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wasm exception handling

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This commit is contained in:
Jan-Mirko Otter 2023-05-01 19:24:21 +00:00
parent 35cdb28c84
commit 82730b4521
5 changed files with 117 additions and 14 deletions
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19
compiler/rustc_codegen_llvm/src/context.rs
View File

@ -8,7 +8,7 @@ use crate::llvm_util;
use crate::type_::Type;
use crate::value::Value;
use rustc_codegen_ssa::base::wants_msvc_seh;
use rustc_codegen_ssa::base::{wants_msvc_seh, wants_wasm_eh};
use rustc_codegen_ssa::traits::*;
use rustc_data_structures::base_n;
use rustc_data_structures::fx::FxHashMap;
@ -532,19 +532,24 @@ impl<'ll, 'tcx> MiscMethods<'tcx> for CodegenCx<'ll, 'tcx> {
if let Some(llpersonality) = self.eh_personality.get() {
return llpersonality;
}
let name = if wants_msvc_seh(self.sess()) {
Some("__CxxFrameHandler3")
} else if wants_wasm_eh(self.sess()) {
Some("__gxx_wasm_personality_v0")
} else {
None
};
let tcx = self.tcx;
let llfn = match tcx.lang_items().eh_personality() {
Some(def_id) if !wants_msvc_seh(self.sess()) => self.get_fn_addr(
Some(def_id) if name.is_none() => self.get_fn_addr(
ty::Instance::resolve(tcx, ty::ParamEnv::reveal_all(), def_id, ty::List::empty())
.unwrap()
.unwrap(),
),
_ => {
let name = if wants_msvc_seh(self.sess()) {
"__CxxFrameHandler3"
} else {
"rust_eh_personality"
};
let name = name.unwrap_or("rust_eh_personality");
if let Some(llfn) = self.get_declared_value(name) {
llfn
} else {

78
compiler/rustc_codegen_llvm/src/intrinsic.rs
View File

@ -7,7 +7,7 @@ use crate::type_of::LayoutLlvmExt;
use crate::va_arg::emit_va_arg;
use crate::value::Value;
use rustc_codegen_ssa::base::{compare_simd_types, wants_msvc_seh};
use rustc_codegen_ssa::base::{compare_simd_types, wants_msvc_seh, wants_wasm_eh};
use rustc_codegen_ssa::common::{IntPredicate, TypeKind};
use rustc_codegen_ssa::errors::{ExpectedPointerMutability, InvalidMonomorphization};
use rustc_codegen_ssa::mir::operand::OperandRef;
@ -452,6 +452,8 @@ fn try_intrinsic<'ll>(
bx.store(bx.const_i32(0), dest, ret_align);
} else if wants_msvc_seh(bx.sess()) {
codegen_msvc_try(bx, try_func, data, catch_func, dest);
} else if wants_wasm_eh(bx.sess()) {
codegen_wasm_try(bx, try_func, data, catch_func, dest);
} else if bx.sess().target.os == "emscripten" {
codegen_emcc_try(bx, try_func, data, catch_func, dest);
} else {
@ -610,6 +612,80 @@ fn codegen_msvc_try<'ll>(
bx.store(ret, dest, i32_align);
}
// WASM's definition of the `rust_try` function.
fn codegen_wasm_try<'ll>(
bx: &mut Builder<'_, 'll, '_>,
try_func: &'ll Value,
data: &'ll Value,
catch_func: &'ll Value,
dest: &'ll Value,
) {
let (llty, llfn) = get_rust_try_fn(bx, &mut |mut bx| {
bx.set_personality_fn(bx.eh_personality());
let normal = bx.append_sibling_block("normal");
let catchswitch = bx.append_sibling_block("catchswitch");
let catchpad = bx.append_sibling_block("catchpad");
let caught = bx.append_sibling_block("caught");
let try_func = llvm::get_param(bx.llfn(), 0);
let data = llvm::get_param(bx.llfn(), 1);
let catch_func = llvm::get_param(bx.llfn(), 2);
// We're generating an IR snippet that looks like:
//
// declare i32 @rust_try(%try_func, %data, %catch_func) {
// %slot = alloca i8*
// invoke %try_func(%data) to label %normal unwind label %catchswitch
//
// normal:
// ret i32 0
//
// catchswitch:
// %cs = catchswitch within none [%catchpad_rust] unwind to caller
//
// catchpad:
// %tok = catchpad within %cs [null]
// %ptr = call @llvm.wasm.get.exception(token %tok)
// %sel = call @llvm.wasm.get.ehselector(token %tok)
// call %catch_func(%data, %ptr)
// catchret from %tok to label %caught
//
// caught:
// ret i32 1
// }
//
let try_func_ty = bx.type_func(&[bx.type_i8p()], bx.type_void());
bx.invoke(try_func_ty, None, None, try_func, &[data], normal, catchswitch, None);
bx.switch_to_block(normal);
bx.ret(bx.const_i32(0));
bx.switch_to_block(catchswitch);
let cs = bx.catch_switch(None, None, &[catchpad]);
bx.switch_to_block(catchpad);
let null = bx.const_null(bx.type_i8p());
let funclet = bx.catch_pad(cs, &[null]);
let ptr = bx.call_intrinsic("llvm.wasm.get.exception", &[funclet.cleanuppad()]);
let _sel = bx.call_intrinsic("llvm.wasm.get.ehselector", &[funclet.cleanuppad()]);
let catch_ty = bx.type_func(&[bx.type_i8p(), bx.type_i8p()], bx.type_void());
bx.call(catch_ty, None, None, catch_func, &[data, ptr], Some(&funclet));
bx.catch_ret(&funclet, caught);
bx.switch_to_block(caught);
bx.ret(bx.const_i32(1));
});
// Note that no invoke is used here because by definition this function
// can't panic (that's what it's catching).
let ret = bx.call(llty, None, None, llfn, &[try_func, data, catch_func], None);
let i32_align = bx.tcx().data_layout.i32_align.abi;
bx.store(ret, dest, i32_align);
}
// Definition of the standard `try` function for Rust using the GNU-like model
// of exceptions (e.g., the normal semantics of LLVM's `landingpad` and `invoke`
// instructions).

