Re: Debugging the RTS

On 05/15/2015 09:17 PM, Simon Peyton Jones wrote:

Good idea. I think it’d great if Jost (or someone else) felt able to update those wiki pages with the info in his email.

Sure, will do that. I am not sure whether either of those pages is the best place for information about the GHC ways. Maybe there is already a page about them in the commentary - I will take a look tomorrow and add the information about ways from the mail. If no page exists I'll add a page, and link to it from the Debugging/RuntimeSystem page. A few years ago, I wrote one page specifically about the parallel ways, http://ghc.haskell.org/trac/ghc/wiki/GpHEden/CompilerWays but the information is outdated. / Jost

thanks!

Simon

*From:*ghc-devs [mailto:ghc-devs-bounces@haskell.org] *On Behalf Of *Lennart Kolmodin *Sent:* 15 May 2015 11:31 *To:* Jost Berthold *Cc:* ghc-devs@haskell.org *Subject:* Re: Debugging the RTS

Searching for online resources brought me to

https://ghc.haskell.org/trac/ghc/wiki/Debugging and

https://ghc.haskell.org/trac/ghc/wiki/Debugging/RuntimeSystem

This mail seems to be a more detailed description than available on the wiki. That page refers to GHC 6.12.

Would it make sense to add some info to the RuntimeSystem https://ghc.haskell.org/trac/ghc/wiki/Debugging/RuntimeSystem page?

2015-05-14 16:21 GMT+02:00 Jost Berthold mailto:berthold@mathematik.uni-marburg.de>:

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 http://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 http://build.mk (also see mk/config.mk http://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 mailto:ghc-devs-request@haskell.org wrote:

Date: Thu, 14 May 2015 18:36:04 +1000 From: Erik de Castro Lopo mailto:mle%2Bhs@mega-nerd.com> To: ghc-devs@haskell.org mailto:ghc-devs@haskell.org Subject: Debugging the RTS Message-ID: <20150514183604.2476baaaacd6a85ef1430b37@mega-nerd.com mailto: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 http://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 http://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

_______________________________________________ ghc-devs mailing list ghc-devs@haskell.org mailto:ghc-devs@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs