Re: [edk2-devel] [PATCH] MdePkg Base.h: Delete prototype for __builtin_return_address

[Jessica Clarke <jrtc27@jrtc27.com>]

It will always look like void *__builtin_return_address(unsigned) and
work like that, just that under the hood it's being implemented
slightly differently, which has the unfortunate side-effect of
triggering this bug. We've been compiling the embedded EDK2 in our
CheriBSD with that line deleted for years now with no issue.

Jess

> On 20 Jul 2020, at 15:58, Gao, Liming <liming.gao@intel.com> wrote:
> 
> Clarke:
>  Do you mean CLANG compiler may have the different prototype for __builtin_return_address()? If so, dose __builtin_return_address (L) always work? 
> 
> Thanks
> Liming
>> -----Original Message-----
>> From: devel@edk2.groups.io <devel@edk2.groups.io> On Behalf Of Leif Lindholm
>> Sent: Monday, July 20, 2020 10:05 PM
>> To: Jessica Clarke <jrtc27@jrtc27.com>
>> Cc: devel@edk2.groups.io; Kinney, Michael D <michael.d.kinney@intel.com>; Gao, Liming <liming.gao@intel.com>
>> Subject: Re: [edk2-devel] [PATCH] MdePkg Base.h: Delete prototype for __builtin_return_address
>> 
>> +Mike, Liming
>> 
>> On Mon, Jul 20, 2020 at 14:49:46 +0100, Jessica Clarke wrote:
>>> REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1004
>>> 
>>> Being a compiler builtin, the type of __builtin_return_address is
>>> already known to the compiler so no prototype is needed. Clang also
>>> errors out when redeclaring certain builtins like this[1], though
>>> currently only for ones with custom type checking. At the moment,
>>> __builtin_return_address does not use custom type checking and so does
>>> not trigger this error, however, the CHERI fork of LLVM, which will form
>>> the basis of the toolchain for Arm's experimental Morello platform, does
>>> use custom type checking for it, and so gives an error. Thus, simply
>>> delete the unnecessary line.
>>> 
>>> [1] https://github.com/llvm/llvm-project/commit/41af97137572ad6d4dafc872e7ecf6bbb08d4984
>>> 
>>> Cc: Leif Lindholm <leif@nuviainc.com>
>>> Signed-off-by: Jessica Clarke <jrtc27@jrtc27.com>
>>> ---
>>> MdePkg/Include/Base.h | 1 -
>>> 1 file changed, 1 deletion(-)
>>> 
>>> diff --git a/MdePkg/Include/Base.h b/MdePkg/Include/Base.h
>>> index 85a091b9d5..8e4271f6ea 100644
>>> --- a/MdePkg/Include/Base.h
>>> +++ b/MdePkg/Include/Base.h
>>> @@ -1273,7 +1273,6 @@ typedef UINTN RETURN_STATUS;
>>>   **/
>>>   #define RETURN_ADDRESS(L)     ((L == 0) ? _ReturnAddress() : (VOID *) 0)
>>> #elif defined (__GNUC__) || defined (__clang__)
>>> -  void * __builtin_return_address (unsigned int level);
>> 
>> Agreed this looks somewhat bonkers.
>> And I can't see any ill effects from dropping it, so:
>> Reviewed-by: Leif Lindholm <leif@nuviainc.com>
>> 
>>>   /**
>>>     Get the return address of the calling function.
>>> 
>>> --
>>> 2.20.1
>>> 
>> 
>> 
>