[Bug tapsets/6580] revamp backtrace-related tapset functions

["mjw at redhat dot com" <sourceware-bugzilla at sourceware dot org>]

------- Additional Comments From mjw at redhat dot com  2008-09-01 12:32 -------
caller()/ucaller() can probably be implemented more efficiently than as full
wrappers around the caller(1)/ucaller(1). For example the following currently
works to get a quick user space symbol, without need to do a full unwind (a full
unwind is necessary for getting anything more). If you just want to get the user
address and symbol (for static binaries included with -d only for now):

# Returns the address in userspace that the current task was at when the
# probe occurred.
function uaddr:long () %{ /* pure */
        #include <asm/processor.h>
        struct pt_regs *uregs;
        uregs = task_pt_regs(current);

        THIS->__retvalue = (int64_t) REG_IP(uregs);
%}

# Translates an address to a function symbol. Might be expensive
# so use sparingly in probes, try translating only in end probes.
function uaddr_symbol:string (uaddr: long) %{ /* pure */
	_stp_symbol_snprint(THIS->__retvalue, MAXSTRINGLEN, THIS->uaddr);
%}

Can be used with something like the following for a quick and dirty "profiler":

stap -d /path/to/my-static-binary -e 'probe timer.ms(100) {t = tid(); if (t !=
0) { printf("%s:.%d 0x%xd:%s\n", execname(), tid(), uaddr(),
uaddr_symbol(uaddr())); } }'

-- 


http://sourceware.org/bugzilla/show_bug.cgi?id=6580

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