On 11/10/14, 5:24 AM, Ingo Molnar wrote:
Programmatic use in user-spaec is very simple - go with my
initial example, tooling can either just display the error string
and bail out, or do:

   if (unlikely(error)) {
        if (!strcmp(attr->error_str, "x86/bts: BTS not supported by this CPU 
architecture")) {
                fprintf(stderr, "x86/BTS: No hardware support falling back to branch 
sampling\n");
                activate_x86_bts_fallback_code();
                goto out;
        }

That makes the exact string content part of the ABI. As I recall ftrace had a problem with format strings changing and tooling then limiting the ability to change it.

David
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