[LTP] [PATCH] syscalls/brk: add direct syscall tst_variant

[Teo Couprie Diaz]

Hi Petr,

On 06/12/2022 14:04, Petr Vorel wrote:
> Hi Teo,
>
>> Direct usage of brk is discouraged in favor of using malloc. Also, brk was
>> removed from POSIX in POSIX.1-2001.
>> In particular, the Musl libc's brk always returns -ENOMEM which causes
>> the LTP tests to exit prematurely. Invoking the syscall directly allows
>> them to properly validate brk behavior. Add a new test variant handling if
>> the libc wrappers are not implemented and testing the direct syscall.
>> Use tst_syscall() and handle the failure cases ourselves, as
>> we don't depend on the libc to do it anymore.
>> The patch also works around the dependency on sbrk to get the current break
>> as it has the same issues. Instead, call tst_syscall(__NR_brk, 0) which
>> always returns the current break.
>> Update brk01 to use void* to unify it with brk02.
> That brought warnings, see below.
>
> ...
>> +++ b/testcases/kernel/syscalls/brk/brk02.c
>> @@ -14,24 +14,51 @@
>>   #include <unistd.h>
>>   #include <sys/mman.h>
>>   #include "tst_test.h"
>> +#include "lapi/syscalls.h"
>> +
>> +inline void *brk_variants(void *addr)
>> +{
>> +	void *brk_addr;
>> +	if (tst_variant) {
>> +		brk_addr = (void *)tst_syscall(__NR_brk, addr);
>> +	} else {
>> +		brk_addr = (void *)brk(addr);
> NOTE using pointer for brk() is problematic, there are complains:
>
> brk02.c: In function ‘brk_variants’:
> brk02.c:26:28: warning: cast to pointer from integer of different size
> [-Wint-to-pointer-cast]
>     26 |                 brk_addr = (void *)brk(addr);
>           |                            ^
>
> Not sure how to fix this. Problem is in both C files, on several places.

Ah yes, of course. That's my mistake: I just realized that I used the 
libc brk as if it returned the break, but it doesn't. It just returns an 
error, so the warning is justified (and a drowned in other messages from 
my build system).

I'll rework and change that, I believe it will work without warnings 
once it is properly used.

> There are also code style problems (you can see it when running make check in
> testcases/kernel/syscalls/brk/), but that's a minor detail.
I wasn't aware of that, good to know thanks ! I will take care of it as 
well.
> Kind regards,
> Petr
Thanks for giving it a look,
Téo