[Bug translator/20394] New: inconsistency in exe/library paths searching between @cast() and process.library.function probes

[Bug translator/20394] New: inconsistency in exe/library paths searching between @cast() and process.library.function probes

[dsmith at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=20394

            Bug ID: 20394
           Summary: inconsistency in exe/library paths searching between
                    @cast() and process.library.function probes
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: translator
          Assignee: systemtap at sourceware dot org
          Reporter: dsmith at redhat dot com
  Target Milestone: ---

When writing probes, you can do the following:

====
probe
  process("python").library("libpython2.7.so*").function("PyEval_EvalFrameEx")
{
  # ... probe contents here ...
}
====

Notice that I'm just probing "python" as the "process" argument, a non-absolute
path. The translator will look up "python" in my PATH and find it. Notice I'm
using a wildcarded and non-absolute path for the "library" argument.

The above works fine and is very user friendly.

So, when using @cast(), I'd like to specify the symbol search path the same
way:

====
# cat pytest1.stp
function foo:long(object:long)
{
  printf("%d\n",
         @cast(object, "PyFrameObject", "python:libpython2.7.so*")->f_lineno)
}

probe 
  process("python").library("libpython2.7.so*").function("PyEval_EvalFrameEx")
{
  foo($f)
  exit()
}
# stap -v ./pytest1.stp -c "python -c 'import sys; sys.exit(0)'"
Pass 1: parsed user script and 117 library scripts using
242808virt/39472res/7568shr/32212data kb, in 190usr/30sys/234real ms.
semantic error: while processing function foo

semantic error: type definition 'PyFrameObject' not found in
'python:libpython2.7.so*': operator '@cast' at ./pytest1.stp:4:3
        source:          @cast(object, "PyFrameObject",
"python:libpython2.7.so*")->f_lineno)
                         ^

Pass 2: analyzed script: 1 probe, 1 function, 0 embeds, 0 globals using
250612virt/48776res/8880shr/40016data kb, in 120usr/380sys/498real ms.
Pass 2: analysis failed.  [man error::pass2]
====

So, that didn't work. Let's try without the wildcard:

====
# cat pytest2.stp
function foo:long(object:long)
{
  printf("%d\n",
         @cast(object, "PyFrameObject", "python:libpython2.7.so")->f_lineno)
}

probe 
  process("python").library("libpython2.7.so*").function("PyEval_EvalFrameEx")
{
  foo($f)
  exit()
}
# stap -v ./pytest2.stp -c "python -c 'import sys; sys.exit(0)'"
Pass 1: parsed user script and 117 library scripts using
242808virt/39644res/7740shr/32212data kb, in 200usr/40sys/240real ms.
semantic error: while processing function foo

semantic error: type definition 'PyFrameObject' not found in
'python:libpython2.7.so': operator '@cast' at ./pytest2.stp:4:3
        source:          @cast(object, "PyFrameObject",
"python:libpython2.7.so")->f_lineno)
                         ^

Pass 2: analyzed script: 1 probe, 3 functions, 0 embeds, 0 globals using
250608virt/48792res/8892shr/40012data kb, in 100usr/400sys/511real ms.
Pass 2: analysis failed.  [man error::pass2]
====

OK, on this system /usr/lib64/libpython2.7.so is a symbolic link to
/usr/lib64/libpython2.7.so.1.0. Let's give that a shot:

====
# cat pytest3.stp
function foo:long(object:long)
{
  printf("%d\n",
         @cast(object, "PyFrameObject",
"python:libpython2.7.so.1.0")->f_lineno)
}

probe 
  process("python").library("libpython2.7.so*").function("PyEval_EvalFrameEx")
{
  foo($f)
  exit()
}
# stap -v ./pytest3.stp -c "python -c 'import sys; sys.exit(0)'"
Pass 1: parsed user script and 117 library scripts using
242804virt/39504res/7604shr/32208data kb, in 210usr/30sys/242real ms.
semantic error: while processing function foo

semantic error: type definition 'PyFrameObject' not found in
'python:libpython2.7.so.1.0': operator '@cast' at ./pytest3.stp:4:3
        source:          @cast(object, "PyFrameObject",
"python:libpython2.7.so.1.0")->f_lineno)
                         ^

Pass 2: analyzed script: 1 probe, 1 function, 0 embeds, 0 globals using
250608virt/48804res/8912shr/40012data kb, in 100usr/370sys/492real ms.
Pass 2: analysis failed.  [man error::pass2]
====

Nope.

