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Refactor unwind generation in Cranelift.

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This commit makes the following changes to unwind information generation in
Cranelift:

* Remove frame layout change implementation in favor of processing the prologue
  and epilogue instructions when unwind information is requested.  This also
  means this work is no longer performed for Windows, which didn't utilize it.
  It also helps simplify the prologue and epilogue generation code.

* Remove the unwind sink implementation that required each unwind information
  to be represented in final form. For FDEs, this meant writing a
  complete frame table per function, which wastes 20 bytes or so for each
  function with duplicate CIEs.  This also enables Cranelift users to collect the
  unwind information and write it as a single frame table.

* For System V calling convention, the unwind information is no longer stored
  in code memory (it's only a requirement for Windows ABI to do so).  This allows
  for more compact code memory for modules with a lot of functions.

* Deletes some duplicate code relating to frame table generation.  Users can
  now simply use gimli to create a frame table from each function's unwind
  information.

Fixes #1181.
This commit is contained in:
Peter Huene
2020-03-30 19:48:02 -07:00
parent 7da6101732
commit f7e9f86ba9
42 changed files with 2678 additions and 3161 deletions
Download Patch File Download Diff File Expand all files Collapse all files

148
crates/jit/src/code_memory.rs
View File

@@ -1,37 +1,33 @@
//! Memory management for executable code.
use crate::function_table::FunctionTable;
use crate::unwind::UnwindRegistry;
use region;
use std::mem::ManuallyDrop;
use std::{cmp, mem};
use wasmtime_environ::{Compilation, CompiledFunction};
use wasmtime_environ::{
isa::{unwind::UnwindInfo, TargetIsa},
Compilation, CompiledFunction,
};
use wasmtime_runtime::{Mmap, VMFunctionBody};
struct CodeMemoryEntry {
mmap: ManuallyDrop<Mmap>,
table: ManuallyDrop<FunctionTable>,
registry: ManuallyDrop<UnwindRegistry>,
}
impl CodeMemoryEntry {
fn new() -> Self {
Self {
mmap: ManuallyDrop::new(Mmap::new()),
table: ManuallyDrop::new(FunctionTable::new()),
}
}
fn with_capacity(cap: usize) -> Result<Self, String> {
Ok(Self {
mmap: ManuallyDrop::new(Mmap::with_at_least(cap)?),
table: ManuallyDrop::new(FunctionTable::new()),
})
let mmap = ManuallyDrop::new(Mmap::with_at_least(cap)?);
let registry = ManuallyDrop::new(UnwindRegistry::new(mmap.as_ptr() as usize));
Ok(Self { mmap, registry })
}
}
impl Drop for CodeMemoryEntry {
fn drop(&mut self) {
unsafe {
// Table needs to be freed before mmap.
ManuallyDrop::drop(&mut self.table);
// The registry needs to be dropped before the mmap
ManuallyDrop::drop(&mut self.registry);
ManuallyDrop::drop(&mut self.mmap);
}
}
@@ -39,7 +35,7 @@ impl Drop for CodeMemoryEntry {
/// Memory manager for executable code.
pub struct CodeMemory {
current: CodeMemoryEntry,
current: Option<CodeMemoryEntry>,
entries: Vec<CodeMemoryEntry>,
position: usize,
published: usize,
@@ -54,7 +50,7 @@ impl CodeMemory {
/// Create a new `CodeMemory` instance.
pub fn new() -> Self {
Self {
current: CodeMemoryEntry::new(),
