Ensure the personality does not panic

library/std/src/sys/personality/gcc.rs

@@ -37,9 +37,12 @@
 //! and the last personality routine transfers control to the catch block.
 #![forbid(unsafe_op_in_unsafe_fn)]
 
+mod dwarf;
+mod eh;
+
 use unwind as uw;
 
-use super::dwarf::eh::{self, EHAction, EHContext};
+use self::eh::{EHAction, EHContext};
 use crate::ffi::c_int;
 
 // Register ids were lifted from LLVM's TargetLowering::getExceptionPointerRegister()
@@ -332,8 +335,7 @@ unsafe fn find_eh_action(context: *mut uw::_Unwind_Context) -> Result<EHAction,
  // `ip = -1` has special meaning, so use wrapping sub to allow for that
  ip: if ip_before_instr != 0 { ip } else { ip.wrapping_sub(1) },
  func_start: uw::_Unwind_GetRegionStart(context),
- get_text_start: &|| uw::_Unwind_GetTextRelBase(context),
- get_data_start: &|| uw::_Unwind_GetDataRelBase(context),
+ raw_context: context,
  };
  eh::find_eh_action(lsda, &eh_context)
  }

library/std/src/sys/personality/dwarf/mod.rs → library/std/src/sys/personality/gcc/dwarf.rs

@@ -10,8 +10,6 @@
 #[cfg(test)]
 mod tests;
 
-pub mod eh;
-
 pub struct DwarfReader {
  pub ptr: *const u8,
 }

library/std/src/sys/personality/dwarf/eh.rs → library/std/src/sys/personality/gcc/eh.rs

@@ -14,7 +14,9 @@
 
 use core::ptr;
 
-use super::DwarfReader;
+use unwind as uw;
+
+use super::dwarf::DwarfReader;
 
 pub const DW_EH_PE_omit: u8 = 0xFF;
 pub const DW_EH_PE_absptr: u8 = 0x00;
@@ -37,11 +39,10 @@ pub const DW_EH_PE_aligned: u8 = 0x50;
 pub const DW_EH_PE_indirect: u8 = 0x80;
 
 #[derive(Copy, Clone)]
-pub struct EHContext<'a> {
- pub ip: *const u8, // Current instruction pointer
- pub func_start: *const u8, // Pointer to the current function
- pub get_text_start: &'a dyn Fn() -> *const u8, // Get pointer to the code section
- pub get_data_start: &'a dyn Fn() -> *const u8, // Get pointer to the data section
+pub struct EHContext {
+ pub(crate) ip: *const u8, // Current instruction pointer
+ pub(crate) func_start: *const u8, // Pointer to the current function
+ pub(crate) raw_context: *mut uw::_Unwind_Context,
 }
 
 /// Landing pad.
@@ -63,7 +64,7 @@ pub enum EHAction {
 pub const USING_SJLJ_EXCEPTIONS: bool =
  cfg!(all(target_vendor = "apple", not(target_os = "watchos"), target_arch = "arm"));
 
-pub unsafe fn find_eh_action(lsda: *const u8, context: &EHContext<'_>) -> Result<EHAction, ()> {
+pub unsafe fn find_eh_action(lsda: *const u8, context: &EHContext) -> Result<EHAction, ()> {
  if lsda.is_null() {
  return Ok(EHAction::None);
  }
@@ -224,7 +225,7 @@ unsafe fn read_encoded_offset(reader: &mut DwarfReader, encoding: u8) -> Result<
 /// [LSB-dwarf-ext]: https://refspecs.linuxfoundation.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/dwarfext.html
 unsafe fn read_encoded_pointer(
  reader: &mut DwarfReader,
- context: &EHContext<'_>,
+ context: &EHContext,
  encoding: u8,
 ) -> Result<*const u8, ()> {
  if encoding == DW_EH_PE_omit {
@@ -241,8 +242,8 @@ unsafe fn read_encoded_pointer(
  }
  context.func_start
  }
- DW_EH_PE_textrel => (*context.get_text_start)(),
- DW_EH_PE_datarel => (*context.get_data_start)(),
+ DW_EH_PE_textrel => unsafe { uw::_Unwind_GetTextRelBase(context.raw_context) },
+ DW_EH_PE_datarel => unsafe { uw::_Unwind_GetDataRelBase(context.raw_context) },
  // aligned means the value is aligned to the size of a pointer
  DW_EH_PE_aligned => {
  reader.ptr = reader.ptr.with_addr(round_up(reader.ptr.addr(), size_of::<*const u8>())?);

library/std/src/sys/personality/mod.rs

@@ -10,8 +10,6 @@
 //! Additionally, ARM EHABI uses the personality function when generating
 //! backtraces.
 
-mod dwarf;
-
 #[cfg(not(any(test, doctest)))]
 cfg_select! {
  target_os = "emscripten" => {

tests/run-make-cargo/panic-free-cdylib/Cargo.toml

@@ -0,0 +1,11 @@
+[package]
+name = "add"
+version = "0.1.0"
+edition = "2024"
+
+[lib]
+path = "lib.rs"
+crate-type = ["cdylib"]
+
+[profile.release]
+lto = "fat"

tests/run-make-cargo/panic-free-cdylib/lib.rs

@@ -0,0 +1,5 @@
+#![crate_type = "cdylib"]
+
+pub extern "C" fn add(a: u64, b: u64) -> u64 {
+ a + b
+}

tests/run-make-cargo/panic-free-cdylib/rmake.rs

@@ -0,0 +1,43 @@
+// This ensures that a cdylib that uses std and panic=unwind but does not
+// have any panics itself will not have *any* panic-related code in the final
+// binary, at least when using fat LTO
+// (since all the necessary nounwind propagation requires fat LTO).
+//
+// This code used to be pulled in via a landing pad in the personality function,
+// (since that is `extern "C"` and therefore panics if something unwinds), so
+// if this failed because you modified the personality function, ensure it contains
+// no potentially unwinding calls.
+
+use run_make_support::{cargo, dynamic_lib_name, llvm_nm, path, rustc, target};
+
+fn main() {
+ let target_dir = path("target");
+
+ // We use build-std to ensure that the sysroot does not have debug assertions,
+ // as this doesn't work with debug assertions.
+ cargo()
+ .args(&[
+ "build",
+ "--manifest-path",
+ "Cargo.toml",
+ "--release",
+ "-Zbuild-std=std",
+ "--target",
+ &target(),
+ ])
+ .env("CARGO_TARGET_DIR", &target_dir)
+ .env("RUSTC_BOOTSTRAP", "1")
+ .run();
+
+ let output_path = target_dir.join(target()).join("release").join(dynamic_lib_name("add"));
+
+ llvm_nm()
+ .input(output_path)
+ .run()
+ // a collection of panic-related strings. if this appears in the output
+ // for other reasons than having panic symbols, I am sorry.
+ .assert_stdout_not_contains("panic")
+ .assert_stdout_not_contains("addr2line")
+ .assert_stdout_not_contains("backtrace")
+ .assert_stdout_not_contains("gimli");
+}