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

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

[fche at redhat dot com]

print_stack, backtrace, probefunc, print_backtrace, caller* are
IMO a mess.  Let's rationalize them by deprecating these and
adding some new functions:

stack:long (n:long)        - return PC at stack unwind level N
ustack:long (n:long)       - return PC at user-space stack unwind level N; 
                             useful if kernel-side probe is active
callers:string (n:long)    - return stack(0) stack(1) ... stack(n) as a string
ucallers:string (n:long)   - return ustack(0) ustack (1) ... ustack(n)
symname:string (addr:long) - return the kernel- or user-space symbol name
                             for the given address
symdata:string (addr:long) - likewise, adding [module] +offset/size 
psyms (callers:string)     - print symdata() for all addresses in callers

Backward compatibility:
  function backtrace() { return callers (-1) }
  function print_stack(s) { psyms (s) }
  function print_backtrace() { psyms (callers (-1)) }
  function caller_addr() { return stack (1) }
  function caller() { return symname (caller_addr()) }
  function probefunc() { return symname (stack (0)) }
  function probemod() { return substr(symdata (stack (0)), ....) }

-- 
           Summary: revamp backtrace-related tapset functions
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: tapsets
        AssignedTo: systemtap at sources dot redhat dot com
        ReportedBy: fche at redhat dot com


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

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

[fche at redhat dot com]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
  BugsThisDependsOn|                            |5951


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

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

[mjw at redhat dot com]

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

[mjw at redhat dot com]

------- Additional Comments From mjw at redhat dot com  2008-09-02 10:14 -------
(In reply to comment #1)
> # 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())); } }'

Franks pointed out that I should mention that _stp_symbol_snprint() only kind of
works by accident for user space and isn't reliable. I filed bug #6866 (Extend
stp_symbol_snprintf for user space) with some more explanation and a plan for
making it reliable.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
  BugsThisDependsOn|                            |6866


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

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

[fche at redhat dot com]

-- 
Bug 6580 depends on bug 5951, which changed state.

Bug 5951 Summary: process lifetime/memorymap monitor
http://sourceware.org/bugzilla/show_bug.cgi?id=5951

           What    |Old Value                   |New Value
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|                            |FIXED

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

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

[mjw at redhat dot com]

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|systemtap at sources dot    |mjw at redhat dot com
                   |redhat dot com              |
             Status|NEW                         |ASSIGNED


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

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

[mjw at redhat dot com]

------- Additional Comments From mjw at redhat dot com  2010-01-05 09:38 -------
The split between sym*/backtrace() for kernel side and usym*/ubacktrace() for
user side is confusing. We really should deduce from the probe context which one
the user wants.

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|mjw at redhat dot com       |systemtap at sources dot
                   |                            |redhat dot com
             Status|ASSIGNED                    |NEW


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

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

[mjw at redhat dot com]

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

--- Comment #6 from Mark Wielaard <mjw at redhat dot com> 2011-09-08 17:11:15 UTC ---
*** Bug 13094 has been marked as a duplicate of this bug. ***

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

[fche at redhat dot com]

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

Frank Ch. Eigler <fche at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
         AssignedTo|systemtap at sourceware dot |fche at redhat dot com
                   |org                         |

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