Messages in this thread Patch in this message | | | Date | Thu, 02 Jul 2009 13:58:13 +0200 | From | Peter Oberparleiter <> | Subject | Re: [BUG] gcov causes vread_tsc to increment kernel memory |
| |
Steven Rostedt wrote: > On bootup of the latest kernel my init segfaults. Debugging it, I found > that vread_tsc (a vsyscall) increments some strange kernel memory: > > 0000000000000000 <vread_tsc>: > 0: 55 push %rbp > 1: 48 ff 05 00 00 00 00 incq 0(%rip) # 8 <vread_tsc+0x8> > 4: R_X86_64_PC32 .bss+0x3c > 8: 48 89 e5 mov %rsp,%rbp > b: 66 66 90 xchg %ax,%ax > e: 48 ff 05 00 00 00 00 incq 0(%rip) # 15 <vread_tsc+0x15> > 11: R_X86_64_PC32 .bss+0x44 > 15: 66 66 90 xchg %ax,%ax > 18: 48 ff 05 00 00 00 00 incq 0(%rip) # 1f <vread_tsc+0x1f> > 1b: R_X86_64_PC32 .bss+0x4c > 1f: 0f 31 rdtsc > > > Those "incq" is very bad to happen in vsyscall memory, since userspace can > not modify it. You need to make something prevent profiling of vsyscall > memory (like I do with ftrace). > > -- Steve
You're right, I missed that file. This should be fixed with the patch below. As the problem didn't occur on my test machine, please retest with the patch applied. Thanks!
Also seeing as function tracer and gcov work on a similar basis and require similar files to be excluded from profiling, it would be nice if we wouldn't need to mark those files separately. Instead it would be great if the Makefile could be used to specify that a certain object file has a certain property (e.g. PROPERTY_USERPACE_file.o := y) and the mechanism (e.g. function tracer) would only need to specify that the extra gcc options should not be applied when that property is set. What do you think?
================= Subject: [PATCH] gcov: exclude code operating in userspace from profiling
From: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Fix for this issue on x86_64:
rostedt@goodmis.org wrote: > On bootup of the latest kernel my init segfaults. Debugging it, > I found that vread_tsc (a vsyscall) increments some strange > kernel memory: > > 0000000000000000 <vread_tsc>: > 0: 55 push %rbp > 1: 48 ff 05 00 00 00 00 incq 0(%rip) > # 8 <vread_tsc+0x8> > 4: R_X86_64_PC32 .bss+0x3c > 8: 48 89 e5 mov %rsp,%rbp > b: 66 66 90 xchg %ax,%ax > e: 48 ff 05 00 00 00 00 incq 0(%rip) > # 15 <vread_tsc+0x15> > 11: R_X86_64_PC32 .bss+0x44 > 15: 66 66 90 xchg %ax,%ax > 18: 48 ff 05 00 00 00 00 incq 0(%rip) > # 1f <vread_tsc+0x1f> > 1b: R_X86_64_PC32 .bss+0x4c > 1f: 0f 31 rdtsc > > > Those "incq" is very bad to happen in vsyscall memory, since > userspace can not modify it. You need to make something prevent > profiling of vsyscall memory (like I do with ftrace).
Signed-off-by: Peter Oberparleiter <oberpar@linux.vnet.ibm.com> --- arch/x86/kernel/Makefile | 2 ++ 1 file changed, 2 insertions(+)
Index: linux-2.6.31-rc1/arch/x86/kernel/Makefile =================================================================== --- linux-2.6.31-rc1.orig/arch/x86/kernel/Makefile +++ linux-2.6.31-rc1/arch/x86/kernel/Makefile @@ -26,6 +26,8 @@ CFLAGS_tsc.o := $(nostackp) CFLAGS_paravirt.o := $(nostackp) GCOV_PROFILE_vsyscall_64.o := n GCOV_PROFILE_hpet.o := n +GCOV_PROFILE_tsc.o := n +GCOV_PROFILE_paravirt.o := n obj-y := process_$(BITS).o signal.o entry_$(BITS).o obj-y += traps.o irq.o irq_$(BITS).o dumpstack_$(BITS).o
| |