Re: [Haskell-cafe] segfault depending on code position in source file

22 Feb 2019

      well , good news :-)

i tested the same code on a 64 bits Linux Centos 7.2 with GHC 8.4 and it
works fine...

so the problem is only under 32bits Linux Fedora Core 29 with GHC 8.2

we had a system failure or security issue last month and i had to upgrade
the 32 bit CPU 3 weeks ago to latest Linux Fedora Core version
but this had the side effect to downgrade the Haskell GHC compiler to 8.2
version
and the 8.2 version or 32 bit platform have bugs
if i can i will try to test with the 8.4 GHC on the 32 bit platform to see
if the problem was with 32bit vs 64bit; possible difference with Fedora and
CentOS also, but i think it's the 8.2 compiler that cause the bug...

regards,
damien

On Fri, Feb 22, 2019 at 10:55 AM Damien Mattei 
wrote:
...
well i understand the difficulty, i just pos because ,really some times i
get incredible help that i coulmdn not even think it possible.
i admit the code is and the database connection is a stop help.
for the database i cannot do ,for the code i commented a lot  and i can
resume with this concise code that recreate the problem:
it's quite simple i noticed that after one lines (see in code the lines
and the upper case comments) the query to DB in getAlphaDelta does not
works anymore (as it worked before ) but other functions making queries
works that what is strange...
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
import Database.MySQL.Simple
import Database.MySQL.Simple.QueryResults
import Database.MySQL.Simple.Result
import Database.MySQL.Simple.QueryParams
import Database.MySQL.Simple.Param
import Control.Monad
import qualified Data.Text as Tx
import Debug.Trace
import Data.Maybe as Maybe
import Text.Read
import Data.Tuple.Extra
getAlphaDelta :: Connection -> String -> IO (Double,Double)
getAlphaDelta conn name = do
            let qry_head_AlphaDelta_AngularDistance = "select alpha,delta
from AngularDistance where Nom = ?" :: Query
            (alpha_delta_rows :: [(Double,Double)]) <- query conn
qry_head_AlphaDelta_AngularDistance (Only (name::String))
            return (head alpha_delta_rows)
main :: IO ()
main =
do
    conn <- connect defaultConnectInfo
      { connectHost = "moita",
        connectUser = "mattei",
        connectPassword = "sidonie2",
        connectDatabase = "sidonie" }
-- check getAlphaDelta works:
-- HERE getAlphaDelta WORKS
    let name = "WOR   7"
    putStrLn $ show name
    ad <- getAlphaDelta conn name
    putStr "ad ="
    putStrLn $ show ad
(names ::[Only Tx.Text])<- query_ conn "SELECT Nom FROM
AngularDistance WHERE distance > 0.000278"
-- AFTER THE PREVIOUS LINE getAlphaDelta WILL NOT WORKS AND ISSUE A
SEGFAULT IN GHCI
    let name3 = "A     7"
    putStrLn $ show name3
    ad3 <- getAlphaDelta conn name3
    putStr "ad3 ="
    putStrLn $ show ad3
close conn
here is the output:
[mattei@localhost Haskell]$ ghci
GHCi, version 8.2.2: http://www.haskell.org/ghc/  :? for help
Prelude> :load UpdateSidonie.hs
[1 of 1] Compiling Main             ( UpdateSidonie.hs, interpreted )
Ok, one module loaded.
*Main> main
"WOR   7"
ad =(17386.0,7120.0)
"A     7"
Segmentation fault (core dumped)
as you see the first call to getAlphaDelta is ok but the second issue a
Segmentation fault.
i will try now with ghci 8.4 .... and hiope to give you some news...
Damien
On Thu, Feb 21, 2019 at 8:15 PM Sven Panne  wrote:
...
Am Do., 21. Feb. 2019 um 19:22 Uhr schrieb Damien Mattei <
damien.mattei@gmail.com>:
...
i had attached the whole file, so anyone can read the whole code,
perheaps it could help, saying me if there is compilation error on other
ghc versions, with mine no error at compilation.
I very much doubt that anyone likes to read >500 lines of Haskell code
with lots of external dependencies to help you with your problem. A good
hint for Open Source SW in general: If you think you might have found a
bug, cut down your example as much as possible, throw out as many external
dependencies as you can while still reproducing your problem, then, and
only then, post it to other people. You simply can't expect that other
people will do that debugging work for you in their spare time. The code
you post doesn't really have to make sense, it should just be the minimum
amount of code needed to reproduce the problem.
In a nutshell: The probability that you get some help is inversely
proportional to the size of your example, and even more inversely
proportional to the number of external dependencies (libraries etc.).
...
The problem to test is that without the database connection which is
behind a firewall of course ,the code can not be executed. [...]
Well, that is basically a show stopper for getting help...
I don't want to be mean, quite the opposite: I just want to explain why
you probably won't receive any help in the current form. This is not
special to the Haskell community, the situation would be very much the same
if you posted an equivalent problem of similar size to the
Racket/Python/... community. I'm quite sure that most maintainer would be
happy to have a look e.g. at a program consisting of a dozen lines without
external dependencies.