[Bug runtime/15783] New: inode-uprobes not handling tail recursion properly

[Bug runtime/15783] New: inode-uprobes not handling tail recursion properly

[dsmith at redhat dot com]

http://sourceware.org/bugzilla/show_bug.cgi?id=15783

            Bug ID: 15783
           Summary: inode-uprobes not handling tail recursion properly
           Product: systemtap
           Version: unspecified
            Status: NEW
          Severity: normal
          Priority: P2
         Component: runtime
          Assignee: systemtap at sourceware dot org
          Reporter: dsmith at redhat dot com

On RHEL6 (2.6.32-358.6.1.el6.x86_64):

====
# gcc -g -O0 testsuite/systemtap.context/fib.c -o fib
# stap -e 'global calls, returns; probe process("fib").function("fib") { calls
<<< 1 } probe process("fib").function("fib").return { returns <<< 1 }' -c
"./fib 10"
89
calls @count=177 @min=1 @max=1 @sum=177 @avg=1
returns @count=177 @min=1 @max=1 @sum=177 @avg=1
====

On rawhide (3.11.0-0.rc0.git7.1.fc20.x86_64):

====
# gcc -g -O0 testsuite/systemtap.context/fib.c -o fib
# stap -e 'global calls, returns; probe process("fib").function("fib") { calls
<<< 1 } probe process("fib").function("fib").return { returns <<< 1 }' -c
"./fib 10"
89
calls @count=177 @min=1 @max=1 @sum=177 @avg=1
returns @count=64 @min=1 @max=1 @sum=64 @avg=1
=====

It appears that inode-uprobes is missing probe hits when tail recursion is
used. This problem was pointed out by the testsuite/systemtap.context/fib.exp
test.


Just for reference sake, on that same rawhide system (with the same 'fib'
executable), using dyninst:

====
# stap --dyninst -e 'global calls, returns; probe
process("fib").function("fib") { calls <<< 1 } probe
process("fib").function("fib").return { returns <<< 1 }' -c "./fib 10"
89
calls @count=177 @min=1 @max=1 @sum=177 @avg=1
returns @count=177 @min=1 @max=1 @sum=177 @avg=1
====

This last test shows that this isn't a compiler issue.

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[Bug runtime/15783] inode-uprobes not handling tail recursion properly

[fche at redhat dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=15783

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |fche at redhat dot com
         Resolution|---                         |INVALID

--- Comment #1 from Frank Ch. Eigler <fche at redhat dot com> ---
Effects of compiler optimizations (with modern gcc -O3 doing a ton of inlining
etc.) make the test in comment #0 a bit misleadinmg.  The calls case should
have been ....function("fib").call, in which case it does happen to match up
calls & returns.

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