[3/6] x32: Avoid unsigned long when installing fast tracepoint jump pads
Commit Message
We're casting through unsigned long to write a 64-bit immediate
operand of movabs (the comment said movl, but that was incorrect).
The problem is that unsigned long is 32-bit on x32, so we were writing
fewer bytes than necessary.
Fix this by using an 8 byte memcpy like in other similar places in the
function.
gdb/gdbserver/ChangeLog:
yyyy-mm-dd Pedro Alves <palves@redhat.com>
* linux-x86-low.c (amd64_install_fast_tracepoint_jump_pad): Fix
comment. Use memcpy instead of casting through unsigned long.
---
gdb/gdbserver/linux-x86-low.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
Comments
On 07/28/2016 04:07 AM, H.J. Lu wrote:
>> Fix this by using an 8 byte memcpy like in other similar places in the
>> function.
...
>> diff --git a/gdb/gdbserver/linux-x86-low.c b/gdb/gdbserver/linux-x86-low.c
>> index d6b67c1..1ba98ba 100644
>> --- a/gdb/gdbserver/linux-x86-low.c
>> +++ b/gdb/gdbserver/linux-x86-low.c
>> @@ -1092,10 +1092,10 @@ amd64_install_fast_tracepoint_jump_pad
> (CORE_ADDR tpoint, CORE_ADDR tpaddr,
>> buf[i++] = 0x41; buf[i++] = 0x51; /* push %r9 */
>> buf[i++] = 0x41; buf[i++] = 0x50; /* push %r8 */
>> buf[i++] = 0x9c; /* pushfq */
>> - buf[i++] = 0x48; /* movl <addr>,%rdi */
>> + buf[i++] = 0x48; /* movabs <addr>,%rdi */
>> buf[i++] = 0xbf;
>> - *((unsigned long *)(buf + i)) = (unsigned long) tpaddr;
>> - i += sizeof (unsigned long);
>> + memcpy (buf + i, &tpaddr, 8);
>> + i += 8;
>> buf[i++] = 0x57; /* push %rdi */
>> append_insns (&buildaddr, i, buf);
>
> Why not use long long here?
>
My initial fix used uint64_t, which would be even more explicit,
but then I noticed that the the rest of the function uses this
same exact memcpy pattern in other cases where it writes other 64-bit
immediates. So this makes everything consistent.
Note also that memcpy instead of casting also avoids worrying
about strict aliasing violations.
Thanks,
Pedro Alves
@@ -1092,10 +1092,10 @@ amd64_install_fast_tracepoint_jump_pad (CORE_ADDR tpoint, CORE_ADDR tpaddr,
buf[i++] = 0x41; buf[i++] = 0x51; /* push %r9 */
buf[i++] = 0x41; buf[i++] = 0x50; /* push %r8 */
buf[i++] = 0x9c; /* pushfq */
- buf[i++] = 0x48; /* movl <addr>,%rdi */
+ buf[i++] = 0x48; /* movabs <addr>,%rdi */
buf[i++] = 0xbf;
- *((unsigned long *)(buf + i)) = (unsigned long) tpaddr;
- i += sizeof (unsigned long);
+ memcpy (buf + i, &tpaddr, 8);
+ i += 8;
buf[i++] = 0x57; /* push %rdi */
append_insns (&buildaddr, i, buf);