Thursday, June 5, 2008

MacOSX and stdin,stdout,stderr

I am in the process of porting a friends software to MacOSX. Don't ask what it does yet, all will be revealed soon. The code compiles quite happily on Solaris and Linux, but fails with the following error on MacOSX...


dbFile.c: In function ‘_setLogfile’:
dbFile.c:243: error: invalid lvalue in assignment
dbFile.c:244: error: invalid lvalue in assignment
dbFile.c: In function ‘fieldFillGen’:

I know what the problem is -
Seems on MacOSX 10.4 and below:
stdin, stdout, and stderr are addresses of a FILE rather than a FILE*
On MacOSX 10.5 they are FILE*

So depending on the OS version you are targeting will determine whether the code compiles or not. The issue goes back to the way FreeBSD originally implemented this in stdio.h which is the base for MacOSX, and it looks like it finally became "correct" i.e. portable and adhering to other implementations in MacOSX 10.5
A quick look at /usr/include/stdio.h confirms this...
the FILE* appears within the ifdef for _DARWIN_UNIX_03

extern FILE *__stdinp;
extern FILE *__stdoutp;
extern FILE *__stderrp;
#else /* !__DARWIN_UNIX03 */
extern FILE __sF[];
#endif /* __DARWIN_UNIX03 */

So I need to come up with a simple workaround for what was originally valid code on other operating systems:

stderr = wk;
stdout = wk;

the following seems to work:

dup2(wk->_file ,STDERR_FILENO);
dup2(wk->_file ,STDOUT_FILENO);

Wednesday, June 4, 2008

Standard delete v's Firebird delete

Alex and I have just committed a slew of changes to the code in Firebird 2.1.
This all started when we did the 32 bit builds for Firebird on MacOSX.

We found that in remote we would get asserts trying to create a database. On deeper and further investigation over a period of a couple of weeks we realised that in some cases the standard delete was being called instead of the redefined version in Firebird i.e. it invoked free() instead of
MemoryPool::globalFree(). After some extensive googling we found other people have also run into similar problems.

As a solution it was suggested to use:
1. Use switches -fvisibility=hidden and -fvisibility-inlines-hidden together.
2. Use switch -fvisibility=hidden and __attribute__((always_inline)).

Trying with second combination we found that we sometimes got (depending on the version of gcc) an error:
sorry, unimplemented: inlining failed in call to 'void operator delete(void*) throw ()'.

It seems that without -fvisibility=hidden and __attribute__((always_inline)) gcc is
using non-inline body for operator delete. And is randomly using the wrong body, the one from the standard
operator delete.

The first combination helps to avoid this bug - but any entrypoint, which is to be exported, now has to be marked with __attribute__((visibility="default")).