Hi - > > The alternative I considered is the nonexistence of global tracing > > support, thus no utrace_global_flags test in the syscall fast path. > > It will never be in the fast path. It will always require > TIF_SYSCALL_TRACE to bet set on each thread, which means the slow path. > [...]
OK, I must have misunderstood your original posting: # [...] # d. Kernel already has checks here, so "almost free". # # The utrace event hooks are at places where the kernel has had old # ptrace checks forever. The old code has fast paths that do: # if (current->ptrace & mask) slow path; # Now in those same places there is: # if (current->utrace_flags & mask) slow path; # So the cost of the checks is identical to what's already there. [...] # For global tracing, those checks would be: # if ((current->utrace_flags | utrace_global_flags) & mask) slow path; # [...] - FChE
