gdb/1870: Cannot display local variables with amd64

[ttomaich at ifltd dot com]

>Number:         1870
>Category:       gdb
>Synopsis:       Cannot  display local variables with amd64
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    unassigned
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Feb 15 19:58:00 UTC 2005
>Closed-Date:
>Last-Modified:
>Originator:     ttomaich@ifltd.com
>Release:        6.1post-1.20040607.52rh
>Organization:
>Environment:
Red Hat Linux ES 3.2, SUN v40z, AMD64 Opteron (x86_64), compiled with gcc 2.96.
>Description:
I cannot display the values of local variables when debuggin using gdb.  I found the following fix on the web, and have tried to implement it myself.  However, I was unable to rebuild gdb, and so I am stuck.  I submitted that rebuild as a separate bug report.

This was found at 

http://lists.gnu.org/archive/html/bug-gdb/2004-12/msg00005.html

and it describes one person's fix of the issue.

Dear Friends:

I reported recently a bug in gdb for amd64. It will not display any
local variables if you use the stabs debug info.


Fix:
This bug disappears if you change in the source code of gdb the
file "findvar.c" line 463 from


<buggy code>
    addr += SYMBOL_VALUE(var);
</buggy code>
to
<fixed code>
    addr += (signed int)SYMBOL_VALUE(var);
</fixed code>


Background:
The value stored in "var" is a negative offset from EBP. This
negative number gets converted to a huge positive number
because of the lack of sign extension when reading the stabs
debug info. Instead of a negative number we have a positive
number greater than 2Giga. When this address is added to the
EBP register value, a wrong address is the result, since
instead of a subtraction an addition is performed. The cast
reconverts the numnber into a signed 32 bit quantity that
is correctly subtracted from addr.
...

Regards,

Tim

>How-To-Repeat:

>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: