[PATCH] Fix usage of posix_spawn_file_actions_addopen

[Rafael Espíndola]

r187208. Thanks!

On 26 July 2013 12:07, Hal Finkel <hfinkel at anl.gov> wrote:
> Rafael,
>
> This also seems to work well (and is simpler), thanks!
>
>  -Hal
>
> ----- Original Message -----
>> How about creating the std::string in the caller? would the attached
>> patch (with comments about what is going on) work?
>>
>> On 26 July 2013 10:25, Hal Finkel <hfinkel at anl.gov> wrote:
>> > Hello,
>> >
>> > The Execute function in Unix/Program.inc uses posix_spawn, when
>> > available (and when no memory limit is requested), to execute
>> > child programs. When file descriptor redirection is specified,
>> > posix_spawn_file_actions_addopen is used to add an open file
>> > action to the posix_spawn request. Unfortunately, the argument to
>> > posix_spawn_file_actions_addopen is obtained by calling
>> > File.c_str(), and so the lifetime of the provided pointer is
>> > limited. On systems using glibc, this does not work. The
>> > implementation assumes that the lifetime of the provided pointer
>> > will not end prior to the call to posix_spawn itself(*).
>> >
>> > This problem was causing bugpoint to (nondeterministically) fail to
>> > execute gcc on some of my systems.
>> >
>> > I've attached a patch which extends the lifetime of the strings
>> > provided to posix_spawn_file_actions_addopen, allowing this to
>> > work correctly with glibc. The standard does not seem to specify
>> > one way or the other what string lifetime is expected.
>> > Alternatively, we could consider glibc broken in this area, and
>> > avoid using posix_spawn with glibc.
>> >
>> > Please review.
>> >
>> > Thanks again,
>> > Hal
>> >
>> > (*) You can see this by looking at the source, see:
>> > http://fossies.org/dox/glibc-2.17/spawn__faction__addopen_8c_source.html#l00027
>> >
>> > As a quick example of something else, here's a different
>> > implementation that does make a copy of the provided string:
>> > https://github.com/evanphx/ulysses-libc/blob/master/src/process/posix_spawn_file_actions_addopen.c
>> >
>> > --
>> > Hal Finkel
>> > Assistant Computational Scientist
>> > Leadership Computing Facility
>> > Argonne National Laboratory
>>
>
> --
> Hal Finkel
> Assistant Computational Scientist
> Leadership Computing Facility
> Argonne National Laboratory