Messages in this thread | | | Date | Tue, 25 Nov 2008 21:35:46 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH 2/5] ftrace: use code patching for ftrace graph tracer |
| |
On Wed, 26 Nov 2008 00:16:24 -0500 Steven Rostedt <rostedt@goodmis.org> wrote:
> From: Steven Rostedt <rostedt@goodmis.org> > > Impact: more efficient code for ftrace graph tracer > > This patch uses the dynamic patching, when available, to patch > the function graph code into the kernel. > > This patch will ease the way for letting both function tracing > and function graph tracing run together. > > ... > > +static int ftrace_mod_jmp(unsigned long ip, > + int old_offset, int new_offset) > +{ > + unsigned char code[MCOUNT_INSN_SIZE]; > + > + if (probe_kernel_read(code, (void *)ip, MCOUNT_INSN_SIZE)) > + return -EFAULT; > + > + if (code[0] != 0xe9 || old_offset != *(int *)(&code[1]))
erk. I suspect that there's a nicer way of doing this amongst our forest of get_unaligned_foo() interfaces. Harvey will know.
> + return -EINVAL; > + > + *(int *)(&code[1]) = new_offset;
Might be able to use put_unaligned_foo() here.
The problem is that these functions use sizeof(*ptr) to work out what to do, so a cast is still needed. A get_unaligned32(ptr) would be nice. One which takes a void* and assumes CPU ordering.
> + if (do_ftrace_mod_code(ip, &code)) > + return -EPERM; > + > + return 0; > +} > +
| |