On Sun, Jan 14, 2018 at 8:39 AM, Uros Bizjak <ubiz...@gmail.com> wrote:
> On Sun, Jan 14, 2018 at 5:35 PM, H.J. Lu <hjl.to...@gmail.com> wrote:
>> On Sun, Jan 14, 2018 at 8:19 AM, Uros Bizjak <ubiz...@gmail.com> wrote:
>>> On Fri, Jan 12, 2018 at 9:01 AM, Uros Bizjak <ubiz...@gmail.com> wrote:
>>>> On Thu, Jan 11, 2018 at 2:28 PM, H.J. Lu <hjl.to...@gmail.com> wrote:
>>>>
>>>>> Hi Uros,
>>>>>
>>>>> Can you take a look at my x86 backend changes so that they are ready
>>>>> to check in once we have consensus.
>>>>
>>>> Please finish the talks about the correct approach first. Once the
>>>> consensus is reached, please post the final version of the patches for
>>>> review.
>>>>
>>>> BTW: I have no detailed insight in these issues, so I'll look mostly
>>>> at the implementation details, probably early next week.
>>>
>>> One general remark is on the usage of -1 as an invalid register
>>
>> This has been rewritten. The checked in patch no longer does that.
>
> Another issue:
>
> +static void
> +indirect_thunk_name (char name[32], int regno, bool need_bnd_p)
> +{
> + if (USE_HIDDEN_LINKONCE)
> + {
> + const char *bnd = need_bnd_p ? "_bnd" : "";
> + if (regno >= 0)
> + {
> + const char *reg_prefix;
> + if (LEGACY_INT_REGNO_P (regno))
> + reg_prefix = TARGET_64BIT ? "r" : "e";
> + else
> + reg_prefix = "";
> + sprintf (name, "__x86_indirect_thunk%s_%s%s",
> + bnd, reg_prefix, reg_names[regno]);
> + }
> + else
> + sprintf (name, "__x86_indirect_thunk%s", bnd);
> + }
>
> What is the benefit of reg_prefix? Can't we just live with e.g.:
>
> __x86_indirect_thunk_ax
>
> which is the true register name and is valid for 32bit and 64bit targets.
They are used in asm statements in kernel:
extern void (*func_p) (void);
void
foo (void)
{
asm ("call __x86_indirect_thunk_%V0" : : "a" (func_p));
}
it generates:
foo:
movq func_p(%rip), %rax
call __x86_indirect_thunk_rax
ret
--
H.J.
