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Rollup merge of #128158 - workingjubilee:unsafe-wrap-personality-gcc, r=ChrisDenton

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std: unsafe-wrap personality::gcc

Nothing seems obviously wrong with these implementations except for some unanswered questions. Admittedly, I don't want to burn excessive time on exceptional exception handlers. Thus this is mostly a brute-force syntactic wrapping and some comments where they seemed correct, creating another largely whitespace diff.

try-job: armhf-gnu
This commit is contained in:
Matthias Krüger 2024-07-25 16:48:20 +02:00 • committed by GitHub
commit 606c9fcb4d
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327
library/std/src/sys/personality/gcc.rs
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@ -35,6 +35,7 @@
//!
//! Once stack has been unwound down to the handler frame level, unwinding stops
//! and the last personality routine transfers control to the catch block.
#![forbid(unsafe_op_in_unsafe_fn)]
use super::dwarf::eh::{self, EHAction, EHContext};
use crate::ffi::c_int;
@ -92,107 +93,116 @@ const UNWIND_DATA_REG: (i32, i32) = (4, 5); // a0, a1
// https://github.com/gcc-mirror/gcc/blob/trunk/libgcc/unwind-c.c
cfg_if::cfg_if! {
if #[cfg(all(not(all(target_vendor = "apple", not(target_os = "watchos"))), target_arch = "arm", not(target_os = "netbsd")))] {
// ARM EHABI personality routine.
// https://web.archive.org/web/20190728160938/https://infocenter.arm.com/help/topic/com.arm.doc.ihi0038b/IHI0038B_ehabi.pdf
//
// Apple 32-bit ARM (but not watchOS) uses the default routine instead
// since it uses SjLj unwinding.
if #[cfg(all(
target_arch = "arm",
not(all(target_vendor = "apple", not(target_os = "watchos"))),
not(target_os = "netbsd"),
))] {
/// personality fn called by [ARM EHABI][armeabi-eh]
///
/// Apple 32-bit ARM (but not watchOS) uses the default routine instead
/// since it uses "setjmp-longjmp" unwinding.
///
/// [armeabi-eh]: https://web.archive.org/web/20190728160938/https://infocenter.arm.com/help/topic/com.arm.doc.ihi0038b/IHI0038B_ehabi.pdf
#[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(_) => {
unsafe {
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);
}
EHAction::Catch(_) | EHAction::Filter(_) => {
// 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::Filter(_) if state & uw::_US_FORCE_UNWIND as c_int != 0 => return continue_unwind(exception_object, context),
EHAction::Cleanup(lpad) | EHAction::Catch(lpad) | EHAction::Filter(lpad) => {
uw::_Unwind_SetGR(
context,
UNWIND_DATA_REG.0,
exception_object as uw::_Unwind_Ptr,
);
uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, core::ptr::null());
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
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 {
uw::_URC_FAILURE
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(_) | EHAction::Filter(_) => {
// 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::Filter(_) if state & uw::_US_FORCE_UNWIND as c_int != 0 => return continue_unwind(exception_object, context),
EHAction::Cleanup(lpad) | EHAction::Catch(lpad) | EHAction::Filter(lpad) => {
uw::_Unwind_SetGR(
context,
UNWIND_DATA_REG.0,
exception_object as uw::_Unwind_Ptr,
);
uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, core::ptr::null());
uw::_Unwind_SetIP(context, lpad);
return uw::_URC_INSTALL_CONTEXT;
}
EHAction::Terminate => return uw::_URC_FAILURE,
}
}
}
// defined in libgcc
extern "C" {
fn __gnu_unwind_frame(
// 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;
) -> uw::_Unwind_Reason_Code {
unsafe {
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.
/// Default personality routine, which is used directly on most targets
/// and indirectly on Windows x86_64 and AArch64 via SEH.
unsafe extern "C" fn rust_eh_personality_impl(
version: c_int,
actions: uw::_Unwind_Action,
@ -200,43 +210,49 @@ cfg_if::cfg_if! {
