[lttng-dev] [PATCH] Force static_alloc setup to be written into memory

[Stefan Seefeld]

On 02/14/2014 09:23 AM, Alexander Monakov wrote:
>
> On Fri, 14 Feb 2014, Paul Woegerer wrote:
>
>> As explained by Alexander Monakov, dlsym() is defined to be pure, thus the
>> compiler is allowed to assume that there is no need to write the changes
>> performed by setup_static_allocator() into memory prior to calling dlsym().
>> The added cmm_barrier() forces the compiler to write the changes into memory.
>>
>> For more details refer to:
>> http://lists.lttng.org/pipermail/lttng-dev/2014-February/022389.html
> If everyone here agrees that this is a workaround for a glibc bug, please add
> a note to that effect in the patch and please notify glibc upstream (again).

I'v just submitted https://sourceware.org/bugzilla/show_bug.cgi?id=16585


> FWIW, when toying with a similar code I implemented a different workaround
> along the lines of
>
> #define dlsym glibc_dlsym_proto_lies_about_leafness
> #include <dlfcn.h>
> #undef dlsym
>
> extern void *dlsym(void *, const char *);
>
>
> Thus avoiding the need to sprinkle unneeded compiler memory barriers in code.

Right, this looks very clean indeed.

        Stefan


-- 
Stefan Seefeld
CodeSourcery / Mentor Graphics
http://www.mentor.com/embedded-software/