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Subject: [Bug gdb/14757] New: Print of expressions with no debug information
 gives wrong results
Date: Tue, 23 Oct 2012 21:28:00 -0000
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http://sourceware.org/bugzilla/show_bug.cgi?id=14757

             Bug #: 14757
           Summary: Print of expressions with no debug information gives
                    wrong results
           Product: gdb
           Version: 7.4
            Status: NEW
          Severity: normal
          Priority: P2
         Component: gdb
        AssignedTo: unassigned@sourceware.org
        ReportedBy: j.b.w@gmx.ch
    Classification: Unclassified


Created attachment 6696
  --> http://sourceware.org/bugzilla/attachment.cgi?id=6696
Example program showing different types of functions

When I print expressions involving functions for which no debug information is
available, the result is wrong.

Consider the attached example program, and the following gdb session:

(gdb) print sqrt
$1 = {<text variable, no debug info>} 0x7ffff7879010 <sqrt>
(gdb) print std::sqrt
No symbol "sqrt" in namespace "std".
(gdb) print mysqrt
$2 = {double (double)} 0x40083c <mysqrt(double)>
(gdb) print sqrt(0.5)
$3 = 0
(gdb) print std::sqrt(0.5)
No symbol "sqrt" in namespace "std".
(gdb) print mysqrt(0.5)
$4 = 0.25

I would expect the call "print sqrt(0.5)" to give an error message indicating
that the expression cannot be printed due to missing debug information. Giving
a wrong result without any indication that something is wrong is... wrong.

Also, I'm puzzled as to why "print std::sqrt(0.5)" fails, given that the
program compiles (so std::sqrt apparently exists).

There is a related StackOverflow question at
http://stackoverflow.com/questions/5122570/why-does-gdb-evaluate-sqrt3-to-0

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