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+//! Implementation of panics backed by libgcc/libunwind (in some form).
+//!
+//! For background on exception handling and stack unwinding please see
+//! "Exception Handling in LLVM" (llvm.org/docs/ExceptionHandling.html) and
+//! documents linked from it.
+//! These are also good reads:
+//! * <https://itanium-cxx-abi.github.io/cxx-abi/abi-eh.html>
+//! * <https://monoinfinito.wordpress.com/series/exception-handling-in-c/>
+//! * <https://www.airs.com/blog/index.php?s=exception+frames>
+//!
+//! ## A brief summary
+//!
+//! Exception handling happens in two phases: a search phase and a cleanup
+//! phase.
+//!
+//! In both phases the unwinder walks stack frames from top to bottom using
+//! information from the stack frame unwind sections of the current process's
+//! modules ("module" here refers to an OS module, i.e., an executable or a
+//! dynamic library).
+//!
+//! For each stack frame, it invokes the associated "personality routine", whose
+//! address is also stored in the unwind info section.
+//!
+//! In the search phase, the job of a personality routine is to examine
+//! exception object being thrown, and to decide whether it should be caught at
+//! that stack frame. Once the handler frame has been identified, cleanup phase
+//! begins.
+//!
+//! In the cleanup phase, the unwinder invokes each personality routine again.
+//! This time it decides which (if any) cleanup code needs to be run for
+//! the current stack frame. If so, the control is transferred to a special
+//! branch in the function body, the "landing pad", which invokes destructors,
+//! frees memory, etc. At the end of the landing pad, control is transferred
+//! back to the unwinder and unwinding resumes.
+//!
+//! Once stack has been unwound down to the handler frame level, unwinding stops
+//! and the last personality routine transfers control to the catch block.
+
+use super::dwarf::eh::{self, EHAction, EHContext};
+use libc::{c_int, uintptr_t};
+use unwind as uw;
+
+// Register ids were lifted from LLVM's TargetLowering::getExceptionPointerRegister()
+// and TargetLowering::getExceptionSelectorRegister() for each architecture,
+// then mapped to DWARF register numbers via register definition tables
+// (typically <arch>RegisterInfo.td, search for "DwarfRegNum").
+// See also https://llvm.org/docs/WritingAnLLVMBackend.html#defining-a-register.
+
+#[cfg(target_arch = "x86")]
+const UNWIND_DATA_REG: (i32, i32) = (0, 2); // EAX, EDX
+
+#[cfg(target_arch = "x86_64")]
+const UNWIND_DATA_REG: (i32, i32) = (0, 1); // RAX, RDX
+
+#[cfg(any(target_arch = "arm", target_arch = "aarch64"))]
+const UNWIND_DATA_REG: (i32, i32) = (0, 1); // R0, R1 / X0, X1
+
+#[cfg(target_arch = "m68k")]
+const UNWIND_DATA_REG: (i32, i32) = (0, 1); // D0, D1
+
+#[cfg(any(target_arch = "mips", target_arch = "mips64"))]
+const UNWIND_DATA_REG: (i32, i32) = (4, 5); // A0, A1
+
+#[cfg(any(target_arch = "powerpc", target_arch = "powerpc64"))]
+const UNWIND_DATA_REG: (i32, i32) = (3, 4); // R3, R4 / X3, X4
+
+#[cfg(target_arch = "s390x")]
+const UNWIND_DATA_REG: (i32, i32) = (6, 7); // R6, R7
+
+#[cfg(any(target_arch = "sparc", target_arch = "sparc64"))]
+const UNWIND_DATA_REG: (i32, i32) = (24, 25); // I0, I1
+
+#[cfg(target_arch = "hexagon")]
+const UNWIND_DATA_REG: (i32, i32) = (0, 1); // R0, R1
+
+#[cfg(any(target_arch = "riscv64", target_arch = "riscv32"))]
+const UNWIND_DATA_REG: (i32, i32) = (10, 11); // x10, x11
+
+// The following code is based on GCC's C and C++ personality routines. For reference, see:
+// https://github.com/gcc-mirror/gcc/blob/master/libstdc++-v3/libsupc++/eh_personality.cc
+// https://github.com/gcc-mirror/gcc/blob/trunk/libgcc/unwind-c.c
+
+cfg_if::cfg_if! {
+ if #[cfg(all(target_arch = "arm", not(target_os = "ios"), not(target_os = "watchos"), not(target_os = "netbsd")))] {
+ // ARM EHABI personality routine.
