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//! Implements a registry of modules for a store.
use crate::{signatures::SignatureCollection, Module};
use std::{
collections::BTreeMap,
sync::{Arc, RwLock},
};
use wasmtime_environ::{EntityRef, FilePos, StackMap, TrapCode};
use wasmtime_jit::CompiledModule;
use wasmtime_runtime::{ModuleInfo, VMCallerCheckedAnyfunc, VMTrampoline};
lazy_static::lazy_static! {
static ref GLOBAL_MODULES: RwLock<GlobalModuleRegistry> = Default::default();
}
/// Used for registering modules with a store.
///
/// The map is from the ending (exclusive) address for the module code to
/// the registered module.
///
/// The `BTreeMap` is used to quickly locate a module based on a program counter value.
#[derive(Default)]
pub struct ModuleRegistry {
modules_with_code: BTreeMap<usize, Arc<RegisteredModule>>,
modules_without_code: Vec<Arc<CompiledModule>>,
}
impl ModuleRegistry {
/// Fetches information about a registered module given a program counter value.
pub fn lookup_module(&self, pc: usize) -> Option<Arc<dyn ModuleInfo>> {
self.module(pc)
.map(|m| -> Arc<dyn ModuleInfo> { m.clone() })
}
fn module(&self, pc: usize) -> Option<&Arc<RegisteredModule>> {
let (end, info) = self.modules_with_code.range(pc..).next()?;
if pc < info.start || *end < pc {
return None;
}
Some(info)
}
/// Registers a new module with the registry.
pub fn register(&mut self, module: &Module) {
let compiled_module = module.compiled_module();
// If there's not actually any functions in this module then we may
// still need to preserve it for its data segments. Instances of this
// module will hold a pointer to the data stored in the module itself,
// and for schemes like uffd this performs lazy initialization which
// could use the module in the future. For that reason we continue to
// register empty modules and retain them.
if compiled_module.finished_functions().len() == 0 {
self.modules_without_code.push(compiled_module.clone());
return;
}
// The module code range is exclusive for end, so make it inclusive as it
// may be a valid PC value
let code = compiled_module.code();
assert!(!code.is_empty());
let start = code.as_ptr() as usize;
let end = start + code.len() - 1;
// Ensure the module isn't already present in the registry
// This is expected when a module is instantiated multiple times in the
// same store
if let Some(m) = self.modules_with_code.get(&end) {
assert_eq!(m.start, start);
return;
}
// Assert that this module's code doesn't collide with any other registered modules
if let Some((_, prev)) = self.modules_with_code.range(end..).next() {
assert!(prev.start > end);
}
if let Some((prev_end, _)) = self.modules_with_code.range(..=start).next_back() {
assert!(*prev_end < start);
}
let prev = self.modules_with_code.insert(
end,
Arc::new(RegisteredModule {
start,
module: compiled_module.clone(),
signatures: module.signatures().clone(),
}),
);
assert!(prev.is_none());
GLOBAL_MODULES.write().unwrap().register(start, end, module);
}
/// Looks up a trampoline from an anyfunc.
pub fn lookup_trampoline(&self, anyfunc: &VMCallerCheckedAnyfunc) -> Option<VMTrampoline> {
let module = self.module(anyfunc.func_ptr.as_ptr() as usize)?;
module.signatures.trampoline(anyfunc.type_index)
}
}
impl Drop for ModuleRegistry {
fn drop(&mut self) {
let mut info = GLOBAL_MODULES.write().unwrap();
for end in self.modules_with_code.keys() {
info.unregister(*end);
}
}
}
struct RegisteredModule {
start: usize,
module: Arc<CompiledModule>,
signatures: Arc<SignatureCollection>,
}
impl ModuleInfo for RegisteredModule {
fn lookup_stack_map(&self, pc: usize) -> Option<&StackMap> {
let text_offset = pc - self.start;
let (index, func_offset) = self.module.func_by_text_offset(text_offset)?;
let info = self.module.func_info(index);
// Do a binary search to find the stack map for the given offset.
let index = match info
.stack_maps
.binary_search_by_key(&func_offset, |i| i.code_offset)
{
// Found it.
Ok(i) => i,
// No stack map associated with this PC.
//
// Because we know we are in Wasm code, and we must be at some kind
// of call/safepoint, then the Cranelift backend must have avoided
// emitting a stack map for this location because no refs were live.
#[cfg(not(feature = "old-x86-backend"))]
Err(_) => return None,
// ### Old x86_64 backend specific code.