current: None,
entries: Vec::new(),
position: 0,
published: 0,
@@ -70,16 +66,14 @@ impl CodeMemory {
) -> Result<&mut [VMFunctionBody], String> {
let size = Self::function_allocation_size(func);
let (buf, table, start) = self.allocate(size)?;
let (buf, registry, start) = self.allocate(size)?;
let (_, _, _, vmfunc) = Self::copy_function(func, start as u32, buf, table);
let (_, _, vmfunc) = Self::copy_function(func, start as u32, buf, registry);
Ok(vmfunc)
}
/// Allocate a continuous memory block for a compilation.
///
/// Allocates memory for both the function bodies as well as function unwind data.
pub fn allocate_for_compilation(
&mut self,
compilation: &Compilation,
@@ -88,33 +82,35 @@ impl CodeMemory {
.into_iter()
.fold(0, |acc, func| acc + Self::function_allocation_size(func));
let (mut buf, mut table, start) = self.allocate(total_len)?;
let (mut buf, registry, start) = self.allocate(total_len)?;
let mut result = Vec::with_capacity(compilation.len());
let mut start = start as u32;
for func in compilation.into_iter() {
let (next_start, next_buf, next_table, vmfunc) =
Self::copy_function(func, start, buf, table);
let (next_start, next_buf, vmfunc) = Self::copy_function(func, start, buf, registry);
result.push(vmfunc);
start = next_start;
buf = next_buf;
table = next_table;
}
Ok(result.into_boxed_slice())
}
/// Make all allocated memory executable.
pub fn publish(&mut self) {
pub fn publish(&mut self, isa: &dyn TargetIsa) {
self.push_current(0)
.expect("failed to push current memory map");
for CodeMemoryEntry { mmap: m, table: t } in &mut self.entries[self.published..] {
for CodeMemoryEntry {
mmap: m,
registry: r,
} in &mut self.entries[self.published..]
{
// Remove write access to the pages due to the relocation fixups.
t.publish(m.as_ptr() as u64)
.expect("failed to publish function table");
r.publish(isa)
.expect("failed to publish function unwind registry");
if !m.is_empty() {
unsafe {
@@ -139,73 +135,79 @@ impl CodeMemory {
/// * The offset within the current mmap that the slice starts at
///
/// TODO: Add an alignment flag.
fn allocate(&mut self, size: usize) -> Result<(&mut [u8], &mut FunctionTable, usize), String> {
if self.current.mmap.len() - self.position < size {
fn allocate(&mut self, size: usize) -> Result<(&mut [u8], &mut UnwindRegistry, usize), String> {
assert!(size > 0);
if match &self.current {
Some(e) => e.mmap.len() - self.position < size,
None => true,
} {
self.push_current(cmp::max(0x10000, size))?;
}
let old_position = self.position;
self.position += size;
let e = self.current.as_mut().unwrap();
Ok((
&mut self.current.mmap.as_mut_slice()[old_position..self.position],
&mut self.current.table,
&mut e.mmap.as_mut_slice()[old_position..self.position],
&mut e.registry,
old_position,
))
}
/// Calculates the allocation size of the given compiled function.
fn function_allocation_size(func: &CompiledFunction) -> usize {
if func.unwind_info.is_empty() {
func.body.len()
} else {
// Account for necessary unwind information alignment padding (32-bit)
((func.body.len() + 3) & !3) + func.unwind_info.len()
match &func.unwind_info {
Some(UnwindInfo::WindowsX64(info)) => {
// Windows unwind information is required to be emitted into code memory
// This is because it must be a positive relative offset from the start of the memory
// Account for necessary unwind information alignment padding (32-bit alignment)
((func.body.len() + 3) & !3) + info.emit_size()
}
_ => func.body.len(),
}
}
/// Copies the data of the compiled function to the given buffer.
///
/// This will also add the function to the current function table.
/// This will also add the function to the current unwind registry.
fn copy_function<'a>(
func: &CompiledFunction,
func_start: u32,
buf: &'a mut [u8],
table: &'a mut FunctionTable,
) -> (
u32,
&'a mut [u8],
&'a mut FunctionTable,
&'a mut [VMFunctionBody],
) {
let func_end = func_start + (func.body.len() as u32);
registry: &mut UnwindRegistry,
) -> (u32, &'a mut [u8], &'a mut [VMFunctionBody]) {
let func_len = func.body.len();
let mut func_end = func_start + (func_len as u32);
let (body, remainder) = buf.split_at_mut(func.body.len());
let (body, mut remainder) = buf.split_at_mut(func_len);
body.copy_from_slice(&func.body);
let vmfunc = Self::view_as_mut_vmfunc_slice(body);
if func.unwind_info.is_empty() {
return (func_end, remainder, table, vmfunc);
if let Some(UnwindInfo::WindowsX64(info)) = &func.unwind_info {
// Windows unwind information is written following the function body
// Keep unwind information 32-bit aligned (round up to the nearest 4 byte boundary)
let unwind_start = (func_end + 3) & !3;
let unwind_size = info.emit_size();
let padding = (unwind_start - func_end) as usize;
let (slice, r) = remainder.split_at_mut(padding + unwind_size);
info.emit(&mut slice[padding..]);
func_end = unwind_start + (unwind_size as u32);
remainder = r;
}
// Keep unwind information 32-bit aligned (round up to the nearest 4 byte boundary)
let padding = ((func.body.len() + 3) & !3) - func.body.len();
let (unwind, remainder) = remainder.split_at_mut(padding + func.unwind_info.len());
let mut relocs = Vec::new();
func.unwind_info
.serialize(&mut unwind[padding..], &mut relocs);
if let Some(info) = &func.unwind_info {
registry
.register(func_start, func_len as u32, info)
.expect("failed to register unwind information");
}
let unwind_start = func_end + (padding as u32);
let unwind_end = unwind_start + (func.unwind_info.len() as u32);
relocs.iter_mut().for_each(move |r| {
r.offset += unwind_start;
r.addend += func_start;
});
table.add_function(func_start, func_end, unwind_start, &relocs);
(unwind_end, remainder, table, vmfunc)
(func_end, remainder, vmfunc)
}
/// Convert mut a slice from u8 to VMFunctionBody.
@@ -215,21 +217,19 @@ impl CodeMemory {
unsafe { &mut *body_ptr }
}
/// Pushes the current Mmap (and function table) and allocates a new Mmap of the given size.
/// Pushes the current entry and allocates a new one with the given size.
fn push_current(&mut self, new_size: usize) -> Result<(), String> {
let previous = mem::replace(
&mut self.current,
if new_size == 0 {
CodeMemoryEntry::new()
None
} else {
CodeMemoryEntry::with_capacity(cmp::max(0x10000, new_size))?
Some(CodeMemoryEntry::with_capacity(cmp::max(0x10000, new_size))?)
},
);
if !previous.mmap.is_empty() {
self.entries.push(previous);
} else {
assert_eq!(previous.table.len(), 0);
if let Some(e) = previous {
self.entries.push(e);
}
self.position = 0;

