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use super::impl_prelude::*;
use minidump::format::ContextFlagsCpu;
use minidump::{
CpuContext, Endian, MinidumpContext, MinidumpContextValidity, MinidumpModuleList,
MinidumpRawContext,
};
use scroll::ctx::{SizeWith, TryFromCtx};
use std::collections::HashSet;
use std::convert::TryFrom;
use tracing::trace;
type MipsContext = minidump::format::CONTEXT_MIPS;
type Pointer = <MipsContext as CpuContext>::Register;
const STACK_POINTER: &str = "sp";
const PROGRAM_COUNTER: &str = "pc";
const CALLEE_SAVED_REGS: &[&str] = &[
"s0", "s1", "s2", "s3", "s4", "s5", "s6", "s7", "gp", "sp", "fp",
];
async fn get_caller_by_cfi<'a, C, P>(
ctx: &'a C,
args: &'a GetCallerFrameArgs<'a, P>,
) -> Option<StackFrame>
where
P: SymbolProvider + Sync,
// all these bounds are essentially duplicated from `CfiStackWalker` :-(
C: CpuContext + IntoRawContext + Clone + Send + Sync,
C::Register: TryFrom<u64>,
u64: TryFrom<C::Register>,
C::Register: TryFromCtx<'a, Endian, [u8], Error = scroll::Error> + SizeWith<Endian>,
{
trace!("trying cfi");
let _last_sp = ctx.get_register(STACK_POINTER, args.valid())?;
let mut stack_walker = CfiStackWalker::from_ctx_and_args(ctx, args, callee_forwarded_regs)?;
args.symbol_provider
.walk_frame(stack_walker.module, &mut stack_walker)
.await?;
let caller_pc = stack_walker.caller_ctx.get_register_always(PROGRAM_COUNTER);
let caller_sp = stack_walker.caller_ctx.get_register_always(STACK_POINTER);
trace!(
"cfi evaluation was successful -- caller_pc: 0x{caller_pc:016x}, caller_sp: 0x{caller_sp:016x}"
);
// Do absolutely NO validation! Yep! As long as CFI evaluation succeeds
// (which does include pc and sp resolving), just blindly assume the
// values are correct. I Don't Like This, but it's what breakpad does and
// we should start with a baseline of parity.
let context = MinidumpContext {
raw: stack_walker.caller_ctx.into_ctx(),
valid: MinidumpContextValidity::Some(stack_walker.caller_validity),
};
Some(StackFrame::from_context(context, FrameTrust::CallFrameInfo))
}
fn callee_forwarded_regs(valid: &MinidumpContextValidity) -> HashSet<&'static str> {
match valid {
MinidumpContextValidity::All => CALLEE_SAVED_REGS.iter().copied().collect(),
MinidumpContextValidity::Some(ref which) => CALLEE_SAVED_REGS
.iter()
.filter(|®| which.contains(reg))
.copied()
.collect(),
}
}
async fn get_caller_by_scan32<P>(
ctx: &Mips32Context,
args: &GetCallerFrameArgs<'_, P>,
) -> Option<StackFrame>
where
P: SymbolProvider + Sync,
{
const MAX_STACK_SIZE: u32 = 1024;
const MIN_ARGS: u32 = 4;
const POINTER_WIDTH: u32 = 4;
trace!("trying scan");
// Stack scanning is just walking from the end of the frame until we encounter
// a value on the stack that looks like a pointer into some code (it's an address
// in a range covered by one of our modules). If we find such an instruction,
// we assume it's a `ra` value that was saved on the stack by the callee in
// its function prologue, following a `jal` (call) instruction of the caller.
// The next frame is then assumed to end just before that `ra` value.
let mut last_sp = ctx.get_register(STACK_POINTER, args.valid())?;
let mut count = MAX_STACK_SIZE / POINTER_WIDTH;
// In case of mips32 ABI the stack frame of a non-leaf function
// must have a minimum stack frame size for 4 arguments (4 words).
