gcov: exclude code operating in userspace from profiling

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>
Cc: Ingo Molnar <mingo@elte.hu>
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Tested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 6c327b852e23b528963dc4f23e59ffa13761463d..430d5b24af7b210faf695f0c3619a1d66ae8acf5 100644 (file)
--- a/arch/x86/kernel/Makefile
+++ b/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