//
// Because GC safepoints are technically only associated with a
// single PC, we should ideally only care about `Ok(index)` values
// returned from the binary search. However, safepoints are inserted
// right before calls, and there are two things that can disturb the
// PC/offset associated with the safepoint versus the PC we actually
// use to query for the stack map:
//
// 1. The `backtrace` crate gives us the PC in a frame that will be
// *returned to*, and where execution will continue from, rather than
// the PC of the call we are currently at. So we would need to
// disassemble one instruction backwards to query the actual PC for
// the stack map.
//
// TODO: One thing we *could* do to make this a little less error
// prone, would be to assert/check that the nearest GC safepoint
// found is within `max_encoded_size(any kind of call instruction)`
// our queried PC for the target architecture.
//
// 2. Cranelift's stack maps only handle the stack, not
// registers. However, some references that are arguments to a call
// may need to be in registers. In these cases, what Cranelift will
// do is:
//
// a. spill all the live references,
// b. insert a GC safepoint for those references,
// c. reload the references into registers, and finally
// d. make the call.
//
// Step (c) adds drift between the GC safepoint and the location of
// the call, which is where we actually walk the stack frame and
// collect its live references.
//
// Luckily, the spill stack slots for the live references are still
// up to date, so we can still find all the on-stack roots.
// Furthermore, we do not have a moving GC, so we don't need to worry
// whether the following code will reuse the references in registers
// (which would not have been updated to point to the moved objects)
// or reload from the stack slots (which would have been updated to
// point to the moved objects).
#[cfg(feature = "old-x86-backend")]
Err(0) => return None,
#[cfg(feature = "old-x86-backend")]
Err(i) => i - 1,
};
Some(&info.stack_maps[index].stack_map)
}
}
// Counterpart to `RegisteredModule`, but stored in the global registry.
struct GlobalRegisteredModule {
start: usize,
module: Arc<CompiledModule>,
wasm_backtrace_details_env_used: bool,
/// Note that modules can be instantiated in many stores, so the purpose of
/// this field is to keep track of how many stores have registered a
/// module. Information is only removed from the global registry when this
/// reference count reaches 0.
references: usize,
}
/// This is the global module registry that stores information for all modules
/// that are currently in use by any `Store`.
///
/// The purpose of this map is to be called from signal handlers to determine
/// whether a program counter is a wasm trap or not. Specifically macOS has
/// no contextual information about the thread available, hence the necessity
/// for global state rather than using thread local state.
///
/// This is similar to `ModuleRegistry` except that it has less information and
/// supports removal. Any time anything is registered with a `ModuleRegistry`
/// it is also automatically registered with the singleton global module
/// registry. When a `ModuleRegistry` is destroyed then all of its entries
/// are removed from the global module registry.
#[derive(Default)]
pub struct GlobalModuleRegistry(BTreeMap<usize, GlobalRegisteredModule>);
impl GlobalModuleRegistry {
/// Returns whether the `pc`, according to globally registered information,
/// is a wasm trap or not.
pub(crate) fn is_wasm_pc(pc: usize) -> bool {
let modules = GLOBAL_MODULES.read().unwrap();
match modules.module(pc) {
Some((entry, text_offset)) => {
wasmtime_environ::lookup_file_pos(entry.module.address_map_data(), text_offset)
.is_some()
}
None => false,
}
}
/// Returns, if found, the corresponding module for the `pc` as well as the
/// pc transformed to a relative offset within the text section.
fn module(&self, pc: usize) -> Option<(&GlobalRegisteredModule, usize)> {
let (end, info) = self.0.range(pc..).next()?;
if pc < info.start || *end < pc {
return None;
}
Some((info, pc - info.start))
}
// Work with the global instance of `GlobalModuleRegistry`. Note that only
// shared access is allowed, this isn't intended to mutate the contents.
pub(crate) fn with<R>(f: impl FnOnce(&GlobalModuleRegistry) -> R) -> R {
f(&GLOBAL_MODULES.read().unwrap())
}
/// Fetches frame information about a program counter in a backtrace.
///
/// Returns an object if this `pc` is known to some previously registered
/// module, or returns `None` if no information can be found. The first
/// boolean returned indicates whether the original module has unparsed
/// debug information due to the compiler's configuration. The second
/// boolean indicates whether the engine used to compile this module is
/// using environment variables to control debuginfo parsing.
pub(crate) fn lookup_frame_info(&self, pc: usize) -> Option<(FrameInfo, bool, bool)> {
let (module, offset) = self.module(pc)?;
module.lookup_frame_info(offset).map(|info| {
(
info,
module.has_unparsed_debuginfo(),
module.wasm_backtrace_details_env_used,
)
})
}
/// Fetches trap information about a program counter in a backtrace.
pub(crate) fn lookup_trap_code(&self, pc: usize) -> Option<TrapCode> {
let (module, offset) = self.module(pc)?;
wasmtime_environ::lookup_trap_code(module.module.trap_data(), offset)
}
/// Registers a new region of code, described by `(start, end)` and with
/// the given function information, with the global information.
