Skip to content
Permalink
Branch: master
Find file Copy path
Find file Copy path
Fetching contributors…
Cannot retrieve contributors at this time
318 lines (288 sloc) 13.4 KB
//! 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;
use libc::{c_int, uintptr_t};
use crate::dwarf::eh::{self, EHContext, EHAction};
#[repr(C)]
struct Exception {
_uwe: uw::_Unwind_Exception,
cause: Option<Box<dyn Any + Send>>,
}
pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
let exception = Box::new(Exception {
_uwe: uw::_Unwind_Exception {
exception_class: rust_exception_class(),
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<dyn 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
}
// 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 = "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(target_arch = "sparc64")]
const UNWIND_DATA_REG: (i32, i32) = (24, 25); // I0, I1
// 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
// The personality routine for most of our targets, except ARM, which has a slightly different ABI
// (however, iOS goes here as it uses SjLj unwinding). Also, the 64-bit Windows implementation
// lives in seh64_gnu.rs
#[cfg(all(any(target_os = "ios", target_os = "netbsd", not(target_arch = "arm"))))]
#[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 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(_) => 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,
}
}
}
// ARM EHABI personality routine.
// http://infocenter.arm.com/help/topic/com.arm.doc.ihi0038b/IHI0038B_ehabi.pdf
#[cfg(all(target_arch = "arm", not(target_os = "ios"), not(target_os = "netbsd")))]
#[lang = "eh_personality"]
#[no_mangle]
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(_) => 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;
}
}
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: 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),
};
eh::find_eh_action(lsda, &eh_context)
}
// See docs in the `unwind` module.
#[cfg(all(target_os="windows", target_arch = "x86", target_env="gnu"))]
#[lang = "eh_unwind_resume"]
#[unwind(allowed)]
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 register 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 {
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);
}
}
You can’t perform that action at this time.