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Kernel: Fix retreiving frame pointer from a thread

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If we're trying to walk the stack for another thread, we can
no longer retreive the EBP register from Thread::m_tss. Instead,
we need to look at the top of the kernel stack, because all threads
not currently running were last in kernel mode. Context switches
now always trigger a brief switch to kernel mode, and Thread::m_tss
only is used to save ESP and EIP.

Fixes #2678
This commit is contained in:
Tom 2020-07-03 12:12:34 -06:00 • committed by Andreas Kling
parent 6d5bd8c76b
commit bb84fad0bf
4 changed files with 67 additions and 28 deletions
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50
Kernel/Thread.cpp
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@ -739,7 +739,7 @@ void Thread::notify_finalizer()
g_finalizer_wait_queue->wake_all();
}
String Thread::backtrace(ProcessInspectionHandle&) const
String Thread::backtrace(ProcessInspectionHandle&)
{
return backtrace_impl();
}
@ -775,37 +775,37 @@ static bool symbolicate(const RecognizedSymbol& symbol, const Process& process,
return true;
}
String Thread::backtrace_impl() const
String Thread::backtrace_impl()
{
Vector<RecognizedSymbol, 128> recognized_symbols;
u32 start_frame;
if (Thread::current() == this) {
asm volatile("movl %%ebp, %%eax"
: "=a"(start_frame));
} else {
start_frame = frame_ptr();
recognized_symbols.append({ tss().eip, symbolicate_kernel_address(tss().eip) });
}
auto& process = const_cast<Process&>(this->process());
auto elf_bundle = process.elf_bundle();
ProcessPagingScope paging_scope(process);
FlatPtr stack_ptr = start_frame;
for (;;) {
if (!process.validate_read_from_kernel(VirtualAddress(stack_ptr), sizeof(void*) * 2))
break;
FlatPtr retaddr;
if (is_user_range(VirtualAddress(stack_ptr), sizeof(FlatPtr) * 2)) {
copy_from_user(&retaddr, &((FlatPtr*)stack_ptr)[1]);
recognized_symbols.append({ retaddr, symbolicate_kernel_address(retaddr) });
copy_from_user(&stack_ptr, (FlatPtr*)stack_ptr);
} else {
memcpy(&retaddr, &((FlatPtr*)stack_ptr)[1], sizeof(FlatPtr));
recognized_symbols.append({ retaddr, symbolicate_kernel_address(retaddr) });
memcpy(&stack_ptr, (FlatPtr*)stack_ptr, sizeof(FlatPtr));
// To prevent a context switch involving this thread, which may happen
// on another processor, we need to acquire the scheduler lock while
// walking the stack
{
ScopedSpinLock lock(g_scheduler_lock);
FlatPtr stack_ptr, eip;
if (Processor::get_context_frame_ptr(*this, stack_ptr, eip)) {
recognized_symbols.append({ eip, symbolicate_kernel_address(eip) });
for (;;) {
if (!process.validate_read_from_kernel(VirtualAddress(stack_ptr), sizeof(void*) * 2))
break;
FlatPtr retaddr;
if (is_user_range(VirtualAddress(stack_ptr), sizeof(FlatPtr) * 2)) {
copy_from_user(&retaddr, &((FlatPtr*)stack_ptr)[1]);
recognized_symbols.append({ retaddr, symbolicate_kernel_address(retaddr) });
copy_from_user(&stack_ptr, (FlatPtr*)stack_ptr);
} else {
memcpy(&retaddr, &((FlatPtr*)stack_ptr)[1], sizeof(FlatPtr));
recognized_symbols.append({ retaddr, symbolicate_kernel_address(retaddr) });
memcpy(&stack_ptr, (FlatPtr*)stack_ptr, sizeof(FlatPtr));
}
}
}
}