[Haskell-cafe] How do I debug this RTS segfault?
lanablack at amok.cc
Sun Jul 24 17:50:31 UTC 2016
I have run into this RTS bug recently. In short, when executing multiple
consequtive forks, after 500-600 or so the process is terminated by
SIGSEGV. I know this kind of thing is totally artificial, but still.
The problem I have is that I can't get any meaningful backtrace in gdb.
For example, for threaded RTS I get this
#0 0x0000000000560d63 in
Backtrace stopped: Cannot access memory at address 0x7fffff7fcea0
For non-threaded RTS I get this
#0 0x00000000007138c9 in stg_makeStablePtrzh ()
Backtrace stopped: Cannot access memory at address 0x7fffff7fc720
Build command: ghc --make -O2 -g -fforce-recomp fork.hs
Add threaded if needed.
I was able to reproduce this bug with both GHC 7.10.3 and todays HEAD
with the code below.
>import System.Exit (exitSuccess)
>import System.Posix.Process (forkProcess)
>fork_ n | n > 0 = processPid =<< forkProcess (fork_ $! n - 1)
> | otherwise = putStrLn "I'm done!"
>processPid pid | pid > 0 = exitSuccess
> | pid < 0 = putStrLn "OOOPS, forkProcess failed!"
> | otherwise = pure ()
>main = fork_ 1000
With best regards.
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