66
crates/jit/src/compiler.rs
View File

@@ -14,9 +14,9 @@ use wasmtime_environ::entity::{EntityRef, PrimaryMap};
use wasmtime_environ::isa::{TargetFrontendConfig, TargetIsa};
use wasmtime_environ::wasm::{DefinedFuncIndex, DefinedMemoryIndex, MemoryIndex};
use wasmtime_environ::{
CacheConfig, CompileError, CompiledFunction, CompiledFunctionUnwindInfo, Compiler as _C,
ModuleAddressMap, ModuleMemoryOffset, ModuleTranslation, ModuleVmctxInfo, Relocation,
RelocationTarget, Relocations, Traps, Tunables, VMOffsets,
CacheConfig, CompileError, CompiledFunction, Compiler as _C, ModuleAddressMap,
ModuleMemoryOffset, ModuleTranslation, ModuleVmctxInfo, Relocation, RelocationTarget,
Relocations, Traps, Tunables, VMOffsets,
};
use wasmtime_runtime::{
InstantiationError, SignatureRegistry, VMFunctionBody, VMSharedSignatureIndex, VMTrampoline,
@@ -46,7 +46,6 @@ pub enum CompilationStrategy {
/// TODO: Consider using cranelift-module.
pub struct Compiler {
isa: Box<dyn TargetIsa>,
code_memory: CodeMemory,
signatures: SignatureRegistry,
strategy: CompilationStrategy,
@@ -102,34 +101,27 @@ impl Compiler {
translation: &ModuleTranslation,
debug_data: Option<DebugInfoData>,
) -> Result<Compilation, SetupError> {
let (
compilation,
relocations,
address_transform,
value_ranges,
stack_slots,
traps,
frame_layouts,
) = match self.strategy {
// For now, interpret `Auto` as `Cranelift` since that's the most stable
// implementation.
CompilationStrategy::Auto | CompilationStrategy::Cranelift => {
wasmtime_environ::cranelift::Cranelift::compile_module(
translation,
&*self.isa,
&self.cache_config,
)
let (compilation, relocations, address_transform, value_ranges, stack_slots, traps) =
match self.strategy {
// For now, interpret `Auto` as `Cranelift` since that's the most stable
// implementation.
CompilationStrategy::Auto | CompilationStrategy::Cranelift => {
wasmtime_environ::cranelift::Cranelift::compile_module(
translation,
&*self.isa,
&self.cache_config,
)
}
#[cfg(feature = "lightbeam")]
CompilationStrategy::Lightbeam => {
wasmtime_environ::lightbeam::Lightbeam::compile_module(
translation,
&*self.isa,
&self.cache_config,
)
}
}
#[cfg(feature = "lightbeam")]
CompilationStrategy::Lightbeam => {
wasmtime_environ::lightbeam::Lightbeam::compile_module(
translation,
&*self.isa,
&self.cache_config,
)
}
}
.map_err(SetupError::Compile)?;
.map_err(SetupError::Compile)?;
// Allocate all of the compiled functions into executable memory,
// copying over their contents.
@@ -202,8 +194,8 @@ impl Compiler {
&module_vmctx_info,
&address_transform,
&value_ranges,
&frame_layouts,
&funcs,
&compilation,
)
.map_err(SetupError::DebugInfo)?;
Some(bytes)
@@ -227,7 +219,7 @@ impl Compiler {
/// Make memory containing compiled code executable.
pub(crate) fn publish_compiled_code(&mut self) {
self.code_memory.publish();
self.code_memory.publish(self.isa.as_ref());
}
/// Shared signature registry.
@@ -264,7 +256,6 @@ pub fn make_trampoline(
let mut context = Context::new();
context.func = ir::Function::with_name_signature(ir::ExternalName::user(0, 0), wrapper_sig);
context.func.collect_frame_layout_info();
{
let mut builder = FunctionBuilder::new(&mut context.func, fn_builder_ctx);
@@ -343,7 +334,7 @@ pub fn make_trampoline(
)))
})?;
let unwind_info = CompiledFunctionUnwindInfo::new(isa, &context).map_err(|error| {
let unwind_info = context.create_unwind_info(isa).map_err(|error| {
SetupError::Compile(CompileError::Codegen(pretty_error(
&context.func,
Some(isa),
@@ -369,6 +360,10 @@ fn allocate_functions(
code_memory: &mut CodeMemory,
compilation: &wasmtime_environ::Compilation,
) -> Result<PrimaryMap<DefinedFuncIndex, *mut [VMFunctionBody]>, String> {
if compilation.is_empty() {
return Ok(PrimaryMap::new());
}
let fat_ptrs = code_memory.allocate_for_compilation(compilation)?;
// Second, create a PrimaryMap from result vector of pointers.
@@ -377,6 +372,7 @@ fn allocate_functions(
let fat_ptr: *mut [VMFunctionBody] = fat_ptrs[i];
result.push(fat_ptr);
}
Ok(result)
}

