279 lines
13 KiB
Rust
279 lines
13 KiB
Rust
//! 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, any(target_arch = "aarch64", 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)
|
|
}
|