warning for possible missing & in foreign import

I am attaching files to hopefully reproduce a problem I am having. I have not upgraded to 6.6.1 yet so let me know if it has been fixed.

$ touch fpenv_c.c fpenv.hs && cc -g -Wall -c fpenv_c.c && ghc -fasm --make fpenv.hs fpenv_c.o -lc
[1 of 1] Compiling Main             ( fpenv.hs, fpenv.o )
Linking fpenv ...
$ ./fpenv
(x,xFP)=(0x08090628,0x08090628)
fin_test: env=0xa7900040, p=0x808e00c
zsh: segmentation fault  ./fpenv
[139]$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 6.6.20070420

Running in valgrind shows:

...
fin_test: env=0x437c008, p=0x1
==12777==
==12777== Jump to the invalid address stated on the next line
==12777==    at 0x1F: ???
==12777==  Address 0x1F is not stack'd, malloc'd or (recently) free'd

I think this is when fin_test exits. I am experiencing this problem in a much larger program, so I wrote this test case to figure out what is going wrong. Am I using the newForeignPtrEnv API incorrectly?

Edited Mar 09, 2019 by Simon Marlow

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warning for possible missing & in foreign import