Re: [PATCH] x86-64/memset: Mark the debugger symbol as hidden

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Mon, May 7, 2018 at 11:22 AM, Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>
>
> On 07/05/2018 14:59, H.J. Lu wrote:
>> On Sat, May 5, 2018 at 8:46 AM, H.J. Lu <hongjiu.lu@intel.com> wrote:
>>> When MEMSET_SYMBOL (__memset, erms) is provided for debugger, mark it
>>> as hidden so that it will be local to the library.
>>>
>>> Any comments?
>>>
>>> H.J.
>>> ---
>>>         * sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
>>>         (MEMSET_SYMBOL (__memset, erms)): Mark the debugger symbol as
>>>         hidden.
>>> ---
>>>  sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S | 3 ++-
>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S b/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
>>> index d0fe79c9f1..a0560cd5c8 100644
>>> --- a/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
>>> +++ b/sysdeps/x86_64/multiarch/memset-vec-unaligned-erms.S
>>> @@ -131,7 +131,8 @@ END (__memset_chk_erms)
>>>  /* Only used to measure performance of REP STOSB.  */
>>>  ENTRY (__memset_erms)
>>>  # else
>>> -/* Provide a symbol to debugger.  */
>>> +/* Provide a hidden symbol to debugger.  */
>>> +       .hidden MEMSET_SYMBOL (__memset, erms)
>>>  ENTRY (MEMSET_SYMBOL (__memset, erms))
>>>  # endif
>>>  L(stosb):
>>> --
>>> 2.17.0
>>>
>>
>> I am checking it in.
>>
>
> Why is this need only for this symbol in particular and not for all other
> ifunc variations? What debugger is missing and does it potentially might
> affect other architectures as well?

This is specific to memset-vec-unaligned-erms.S.   The code looks like

function 1 entry:
   ..
   ret

local label:
  ...
  ret

function 2 entry:
  ...
  jump to local label

If "local label" isn't in the symbol table, gdb will think you jump to
"function 1"
when single-stepping over "jump to local label".

-- 
H.J.