[Bug corefiles/10439] New: AIX/Power registers incorrectly represented as 32-bits instead of 64-bits

["andrew at ishiboo dot com" <sourceware-bugzilla at sourceware dot org>]

GDB currently treats r* registers under AIX/Power 64-bit CPU as uint32_t:
(gdb) maintenance print registers
 Name         Nr  Rel Offset    Size  Type
 r0            0    0      0       4 uint32_t

This is incorrect because the registers themselves are 64-bit wide even though a
32-bit program is running on them. The IBM xlc compiler takes advantage of this
fact and actually outputs 64-bit assembler instructions when the "-qarch=pwr4
-qtune=pwr5" optimizations are used when compiling a 32-bit binary.

Since GDB treats the registers as 32-bits, GDB can modify runtime program
behavior by truncating the high 32 bits of a register in certain cases. In order
to properly debug binaries on this system, GDB needs to treat registers as
64-bit so that values are not modified.

I've created a contrived example which shows GDB modifying the runtime behavior:

$ ./gdb_reg_clobber
before: space[0..1]=0x0000000000000000
after:  space[0..1]=0x000020ffffffffff

$ gdb ./gdb_reg_clobber
(gdb) break atomic_set_int64
Breakpoint 1 at 0x100004e4
(gdb) run
Starting program: /home8/apaprock/aix_gdb/gdb_reg_clobber
before: space[0..1]=0x0000000000000000

Breakpoint 1, 0x100004e4 in atomic_set_int64 ()
(gdb) cont
Continuing.
after:  space[0..1]=0x00000000ffffffff

In the GDB case, the "after:" printf shows different behavior due to the fact
that a breakpoint was set on the atomic function which uses 64-bit instructions
to atomically set 64-bits. If a breakpoint is not set on that function, the
correct output is seen when running inside GDB.

-- 
           Summary: AIX/Power registers incorrectly represented as 32-bits
                    instead of 64-bits
           Product: gdb
           Version: 6.8
            Status: UNCONFIRMED
          Severity: critical
          Priority: P2
         Component: corefiles
        AssignedTo: unassigned at sourceware dot org
        ReportedBy: andrew at ishiboo dot com
                CC: gdb-prs at sourceware dot org
 GCC build triplet: powerpc-ibm-aix5.3.0.0
  GCC host triplet: powerpc-ibm-aix5.3.0.0
GCC target triplet: powerpc-ibm-aix5.3.0.0


http://sourceware.org/bugzilla/show_bug.cgi?id=10439

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