[patch] Cut memory address width

[Jan Kratochvil <jan dot kratochvil at redhat dot com>]

Hi,

`x/x $ebx' on gdb/amd64 debugging inferior/i386 causes Cannot access memory at
address 0xffffce70 (or so) as $ebx is considered `int' and sign-extended to
64-bit while the resulting address 0xffffffffffffce70 fails to be accessed.

$esp does not exhibit this problem as it is `builtin_type_void_data_ptr' not
`builtin_type_int' as $ebx is.  Therefore it gets extended as unsigned.

Simulate the part of paddress(); it is questionable how deep in the functions
calling stack the address width cut should be.


Regards,
Jan


As bugreported by John Reiser <jreiser(at)BitWagon.com>:

When debugging a 32-bit executable on x86_64, gdb does not allow examining the stack if pointed to by a non-$esp register.  For example,
-----foo.S
_start: .globl _start
        nop
        int3
        movl %esp,%ebx
        int3  # examining memory from $ebx fails, from $esp succeeds
        nop
        nop
-----
$ gcc -m32 -o foo -nostartfiles -nostdlib foo.S
$ gdb foo
Program received signal SIGTRAP, Trace/breakpoint trap.
0x08048076 in _start ()
(gdb) x/i $pc
0x8048076 <_start+2>:   mov    %esp,%ebx
(gdb) stepi
0x08048078 in _start ()
(gdb) x/x $esp
0xffffce70:     0x00000001
(gdb) x/x $ebx
0xffffce70:     Cannot access memory at address 0xffffce70
(gdb) x/x 0xffffce70
0xffffce70:     0x00000001

Expected Results:  "x/x $ebx" should have succeeded, too, when %ebx has the
same value as %esp and examining from $esp works.

Attachment: gdb-6.5-memory-address-width.patch
Description: Text document