Re: Debugging the RTS

Hi Eric, definitely not bit-rotted - the #if DEBUG code is what you get when you compile with -debug. Short roadmap: In general, GHC is built in many "ways", the -debug way is one. Some ways (like -threaded, -eventlog, -debug) are RTS-only, others (like -prof) lead to different library code. Ways are defined in compiler/main/DynFlags.hs as a Haskell data structure. In _dynamic_flags_, the actual flag strings for the ghc invocation are defined (like -prof, -threaded), they will activate the respective _Way_. _wayTag_, in turn, defines short names used as a suffix for *.o and *.a files, for instance *.p_o for profiling, *.l_o for eventlog. A number of other functions in there customise behaviour depending on the ways. Note _wayOptc_ which sets some options for the C compiler, like -DTRACING for the -eventlog way. However, it does not define DEBUG for the debug way! In mk/ways.mk you will find all the short names, and some more options are defined (WAY_*_HC_OPTS). These definitions are for the driver script, and pass on the right (long-name) options to the Haskell compiler to activate what is inside DynFlags (like -prof for WAY_p_HC_OPTS). Here we find WAY_debug_HC_OPTS= -static -optc-DDEBUG -ticky -DTICKY_TICKY which is what you were looking for To build a GHC with debug-way RTS, you need to add GhcRtsWays += debug to your build.mk (also see mk/config.mk{.in}, which gathers the default ways to build depending on platform and build configuration). I guess this might produce quite a number of new warnings and errors if you do it on a new platform... Once you have built this, you can compile with -debug and pass RTS options to get debug traces and activate sanity checks, like so: ghc -debug -myprogram.hs -o myprogramDebug ./myprogramDebug +RTS -Ds -DS (-DS = sanity checks on, -Ds = scheduler tracing) The usage message (see /rts/RtsFlags.c) tells you more options you can use. Happy debugging! / Jost On 05/14/2015 10:00 PM, ghc-devs-request@haskell.org wrote:

Date: Thu, 14 May 2015 18:36:04 +1000 From: Erik de Castro Lopo To: ghc-devs@haskell.org Subject: Debugging the RTS Message-ID: <20150514183604.2476baaaacd6a85ef1430b37@mega-nerd.com> Content-Type: text/plain; charset=US-ASCII

Hi all,

I'm trying to debug a AArch64/Linux specific RTS issue and digging around in the rts C code, I see a large amount of code wrapped in "#if DEBUG" type statements, but no way to enable in either mk/build.mk or it seems in any of the other build related settings files in the mk/ directory.

The only way I have found to enable this debug code that actually works is to enable this DEBUG code is to edit mk/ghc.mk as follows:

-STANDARD_OPTS += -DCOMPILING_RTS +STANDARD_OPTS += -DCOMPILING_RTS -DDEBUG

However, once I do that I get a bunch of C synatx errors.

I am doing this wrong or has the DEBUG code bit rotted?

Cheers, Erik