Hi Steven,
(2014/10/28 3:27), Steven Rostedt wrote:
> +static unsigned long create_trampoline(struct ftrace_ops *ops)
> +{
> + unsigned const char *jmp;
> + unsigned long start_offset;
> + unsigned long end_offset;
> + unsigned long op_offset;
> + unsigned long offset;
> + unsigned long size;
> + unsigned long ip;
> + unsigned long *ptr;
> + void *trampoline;
> + /* 48 8b 15 <offset> is movq <offset>(%rip), %rdx */
> + unsigned const char op_ref[] = { 0x48, 0x8b, 0x15 };
> + union ftrace_op_code_union op_ptr;
> + int ret;
> +
> + if (ops->flags & FTRACE_OPS_FL_SAVE_REGS) {
> + start_offset = (unsigned long)ftrace_regs_caller;
> + end_offset = (unsigned long)ftrace_regs_caller_end;
> + op_offset = (unsigned long)ftrace_regs_caller_op_ptr;
> + } else {
> + start_offset = (unsigned long)ftrace_caller;
> + end_offset = (unsigned long)ftrace_caller_end;
> + op_offset = (unsigned long)ftrace_caller_op_ptr;
> + }
> +
> + size = end_offset - start_offset;
> +
> + /*
> + * Allocate enough size to store the ftrace_caller code,
> + * the jmp to ftrace_return, as well as the address of
> + * the ftrace_ops this trampoline is used for.
> + */
> + trampoline = alloc_tramp(size + MCOUNT_INSN_SIZE + sizeof(void *));
> + if (!trampoline)
> + return 0;
> +
> + /* Copy ftrace_caller onto the trampoline memory */
> + ret = probe_kernel_read(trampoline, (void *)start_offset, size);
> + if (WARN_ON(ret < 0)) {
> + tramp_free(trampoline);
> + return 0;
> + }
> +
> + ip = (unsigned long)trampoline + size;
> +
> + /* The trampoline ends with a jmp to ftrace_return */
> + jmp = ftrace_jmp_replace(ip, (unsigned long)ftrace_return);
> + memcpy(trampoline + size, jmp, MCOUNT_INSN_SIZE);
> +
> + /*
> + * The address of the ftrace_ops that is used for this trampoline
> + * is stored at the end of the trampoline. This will be used to
> + * load the third parameter for the callback. Basically, that
> + * location at the end of the trampoline takes the place of
> + * the global function_trace_op variable.
> + */
> +
> + ptr = (unsigned long *)(trampoline + size + MCOUNT_INSN_SIZE);
> + *ptr = (unsigned long)ops;
> +
> + op_offset -= start_offset;
> + memcpy(&op_ptr, trampoline + op_offset, OP_REF_SIZE);
> +
> + /* Are we pointing to the reference? */
> + if (WARN_ON(memcmp(op_ptr.op, op_ref, 3) != 0)) {
> + tramp_free(trampoline);
> + return 0;
> + }
> +
> + /* Load the contents of ptr into the callback parameter */
> + offset = (unsigned long)ptr;
> + offset -= (unsigned long)trampoline + op_offset + OP_REF_SIZE;
> +
> + op_ptr.offset = offset;
> +
> + /* put in the new offset to the ftrace_ops */
> + memcpy(trampoline + op_offset, &op_ptr, OP_REF_SIZE);
Would we better call flush_icache_range here?
Thank you,
> +
> + /* ALLOC_TRAMP flags lets us know we created it */
> + ops->flags |= FTRACE_OPS_FL_ALLOC_TRAMP;
> +
> + return (unsigned long)trampoline;
> +}
--
Masami HIRAMATSU
Software Platform Research Dept. Linux Technology Research Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: [email protected]
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