Re: [Tinycc-devel] [FreeBSD support] __aligned(n) + __pure issues

[Michael Matz]

Hi,

On Sun, 16 Oct 2016, Christian Jullien wrote:

> Ok Michael,
> It is defined in sys/cdefs.h as:
>
> #if __GNUC_PREREQ__(2, 7) || defined(__INTEL_COMPILER)
> #define __dead2         __attribute__((__noreturn__))
> #define __pure2         __attribute__((__const__))
> #define __unused        __attribute__((__unused__))
> #define __used          __attribute__((__used__))
> #define __packed        __attribute__((__packed__))
> #define __aligned(x)    __attribute__((__aligned__(x)))
> #define __section(x)    __attribute__((__section__(x)))
> #endif

Yeah, we gathered this meanwhile from grischkas research.  A bug in 
FreeBSDs header (the bug being that there's no fallback definition of the 
macros that are nevertheless used unconditionally in standard headers).

Now, I do agree that we'd want to add a work around for this in tcc.  I 
think a better work-around than defining __GNUC__ is to define the above 
macros instead.  __GNUC__ simply has quite some side-effects.  (E.g. after 
the patch you can't compile programs on some versions of glibc anymore 
because it then uses facilities of GNU C that tcc simply doesn't 
implement).

> -    tcc_define_symbol(s, "__GNUC_MINOR__", "1");
> +    tcc_define_symbol(s, "__GNUC_MINOR__", "7");
>
> And it helps a little bit, now I get the same result as if I define
> __aligned(x) __attribute__((__aligned__(x))) i.e. code compiles (with
> __aligned defined) but std C library is not found.
>
> ------------ test3 ------------
> ../tcc -B.. -I../include -I.. -I.. -DTCC_TARGET_I386 -DONE_SOURCE -run
> ../tcc.c -B.. -I../include -I.. -I.. -DTCC_TARGET_I386 -DONE_SOURCE -run
> ../tcc.c -B.. -I../include -I.. -I.. -DTCC_TARGET_I386 -DONE_SOURCE -run
> ../tcc.c -B.. -I../include -I.. -I.. -run tcctest.c > test.out3
> tcc: error: undefined symbol 'memcpy'
> ...

Yes, I wrote a paragraph about this in my initial answer of how you should 
start trying to corner this problem.


Ciao,
Michael.