On Fri, Jan 22, 2016 at 09:58:04AM -0600, Josh Poimboeuf wrote: > On Thu, Jan 21, 2016 at 08:18:46PM -0800, Alexei Starovoitov wrote: > > On Thu, Jan 21, 2016 at 09:55:31PM -0600, Josh Poimboeuf wrote: > > > On Thu, Jan 21, 2016 at 06:44:28PM -0800, Alexei Starovoitov wrote: > > > > 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 +++++++-- ... > > > > > /* 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 ... > > > Well, but the point of these patches isn't to make the tool happy. It's > > > really to make sure that runtime stack traces can be made reliable. > > > Maybe I'm missing something but I don't see why JIT code can't honor > > > CONFIG_FRAME_POINTER just like any other code. > > > > It can if there is no performance cost added. > > CONFIG_FRAME_POINTER always adds a small performance cost but as you > mentioned it only affects the slow path here. And hopefully we'll soon > have an in-kernel DWARF unwinder on x86 so we can get rid of the need > for frame pointers.
ok. fair enough. Acked-by: Alexei Starovoitov <a...@kernel.org>