fn register(&mut self, start: usize, end: usize, module: &Module) {
let info = self.0.entry(end).or_insert_with(|| GlobalRegisteredModule {
start,
module: module.compiled_module().clone(),
wasm_backtrace_details_env_used: module
.engine()
.config()
.wasm_backtrace_details_env_used,
references: 0,
});
// Note that ideally we'd debug_assert that the information previously
// stored, if any, matches the `functions` we were given, but for now we
// just do some simple checks to hope it's the same.
assert_eq!(info.start, start);
info.references += 1;
}
/// Unregisters a region of code (keyed by the `end` address) from the
/// global information.
fn unregister(&mut self, end: usize) {
let info = self.0.get_mut(&end).unwrap();
info.references -= 1;
if info.references == 0 {
self.0.remove(&end);
}
}
}
impl GlobalRegisteredModule {
/// Determines if the related module has unparsed debug information.
pub fn has_unparsed_debuginfo(&self) -> bool {
self.module.has_unparsed_debuginfo()
}
/// Fetches frame information about a program counter in a backtrace.
///
/// Returns an object if this `pc` is known to this module, or returns `None`
/// if no information can be found.
pub fn lookup_frame_info(&self, text_offset: usize) -> Option<FrameInfo> {
let (index, _func_offset) = self.module.func_by_text_offset(text_offset)?;
let info = self.module.func_info(index);
let instr = wasmtime_environ::lookup_file_pos(self.module.address_map_data(), text_offset);
// In debug mode for now assert that we found a mapping for `pc` within
// the function, because otherwise something is buggy along the way and
// not accounting for all the instructions. This isn't super critical
// though so we can omit this check in release mode.
debug_assert!(
instr.is_some(),
"failed to find instruction for {:#x}",
text_offset
);
let instr = instr.unwrap_or(info.start_srcloc);
// Use our wasm-relative pc to symbolize this frame. If there's a
// symbolication context (dwarf debug info) available then we can try to
// look this up there.
//
// Note that dwarf pcs are code-section-relative, hence the subtraction
// from the location of `instr`. Also note that all errors are ignored
// here for now since technically wasm modules can always have any
// custom section contents.
let mut symbols = Vec::new();
if let Some(s) = &self.module.symbolize_context().ok().and_then(|c| c) {
if let Some(offset) = instr.file_offset() {
let to_lookup = u64::from(offset) - s.code_section_offset();
if let Ok(mut frames) = s.addr2line().find_frames(to_lookup) {
while let Ok(Some(frame)) = frames.next() {
symbols.push(FrameSymbol {
name: frame
.function
.as_ref()
.and_then(|l| l.raw_name().ok())
.map(|s| s.to_string()),
file: frame
.location
.as_ref()
.and_then(|l| l.file)
.map(|s| s.to_string()),
line: frame.location.as_ref().and_then(|l| l.line),
column: frame.location.as_ref().and_then(|l| l.column),
});
}
}
}
}
let module = self.module.module();
let index = module.func_index(index);
Some(FrameInfo {
module_name: module.name.clone(),
func_index: index.index() as u32,
func_name: module.func_names.get(&index).cloned(),
instr,
func_start: info.start_srcloc,
symbols,
})
}
}
/// Description of a frame in a backtrace for a [`Trap`].
///
/// Whenever a WebAssembly trap occurs an instance of [`Trap`] is created. Each
/// [`Trap`] has a backtrace of the WebAssembly frames that led to the trap, and
/// each frame is described by this structure.
///
/// [`Trap`]: crate::Trap
#[derive(Debug)]
pub struct FrameInfo {
module_name: Option<String>,
func_index: u32,
func_name: Option<String>,
func_start: FilePos,
instr: FilePos,
symbols: Vec<FrameSymbol>,
}
impl FrameInfo {
/// Returns the WebAssembly function index for this frame.
///
/// This function index is the index in the function index space of the
/// WebAssembly module that this frame comes from.
pub fn func_index(&self) -> u32 {
self.func_index
}
/// Returns the identifer of the module that this frame is for.
///
/// Module identifiers are present in the `name` section of a WebAssembly
/// binary, but this may not return the exact item in the `name` section.
/// Module names can be overwritten at construction time or perhaps inferred
/// from file names. The primary purpose of this function is to assist in
/// debugging and therefore may be tweaked over time.
///
/// This function returns `None` when no name can be found or inferred.
pub fn module_name(&self) -> Option<&str> {
self.module_name.as_deref()
}
/// Returns a descriptive name of the function for this frame, if one is
/// available.
///
/// The name of this function may come from the `name` section of the
/// WebAssembly binary, or wasmtime may try to infer a better name for it if
/// not available, for example the name of the export if it's exported.
