Ingo, Thomas and Linus, I know Thomas did a patch to force the -mtune=generic, but just in case gcc decides to do something crazy again, this patch will catch it.
Should we try to get this in now? -- Steve On Fri, 2009-11-20 at 00:23 -0500, Steven Rostedt wrote: > commit c7715fb611c69ac4b7f722a891de08b206fb7686 > Author: Steven Rostedt <srost...@redhat.com> > Date: Thu Nov 19 23:41:02 2009 -0500 > > tracing/x86: Add check to detect GCC messing with mcount prologue > > Latest versions of GCC create a funny prologue for some functions. > Instead of the typical: > > push %ebp > mov %esp,%ebp > and $0xffffffe0,%esp > [...] > call mcount > > GCC may try to align the stack before setting up the frame pointer > register: > > push %edi > lea 0x8(%esp),%edi > and $0xffffffe0,%esp > pushl -0x4(%edi) > push %ebp > mov %esp,%ebp > [...] > call mcount > > This crazy code places a copy of the return address into the > frame pointer. The function graph tracer uses this pointer to > save and replace the return address of the calling function to jump > to the function graph tracer's return handler, which will put back > the return address. But instead instead of the typical return: > > mov %ebp,%esp > pop %ebp > ret > > The return of the function performs: > > lea -0x8(%edi),%esp > pop %edi > ret > > The function graph tracer return handler will not be called at the exit > of the function, but the parent function will call it. Because we missed > the return of the child function, the handler will replace the parent's > return address with that of the child. Obviously this will cause a crash > (Note, there is code to detect this case and safely panic the kernel). > > The kicker is that this happens to just a handful of functions. > And only with certain gcc options. > > Compiling with: -march=pentium-mmx > will cause the problem to appear. But if you were to change > pentium-mmx to i686 or add -mtune=generic, then the problem goes away. > > I first saw this problem when compiling with optimize for size. > But it seems that various other options may cause this issue to arise. > > Instead of completely disabling the function graph tracer for i386 builds > this patch adds a check to recordmcount.pl to make sure that all > functions that contain a call to mcount start with "push %ebp". > If not, it will fail the compile and print out the nasty warning: > > CC kernel/time/timer_stats.o > > ******************************************************** > Your version of GCC breaks the function graph tracer > Please disable CONFIG_FUNCTION_GRAPH_TRACER > Failed function was "timer_stats_update_stats" > ******************************************************** > > The script recordmcount.pl is given a new parameter "do_check". If > this is negative, the script will only perform this check without > creating the mcount caller section. This will be executed for x86_32 > when CONFIG_FUNCTION_GRAPH_TRACER is enabled and CONFIG_DYNAMIC_FTRACE > is not. > > If the arch is x86_32 and $do_check is greater than 1, it will perform > the check while processing the mcount callers. If $do_check is 0, then > no check will be performed. This is for non x86_32 archs and when > compiling without CONFIG_FUNCTION_GRAPH_TRACER enabled, even on x86_32. > > Reported-by: Thomas Gleixner <t...@linutronix.de> > LKML-Reference: > <alpine.lfd.2.00.0911191423190.24...@localhost.localdomain> > Signed-off-by: Steven Rostedt <rost...@goodmis.org>
