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Auto merge of #92845 - Amanieu:std_personality, r=Mark-Simulacrum

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Move EH personality functions to std

These were previously in the panic_unwind crate with dummy stubs in the
panic_abort crate. However it turns out that this is insufficient: we
still need a proper personality function even with -C panic=abort to
handle the following cases:

1) `extern "C-unwind"` still needs to catch foreign exceptions with -C
panic=abort to turn them into aborts. This requires landing pads and a
personality function.

2) ARM EHABI uses the personality function when creating backtraces.
The dummy personality function in panic_abort was causing backtrace
generation to get stuck in a loop since the personality function is
responsible for advancing the unwind state to the next frame.

Fixes #41004
This commit is contained in:
bors 2022-08-28 04:16:29 +00:00
commit 91f128baf7
16 changed files with 379 additions and 339 deletions
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18
compiler/rustc_codegen_ssa/src/back/symbol_export.rs
View File

@ -103,18 +103,14 @@ fn reachable_non_generics_provider(tcx: TyCtxt<'_>, cnum: CrateNum) -> DefIdMap<
}
})
.map(|def_id| {
let (export_level, used) = if special_runtime_crate {
let name = tcx.symbol_name(Instance::mono(tcx, def_id.to_def_id())).name;
// We won't link right if these symbols are stripped during LTO.
let used = match name {
"rust_eh_personality"
| "rust_eh_register_frames"
| "rust_eh_unregister_frames" => true,
_ => false,
};
(SymbolExportLevel::Rust, used)
// We won't link right if this symbol is stripped during LTO.
let name = tcx.symbol_name(Instance::mono(tcx, def_id.to_def_id())).name;
let used = name == "rust_eh_personality";
let export_level = if special_runtime_crate {
SymbolExportLevel::Rust
} else {
(symbol_export_level(tcx, def_id.to_def_id()), false)
symbol_export_level(tcx, def_id.to_def_id())
};
let codegen_attrs = tcx.codegen_fn_attrs(def_id.to_def_id());
debug!(

33
library/panic_abort/src/lib.rs
View File

@ -113,27 +113,11 @@ unsafe fn abort() -> ! {
// binaries, but it should never be called as we don't link in an unwinding
// runtime at all.
pub mod personalities {
#[rustc_std_internal_symbol]
#[cfg(not(any(
all(target_family = "wasm", not(target_os = "emscripten")),
all(target_os = "windows", target_env = "gnu", target_arch = "x86_64",),
)))]
pub extern "C" fn rust_eh_personality() {}
// In the past this module used to contain stubs for the personality
// functions of various platforms, but these where removed when personality
// functions were moved to std.
// On x86_64-pc-windows-gnu we use our own personality function that needs
// to return `ExceptionContinueSearch` as we're passing on all our frames.
#[rustc_std_internal_symbol]
#[cfg(all(target_os = "windows", target_env = "gnu", target_arch = "x86_64"))]
pub extern "C" fn rust_eh_personality(
_record: usize,
_frame: usize,
_context: usize,
_dispatcher: usize,
) -> u32 {
1 // `ExceptionContinueSearch`
}
// Similar to above, this corresponds to the `eh_catch_typeinfo` lang item
// This corresponds to the `eh_catch_typeinfo` lang item
// that's only used on Emscripten currently.
//
// Since panics don't generate exceptions and foreign exceptions are
@ -143,13 +127,4 @@ pub extern "C" fn rust_eh_personality(
#[allow(non_upper_case_globals)]
#[cfg(target_os = "emscripten")]
static rust_eh_catch_typeinfo: [usize; 2] = [0; 2];
// These two are called by our startup objects on i686-pc-windows-gnu, but
// they don't need to do anything so the bodies are nops.
#[rustc_std_internal_symbol]
#[cfg(all(target_os = "windows", target_env = "gnu", target_arch = "x86"))]
pub extern "C" fn rust_eh_register_frames() {}
#[rustc_std_internal_symbol]
#[cfg(all(target_os = "windows", target_env = "gnu", target_arch = "x86"))]
pub extern "C" fn rust_eh_unregister_frames() {}
}