14
compiler/rustc_codegen_ssa/src/base.rs
View File

@ -357,6 +357,13 @@ pub fn cast_shift_expr_rhs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
}
}
// Returns `true` if this session's target will use native wasm
// exceptions. This means that the VM does the unwinding for
// us
pub fn wants_wasm_eh(sess: &Session) -> bool {
sess.target.is_like_wasm && sess.target.os != "emscripten"
}
/// Returns `true` if this session's target will use SEH-based unwinding.
///
/// This is only true for MSVC targets, and even then the 64-bit MSVC target
@ -366,6 +373,13 @@ pub fn wants_msvc_seh(sess: &Session) -> bool {
sess.target.is_like_msvc
}
/// Returns `true` if this session's target requires the new exception
/// handling LLVM IR instructions (catchpad / cleanuppad / ... instead
/// of landingpad)
pub fn wants_new_eh_instructions(sess: &Session) -> bool {
wants_wasm_eh(sess) || wants_msvc_seh(sess)
}
pub fn memcpy_ty<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
bx: &mut Bx,
dst: Bx::Value,

17
compiler/rustc_codegen_ssa/src/mir/block.rs
View File

@ -79,8 +79,8 @@ impl<'a, 'tcx> TerminatorCodegenHelper<'tcx> {
lltarget = fx.landing_pad_for(target);
}
if is_cleanupret {
// MSVC cross-funclet jump - need a trampoline
debug_assert!(base::wants_msvc_seh(fx.cx.tcx().sess));
// Cross-funclet jump - need a trampoline
debug_assert!(base::wants_new_eh_instructions(fx.cx.tcx().sess));
debug!("llbb_with_cleanup: creating cleanup trampoline for {:?}", target);
let name = &format!("{:?}_cleanup_trampoline_{:?}", self.bb, target);
let trampoline_llbb = Bx::append_block(fx.cx, fx.llfn, name);
@ -177,9 +177,16 @@ impl<'a, 'tcx> TerminatorCodegenHelper<'tcx> {
mir::UnwindAction::Continue => None,
mir::UnwindAction::Unreachable => None,
mir::UnwindAction::Terminate => {
if fx.mir[self.bb].is_cleanup && base::wants_msvc_seh(fx.cx.tcx().sess) {
// SEH will abort automatically if an exception tries to
if fx.mir[self.bb].is_cleanup && base::wants_new_eh_instructions(fx.cx.tcx().sess) {
// MSVC SEH will abort automatically if an exception tries to
// propagate out from cleanup.
// FIXME(@mirkootter): For wasm, we currently do not support terminate during
// cleanup, because this requires a few more changes: The current code
// caches the `terminate_block` for each function; funclet based code - however -
// requires a different terminate_block for each funclet
// Until this is implemented, we just do not unwind inside cleanup blocks
None
} else {
Some(fx.terminate_block())
@ -1528,7 +1535,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
// FIXME(eddyb) rename this to `eh_pad_for_uncached`.
fn landing_pad_for_uncached(&mut self, bb: mir::BasicBlock) -> Bx::BasicBlock {
let llbb = self.llbb(bb);
if base::wants_msvc_seh(self.cx.sess()) {
if base::wants_new_eh_instructions(self.cx.sess()) {
let cleanup_bb = Bx::append_block(self.cx, self.llfn, &format!("funclet_{:?}", bb));
let mut cleanup_bx = Bx::build(self.cx, cleanup_bb);
let funclet = cleanup_bx.cleanup_pad(None, &[]);

3
compiler/rustc_codegen_ssa/src/mir/mod.rs
View File

@ -169,7 +169,8 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
start_bx.set_personality_fn(cx.eh_personality());
}
let cleanup_kinds = base::wants_msvc_seh(cx.tcx().sess).then(|| analyze::cleanup_kinds(&mir));
let cleanup_kinds =
base::wants_new_eh_instructions(cx.tcx().sess).then(|| analyze::cleanup_kinds(&mir));
let cached_llbbs: IndexVec<mir::BasicBlock, CachedLlbb<Bx::BasicBlock>> =
mir.basic_blocks