///
/// This return value is primarily used for debugging and human-readable
/// purposes for things like traps. Note that the exact return value may be
/// tweaked over time here and isn't guaranteed to be something in
/// particular about a wasm module due to its primary purpose of assisting
/// in debugging.
///
/// This function returns `None` when no name could be inferred.
pub fn func_name(&self) -> Option<&str> {
self.func_name.as_deref()
}
/// Returns the offset within the original wasm module this frame's program
/// counter was at.
///
/// The offset here is the offset from the beginning of the original wasm
/// module to the instruction that this frame points to.
pub fn module_offset(&self) -> usize {
self.instr.file_offset().unwrap_or(u32::MAX) as usize
}
/// Returns the offset from the original wasm module's function to this
/// frame's program counter.
///
/// The offset here is the offset from the beginning of the defining
/// function of this frame (within the wasm module) to the instruction this
/// frame points to.
pub fn func_offset(&self) -> usize {
match self.instr.file_offset() {
Some(i) => (i - self.func_start.file_offset().unwrap()) as usize,
None => u32::MAX as usize,
}
}
/// Returns the debug symbols found, if any, for this function frame.
///
/// When a wasm program is compiled with DWARF debug information then this
/// function may be populated to return symbols which contain extra debug
/// information about a frame including the filename and line number. If no
/// debug information was found or if it was malformed then this will return
/// an empty array.
pub fn symbols(&self) -> &[FrameSymbol] {
&self.symbols
}
}
/// Debug information for a symbol that is attached to a [`FrameInfo`].
///
/// When DWARF debug information is present in a wasm file then this structure
/// can be found on a [`FrameInfo`] and can be used to learn about filenames,
/// line numbers, etc, which are the origin of a function in a stack trace.
#[derive(Debug)]
pub struct FrameSymbol {
name: Option<String>,
file: Option<String>,
line: Option<u32>,
column: Option<u32>,
}
impl FrameSymbol {
/// Returns the function name associated with this symbol.
///
/// Note that this may not be present with malformed debug information, or
/// the debug information may not include it. Also note that the symbol is
/// frequently mangled, so you might need to run some form of demangling
/// over it.
pub fn name(&self) -> Option<&str> {
self.name.as_deref()
}
/// Returns the source code filename this symbol was defined in.
///
/// Note that this may not be present with malformed debug information, or
/// the debug information may not include it.
pub fn file(&self) -> Option<&str> {
self.file.as_deref()
}
/// Returns the 1-indexed source code line number this symbol was defined
/// on.
///
/// Note that this may not be present with malformed debug information, or
/// the debug information may not include it.
pub fn line(&self) -> Option<u32> {
self.line
}
/// Returns the 1-indexed source code column number this symbol was defined
/// on.
///
/// Note that this may not be present with malformed debug information, or
/// the debug information may not include it.
pub fn column(&self) -> Option<u32> {
self.column
}
}
#[test]
fn test_frame_info() -> Result<(), anyhow::Error> {
use crate::*;
let mut store = Store::<()>::default();
let module = Module::new(
store.engine(),
r#"
(module
(func (export "add") (param $x i32) (param $y i32) (result i32) (i32.add (local.get $x) (local.get $y)))
(func (export "sub") (param $x i32) (param $y i32) (result i32) (i32.sub (local.get $x) (local.get $y)))
(func (export "mul") (param $x i32) (param $y i32) (result i32) (i32.mul (local.get $x) (local.get $y)))
(func (export "div_s") (param $x i32) (param $y i32) (result i32) (i32.div_s (local.get $x) (local.get $y)))
(func (export "div_u") (param $x i32) (param $y i32) (result i32) (i32.div_u (local.get $x) (local.get $y)))
(func (export "rem_s") (param $x i32) (param $y i32) (result i32) (i32.rem_s (local.get $x) (local.get $y)))
(func (export "rem_u") (param $x i32) (param $y i32) (result i32) (i32.rem_u (local.get $x) (local.get $y)))
)
"#,
)?;
// Create an instance to ensure the frame information is registered.
Instance::new(&mut store, &module, &[])?;
GlobalModuleRegistry::with(|modules| {
for (i, alloc) in module.compiled_module().finished_functions() {
let (start, end) = unsafe {
let ptr = (*alloc).as_ptr();
let len = (*alloc).len();
(ptr as usize, ptr as usize + len)
};
for pc in start..end {
let (frame, _, _) = modules.lookup_frame_info(pc).unwrap();
assert!(
frame.func_index() == i.as_u32(),
"lookup of {:#x} returned {}, expected {}",
pc,
frame.func_index(),
i.as_u32()
);
}
}
});
Ok(())
}