Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Move EH personality functions to std #92845

Merged
merged 7 commits into from
Aug 28, 2022
Merged

Move EH personality functions to std #92845

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
7 commits
Select commit Hold shift + click to select a range
db94dbc
Fix comment on the SEH personality function
Amanieu Feb 9, 2022
5ff0876
Move personality functions to std
Amanieu Feb 9, 2022
c110329
Remove custom frame info registration on i686-pc-windows-gnu
Amanieu Feb 9, 2022
a54ddd4
Update comment about personalities in panic_abort
Amanieu Feb 9, 2022
2a24a69
Relax tidy rules for OS-specific code
Amanieu Feb 9, 2022
d8c8148
Fix test
Amanieu Feb 9, 2022
a7e4794
Fix handling of rust_eh_personality in reachable_non_generics
Amanieu Aug 27, 2022
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
18 changes: 7 additions & 11 deletions compiler/rustc_codegen_ssa/src/back/symbol_export.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -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 {
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

This means that rust_eh_personality is now exported from cdylibs as it doesn't use SymbolExportLevel::Rust, right? That is going to give troubles when depending on two cdylibs compiled by different versions of rustc if we change the eh_personality implementation as one version of this symbol will override the other.

Copy link
Member Author

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I think symbol_export_level still returns Rust for rust_eh_personality since it doesn't have any attribute such as no_mangle that marks it as externally visible.

Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

I just checked it and you are indeed right. rust_eh_personality is not exported.

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!(
Expand Down
33 changes: 4 additions & 29 deletions library/panic_abort/src/lib.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -113,27 +113,11 @@ pub unsafe fn __rust_start_panic(_payload: *mut &mut dyn BoxMeUp) -> u32 {
// 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() {}

// 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`
}
// 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.

// 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
Expand All @@ -143,13 +127,4 @@ pub mod personalities {
#[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 changes: 0 additions & 16 deletions library/panic_unwind/src/emcc.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,6 @@ use core::intrinsics;
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++
Expand Down Expand Up @@ -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;
Expand Down
262 changes: 0 additions & 262 deletions library/panic_unwind/src/gcc.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -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)]
Expand Down Expand Up @@ -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 changes: 0 additions & 5 deletions library/panic_unwind/src/lib.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -52,9 +52,6 @@ cfg_if::cfg_if! {
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 {
Expand Down Expand Up @@ -92,8 +89,6 @@ extern "C" {
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) {
Expand Down
Loading