Inspecting environment variables from a core dump?

Inspecting environment variables from a core dump?

[Ludovic Brenta]

Hello,

After searching the GDB documentation, mailing list and bug database I
have not found an answer to my question, so as a last resort I post it
here.

Does a core dump contain the environment of the program that dumped core?
If so, how can I inspect the environment variables?  "show environment"
shows the environment that GDB is running in, not the environment of the
debuggee.

(context: I am analyzing a core dump that was produced on another machine
and I supect the bug was caused by a bad environment variable).

Thanks for any help.

-- 
Ludovic Brenta.

Re: Inspecting environment variables from a core dump?

[Andreas Schwab]

Ludovic Brenta <ludovic@ludovic-brenta.org> writes:

> Does a core dump contain the environment of the program that dumped core?

A core dump contains the whole used address space of the program, and
the environment is of course part of it.

> If so, how can I inspect the environment variables?

The environment is always stored in the variable environ.

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

Re: Inspecting environment variables from a core dump?

[Ludovic Brenta]

Andreas Schwab wrote:
> Ludovic Brenta <ludovic@ludovic-brenta.org> writes:
> 
>> Does a core dump contain the environment of the program that dumped
core?
> 
> A core dump contains the whole used address space of the program, and
> the environment is of course part of it.
> 
>> If so, how can I inspect the environment variables?
> 
> The environment is always stored in the variable environ.

Thanks but:

(gdb) p environ
$13 = 0
(gdb) whatis environ
type = <data variable, no debug info>

Am I simply out of luck or doing something wrong?

-- 
Ludovic Brenta.

Re: Inspecting environment variables from a core dump?

[Paul Pluzhnikov]

On Wed, Apr 20, 2011 at 5:24 AM, Ludovic Brenta
<ludovic@ludovic-brenta.org> wrote:
>
> Andreas Schwab wrote:
>> Ludovic Brenta <ludovic@ludovic-brenta.org> writes:
>>
>>> Does a core dump contain the environment of the program that dumped
> core?
>>
>> A core dump contains the whole used address space of the program, and
>> the environment is of course part of it.
>>
>>> If so, how can I inspect the environment variables?
>>
>> The environment is always stored in the variable environ.

There are possibly two environments: "the environment passed from the
kernel at execve(2) time", and "the environment as it was possibly
modified by putenv/setenv etc. at crash point". The latter is pointed
at by the 'environ' variable.

> Thanks but:
>
> (gdb) p environ
> $13 = 0
> (gdb) whatis environ
> type = <data variable, no debug info>
>
> Am I simply out of luck or doing something wrong?

You aren't doing anything wrong, but you lack debug info needed to
make it work. GDB has no special knowledge about the 'environ', but
you *do*. Use it!

(gdb) print (char ***) &environ
$1 = (char ***) 0x7ffff7ffe9a0
(gdb) print $1[0][0]@100   # should print the first 100 env variables.


HTH,
-- 
Paul Pluzhnikov