+ // https://infocenter.arm.com/help/topic/com.arm.doc.ihi0038b/IHI0038B_ehabi.pdf
+ //
+ // iOS uses the default routine instead since it uses SjLj unwinding.
+ #[lang = "eh_personality"]
+ unsafe extern "C" fn rust_eh_personality(
+ state: uw::_Unwind_State,
+ exception_object: *mut uw::_Unwind_Exception,
+ context: *mut uw::_Unwind_Context,
+ ) -> uw::_Unwind_Reason_Code {
+ let state = state as c_int;
+ let action = state & uw::_US_ACTION_MASK as c_int;
+ let search_phase = if action == uw::_US_VIRTUAL_UNWIND_FRAME as c_int {
+ // Backtraces on ARM will call the personality routine with
+ // state == _US_VIRTUAL_UNWIND_FRAME | _US_FORCE_UNWIND. In those cases
+ // we want to continue unwinding the stack, otherwise all our backtraces
+ // would end at __rust_try
+ if state & uw::_US_FORCE_UNWIND as c_int != 0 {
+ return continue_unwind(exception_object, context);
+ }
+ true
+ } else if action == uw::_US_UNWIND_FRAME_STARTING as c_int {
+ false
+ } else if action == uw::_US_UNWIND_FRAME_RESUME as c_int {
+ return continue_unwind(exception_object, context);
+ } else {
+ return uw::_URC_FAILURE;
+ };
+
+ // The DWARF unwinder assumes that _Unwind_Context holds things like the function
+ // and LSDA pointers, however ARM EHABI places them into the exception object.
+ // To preserve signatures of functions like _Unwind_GetLanguageSpecificData(), which
+ // take only the context pointer, GCC personality routines stash a pointer to
+ // exception_object in the context, using location reserved for ARM's
+ // "scratch register" (r12).
+ uw::_Unwind_SetGR(context, uw::UNWIND_POINTER_REG, exception_object as uw::_Unwind_Ptr);
+ // ...A more principled approach would be to provide the full definition of ARM's
+ // _Unwind_Context in our libunwind bindings and fetch the required data from there
+ // directly, bypassing DWARF compatibility functions.
+
+ let eh_action = match find_eh_action(context) {
+ Ok(action) => action,
+ Err(_) => return uw::_URC_FAILURE,
+ };
+ if search_phase {
+ match eh_action {
+ EHAction::None | EHAction::Cleanup(_) => {
+ return continue_unwind(exception_object, context);
+ }
+ EHAction::Catch(_) => {
+ // EHABI requires the personality routine to update the
+ // SP value in the barrier cache of the exception object.
+ (*exception_object).private[5] =
+ uw::_Unwind_GetGR(context, uw::UNWIND_SP_REG);
+ return uw::_URC_HANDLER_FOUND;
+ }
+ EHAction::Terminate => return uw::_URC_FAILURE,
+ }
+ } else {
+ match eh_action {
+ EHAction::None => return continue_unwind(exception_object, context),
+ EHAction::Cleanup(lpad) | EHAction::Catch(lpad) => {
+ uw::_Unwind_SetGR(
+ context,
+ UNWIND_DATA_REG.0,
+ exception_object as uintptr_t,
+ );
+ uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, 0);
+ uw::_Unwind_SetIP(context, lpad);
+ return uw::_URC_INSTALL_CONTEXT;
+ }
+ EHAction::Terminate => return uw::_URC_FAILURE,
+ }
+ }
+
+ // On ARM EHABI the personality routine is responsible for actually
+ // unwinding a single stack frame before returning (ARM EHABI Sec. 6.1).
+ unsafe fn continue_unwind(
+ exception_object: *mut uw::_Unwind_Exception,
+ context: *mut uw::_Unwind_Context,
+ ) -> uw::_Unwind_Reason_Code {
+ if __gnu_unwind_frame(exception_object, context) == uw::_URC_NO_REASON {
+ uw::_URC_CONTINUE_UNWIND
+ } else {
+ uw::_URC_FAILURE
+ }
+ }
+ // defined in libgcc
+ extern "C" {
+ fn __gnu_unwind_frame(
+ exception_object: *mut uw::_Unwind_Exception,
+ context: *mut uw::_Unwind_Context,
+ ) -> uw::_Unwind_Reason_Code;
+ }
+ }
+ } else {
+ // Default personality routine, which is used directly on most targets
+ // and indirectly on Windows x86_64 via SEH.
