rust/src/libpanic_unwind/gcc.rs

// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! 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:
//!     http://mentorembedded.github.io/cxx-abi/abi-eh.html
//!     http://monoinfinito.wordpress.com/series/exception-handling-in-c/
//!     http://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.
//!
//! ## `eh_personality` and `eh_unwind_resume`
//!
//! These language items are used by the compiler when generating unwind info.
//! The first one is the personality routine described above.  The second one
//! allows compilation target to customize the process of resuming unwind at the
//! end of the landing pads. `eh_unwind_resume` is used only if
//! `custom_unwind_resume` flag in the target options is set.

#![allow(private_no_mangle_fns)]

use core::any::Any;
use core::ptr;
use alloc::boxed::Box;

use unwind as uw;

#[repr(C)]
struct Exception {
    _uwe: uw::_Unwind_Exception,
    cause: Option<Box<Any + Send>>,
}

pub unsafe fn panic(data: Box<Any + Send>) -> u32 {
    let exception = Box::new(Exception {
        _uwe: uw::_Unwind_Exception {
            exception_class: rust_exception_class(),
            exception_cleanup: exception_cleanup,
            private: [0; uw::unwinder_private_data_size],
        },
        cause: Some(data),
    });
    let exception_param = Box::into_raw(exception) as *mut uw::_Unwind_Exception;
    return uw::_Unwind_RaiseException(exception_param) as u32;

    extern "C" fn exception_cleanup(_unwind_code: uw::_Unwind_Reason_Code,
                                    exception: *mut uw::_Unwind_Exception) {
        unsafe {
            let _: Box<Exception> = Box::from_raw(exception as *mut Exception);
        }
    }
}

pub fn payload() -> *mut u8 {
    ptr::null_mut()
}

pub unsafe fn cleanup(ptr: *mut u8) -> Box<Any + Send> {
    let my_ep = ptr as *mut Exception;
    let cause = (*my_ep).cause.take();
    uw::_Unwind_DeleteException(ptr as *mut _);
    cause.unwrap()
}

// Rust's exception class identifier.  This is used by personality routines to
// determine whether the exception was thrown by their own runtime.
fn rust_exception_class() -> uw::_Unwind_Exception_Class {
    // M O Z \0  R U S T -- vendor, language
    0x4d4f5a_00_52555354
}

// All targets, except ARM which uses a slightly different ABI (however, iOS goes here as it uses
// SjLj unwinding).  Also, 64-bit Windows implementation lives in seh64_gnu.rs
#[cfg(all(any(target_os = "ios", not(target_arch = "arm"))))]
pub mod eabi {
    use unwind as uw;
    use libc::{c_int, uintptr_t};
    use dwarf::eh::{EHContext, EHAction, find_eh_action};

    // 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 http://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(any(target_arch = "mips", target_arch = "mipsel"))]
    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

    // 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
    #[lang = "eh_personality"]
    #[no_mangle]
    #[allow(unused)]
    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 {
        if version != 1 {
            return uw::_URC_FATAL_PHASE1_ERROR;
        }
        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: if ip_before_instr != 0 { ip } else { ip - 1 },
            func_start: uw::_Unwind_GetRegionStart(context),
            get_text_start: &|| uw::_Unwind_GetTextRelBase(context),
            get_data_start: &|| uw::_Unwind_GetDataRelBase(context),
        };
        let eh_action = find_eh_action(lsda, &eh_context);

        if actions as i32 & uw::_UA_SEARCH_PHASE as i32 != 0 {
            match eh_action {
                EHAction::None | EHAction::Cleanup(_) => return uw::_URC_CONTINUE_UNWIND,
                EHAction::Catch(_) => return uw::_URC_HANDLER_FOUND,
                EHAction::Terminate => return uw::_URC_FATAL_PHASE1_ERROR,
            }
        } else {
            match eh_action {
                EHAction::None => return 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);
                    return uw::_URC_INSTALL_CONTEXT;
                }
                EHAction::Terminate => return uw::_URC_FATAL_PHASE2_ERROR,
            }
        }
    }

