POSIX: check if strtod() can handle hex

[gperciva]

No description provided.

[gperciva]

I'm not certain we want this solution; it doesn't help with clang. See #320 for discussion.

[cperciva]

I don't like this:

1. I don't want to run binaries we compiled unless absolutely necessary; it breaks cross-compiling.

2. If some tests fail on Solaris because Solaris is broken, well... that seems like how things should be?

[gperciva]

Hmm. There's two sorts of run-time problems:

1. runtime broken systems which we can work around at compile-time.
   (e.g., OSX 10.11 with XCode 8: we can avoid a run-time error by compiling with -DPOSIXFAIL_CLOCK_GETTIME; this is currently checked in posix-cflags.sh).
2. runtime broken systems which we cannot work around.
   (e.g., solaris + clang 6 with any ANSI-C vs. C99 function)

In the case of 1, I think that it would be nice to continue to detect & use the workarounds. I'd be happy to move that code to posix-cflags-runtime.sh for clarity, if that would help?

Alternatively, we could add a tests/POSIX/check-runtime.sh, which would be added to all software which uses libcperciva? If there's an error of type 1, we could output a message to the user saying

your platform is broken. Please recompile after manually setting
CFLAGS="-DPOSIXFAIL_CLOCK_GETTIME"

and if there's an error of type 2, the message could just be

your platform is broken, period.

Asking for somebody to set a compiler flag manually would be a bit weird, but it would satisfy the concern about cross-compiling? Maybe? (Note that this would apply to tarsnap as well. I'm really not a fan of asking users to manually set CFLAGS if we can avoid it.)

The status quo which I want to avoid is this: the libcperciva tests fail on solaris + gcc, we don't change anything in kivaloo, we forget about this, then two years from now we get a confused bug report about kivaloo failing in a weird way, and after a few hours of debugging we figure out that strtod() can't handle hex if it's on solaris + gcc unless we link it with -std=c99.

Also, remember that there's a number of other functions whose behaviour differs between ANSI-C and C99. As far as I know, the only one that we use is strtod, but there could be others. (I've only spent 2 minutes reading the ANSI-C standard, to double-check the difference with strtod.)

[cperciva]

I'm ok with the existing OS X hack. It's ugly but it's necessary for a widely used platform. (Hopefully at some point we can remove it though? I don't know how common that version is these days.)

For the case of "Solaris and clang 6 a broken combination", I would probably just document in BUILDING.

[gperciva]

What about "solaris and gcc", which is a broken-but-fixable combination? Likewise just document it in BUILDING?

[cperciva]

I'd be inclined to just document that. I mean, the official way of building is make, which should use a C99-compatible compiler by default; if someone goes out of their way to select a non-default compiler, it's up to them to make sure their selection is C99-compatible.

[gperciva]

That works for our POSIX Makefiles, but do you feel like taking a wild guess as to which compiler is the first choice of GNU autotools? :(

I see three possibilities to allow tarsnap and scrypt to compile safely with a simple ./configure && make:

1. change the order of compilers it checks on Solaris, to prioritize cc and c99 over gcc. So far I've failed to do this. I suspect that AC_PROG_CC can't appear in a conditional context, because configure only contained code arising from the first instance of that command.

2. change the default order of compilers for all platforms. (That is a much more invasive change than seems warrented.)

3. add this check to autoconf, i.e. Fix solaris linking to a c89 library scrypt#285. (That's a draft PR, but it only needs a little bit of cleaning up.) Note that AC_TRY_RUN has a built-in capability to disable itself if you're doing a cross-compile.

Of course, there's also:

4. document that we cannot build scrypt and tarsnap safely on Solaris unless the user manually does ./configure CC=cc or ./configure CC=c99 or ./configure LDFLAGS=-std=c99.