224
crates/jit/src/function_table.rs
View File

@@ -1,224 +0,0 @@
//! Runtime function table.
//!
//! This module is primarily used to track JIT functions on Windows for stack walking and unwind.
type FunctionTableReloc = wasmtime_environ::CompiledFunctionUnwindInfoReloc;
/// Represents a runtime function table.
///
/// This is used to register JIT code with the operating system to enable stack walking and unwinding.
#[cfg(all(target_os = "windows", target_arch = "x86_64"))]
pub(crate) struct FunctionTable {
functions: Vec<winapi::um::winnt::RUNTIME_FUNCTION>,
published: bool,
}
#[cfg(all(target_os = "windows", target_arch = "x86_64"))]
impl FunctionTable {
/// Creates a new function table.
pub fn new() -> Self {
Self {
functions: Vec::new(),
published: false,
}
}
/// Returns the number of functions in the table, also referred to as its 'length'.
pub fn len(&self) -> usize {
self.functions.len()
}
/// Adds a function to the table based off of the start offset, end offset, and unwind offset.
///
/// The offsets are from the "module base", which is provided when the table is published.
pub fn add_function(
&mut self,
start: u32,
end: u32,
unwind: u32,
_relocs: &[FunctionTableReloc],
) {
assert_eq!(_relocs.len(), 0);
use winapi::um::winnt;
assert!(!self.published, "table has already been published");
let mut entry = winnt::RUNTIME_FUNCTION::default();
entry.BeginAddress = start;
entry.EndAddress = end;
unsafe {
*entry.u.UnwindInfoAddress_mut() = unwind;
}
self.functions.push(entry);
}
/// Publishes the function table using the given base address.
///
/// A published function table will automatically be deleted when it is dropped.
pub fn publish(&mut self, base_address: u64) -> Result<(), String> {
use winapi::um::winnt;
if self.published {
return Err("function table was already published".into());
}
self.published = true;
if self.functions.is_empty() {
return Ok(());
}
unsafe {
// Windows heap allocations are 32-bit aligned, but assert just in case
assert_eq!(
(self.functions.as_mut_ptr() as u64) % 4,
0,
"function table allocation was not aligned"
);
if winnt::RtlAddFunctionTable(
self.functions.as_mut_ptr(),
self.functions.len() as u32,
base_address,
) == 0
{
return Err("failed to add function table".into());
}
}
Ok(())
}
}
#[cfg(target_os = "windows")]
impl Drop for FunctionTable {
fn drop(&mut self) {
use winapi::um::winnt;
if self.published {
unsafe {
winnt::RtlDeleteFunctionTable(self.functions.as_mut_ptr());
}
}
}
}
/// Represents a runtime function table.
///
/// This is used to register JIT code with the operating system to enable stack walking and unwinding.
#[cfg(unix)]
pub(crate) struct FunctionTable {
functions: Vec<u32>,
relocs: Vec<FunctionTableReloc>,
published: Option<Vec<usize>>,
}
#[cfg(unix)]
impl FunctionTable {
/// Creates a new function table.
pub fn new() -> Self {
Self {
functions: Vec::new(),
relocs: Vec::new(),
published: None,
}
}
/// Returns the number of functions in the table, also referred to as its 'length'.
pub fn len(&self) -> usize {
self.functions.len()
}
/// Adds a function to the table based off of the start offset, end offset, and unwind offset.
///
/// The offsets are from the "module base", which is provided when the table is published.
pub fn add_function(
&mut self,
_start: u32,
_end: u32,
unwind: u32,
relocs: &[FunctionTableReloc],
) {
assert!(self.published.is_none(), "table has already been published");
self.functions.push(unwind);
self.relocs.extend_from_slice(relocs);
}
/// Publishes the function table using the given base address.
///
/// A published function table will automatically be deleted when it is dropped.
pub fn publish(&mut self, base_address: u64) -> Result<(), String> {
if self.published.is_some() {
return Err("function table was already published".into());
}
if self.functions.is_empty() {
assert_eq!(self.relocs.len(), 0);
self.published = Some(vec![]);
return Ok(());
}
extern "C" {
// libunwind import
fn __register_frame(fde: *const u8);
}
for reloc in self.relocs.iter() {
let addr = base_address + (reloc.offset as u64);
let target = base_address + (reloc.addend as u64);
unsafe {
std::ptr::write(addr as *mut u64, target);
}
}
let mut fdes = Vec::with_capacity(self.functions.len());
for unwind_offset in self.functions.iter() {
let addr = base_address + (*unwind_offset as u64);
let off = unsafe { std::ptr::read::<u32>(addr as *const u32) } as usize + 4;
let fde = (addr + off as u64) as usize;
unsafe {
__register_frame(fde as *const _);
}
fdes.push(fde);
}
self.published = Some(fdes);
Ok(())
}
}
#[cfg(unix)]
impl Drop for FunctionTable {
fn drop(&mut self) {
extern "C" {
// libunwind import
fn __deregister_frame(fde: *const u8);
}
if let Some(published) = &self.published {
unsafe {
// I'm not really sure why, but it appears to be way faster to
// unregister frames in reverse order rather than in-order. This
// way we're deregistering in LIFO order, and maybe there's some
// vec shifting or something like that in libgcc?
//
// Locally on Ubuntu 18.04 a wasm module with 40k empty
// functions takes 0.1s to compile and drop with reverse
// iteration. With forward iteration it takes 3s to compile and
// drop!
//
// Poking around libgcc sources seems to indicate that some sort
// of linked list is being traversed... We may need to figure
// out something else for backtraces in the future since this
// API may not be long-lived to keep calling.
for fde in published.iter().rev() {
__deregister_frame(*fde as *const _);
}
}
}
}
}

