[LTP] Can we assume at least GCC 4.1 for building LTP tests? (__builtin___clear_cache())

[Jan Stancek]

----- Original Message -----
> From: "Peter Maydell" <peter.maydell@linaro.org>
> To: ltp@lists.linux.it
> Sent: Tuesday, 26 July, 2016 3:08:36 PM
> Subject: [LTP] Can we assume at least GCC 4.1 for building LTP tests?	(__builtin___clear_cache())
> 
> Hi; is there a minimum GCC version we can assume for LTP tests,
> and is it GCC 4.1 or better?

Hmm, I don't seem to have this available with gcc version 4.1.2 on RHEL5.6.

> 
> I ask because the mprotect04.c test case currently does this:
> 
> #ifdef __powerpc__
>     for (i = 0; i < copy_sz; i += 4)
>         __asm__ __volatile__("dcbst 0,%0; sync; icbi 0,%0; sync; isync"
>             :: "r"(mem_start + i));
> #endif
> 
> to synchronize the icache and dcache following copying some code,
> but this only works on PPC, not on other architectures which
> require explicit cache maintenance (like ARM). The easy way to
> do this portably is:
> 
>     __builtin___clear_cache(mem_start, mem_start + copy_sz);
> 
> which uses the GCC (and clang) builtin which should work on any
> architecture (and do nothing on ones like x86 which don't need
> special handling). However it doesn't exist prior to GCC 4.1
> (which was released a decade ago), so if LTP still has to
> support ancient compilers it gets a bit more awkward. (Perhaps
> the easiest thing would be to TCONF the test on ancient gcc.)

I'd go with configure check and TCONF testcases that needs it.
I recall only 2 testcases that needed icache flush, and given
that RHELs with this old gcc should EOL in 2017, I don't mind
if few testcases get skipped.

Regards,
Jan

> 
> thanks
> -- PMM
> 
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