poc hotpatch

Author: nebulark

compiler/rustc_codegen_llvm/src/attributes.rs

@@ -341,6 +341,10 @@ pub fn from_fn_attrs<'ll, 'tcx>(
         to_add.push(llvm::CreateAttrString(cx.llcx, "use-sample-profile"));
     }
 
+    if cx.sess().opts.unstable_opts.ms_hotpatch && cx.sess().target.is_x86() && cx.sess().target.is_like_msvc {
+        to_add.push(llvm::CreateAttrStringValue(cx.llcx, "patchable-function", "prologue-short-redirect"));
+    }
+
     // FIXME: none of these functions interact with source level attributes.
     to_add.extend(frame_pointer_type_attr(cx));
     to_add.extend(function_return_attr(cx));

compiler/rustc_codegen_llvm/src/back/owned_target_machine.rs

@@ -36,6 +36,7 @@ impl OwnedTargetMachine {
         emit_stack_size_section: bool,
         relax_elf_relocations: bool,
         use_init_array: bool,
+        use_hotpatch: bool,
         split_dwarf_file: &CStr,
         output_obj_file: &CStr,
         debug_info_compression: &CStr,
@@ -68,6 +69,7 @@ impl OwnedTargetMachine {
                 emit_stack_size_section,
                 relax_elf_relocations,
                 use_init_array,
+                use_hotpatch,
                 split_dwarf_file.as_ptr(),
                 output_obj_file.as_ptr(),
                 debug_info_compression.as_ptr(),

compiler/rustc_codegen_llvm/src/back/write.rs

@@ -220,6 +220,8 @@ pub fn target_machine_factory(
     let use_init_array =
         !sess.opts.unstable_opts.use_ctors_section.unwrap_or(sess.target.use_ctors_section);
 
+    let use_hotpatch = sess.opts.unstable_opts.ms_hotpatch && sess.target.is_x86() && sess.target.is_like_msvc;
+
     let path_mapping = sess.source_map().path_mapping().clone();
 
     let use_emulated_tls = matches!(sess.tls_model(), TlsModel::Emulated);
@@ -292,6 +294,7 @@ pub fn target_machine_factory(
             emit_stack_size_section,
             relax_elf_relocations,
             use_init_array,
+            use_hotpatch,
             &split_dwarf_file,
             &output_obj_file,
             &debuginfo_compression,

compiler/rustc_codegen_llvm/src/llvm/ffi.rs

@@ -2189,6 +2189,7 @@ extern "C" {
         EmitStackSizeSection: bool,
         RelaxELFRelocations: bool,
         UseInitArray: bool,
+        UseHotpatch: bool,
         SplitDwarfFile: *const c_char,
         OutputObjFile: *const c_char,
         DebugInfoCompression: *const c_char,

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -2347,6 +2347,17 @@ fn add_order_independent_options(
 
     add_link_script(cmd, sess, tmpdir, crate_type);
 
+    if sess.opts.unstable_opts.ms_hotpatch && sess.target.is_x86() && sess.target.is_like_msvc {
+        // when using hotpatch also automatically instruct the linker to pad the functions
+        // so there is space for a absolute jump instructions
+        match flavor {
+            LinkerFlavor::Msvc(_) => {
+                cmd.arg("-functionpadmin");
+            },
+            _ => (),
+        }
+    }
+
     if sess.target.os == "fuchsia"
         && crate_type == CrateType::Executable
         && !matches!(flavor, LinkerFlavor::Gnu(Cc::Yes, _))

compiler/rustc_interface/src/tests.rs

@@ -799,6 +799,7 @@ fn test_unstable_options_tracking_hash() {
     tracked!(mir_opt_level, Some(4));
     tracked!(move_size_limit, Some(4096));
     tracked!(mutable_noalias, false);
+    tracked!(ms_hotpatch, true);
     tracked!(
         next_solver,
         Some(NextSolverConfig { coherence: true, globally: false, dump_tree: Default::default() })

compiler/rustc_llvm/llvm-wrapper/PassWrapper.cpp

@@ -405,6 +405,7 @@ extern "C" LLVMTargetMachineRef LLVMRustCreateTargetMachine(
     bool EmitStackSizeSection,
     bool RelaxELFRelocations,
     bool UseInitArray,
+    bool UseHotpatch,
     const char *SplitDwarfFile,
     const char *OutputObjFile,
     const char *DebugInfoCompression,
@@ -436,6 +437,7 @@ extern "C" LLVMTargetMachineRef LLVMRustCreateTargetMachine(
   Options.MCOptions.AsmVerbose = AsmComments;
   Options.MCOptions.PreserveAsmComments = AsmComments;
   Options.MCOptions.ABIName = ABIStr;
+  Options.Hotpatch = UseHotpatch;
   if (SplitDwarfFile) {
       Options.MCOptions.SplitDwarfFile = SplitDwarfFile;
   }

compiler/rustc_session/src/options.rs

@@ -1815,6 +1815,10 @@ options! {
         "the size at which the `large_assignments` lint starts to be emitted"),
     mutable_noalias: bool = (true, parse_bool, [TRACKED],
         "emit noalias metadata for mutable references (default: yes)"),
+    ms_hotpatch: bool = (false, parse_bool, [TRACKED],
+        "ensures hotpatching is always possible by ensuring that the first instruction of \
+        each function is at least two bytes, and no jump within the function goes to the first instruction \
+        and adding enough padding to the beginning of each function. Only relevant for x86 with MSVC (default: false)"),
     next_solver: Option<NextSolverConfig> = (None, parse_next_solver_config, [TRACKED],
         "enable and configure the next generation trait solver used by rustc"),
     nll_facts: bool = (false, parse_bool, [UNTRACKED],

compiler/rustc_target/src/spec/mod.rs

@@ -1910,6 +1910,10 @@ impl Target {
 
         Ok(dl)
     }
+    pub fn is_x86(&self) -> bool {
+        // ["x86", "x86_64"].contains(&self.arch.as_ref())
+        ["x86", "x86_64"].contains(&&self.arch[..])
+    }
 }
 
 pub trait HasTargetSpec {