+ unsafe extern "C" fn rust_eh_personality_impl(
+ version: c_int,
+ actions: uw::_Unwind_Action,
+ _exception_class: uw::_Unwind_Exception_Class,
+ exception_object: *mut uw::_Unwind_Exception,
+ context: *mut uw::_Unwind_Context,
+ ) -> uw::_Unwind_Reason_Code {
+ if version != 1 {
+ return uw::_URC_FATAL_PHASE1_ERROR;
+ }
+ let eh_action = match find_eh_action(context) {
+ Ok(action) => action,
+ Err(_) => return uw::_URC_FATAL_PHASE1_ERROR,
+ };
+ if actions as i32 & uw::_UA_SEARCH_PHASE as i32 != 0 {
+ match eh_action {
+ EHAction::None | EHAction::Cleanup(_) => uw::_URC_CONTINUE_UNWIND,
+ EHAction::Catch(_) => uw::_URC_HANDLER_FOUND,
+ EHAction::Terminate => uw::_URC_FATAL_PHASE1_ERROR,
+ }
+ } else {
+ match eh_action {
+ EHAction::None => uw::_URC_CONTINUE_UNWIND,
+ EHAction::Cleanup(lpad) | EHAction::Catch(lpad) => {
+ uw::_Unwind_SetGR(
+ context,
+ UNWIND_DATA_REG.0,
+ exception_object as uintptr_t,
+ );
+ uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, 0);
+ uw::_Unwind_SetIP(context, lpad);
+ uw::_URC_INSTALL_CONTEXT
+ }
+ EHAction::Terminate => uw::_URC_FATAL_PHASE2_ERROR,
+ }
+ }
+ }
+
+ cfg_if::cfg_if! {
+ if #[cfg(all(windows, target_arch = "x86_64", target_env = "gnu"))] {
+ // On x86_64 MinGW targets, the unwinding mechanism is SEH however the unwind
+ // handler data (aka LSDA) uses GCC-compatible encoding.
+ #[lang = "eh_personality"]
+ #[allow(nonstandard_style)]
+ unsafe extern "C" fn rust_eh_personality(
+ exceptionRecord: *mut uw::EXCEPTION_RECORD,
+ establisherFrame: uw::LPVOID,
+ contextRecord: *mut uw::CONTEXT,
+ dispatcherContext: *mut uw::DISPATCHER_CONTEXT,
+ ) -> uw::EXCEPTION_DISPOSITION {
+ uw::_GCC_specific_handler(
+ exceptionRecord,
+ establisherFrame,
+ contextRecord,
+ dispatcherContext,
+ rust_eh_personality_impl,
+ )
+ }
+ } else {
+ // The personality routine for most of our targets.
+ #[lang = "eh_personality"]
+ unsafe extern "C" fn rust_eh_personality(
+ version: c_int,
+ actions: uw::_Unwind_Action,
+ exception_class: uw::_Unwind_Exception_Class,
+ exception_object: *mut uw::_Unwind_Exception,
+ context: *mut uw::_Unwind_Context,
+ ) -> uw::_Unwind_Reason_Code {
+ rust_eh_personality_impl(
+ version,
+ actions,
+ exception_class,
+ exception_object,
+ context,
+ )
+ }
+ }
+ }
+ }
+}
+
+unsafe fn find_eh_action(context: *mut uw::_Unwind_Context) -> Result<EHAction, ()> {
+ let lsda = uw::_Unwind_GetLanguageSpecificData(context) as *const u8;
+ let mut ip_before_instr: c_int = 0;
+ let ip = uw::_Unwind_GetIPInfo(context, &mut ip_before_instr);
+ let eh_context = EHContext {
+ // The return address points 1 byte past the call instruction,
+ // which could be in the next IP range in LSDA range table.
+ //
+ // `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),
+ };
+ eh::find_eh_action(lsda, &eh_context)
+}