                let mangled_symbol;
+                let name = match name {
+                    Some(name) => name,
+                    None => {
+                        mangled_symbol = rustc_symbol_mangling::mangle_internal_symbol(
+                            tcx,
+                            "rust_eh_personality",
+                        );
+                        mangled_symbol.as_str()
+                    }
+                };
                 if let Some(llfn) = self.get_declared_value(name) {
                     llfn
                 } else {

compiler/rustc_codegen_ssa/src/back/symbol_export.rs

@@ -5,6 +5,7 @@ use rustc_ast::expand::allocator::{
     ALLOC_ERROR_HANDLER, ALLOCATOR_METHODS, NO_ALLOC_SHIM_IS_UNSTABLE, global_fn_name,
 };
 use rustc_data_structures::unord::UnordMap;
+use rustc_hir::LangItem;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LOCAL_CRATE, LocalDefId};
 use rustc_middle::bug;
@@ -105,8 +106,7 @@ fn reachable_non_generics_provider(tcx: TyCtxt<'_>, _: LocalCrate) -> DefIdMap<S
         })
         .map(|def_id| {
             // We won't link right if this symbol is stripped during LTO.
-            let name = tcx.symbol_name(Instance::mono(tcx, def_id.to_def_id())).name;
-            let used = name == "rust_eh_personality";
+            let used = tcx.is_lang_item(def_id.to_def_id(), LangItem::EhPersonality);
 
             let export_level = if special_runtime_crate {
                 SymbolExportLevel::Rust

compiler/rustc_symbol_mangling/src/v0.rs

@@ -83,8 +83,6 @@ pub(super) fn mangle<'tcx>(
 
 pub fn mangle_internal_symbol<'tcx>(tcx: TyCtxt<'tcx>, item_name: &str) -> String {
     match item_name {
-        // rust_eh_personality must not be renamed as LLVM hard-codes the name
-        "rust_eh_personality" => return item_name.to_owned(),
         // Apple availability symbols need to not be mangled to be usable by
         // C/Objective-C code.
         "__isPlatformVersionAtLeast" | "__isOSVersionAtLeast" => return item_name.to_owned(),