2
crates/jit/src/lib.rs
View File

@@ -23,11 +23,11 @@
mod code_memory;
mod compiler;
mod function_table;
mod imports;
mod instantiate;
mod link;
mod resolver;
mod unwind;
pub mod native;
pub mod trampoline;

11
crates/jit/src/unwind.rs Normal file
View File

@@ -0,0 +1,11 @@
cfg_if::cfg_if! {
if #[cfg(all(windows, target_arch = "x86_64"))] {
mod winx64;
pub use self::winx64::*;
} else if #[cfg(unix)] {
mod systemv;
pub use self::systemv::*;
} else {
compile_error!("unsupported target platform for unwind");
}
}

140
crates/jit/src/unwind/systemv.rs Normal file
View File

@@ -0,0 +1,140 @@
//! Module for System V ABI unwind registry.
use anyhow::{bail, Result};
use cranelift_codegen::isa::{unwind::UnwindInfo, TargetIsa};
use gimli::{
write::{Address, EhFrame, EndianVec, FrameTable, Writer},
RunTimeEndian,
};
/// Represents a registry of function unwind information for System V ABI.
pub struct UnwindRegistry {
base_address: usize,
functions: Vec<gimli::write::FrameDescriptionEntry>,
frame_table: Vec<u8>,
registrations: Vec<usize>,
published: bool,
}
extern "C" {
// libunwind import
fn __register_frame(fde: *const u8);
fn __deregister_frame(fde: *const u8);
}
impl UnwindRegistry {
/// Creates a new unwind registry with the given base address.
pub fn new(base_address: usize) -> Self {
Self {
base_address,
functions: Vec::new(),
frame_table: Vec::new(),
registrations: Vec::new(),
published: false,
}
}
/// Registers a function given the start offset, length, and unwind information.
pub fn register(&mut self, func_start: u32, _func_len: u32, info: &UnwindInfo) -> Result<()> {
if self.published {
bail!("unwind registry has already been published");
}
match info {
UnwindInfo::SystemV(info) => {
self.functions.push(info.to_fde(Address::Constant(
self.base_address as u64 + func_start as u64,
)));
}
_ => bail!("unsupported unwind information"),
}
Ok(())
}
/// Publishes all registered functions.
pub fn publish(&mut self, isa: &dyn TargetIsa) -> Result<()> {
if self.published {
bail!("unwind registry has already been published");
}
if self.functions.is_empty() {
self.published = true;
return Ok(());
}
self.set_frame_table(isa)?;
unsafe {
self.register_frames();
}
self.published = true;
Ok(())
}
fn set_frame_table(&mut self, isa: &dyn TargetIsa) -> Result<()> {
let mut table = FrameTable::default();
let cie_id = table.add_cie(match isa.create_systemv_cie() {
Some(cie) => cie,
None => bail!("ISA does not support System V unwind information"),
});
let functions = std::mem::replace(&mut self.functions, Vec::new());
for func in functions {
table.add_fde(cie_id, func);
}
let mut eh_frame = EhFrame(EndianVec::new(RunTimeEndian::default()));
table.write_eh_frame(&mut eh_frame).unwrap();
// GCC expects a terminating "empty" length, so write a 0 length at the end of the table.
eh_frame.0.write_u32(0).unwrap();
self.frame_table = eh_frame.0.into_vec();
Ok(())
}
unsafe fn register_frames(&mut self) {
let start = self.frame_table.as_ptr();
let end = start.add(self.frame_table.len());
let mut current = start;
// Walk all of the entries in the frame table and register them
while current < end {
let len = std::ptr::read::<u32>(current as *const u32) as usize;
// Skip over the CIE
if current != start {
__register_frame(current);
self.registrations.push(current as usize);
}
// Move to the next table entry (+4 because the length itself is not inclusive)
current = current.add(len + 4);
}
}
}
impl Drop for UnwindRegistry {
fn drop(&mut self) {
if self.published {
unsafe {
// libgcc stores the frame entries as a linked list in decreasing sort order
// based on the PC value of the registered entry.
//
// As we store the registrations in increasing order, it would be O(N^2) to
// deregister in that order.
//
// To ensure that we just pop off the first element in the list upon every
// deregistration, walk our list of registrations backwards.
for fde in self.registrations.iter().rev() {
__deregister_frame(*fde as *const _);
}
}
}
}
}