The only thing I can seem to get to work for @cast() is a full absolute path to
the library. One reason why this is annoying is that to handle both 32-bit
distros and 64-bit distros, I'll have to specify the library in both /usr/lib/
and /usr/lib64:

====
# cat pytest4.stp
function foo:long(object:long)
{
  printf("%d\n",
         @cast(object, "PyFrameObject",
"python:/usr/lib64/libpython2.7.so:/usr/lib/libpython2.7.so")->f_lineno)
}

probe 
  process("python").library("libpython2.7.so*").function("PyEval_EvalFrameEx")
{
  foo($f)
  exit()
}
# stap -v ./pytest4.stp -c "python -c 'import sys; sys.exit(0)'"
Pass 1: parsed user script and 117 library scripts using
242808virt/39712res/7812shr/32212data kb, in 210usr/30sys/238real ms.
Pass 2: analyzed script: 1 probe, 4 functions, 0 embeds, 0 globals using
251388virt/49532res/8828shr/40792data kb, in 120usr/190sys/317real ms.
Pass 3: translated to C into
"/tmp/stapYGfpK4/stap_d4c98f72a2d5b7cef816271d6bd3e397_3084_src.c" using
251388virt/49724res/9020shr/40792data kb, in 20usr/190sys/206real ms.
Pass 4: compiled C into "stap_d4c98f72a2d5b7cef816271d6bd3e397_3084.ko" in
4730usr/1000sys/5459real ms.
Pass 5: starting run.
59
Pass 5: run completed in 30usr/70sys/392real ms.
====

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[Bug translator/20394] inconsistency in exe/library paths searching between @cast() and process.library.function probes

[fche at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=20394

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |fche at redhat dot com

--- Comment #1 from Frank Ch. Eigler <fche at redhat dot com> ---
Having a search path in @cast in a function() makes it possible that a mismatch
will exist between the probe (whose $context variable is being passed) and the
@cast (who interprets that pointer).  What you seem to really want is to make
@cast() in a function refer to - match - the context of the probe that invoked
it.  This is kind of what we do already for @cast()s in probe handler bodies.

It's as though we want to specialize the functions invoked from a probe handler
by the probe handler, almost as if they were inlined.  Then syntactic elements
inside the functions (even $vars) could conceivably be resolved in the context
of each probe where those functions are actually called from.

What do you think?

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[Bug translator/20394] inconsistency in exe/library paths searching between @cast() and process.library.function probes

[dsmith at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=20394

--- Comment #2 from David Smith <dsmith at redhat dot com> ---
(In reply to Frank Ch. Eigler from comment #1)
> Having a search path in @cast in a function() makes it possible that a
> mismatch will exist between the probe (whose $context variable is being
> passed) and the @cast (who interprets that pointer).  What you seem to
> really want is to make @cast() in a function refer to - match - the context
> of the probe that invoked it.  This is kind of what we do already for
> @cast()s in probe handler bodies.
> 
> It's as though we want to specialize the functions invoked from a probe
> handler by the probe handler, almost as if they were inlined.  Then
> syntactic elements inside the functions (even $vars) could conceivably be
> resolved in the context of each probe where those functions are actually
> called from.
> 
> What do you think?

That's an interesting idea. If it is doable, I'd say it would be quite handy.

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[Bug translator/20394] inconsistency in exe/library paths searching between @cast() and process.library.function probes

[fche at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=20394

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #3 from Frank Ch. Eigler <fche at redhat dot com> ---
more general solution

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