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Date: Tue, 13 Oct 2015 16:16:30 +0200
From: Ruben Winistörfer <r.winist@...ewin.ch>
To: musl@...ts.openwall.com
Subject: Re: Re: musl and kernel headers [was Re: system-images 1.4.2:
od is broken; bzip2 is missing]
I just have modified the Alpine Linux kernel header patches to use them
with the 4.2.3 version.
(Not sure if that is a good idea, but why not try it...)
So I am wondering right now, if they haven't solved the problem already
you're discussing about.
http://git.alpinelinux.org/cgit/aports/tree/main/linux-headers
There is a patch for libc-compat.h...
Maybe it helps, otherwise ignore my "interruption". ;-)
Ruben
Denys Vlasenko schrieb:
> On Fri, Oct 9, 2015 at 9:46 PM, Rich Felker<dalias@...ifal.cx> wrote:
>>> Looking at kernel's libc-compat.h, it looks like you can get away
>>> with using __UAPI_DEF_foo's like this?
>>>
>>>
>>> #if defined(__UAPI_DEF_SOCKADDR_IN)&& __UAPI_DEF_SOCKADDR_IN == 1
>>> /* kernel already defined the struct, do nothing */
>>> #else
>>> struct sockaddr_in {
>>> ...
>>> };
>> This would address the case where the kernel header is included first,
>> but it's not a case I or most of the musl community wants to support,
>> because there's no guarantee that the kernel's definitions of these
>> structures will actually be compatible with use elsewhere in the libc
>> headers, etc.
>
> If kernel's definition does not match yours, there is a much
> bigger problem than "includes do not compile":
> kernel and userspace definitions of these structs *must* match
> (modulo harmless things like different typedef names for field types).
>
> So in this case either kernel or libc would need to be fixed.
>
>> The other direction, suppressing kernel headers' definition of the
>> structs, is what we want to work, but they've restricted their logic
>> for that to only work when __GLIBC__ is defined. :(
>
> Yes, you will have to do by hand the thing which kernel
> automagically does for glibc - namely, define to 0:
>
>>> #undef __UAPI_DEF_SOCKADDR_IN
>>> /* tell kernel to not define the struct */
>>> #define __UAPI_DEF_SOCKADDR_IN 0
>>> #endif
>
>> We could do something like this but then we would need to keep up with
>> the list of all the __UAPI defines we need to suppress unwanted kernel
>> definitions.
>
> Looking at libc-compat.h, this list is at the moment only about
> 13 defines long:
>
> #define __UAPI_DEF_IN_ADDR 0
> #define __UAPI_DEF_IN_IPPROTO 0
> #define __UAPI_DEF_IN_PKTINFO 0
> #define __UAPI_DEF_IP_MREQ 0
> #define __UAPI_DEF_SOCKADDR_IN 0
> #define __UAPI_DEF_IN_CLASS 0
> #define __UAPI_DEF_IN6_ADDR 0
> #define __UAPI_DEF_SOCKADDR_IN6 0
> #define __UAPI_DEF_IPV6_MREQ 0
> #define __UAPI_DEF_IPPROTO_V6 0
> #define __UAPI_DEF_IPV6_OPTIONS 0
> #define __UAPI_DEF_IN6_PKTINFO 0
> #define __UAPI_DEF_IP6_MTUINFO 0
>
>
>> What if we could get the kernel to change the #if defined(__GLIBC__)
>> to #if defined(__GLIBC__) || defined(__UAPI_DONTNEED_DEFS) or similar,
>> so that there would only be one macro we need to define, and the
>> kernel would then use the same logic it uses with glibc to suppress
>> all of these.
>
> Or ask kernel to remove "define to 0" glibc hack and ask glibc to
> do its own job. Why one libc should have preferential treatment?
>
> Or ask kernel to stop using structures with userspace names.
> This should not be that hard:
>
> struct __kernel_sockaddr_in {...}
> #if __KERNEL__
> # define sockaddr_in __kernel_sockaddr_in
> #endif
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