// Move stack pointer for 4 words to avoid reporting non-existing frames
// for all frames except the topmost one.
// There is no way of knowing if topmost frame belongs to a leaf or
// a non-leaf function.
if args.callee_frame.trust != FrameTrust::Context {
last_sp = last_sp.checked_add(MIN_ARGS * POINTER_WIDTH)?;
count -= MIN_ARGS;
}
for i in 0..count {
let address_of_pc = last_sp.checked_add(i * POINTER_WIDTH)?;
let caller_pc: u32 = args
.stack_memory
.get_memory_at_address(address_of_pc as u64)?;
//trace!("unwind: trying addr 0x{address_of_pc:08x}: 0x{caller_pc:08x}");
if instruction_seems_valid(caller_pc as u64, args.modules, args.symbol_provider).await {
// `ra` is usually saved directly at the bottom of the frame,
// so sp is just address_of_pc + ptr
let caller_sp = address_of_pc.checked_add(POINTER_WIDTH)?;
// Don't do any more validation, and don't try to restore fp
// (that's what breakpad does!)
trace!(
"scan seems valid -- caller_pc: 0x{caller_pc:016x}, caller_sp: 0x{caller_sp:016x}"
);
let mut caller_ctx = MipsContext::default();
caller_ctx.set_register(PROGRAM_COUNTER, caller_pc as u64);
caller_ctx.set_register(STACK_POINTER, caller_sp as u64);
let mut valid = HashSet::new();
valid.insert(PROGRAM_COUNTER);
valid.insert(STACK_POINTER);
let context = MinidumpContext {
raw: MinidumpRawContext::Mips(caller_ctx),
valid: MinidumpContextValidity::Some(valid),
};
return Some(StackFrame::from_context(context, FrameTrust::Scan));
}
}
None
}
async fn get_caller_by_scan64<P>(
ctx: &MipsContext,
args: &GetCallerFrameArgs<'_, P>,
) -> Option<StackFrame>
where
P: SymbolProvider + Sync,
{
const MAX_STACK_SIZE: u64 = 1024;
const POINTER_WIDTH: u64 = 8;
trace!("trying scan");
// Stack scanning is just walking from the end of the frame until we encounter
// a value on the stack that looks like a pointer into some code (it's an address
// in a range covered by one of our modules). If we find such an instruction,
// we assume it's a `ra` value that was saved on the stack by the callee in
// its function prologue, following a `jal` (call) instruction of the caller.
// The next frame is then assumed to end just before that `ra` value.
let last_sp = ctx.get_register(STACK_POINTER, args.valid())?;
let count = MAX_STACK_SIZE / POINTER_WIDTH;
for i in 0..count {
let address_of_pc = last_sp.checked_add(i * POINTER_WIDTH)?;
let caller_pc = args.stack_memory.get_memory_at_address(address_of_pc)?;
if instruction_seems_valid(caller_pc, args.modules, args.symbol_provider).await {
// `ra` is usually saved directly at the bottom of the frame,
// so sp is just address_of_pc + ptr
let caller_sp = address_of_pc.checked_add(POINTER_WIDTH)?;
// Don't do any more validation, and don't try to restore fp
// (that's what breakpad does!)
trace!(
"scan seems valid -- caller_pc: 0x{caller_pc:016x}, caller_sp: 0x{caller_sp:016x}"
);
let mut caller_ctx = MipsContext::default();
caller_ctx.set_register(PROGRAM_COUNTER, caller_pc);
caller_ctx.set_register(STACK_POINTER, caller_sp);
let mut valid = HashSet::new();
valid.insert(PROGRAM_COUNTER);
valid.insert(STACK_POINTER);
let context = MinidumpContext {
raw: MinidumpRawContext::Mips(caller_ctx),
valid: MinidumpContextValidity::Some(valid),
};
return Some(StackFrame::from_context(context, FrameTrust::Scan));
}
}
None
}
async fn instruction_seems_valid<P>(
instruction: Pointer,
modules: &MinidumpModuleList,
symbol_provider: &P,
) -> bool
where
P: SymbolProvider + Sync,
{
if instruction < 0x1000 {
return false;
}
super::instruction_seems_valid_by_symbols(instruction, modules, symbol_provider).await
}
pub async fn get_caller_frame<P>(
ctx: &MipsContext,
args: &GetCallerFrameArgs<'_, P>,
) -> Option<StackFrame>
where
P: SymbolProvider + Sync,
{
let ctx32 = Mips32Context::try_from(ctx.clone());
// .await doesn't like closures, so don't use Option chaining
let mut frame = None;
if frame.is_none() {
match &ctx32 {
Ok(mips32) => frame = get_caller_by_cfi(mips32, args).await,
Err(mips64) => frame = get_caller_by_cfi(mips64, args).await,
}
}
if frame.is_none() {
match &ctx32 {
Ok(mips32) => frame = get_caller_by_scan32(mips32, args).await,
Err(mips64) => frame = get_caller_by_scan64(mips64, args).await,
}
}
let mut frame = frame?;
// We now check the frame to see if it looks like unwinding is complete,
// based on the frame we computed having a nonsense value. Returning
// None signals to the unwinder to stop unwinding.
// if the instruction is within the first ~page of memory, it's basically
// null, and we can assume unwinding is complete.
if frame.context.get_instruction_pointer() < 4096 {
trace!("instruction pointer was nullish, assuming unwind complete");
return None;
}
// If the new stack pointer is at a lower address than the old,
// then that's clearly incorrect. Treat this as end-of-stack to
// enforce progress and avoid infinite loops.
let sp = frame.context.get_stack_pointer();
let last_sp = ctx.get_register_always(STACK_POINTER);
if sp <= last_sp {
// Mips leaf functions may not actually touch the stack (thanks
// to the return address register allowing you to "push" the return address
// to a register), so we need to permit the stack pointer to not
// change for the first frame of the unwind. After that we need
// more strict validation to avoid infinite loops.
let is_leaf = args.callee_frame.trust == FrameTrust::Context && sp == last_sp;
if !is_leaf {
trace!("stack pointer went backwards, assuming unwind complete");
return None;
}
}
// Ok, the frame now seems well and truly valid, do final cleanup.
// The Mips `jal` instruction always sets $ra to PC + 8
let ip = frame.context.get_instruction_pointer();
frame.instruction = ip - 8;
Some(frame)
}
/// This is a hack to have a different [`CpuContext`] type/impl depending on the
/// context flags of the inner [`MipsContext`]
#[derive(Clone)]
struct Mips32Context(MipsContext);
impl CpuContext for Mips32Context {
type Register = u32;
const REGISTERS: &'static [&'static str] = <MipsContext as CpuContext>::REGISTERS;
fn get_register_always(&self, reg: &str) -> Self::Register {
self.0.get_register_always(reg) as u32
}
fn set_register(&mut self, reg: &str, val: Self::Register) -> Option<()> {
self.0.set_register(reg, val.into())
}
fn stack_pointer_register_name(&self) -> &'static str {
self.0.stack_pointer_register_name()
}
fn instruction_pointer_register_name(&self) -> &'static str {
self.0.instruction_pointer_register_name()
}
}
impl IntoRawContext for Mips32Context {
fn into_ctx(self) -> MinidumpRawContext {
MinidumpRawContext::Mips(self.0)
}
}
trait IntoRawContext {
fn into_ctx(self) -> MinidumpRawContext;
}
impl IntoRawContext for MipsContext {
fn into_ctx(self) -> MinidumpRawContext {
MinidumpRawContext::Mips(self)
}
}
impl TryFrom<MipsContext> for Mips32Context {
type Error = MipsContext;
fn try_from(ctx: MipsContext) -> Result<Self, Self::Error> {
if ContextFlagsCpu::from_flags(ctx.context_flags).contains(ContextFlagsCpu::CONTEXT_MIPS64)
{
Err(ctx)
} else {
Ok(Self(ctx))
}
}
}