91
crates/jit/src/unwind/winx64.rs Normal file
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//! Module for Windows x64 ABI unwind registry.
use anyhow::{bail, Result};
use cranelift_codegen::isa::{unwind::UnwindInfo, TargetIsa};
use winapi::um::winnt;
/// Represents a registry of function unwind information for Windows x64 ABI.
pub struct UnwindRegistry {
base_address: usize,
functions: Vec<winnt::RUNTIME_FUNCTION>,
published: bool,
}
impl UnwindRegistry {
/// Creates a new unwind registry with the given base address.
pub fn new(base_address: usize) -> Self {
Self {
base_address,
functions: Vec::new(),
published: false,
}
}
/// Registers a function given the start offset, length, and unwind information.
pub fn register(&mut self, func_start: u32, func_len: u32, info: &UnwindInfo) -> Result<()> {
if self.published {
bail!("unwind registry has already been published");
}
match info {
UnwindInfo::WindowsX64(_) => {
let mut entry = winnt::RUNTIME_FUNCTION::default();
entry.BeginAddress = func_start;
entry.EndAddress = func_start + func_len;
// The unwind information should be immediately following the function
// with padding for 4 byte alignment
unsafe {
*entry.u.UnwindInfoAddress_mut() = ((entry.EndAddress + 3) & !3);
}
self.functions.push(entry);
Ok(())
}
_ => bail!("unsupported unwind information"),
}
}
/// Publishes all registered functions.
pub fn publish(&mut self, isa: &dyn TargetIsa) -> Result<()> {
if self.published {
bail!("unwind registry has already been published");
}
self.published = true;
if !self.functions.is_empty() {
// Windows heap allocations are 32-bit aligned, but assert just in case
assert_eq!(
(self.functions.as_mut_ptr() as u64) % 4,
0,
"function table allocation was not aligned"
);
unsafe {
if winnt::RtlAddFunctionTable(
self.functions.as_mut_ptr(),
self.functions.len() as u32,
base_address as u64,
) == 0
{
bail!("failed to register function table");
}
}
}
Ok(())
}
}
impl Drop for UnwindRegistry {
fn drop(&mut self) {
if self.published {
unsafe {
winnt::RtlDeleteFunctionTable(self.functions.as_mut_ptr());
}
}
}
}