16
library/panic_unwind/src/emcc.rs
View File

@ -12,7 +12,6 @@
use core::mem;
use core::ptr;
use core::sync::atomic::{AtomicBool, Ordering};
use libc::{self, c_int};
use unwind as uw;
// This matches the layout of std::type_info in C++
@ -105,21 +104,6 @@ extern "C" fn exception_cleanup(ptr: *mut libc::c_void) -> *mut libc::c_void {
}
}
// This is required by the compiler to exist (e.g., it's a lang item), but it's
// never actually called by the compiler. Emscripten EH doesn't use a
// personality function at all, it instead uses __cxa_find_matching_catch.
// Wasm error handling would use __gxx_personality_wasm0.
#[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 {
core::intrinsics::abort()
}
extern "C" {
fn __cxa_allocate_exception(thrown_size: libc::size_t) -> *mut libc::c_void;
fn __cxa_begin_catch(thrown_exception: *mut libc::c_void) -> *mut libc::c_void;

262
library/panic_unwind/src/gcc.rs
View File

@ -39,8 +39,6 @@
use alloc::boxed::Box;
use core::any::Any;
use crate::dwarf::eh::{self, EHAction, EHContext};
use libc::{c_int, uintptr_t};
use unwind as uw;
#[repr(C)]
@ -89,263 +87,3 @@ 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 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)
}
// 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);
}
#[rustc_std_internal_symbol]
pub unsafe extern "C" fn rust_eh_register_frames(eh_frame_begin: *const u8, object: *mut u8) {
__register_frame_info(eh_frame_begin, object);
}
#[rustc_std_internal_symbol]
pub unsafe extern "C" fn rust_eh_unregister_frames(eh_frame_begin: *const u8, object: *mut u8) {
__deregister_frame_info(eh_frame_begin, object);
}
}

5
library/panic_unwind/src/lib.rs
View File

@ -52,9 +52,6 @@
all(target_family = "unix", not(target_os = "espidf")),
all(target_vendor = "fortanix", target_env = "sgx"),
))] {
// Rust runtime's startup objects depend on these symbols, so make them public.
#[cfg(all(target_os="windows", target_arch = "x86", target_env="gnu"))]
pub use real_imp::eh_frame_registry::*;
#[path = "gcc.rs"]
mod real_imp;
} else {
@ -92,8 +89,6 @@
fn __rust_foreign_exception() -> !;
}
mod dwarf;
#[rustc_std_internal_symbol]
#[allow(improper_ctypes_definitions)]
pub unsafe extern "C" fn __rust_panic_cleanup(payload: *mut u8) -> *mut (dyn Any + Send + 'static) {

10
library/panic_unwind/src/seh.rs
View File

@ -326,13 +326,3 @@ pub unsafe fn cleanup(payload: *mut u8) -> Box<dyn Any + Send> {
exception.data.take().unwrap()
}
}
// This is required by the compiler to exist (e.g., it's a lang item), but
// it's never actually called by the compiler because __C_specific_handler
// or _except_handler3 is the personality function that is always used.
// Hence this is just an aborting stub.
#[lang = "eh_personality"]
#[cfg(not(test))]
fn rust_eh_personality() {
core::intrinsics::abort()
}

19
library/rtstartup/rsbegin.rs
View File

@ -35,6 +35,16 @@ pub unsafe fn drop_in_place<T: ?Sized>(to_drop: *mut T) {
drop_in_place(to_drop);
}
// 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.
#[cfg(all(target_os = "windows", target_arch = "x86", target_env = "gnu"))]
pub mod eh_frames {
#[no_mangle]
@ -62,20 +72,19 @@ impl ::Copy for $t {}
}
// Unwind info registration/deregistration routines.
// See the docs of libpanic_unwind.
extern "C" {
fn rust_eh_register_frames(eh_frame_begin: *const u8, object: *mut u8);
fn rust_eh_unregister_frames(eh_frame_begin: *const u8, object: *mut u8);
fn __register_frame_info(eh_frame_begin: *const u8, object: *mut u8);
fn __deregister_frame_info(eh_frame_begin: *const u8, object: *mut u8);
}
unsafe extern "C" fn init() {
// register unwind info on module startup
rust_eh_register_frames(&__EH_FRAME_BEGIN__ as *const u8, &mut OBJ as *mut _ as *mut u8);
__register_frame_info(&__EH_FRAME_BEGIN__ as *const u8, &mut OBJ as *mut _ as *mut u8);
}
unsafe extern "C" fn uninit() {
// unregister on shutdown
rust_eh_unregister_frames(&__EH_FRAME_BEGIN__ as *const u8, &mut OBJ as *mut _ as *mut u8);
__deregister_frame_info(&__EH_FRAME_BEGIN__ as *const u8, &mut OBJ as *mut _ as *mut u8);
}
// MinGW-specific init/uninit routine registration

