> Am Donnerstag 14 April 2011, 09:49:14 schrieb Mikael Pettersson: > > Richard Weinberger writes: > > > Hi, > > > > > > I'm facing a very strange issue with gcc-4.6.0 and UML. > > > Within __local_bh_enable() gcc generates no code for > > > sub_preempt_count(). > > > > > > See: > > > http://userweb.kernel.org/~rw/uml-gcc460/__local_bh_enable-gcc460.txt > > > vs. > > > http://userweb.kernel.org/~rw/uml-gcc460/__local_bh_enable-gcc431.txt > > > > > > Interestingly it generates code for add_preempt_count(). > > > I can reproduce this on x86 and x86_64. > > > > > > The problem has to do with UML's current_thread_info() function. > > > When I replace it with arch/x86's (unportable) variant gcc generates > > > code. > > > > > > Any ideas whether this is a gcc or a kernel issue?
It looks like a gcc error with one of the optimization passes > > Please provide a standalone test case. > > There you go! > http://userweb.kernel.org/~rw/uml-gcc460/testcase.c Replacing inline with __attribute__((noinline)) makes it produce code again without requiring asm("esp")/asm("rsp") tricks and the code appears to be working I think gcc is assuming only low bits in the address of stack vars and thought they were all masked out :( with this change my test version of gcc-4.6.0 works for x86/amd64 I have not yet gotten 4.6.0 to install yet so I was testing with xgcc from the failed build --- testcase.orig 2011-04-14 08:34:24.000000000 -0700 +++ testcase.c 2011-04-14 12:17:44.000000000 -0700 @@ -31,7 +31,7 @@ } #else /* UML */ -static inline struct thread_info *current_thread_info(void) +static __attribute__((noinline)) struct thread_info *current_thread_info(void) { struct thread_info *ti; unsigned long mask = THREAD_SIZE - 1;> > Thanks, > //richard ------------------------------------------------------------------------------ Benefiting from Server Virtualization: Beyond Initial Workload Consolidation -- Increasing the use of server virtualization is a top priority.Virtualization can reduce costs, simplify management, and improve application availability and disaster protection. Learn more about boosting the value of server virtualization. http://p.sf.net/sfu/vmware-sfdev2dev _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
