There was a single call to stacktrace() under an #ifdef DEBUG to obtain
a stack trace during a fault that resulted in a function pointer to a
printf function being passed to stacktrace_subr() in db_trace.c. The
kernel now has existing interfaces for obtaining a stack trace outside
of DDB (kdb_backtrace(), or the stack_*() API) that should be used instead.
Rather than fix the one call however, remove it since the kernel will
dump a trace anyway once it panics.
Make stacktrace_subr() static, remove the function pointer and change it
to use db_printf() explicitly.
Discussed with: kan
Sponsored by: DARPA / AFRL
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