1
library/std/src/lib.rs
View File

@ -594,6 +594,7 @@ pub mod arch {
// Private support modules
mod panicking;
mod personality;
#[path = "../../backtrace/src/lib.rs"]
#[allow(dead_code, unused_attributes)]

46
library/std/src/personality.rs Normal file
View File

@ -0,0 +1,46 @@
//! This module contains the implementation of the `eh_personality` lang item.
//!
//! The actual implementation is heavily dependent on the target since Rust
//! tries to use the native stack unwinding mechanism whenever possible.
//!
//! This personality function is still required with `-C panic=abort` because
//! it is used to catch foreign exceptions from `extern "C-unwind"` and turn
//! them into aborts.
//!
//! Additionally, ARM EHABI uses the personality function when generating
//! backtraces.
mod dwarf;
#[cfg(not(test))]
cfg_if::cfg_if! {
if #[cfg(target_os = "emscripten")] {
mod emcc;
} else if #[cfg(target_env = "msvc")] {
// This is required by the compiler to exist (e.g., it's a lang item),
// but it's never actually called by the compiler because
// _CxxFrameHandler3 is the personality function that is always used.
// Hence this is just an aborting stub.
#[lang = "eh_personality"]
fn rust_eh_personality() {
core::intrinsics::abort()
}
} else if #[cfg(any(
all(target_family = "windows", target_env = "gnu"),
target_os = "psp",
target_os = "solid_asp3",
all(target_family = "unix", not(target_os = "espidf")),
all(target_vendor = "fortanix", target_env = "sgx"),
))] {
mod gcc;
} else {
// Targets that don't support unwinding.
// - family=wasm
// - os=none ("bare metal" targets)
// - os=uefi
// - os=espidf
// - os=hermit
// - nvptx64-nvidia-cuda
// - arch=avr
}
}

2
library/panic_unwind/src/dwarf/eh.rs → library/std/src/personality/dwarf/eh.rs
View File

@ -11,7 +11,7 @@
#![allow(non_upper_case_globals)]
#![allow(unused)]
use crate::dwarf::DwarfReader;
use super::DwarfReader;
use core::mem;
pub const DW_EH_PE_omit: u8 = 0xFF;

0
library/panic_unwind/src/dwarf/mod.rs → library/std/src/personality/dwarf/mod.rs
View File

0
library/panic_unwind/src/dwarf/tests.rs → library/std/src/personality/dwarf/tests.rs
View File

20
library/std/src/personality/emcc.rs Normal file
View File

@ -0,0 +1,20 @@
//! On Emscripten Rust panics are wrapped in C++ exceptions, so we just forward
//! to `__gxx_personality_v0` which is provided by Emscripten.
use libc::c_int;
use unwind as uw;
// This is required by the compiler to exist (e.g., it's a lang item), but it's
// never actually called by the compiler. Emscripten EH doesn't use a
// personality function at all, it instead uses __cxa_find_matching_catch.
// Wasm error handling would use __gxx_personality_wasm0.
#[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 {
core::intrinsics::abort()
}

279
library/std/src/personality/gcc.rs Normal file
View File

@ -0,0 +1,279 @@
//! 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)
}

5
src/test/run-make-fulldeps/issue-69368/a.rs
View File

@ -19,3 +19,8 @@ extern "C" fn __rust_drop_panic() -> ! {
extern "C" fn __rust_foreign_exception() -> ! {
loop {}
}
#[lang = "eh_personality"]
fn eh_personality() {
loop {}
}

2
src/tools/tidy/src/pal.rs
View File

@ -59,6 +59,8 @@
"library/std/src/sys_common", // Should only contain abstractions over platforms
"library/std/src/net/test.rs", // Utility helpers for tests
"library/std/src/panic.rs", // fuchsia-specific panic backtrace handling
"library/std/src/personality.rs",
"library/std/src/personality/",
];
pub fn check(path: &Path, bad: &mut bool) {