Re: [Minios-devel] [UNIKRAFT PATCH 03/22] plat/kvm: Use the same declaration for _text and _end for Arm64

["Wei Chen (Arm Technology China)" <Wei.Chen@xxxxxxx>]

> -----Original Message-----
> From: Julien Grall <julien.grall@xxxxxxx>
> Sent: 2018年11月9日 18:06
> To: Wei Chen (Arm Technology China) <Wei.Chen@xxxxxxx>; minios-
> devel@xxxxxxxxxxxxxxxxxxxx; simon.kuenzer@xxxxxxxxx
> Cc: Kaly Xin (Arm Technology China) <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> Subject: Re: [Minios-devel] [UNIKRAFT PATCH 03/22] plat/kvm: Use the same
> declaration for _text and _end for Arm64
> 
> On 09/11/2018 06:52, Wei Chen (Arm Technology China) wrote:
> > Hi Julien,
> 
> Hi,
> 
> >> -----Original Message-----
> >> From: Julien Grall <julien.grall@xxxxxxx>
> >> Sent: 2018年11月8日 20:02
> >> To: Wei Chen (Arm Technology China) <Wei.Chen@xxxxxxx>; minios-
> >> devel@xxxxxxxxxxxxxxxxxxxx; simon.kuenzer@xxxxxxxxx
> >> Cc: Kaly Xin (Arm Technology China) <Kaly.Xin@xxxxxxx>; nd <nd@xxxxxxx>
> >> Subject: Re: [Minios-devel] [UNIKRAFT PATCH 03/22] plat/kvm: Use the same
> >> declaration for _text and _end for Arm64
> >>
> >> Hi,
> >>
> >> On 11/8/18 9:51 AM, Wei Chen wrote:
> >>> We get a warning that _end and _text are differently defined within
> >>> setup.c and memory.c:
> >>>
> >>> warning: type of ‘_end’ does not match original declaration
> >>>         extern char _end[];
> >>>                     ^
> >>> note: previously declared here
> >>>              _ctors, _ectors, __bss_start, _end;
> >>>
> >>> We should use the same definition  in both files and then this warning
> >>> goes away.
> >>
> >> That's a call to have the _end and _text defined in an header.
> >>
> >
> > Yes, it would be better to have a clean-up patch to do this.
> >
> >> Also, keep in mind that you can't compare two pointers that points to a
> >
> > I don't quite understand this comment. We treat all these pointers as char
> > pointers. Why did you think they are different?
> Whether the pointers are treated as char * or anything else does not matter
> here. The problem is the C spec states that comparing 2 pointers belonging to
> distinct object is undefined (see [1] and [2]).
> 
> So check such as "mem_base > (uint64_t)&_text" is undefined because the
> compiler
> could see-through the cast. So you have to hide it from the compiler (see
> __pa_symbol in Linux).
> 

Ok, thanks.

> >
> >> different object. So you may want to find a different way to access _end
> >> & co.
> >>
> >
> > Sorry, what's "co" here?
> 
> "and company" by that I meant all the other cases similar to _end.
> 
> Cheers,
> 
> [1]
> https://wiki.sei.cmu.edu/confluence/display/c/ARR36-
> C.+Do+not+subtract+or+compare+two+pointers+that+do+not+refer+to+the+same+array
> [2] 6.5.8 http://www.dii.uchile.cl/~daespino/files/Iso_C_1999_definition.pdf
> 
> --
> Julien Grall
_______________________________________________
Minios-devel mailing list
Minios-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/minios-devel