Re: [PATCH 3/4] In _IEEE_LIBM mode, use weak symbols instead of wrapper funcs

On Mon, Aug 27, 2018 at 2:23 PM, Craig Howland <[email protected]>
wrote:

> On 08/27/2018 02:32 PM, [email protected] wrote:
>
>> From: Keith Packard <[email protected]>
>>
>> When the math library is compiled to just use bare IEEE_LIBM mode, many
>> public functions are just wrappers around the __ieee754 version.
>> Eliminate the extra function by creating a weak alias symbol for the
>> public name directly from the ieee754 name.
>>
>> Signed-off-by: Keith Packard <[email protected]>
>> ---
>>   newlib/libm/math/e_acos.c       |  5 +++++
>>   ...
>>   86 files changed, 360 insertions(+), 197 deletions(-)
>>
>> diff --git a/newlib/libm/math/e_acos.c b/newlib/libm/math/e_acos.c
>> index 319b1d56f..25509c0f0 100644
>> --- a/newlib/libm/math/e_acos.c
>> +++ b/newlib/libm/math/e_acos.c
>> @@ -59,6 +59,11 @@ qS2 =  2.02094576023350569471e+00, /* 0x40002AE5,
>> 0x9C598AC8 */
>>   qS3 = -6.88283971605453293030e-01, /* 0xBFE6066C, 0x1B8D0159 */
>>   qS4 =  7.70381505559019352791e-02; /* 0x3FB3B8C5, 0xB12E9282 */
>>   +#ifdef _IEEE_LIBM
>> +double acos(double x)
>> +       __attribute__((weak, alias("__ieee754_acos")));
>> +#endif
>> +
>>   #ifdef __STDC__
>>         double __ieee754_acos(double x)
>>   #else
>> ...
>>
> While this is a nice idea, it is a problem for targets which don't support
> weak aliases (i.e. those without proper object file support for them).
> (Does anyone know for certain if this is a real problem instead of just a
> theoretical one?  (I'd guess so.)  All my Newlib targets are ELF.)  An
> alternative implementation could be macro definitions in math.h.


My suggestion is to use the macro __weak_reference() from newlib's
sys/cdefs.h which appears to account for ELF and not-ELF.

This is from FreeBSD so I would have confidence that they got it right.

--joel


>
> Craig
>