    #[cfg(stage0)]
    #[lang = "eh_personality_catch"]
    #[no_mangle]
    pub unsafe extern "C" fn rust_eh_personality_catch(version: c_int,
                                                       actions: uw::_Unwind_Action,
                                                       exception_class: uw::_Unwind_Exception_Class,
                                                       ue_header: *mut uw::_Unwind_Exception,
                                                       context: *mut uw::_Unwind_Context)
                                                       -> uw::_Unwind_Reason_Code {
        rust_eh_personality(version, actions, exception_class, ue_header, context)
    }
}

// ARM EHABI uses a slightly different personality routine signature,
// but otherwise works the same.
#[cfg(all(target_arch = "arm", not(target_os = "ios")))]
pub mod eabi {
    use unwind as uw;
    use libc::c_int;

    extern "C" {
        fn __gcc_personality_v0(state: uw::_Unwind_State,
                                ue_header: *mut uw::_Unwind_Exception,
                                context: *mut uw::_Unwind_Context)
                                -> uw::_Unwind_Reason_Code;
    }

    #[lang = "eh_personality"]
    #[no_mangle]
    extern "C" fn rust_eh_personality(state: uw::_Unwind_State,
                                      ue_header: *mut uw::_Unwind_Exception,
                                      context: *mut uw::_Unwind_Context)
                                      -> uw::_Unwind_Reason_Code {
        unsafe { __gcc_personality_v0(state, ue_header, context) }
    }

    #[lang = "eh_personality_catch"]
    #[no_mangle]
    pub extern "C" fn rust_eh_personality_catch(state: uw::_Unwind_State,
                                                ue_header: *mut uw::_Unwind_Exception,
                                                context: *mut uw::_Unwind_Context)
                                                -> uw::_Unwind_Reason_Code {
        // 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 as c_int & uw::_US_ACTION_MASK as c_int) ==
           uw::_US_VIRTUAL_UNWIND_FRAME as c_int &&
           (state as c_int & uw::_US_FORCE_UNWIND as c_int) == 0 {
            // search phase
            uw::_URC_HANDLER_FOUND // catch!
        } else {
            // cleanup phase
            unsafe { __gcc_personality_v0(state, ue_header, context) }
        }
    }
}

// See docs in the `unwind` module.
#[cfg(all(target_os="windows", target_arch = "x86", target_env="gnu"))]
#[lang = "eh_unwind_resume"]
#[unwind]
unsafe extern "C" fn rust_eh_unwind_resume(panic_ctx: *mut u8) -> ! {
    uw::_Unwind_Resume(panic_ctx as *mut uw::_Unwind_Exception);
}

// Frame unwind info registration
//
// Each module's image contains a frame unwind info section (usually
// ".eh_frame").  When a module is loaded/unloaded into the process, the
// unwinder must be informed about the location of this section in memory. The
// methods of achieving that vary by the platform.  On some (e.g. Linux), the
// unwinder can discover unwind info sections on its own (by dynamically
// enumerating currently loaded modules via the dl_iterate_phdr() API and
// finding their ".eh_frame" sections); Others, like Windows, require modules
// to actively register their unwind info sections via unwinder API.
//
// This module defines two symbols which are referenced and called from
// rsbegin.rs to reigster our information with the GCC runtime. The
// implementation of stack unwinding is (for now) deferred to libgcc_eh, however
// Rust crates use these Rust-specific entry points to avoid potential clashes
// with any GCC runtime.
#[cfg(all(target_os="windows", target_arch = "x86", target_env="gnu"))]
pub mod eh_frame_registry {
    #[link(name = "gcc_eh")]
    #[cfg(not(cargobuild))]
    extern "C" {}

    extern "C" {
        fn __register_frame_info(eh_frame_begin: *const u8, object: *mut u8);
        fn __deregister_frame_info(eh_frame_begin: *const u8, object: *mut u8);
    }

    #[no_mangle]
    pub unsafe extern "C" fn rust_eh_register_frames(eh_frame_begin: *const u8, object: *mut u8) {
        __register_frame_info(eh_frame_begin, object);
    }

    #[no_mangle]
    pub unsafe extern "C" fn rust_eh_unregister_frames(eh_frame_begin: *const u8,
                                                       object: *mut u8) {
        __deregister_frame_info(eh_frame_begin, object);
    }
}