On Thu, Jan 21, 2016 at 04:49:27PM -0600, Josh Poimboeuf wrote: > bpf_jit.S has several callable non-leaf functions which don't honor > CONFIG_FRAME_POINTER, which can result in bad stack traces. > > Create a stack frame before the call instructions when > CONFIG_FRAME_POINTER is enabled. > > Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com> > Cc: Alexei Starovoitov <a...@kernel.org> > Cc: net...@vger.kernel.org > --- > arch/x86/net/bpf_jit.S | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/net/bpf_jit.S b/arch/x86/net/bpf_jit.S > index eb4a3bd..f2a7faf 100644 > --- a/arch/x86/net/bpf_jit.S > +++ b/arch/x86/net/bpf_jit.S > @@ -8,6 +8,7 @@ > * of the License. > */ > #include <linux/linkage.h> > +#include <asm/frame.h> > > /* > * Calling convention : > @@ -65,16 +66,18 @@ FUNC(sk_load_byte_positive_offset) > > /* rsi contains offset and can be scratched */ > #define bpf_slow_path_common(LEN) \ > + lea -MAX_BPF_STACK + 32(%rbp), %rdx;\ > + FRAME_BEGIN; \ > mov %rbx, %rdi; /* arg1 == skb */ \ > push %r9; \ > push SKBDATA; \ > /* rsi already has offset */ \ > mov $LEN,%ecx; /* len */ \ > - lea - MAX_BPF_STACK + 32(%rbp),%rdx; \ > call skb_copy_bits; \ > test %eax,%eax; \ > pop SKBDATA; \ > - pop %r9; > + pop %r9; \ > + FRAME_END
I'm not sure what above is doing. There is already 'push rbp; mov rbp,rsp' at the beginning of generated code and with above the stack trace will show two function at the same ip? since there were no calls between them? I think the stack walker will get even more confused? Also the JIT of bpf_call insn will emit variable number of push/pop around the call and I definitely don't want to add extra push rbp there, since it's the critical path and callee will do its own push rbp. Also there are push/pops emitted around div/mod and there is indirect goto emitted as well for bpf_tail_call that jumps into different function body without touching current stack. Also none of the JITed function are dwarf annotated. I could be missing something. I think either this patch is not need or you need to teach the tool to ignore all JITed stuff. I don't think it's practical to annotate everything. Different JITs do their own magic. s390 JIT is even more fancy.
