[lttng-dev] Debian specific userspace RCU configure override

[Ondřej Surý]

JFTR I did build the urcu and ltt-control on same machine and urcu build went ok, but ltt-control failed. So there might be something broken.

Although yes, more generally there could be a problem with difference between build machines, so --disable flag might be helpful.

O.
-- 
Ondřej Surý <ondrej at sury.org>
Knot DNS (https://www.knot-dns.cz/) – a high-performance DNS server

> On 24. 5. 2014, at 0:21, Jon Bernard <jbernard at debian.org> wrote:
> 
> * Mathieu Desnoyers <mathieu.desnoyers at efficios.com> wrote:
>> Hi,
>> 
>> I recently stumbled on this patch:
>> 
>> http://sprunge.us/jYcJ
>> 
>> It overrides the generated config.h to ensure the
>> "dmb" instruction is not used.
>> 
>> However, the proper checks seems to be in place within
>> configure.ac to automatically detect whether to use dmb
>> or not:
>> 
>> # ARM-specific checks
>> AS_IF([test "x$ARCHTYPE" = "xarm"],[
>>        AC_MSG_CHECKING([for dmb instruction])
>>        AC_COMPILE_IFELSE([AC_LANG_SOURCE([[
>>                                int main()
>>                                {
>>                                        asm volatile("dmb":::"memory");
>>                                        return 0;
>>                                }
>>                ]])
>>        ],[
>>                AC_MSG_RESULT([yes])
>>                AC_DEFINE([CONFIG_RCU_ARM_HAVE_DMB], [1])
>>        ],[
>>                AC_MSG_RESULT([no])
>>        ])
>> ])
>> 
>> My thinking here is that perhaps inappropriate compiler flags
>> are used when the compiler is invoked from within "configure",
>> which leads it to think that it targets an ARMv7+ with dmb.
>> The Debian "armel" architecture AFAIU needs to target older
>> ARM architectures.
> 
> I also wonder if there are some differences between of the arm build
> machines.  I don't have shell access to the machine on which urcu was
> built so I cannot check, but perhaps that particular machine has dmb.
> 
>> It would be much better to fix the compiler flags passed to
>> configure and let urcu autodetection do what it is intended
>> to do rather than override the generated file.
> 
> I'll gather and post the compiler flags used for urcu and we'll see.
> 
> -- 
> Jon
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