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(_) | EHAction::Filter(_) => uw::_URC_HANDLER_FOUND,
EHAction::Terminate => uw::_URC_FATAL_PHASE1_ERROR,
unsafe {
if version != 1 {
return uw::_URC_FATAL_PHASE1_ERROR;
}
} else {
match eh_action {
EHAction::None => uw::_URC_CONTINUE_UNWIND,
// Forced unwinding hits a terminate action.
EHAction::Filter(_) if actions as i32 & uw::_UA_FORCE_UNWIND as i32 != 0 => uw::_URC_CONTINUE_UNWIND,
EHAction::Cleanup(lpad) | EHAction::Catch(lpad) | EHAction::Filter(lpad) => {
uw::_Unwind_SetGR(
context,
UNWIND_DATA_REG.0,
exception_object.cast(),
);
uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, core::ptr::null());
uw::_Unwind_SetIP(context, lpad);
uw::_URC_INSTALL_CONTEXT
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(_) | EHAction::Filter(_) => uw::_URC_HANDLER_FOUND,
EHAction::Terminate => uw::_URC_FATAL_PHASE1_ERROR,
}
} else {
match eh_action {
EHAction::None => uw::_URC_CONTINUE_UNWIND,
// Forced unwinding hits a terminate action.
EHAction::Filter(_) if actions as i32 & uw::_UA_FORCE_UNWIND as i32 != 0 => uw::_URC_CONTINUE_UNWIND,
EHAction::Cleanup(lpad) | EHAction::Catch(lpad) | EHAction::Filter(lpad) => {
uw::_Unwind_SetGR(
context,
UNWIND_DATA_REG.0,
exception_object.cast(),
);
uw::_Unwind_SetGR(context, UNWIND_DATA_REG.1, core::ptr::null());
uw::_Unwind_SetIP(context, lpad);
uw::_URC_INSTALL_CONTEXT
}
EHAction::Terminate => uw::_URC_FATAL_PHASE2_ERROR,
}
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.
/// personality fn called by [Windows Structured Exception Handling][windows-eh]
///
/// On x86_64 and AArch64 MinGW targets, the unwinding mechanism is SEH,
/// however the unwind handler data (aka LSDA) uses GCC-compatible encoding
///
/// [windows-eh]: https://learn.microsoft.com/en-us/cpp/cpp/structured-exception-handling-c-cpp?view=msvc-170
#[lang = "eh_personality"]
#[allow(nonstandard_style)]
unsafe extern "C" fn rust_eh_personality(
@ -245,16 +261,33 @@ cfg_if::cfg_if! {
contextRecord: *mut uw::CONTEXT,
dispatcherContext: *mut uw::DISPATCHER_CONTEXT,
) -> uw::EXCEPTION_DISPOSITION {
uw::_GCC_specific_handler(
exceptionRecord,
establisherFrame,
contextRecord,
dispatcherContext,
rust_eh_personality_impl,
)
// SAFETY: the cfg is still target_os = "windows" and target_env = "gnu",
// which means that this is the correct function to call, passing our impl fn
// as the callback which gets actually used
unsafe {
uw::_GCC_specific_handler(
exceptionRecord,
establisherFrame,
contextRecord,
dispatcherContext,
rust_eh_personality_impl,
)
}
}
} else {
// The personality routine for most of our targets.
/// personality fn called by [Itanium C++ ABI Exception Handling][itanium-eh]
///
/// The personality routine for most non-Windows targets. This will be called by
/// the unwinding library:
/// - "In the search phase, the framework repeatedly calls the personality routine,
/// with the _UA_SEARCH_PHASE flag as described below, first for the current PC
/// and register state, and then unwinding a frame to a new PC at each step..."
/// - "If the search phase reports success, the framework restarts in the cleanup
/// phase. Again, it repeatedly calls the personality routine, with the
/// _UA_CLEANUP_PHASE flag as described below, first for the current PC and
/// register state, and then unwinding a frame to a new PC at each step..."i
///
/// [itanium-eh]: https://itanium-cxx-abi.github.io/cxx-abi/abi-eh.html
#[lang = "eh_personality"]
unsafe extern "C" fn rust_eh_personality(
version: c_int,
@ -263,13 +296,17 @@ cfg_if::cfg_if! {
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,
)
// SAFETY: the platform support must modify the cfg for the inner fn
// if it needs something different than what is currently invoked.
unsafe {
rust_eh_personality_impl(
version,
actions,
exception_class,
exception_object,
context,
)
}
}
}
}
@ -277,18 +314,20 @@ cfg_if::cfg_if! {
}
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)
unsafe {
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)
}
}