[PATCH] Fix hang when calling functions in a module with an on_load attribute from a native module

[Paul Guyot]

>> --- otp_src_R14B/lib/kernel/src/error_handler.erl.~1~   2010-09-13
>> 19:00:22.000000000 +0200
>> +++ otp_src_R14B/lib/kernel/src/error_handler.erl       2010-09-24
>> 13:44:09.000000000 +0200
>> @@ -17,6 +17,7 @@
>>  %% %CopyrightEnd%
>>  %%
>>  -module(error_handler).
>> +-compile(no_native).
>> 
>>  %% A simple error handler.
> 
> Any objections to applying this fix to dev? Otherwise let's include it
> as a trivial workaround that makes enable-native-libs useable.


This is no trivial workaround and it works by sheer luck. What this bug reveals is that there is a major design flaw with on_load and HiPE, as illustrated by the fact that the emulator goes into an infinite loop if error_handler is natively compiled: every time there is a remote call to a function in a module that has an on_load attribute, the emulator goes through error_handler:undefined_function! I think it doesn't infinite loop when error_handler is not native because it goes through the apply BIF which works around the linkage issue.

A quick benchmark shows that (on dev, without --enable-native-libs) calling a remote function in an on_load attribute currently takes 100+ times longer from HiPE than from BEAM.

The way things work for BEAM is that final_touch disables export entries if there is an on_load handler, and finish_after_on_load_2 BIF, which is called from init/code_server, fixes them by using the saved address. The same should be done for HiPE, but of course it's more complicated because dynamic linking works differently in HiPE.

I can only see three solutions:
- fix the pointers in each callers (which doesn't sound doable);
- change the way dynamic linking works in HiPE as Mikael suggests;
- or add a small stub, as implemented in my patch -- this is still three to five times slower than BEAM.

Simply ignoring the problem will not make it go away.

Paul
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