Why does gdb think my x86-64 program is i386? [closed]

Question

I am attempting to debug a 64-bit program but gdb seems to think it has an i386 architecture.

# file /usr/local/bin/foo
/usr/local/bin/foo: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.4.0, not stripped


# gdb --args foo bar
GNU gdb (GDB) 7.3.1
Copyright (C) 2011 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "x86_64-pc-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>...
Reading symbols from /usr/local/bin/foo...done.
(gdb) set debug arch 1
(gdb) show debug arch
Architecture debugging is 1.
(gdb) info target
Symbols from "/usr/local/bin/foo".
Local exec file:
gdbarch_find_by_info: info.bfd_arch_info i386:x86-64
gdbarch_find_by_info: info.byte_order 1 (little)
gdbarch_find_by_info: info.osabi 5 (GNU/Linux)
gdbarch_find_by_info: info.abfd 0xaf4a90
gdbarch_find_by_info: info.tdep_info 0x0
gdbarch_find_by_info: Previous architecture 0xb05790 (i386:x86-64) selected
    `/usr/local/bin/foo', file type elf64-x86-64.
    Entry point: 0x419730
    0x00000000004001c8 - 0x00000000004001e4 is .interp
    0x00000000004001e4 - 0x0000000000400204 is .note.ABI-tag
    0x0000000000400208 - 0x0000000000402560 is .hash
    0x0000000000402560 - 0x0000000000409898 is .dynsym
    0x0000000000409898 - 0x0000000000411188 is .dynstr
    0x0000000000411188 - 0x0000000000411b22 is .gnu.version
    0x0000000000411b28 - 0x0000000000411b88 is .gnu.version_r
    0x0000000000411b88 - 0x00000000004181a0 is .rela.dyn
    0x00000000004181a0 - 0x0000000000418e78 is .rela.plt
    0x0000000000418e78 - 0x0000000000418e90 is .init
    0x0000000000418e90 - 0x0000000000419730 is .plt
    0x0000000000419730 - 0x00000000004ede38 is .text
    0x00000000004ede38 - 0x00000000004ede46 is .fini
    0x00000000004ede48 - 0x00000000004ede4c is .eh_frame
    0x00000000006ee000 - 0x00000000006ee010 is .ctors
    0x00000000006ee010 - 0x00000000006ee020 is .dtors
    0x00000000006ee020 - 0x00000000006ee028 is .jcr
    0x00000000006ee028 - 0x00000000006ee1f8 is .dynamic
    0x00000000006ee1f8 - 0x00000000006f07f0 is .got
    0x00000000006f07f0 - 0x00000000006f0c50 is .got.plt
    0x00000000006f0c50 - 0x0000000000736c70 is .data
    0x0000000000736c70 - 0x000000000073b420 is .bss
(gdb) start
Temporary breakpoint 1 at 0x419e70: file foo.lpr, line 69.
Starting program: /usr/local/bin/foo bar
warning: Selected architecture i386:x86-64 is not compatible with reported target architecture i386
gdbarch_find_by_info: info.bfd_arch_info i386:x86-64
gdbarch_find_by_info: info.byte_order 1 (little)
gdbarch_find_by_info: info.osabi 5 (GNU/Linux)
gdbarch_find_by_info: info.abfd 0xaf4a90
gdbarch_find_by_info: info.tdep_info 0x0
gdbarch_find_by_info: Target rejected architecture
gdbarch_update_p: Architecture not found
warning: Architecture rejected target-supplied description
gdbarch_find_by_info: info.bfd_arch_info i386:x86-64
gdbarch_find_by_info: info.byte_order 1 (little)
gdbarch_find_by_info: info.osabi 5 (GNU/Linux)
gdbarch_find_by_info: info.abfd 0xd6ce90
gdbarch_find_by_info: info.tdep_info 0x0
gdbarch_find_by_info: Previous architecture 0xb05790 (i386:x86-64) selected
Error in re-setting breakpoint 1: Cannot access memory at address 0x419e60
Error in re-setting breakpoint 1: Cannot access memory at address 0x419e60
process 5299 is executing new program: /usr/local/bin/foo
warning: Selected architecture i386:x86-64 is not compatible with reported target architecture i386
gdbarch_find_by_info: info.bfd_arch_info i386:x86-64
gdbarch_find_by_info: info.byte_order 1 (little)
gdbarch_find_by_info: info.osabi 5 (GNU/Linux)
gdbarch_find_by_info: info.abfd 0xb21790
gdbarch_find_by_info: info.tdep_info 0x0
gdbarch_find_by_info: Target rejected architecture
Architecture of file not recognized.

Note the warning:

warning: Selected architecture i386:x86-64 is not compatible with reported target architecture i386

and then:

gdbarch_find_by_info: Target rejected architecture
gdbarch_update_p: Architecture not found
warning: Architecture rejected target-supplied description

In gdb, if I type 'set architecture' and hit tab, I see the following:

(gdb) set architecture 
auto               i386:intel         i386:x64-32:intel  i386:x86-64:intel  
i386               i386:x64-32        i386:x86-64        i8086

My question is: why does gdb think my file has an i386 architecture even though it is obviously an x86-64 binary and what can I do to fix it?

My program was compiled using FreePascal version 2.6.0.

UPDATE: I do not get any warnings using the same gdb binary and the same freepascal binary on my Ubuntu 12.04 machine (with a 3.2.0-31 kernel). The server I am attempting to debug on is running a 2.6.34.10-24 kernel. Could something be misconfigured in the kernel or on the server that would affect gdb?

Answer 1

Your problem starts here:

gdbarch_find_by_info: Target rejected architecture

This means that target-dependent code in GDB didn't like something about the i386:x86-64 architecture. Unfortunately there is no easy way to tell what it didn't like -- you'll have to debug GDB itself to find that out.

Can you debug other binaries (e.g. /bin/date) on the machine where GDB fails?