Re: How does TH know to load non-profiled object code when compiling profiled?
Thanks! In fact, I have just realized that Template Haskell does something very dodgy when it is loading profiled code: it will use the *profiled* interface files (things that are used in splices are brought into scope with import) to figure out what is going on with the *non-profiled* object files. I'm a bit surprised that we haven't had any terrifying bugs related to this. (It should be relatively easy to trigger horrible brokenness; just compile hi and p_hi with different code so that they are inconsistent.) Edward Excerpts from Simon Marlow's message of 2016-01-07 09:42:27 -0800:
On 07/01/2016 16:28, Edward Z. Yang wrote:
I've been looking for the code that implements this logic, but I can't seem to find it. (For what it's worth, compiler plugins *incorrectly* load the profiling interface when compiling profiled, which is wrong and something I'd like to fix.) Simon Marlow, do you happen to know?
Yeah, I've been fiddling with this lately. It's this function here: https://phabricator.haskell.org/diffusion/GHC/browse/master/compiler/ghci/Li...
Cheers, Simon
Correct, it's entirely dodgy. (I seem to remember a Note about this somewhere, but I can't find it right now) In any case, -fexternal-interpreter fixes this properly. Cheers, Simon On 08/01/2016 05:21, Edward Z. Yang wrote:
Thanks!
In fact, I have just realized that Template Haskell does something very dodgy when it is loading profiled code: it will use the *profiled* interface files (things that are used in splices are brought into scope with import) to figure out what is going on with the *non-profiled* object files. I'm a bit surprised that we haven't had any terrifying bugs related to this. (It should be relatively easy to trigger horrible brokenness; just compile hi and p_hi with different code so that they are inconsistent.)
Edward
Excerpts from Simon Marlow's message of 2016-01-07 09:42:27 -0800:
On 07/01/2016 16:28, Edward Z. Yang wrote:
I've been looking for the code that implements this logic, but I can't seem to find it. (For what it's worth, compiler plugins *incorrectly* load the profiling interface when compiling profiled, which is wrong and something I'd like to fix.) Simon Marlow, do you happen to know?
Yeah, I've been fiddling with this lately. It's this function here: https://phabricator.haskell.org/diffusion/GHC/browse/master/compiler/ghci/Li...
Cheers, Simon
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Edward Z. Yang -
Simon Marlow