Segfault with Data.Text.Lazy.Builder.Int(decimal)

[argiopetech]

I'm seeing segfaults when using decimal with large numbers, particularly in interpreted code. I first noticed the problem under GHC 7.8.2, and it persists with GHC 7.8.3. Text version is 1.2.0.0.

The attached should segfault without output if compiled and run, and segfault after some small quantity of output if interpreted (I've seen just ", as well as "2"). . I have had similar failures with numbers as small as 3 * (fromIntegral (maxBound :: Int) :: Integer); however, it sometimes takes 2-3 evaluations in GHCI to segfault. Conversely, the following fails consistently.

import Data.Text.Lazy.Builder     (toLazyText)
import Data.Text.Lazy.Builder.Int (decimal)

main = print (toLazyText (decimal 10000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002))

This is possibly a compiler issue, as I've received 'internal error: stg_ap_p_ret' from GHCI while playing with it. I haven't been able to reproduce that, so I'm bouncing it here first.

This seems to be in toLazyText or decimal, as simply packing the large decimal value from a string with Data.Text.Lazy.pack and printing it does not cause a problem.

[argiopetech]

This appears only to be an issue when compiling without optimization. Compiling with any optimization level causes output as expected, while compiling without an optimization flag or interpreting seems to cause issues.

Amusingly, testing this seems to have stumbled on another consistent failure. With the code from above in a sandbox with only Text-1.2.0.0 installed, the following occurs:

$ cabal exec -- runhaskell -O0 Main.hs 
"2"
Bus error

Whereas without the optimization flag, the output is still consistent, but different:

$ cabal exec -- runhaskell nMain.hs
"Segmentation fault

[argiopetech]

Some tracing shows this is directly related to a conversion in countDigits.

countDigits v0 = go 1 (fromIntegral v0 :: Word64)

This causes v0 to be truncated to 2, so countDigits returns 1 and vastly undershoots the storage space needed (actually 362 digits-worth).

[RyanGlScott]

I believe this also fixes issue #91, so I'll go ahead and close it.

[bos]

Thanks, Ryan!