Re: Debugging 32bit apps with 64bit target gdb

[Paul Smith <psmith@gnu.org>]

Anyone have any help for me?

A short summary, I'm trying to see if I can build one GDB executable
with all these properties:

      * Is a 32bit application so it can run on both 32bit and 64bit
        systems
      * Can debug 32bit applications
      * Can debug 64bit applications (when run on a 64bit system
        obviously)
      * If I can get it to debug a 64bit core file when running on a
        32bit system (with --sysroot pointing to a 64bit sysroot of
        course) that would be awesome.

I'm only concerned with x86 architectures (for now?)

Is such a thing possible?  Or should I just build two different GDB
binaries, one for 32bit and one for 64bit, and be satisfied?


On Thu, 2011-05-19 at 16:17 -0400, Paul Smith wrote:
> Hi all;
> 
> Maybe this is a naive question.  I have an environment (x86) with both
> 32bit and 64bit applications running in it.  I would like to use the
> same GDB binary to debug both types of applications.  Ideally, though,
> GDB would be a 32bit application because sometimes I run on 32bit
> systems (obviously the 64bit applications do not run and cannot be
> debugged on those systems, but the 32bit ones can).
> 
> I will also be doing remote debugging (with gdbserver) from a 32bit host
> to a 64bit target (at least I would like to be able to do that).
> 
> I configured GDB (7.2) with --host=i686-generic-linux-gnu and
> --target=x86_64-generic-linux-gnu (and --enable-targets=all but I don't
> know if GDB configure groks this flag).
> 
> This compiled just fine, but when I have a 32bit core file and I try to
> access it with GDB, I get an error:
> 
> warning: Could not load shared library symbols for 8 libraries, e.g. /lib/tls/librt.so.1.
> Use the "info sharedlibrary" command to see the complete listing.
> Do you need "set solib-search-path" or "set sysroot"?
> warning: Unable to find dynamic linker breakpoint function.
> GDB will be unable to debug shared library initializers
> and track explicitly loaded dynamic code.
> Core was generated by `app32bit'.
> Program terminated with signal 11, Segmentation fault.
> #0  0x00b187a2 in ?? ()
> #0  0x00b187a2 in ?? ()
> #1  0x00d9c6f4 in ?? ()
> #2  0x00000000 in ?? ()
> 
> and I can't get a backtrace or anything.  "info sharedlibrary" shows:
> 
> From        To          Syms Read   Shared Object Library
>                         No          /lib/tls/librt.so.1
>                         No          /usr/lib/libz.so.1
>                         No          /lib/libdl.so.2
>                         No          /lib/tls/libpthread.so.0
>                         No          /lib/tls/libm.so.6
>                         No          /lib/tls/libc.so.6
>                         No          /lib/ld-linux.so.2
>                         No          /lib/libgcc_s.so.1
> 
> which are all perfectly reasonable 32bit shared libs.
> 
> On the other hand, if I build a 32bit GDB (same version of code but
> compiled on a 32bit Linux without the --target=x6_64-generic-linux-gnu
> flag) then I get a perfectly usable backtrace for this identical
> coredump on the same system.
> 
> Is what I want to do simply not possible?  Or am I missing some trick?
> It seems to me that on the 64bit multiarch Linux systems I've used, the
> GDB versions that come with them can debug 32bit applications.  Or am I
> just imagining that this is possible?
> 


-- 
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 Paul D. Smith <psmith@gnu.org>          Find some GNU make tips at:
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