Bug #9009
Wrong binding when tracing c-calls
Description
When I use set_trace_func to trace ruby code, I get a wrong binding in
case of c-calls. In this case binding.eval("self") is not the receiver
of the call. Whereas in case of ruby-calls binding.eval("self") yields
the receiver of the call.
The underlying problem is that c-calls aren't pushed onto the frame stack.
It seems that currently there is no way to find out the receiver of c-call
inside tracing function.
Example of code:
$ cat test.rb
class IO
def some_method
end
end
puts "true receiver is #{$stdout}\n\n"
set_trace_func proc { |event, file, line, id, binding, classname|
if event == "call" or event == "c-call"
puts "#{event} #{id}:"
puts "\tapparent receiver = #{binding.eval("self")}"
puts "\tbacktrace:"
caller.each { |l| puts "\t\t#{l}" }
puts
end
}
$stdout.write "" # c-call
$stdout.some_method # ruby-call
Execution:
$ ruby test.rb
true receiver is #IO:0x00000000bed2a0
c-call write:
apparent receiver = main
backtrace:
test.rb:18:in `'
call some_method:
apparent receiver = #IO:0x00000000bed2a0
backtrace:
test.rb:2:in some_method'
'
test.rb:19:in
Expected result:
true receiver is #IO:0x00000000bed2a0
c-call write:
apparent receiver = #IO:0x00000000bed2a0
backtrace:
somewhere:in write'
'
test.rb:18:in
call some_method:
apparent receiver = #IO:0x00000000bed2a0
backtrace:
test.rb:2:in some_method'
'
test.rb:19:in
Updated by deivid (David RodrÃguez) over 7 years ago
=begin
Hi, I've translate your example to use the TracePoint API
This is the example and result:
class IO def some_method end end puts "true receiver is #{$stdout}\n\n" TracePoint.trace(:c_call, :call) do |tp| puts "#{tp.event} #{tp.defined_class} #{tp.method_id}" puts " apparent receiver = #{tp.self} vs #{tp.binding.eval('self')}" Thread.current.backtrace_locations(2).each { |loc| puts " #{loc}" } end $stdout.write "" $stdout.some_method
results in
true receiver is #<IO:0x8bf4e58> c_call IO write apparent receiver = #<IO:0x8bf4e58> vs main test.rb:15:in `<main>' call IO some_method apparent receiver = #<IO:0x8bf4e58> vs #<IO:0x8bf4e58> test.rb:2:in `some_method' test.rb:16:in `<main>'
My comments:
Seems like the new way to get the receiver is the (({#self})) instance method of the (({TracePoint})) class. However, the documentation states "(({Same as #binding: trace.binding.eval('self')}))", so that should probably be corrected or further explained.
- Regarding c-frames not being pushed onto the frame stack, they actually are, but after the Tracepoint/set_trace_func event. I made the same mistake here: #8538. Have a look at source:vm_insnhelper.c#L1514 and observe how (({vm_push_frame})) is called after (({EXEC_EVENT_HOOK})).
I still think the behaviour should be consistent and when inside a TracePoint event the current frame should either be already in the backtrace or not, but not behave differently for c methods and ruby methods.
=end