Date: Tue, 8 Nov 2016 21:14:56 -0500 From: Rich Felker <dalias@...c.org> To: musl@...ts.openwall.com Subject: Re: kernel header compatibility On Tue, Nov 08, 2016 at 08:54:23PM -0500, Felix Janda wrote: > Rich Felker wrote: > > On Tue, Nov 08, 2016 at 08:11:45PM -0500, Felix Janda wrote: > > > The recent commit 04983f2272382af92eb8f8838964ff944fbb8258 (make > > > netinet/in.h suppress clashing definitions from kernel headers) > > > intends to address some of the conflicts between the kernel and musl > > > libc headers. Namely it tries to allow the inclusion of kernel headers > > > after libc header by defining __UAP_DEF_* macros. However this doesn't > > > work because the relevant linux headers include <linux/libc-compat.h>, > > > which unconditionally redefines the constants. For example > > > > Oh, how awful. I missed the whole bogus #else part after the #if > > defined(__GLIBC__) block. > > > > > > #include <netinet/in.h> > > > #include <linux/in6.h> > > > > > > leads to > > > > > > #define __UAPI_DEF_IN_ADDR 0 // from <netinet/in.h> > > > #define __UAPI_DEF_IN_ADDR 1 // from <linux/libc-compat.h> > > > > Conflicting defines should be an error already. > > Strangely gcc-6.2.0 just warns (and the warning is not displayed when > it is in system headers). > > > > So we still get two conflicting definitions of struct in6_addr. > > > > > > > > > By adding the hack "#define _LIBC_COMPAT_H" to <netinet/in.h>, this > > > particular example compiles. > > > > > > > > > Maybe the kernel people can be convinced to add #ifdef guards around > > > all of the (non glibc) __UAPI_* definitions in <linux/libc-compat.h>. > > > > I think they should, but I don't mind just suppressing the whole > > header by defining _UAPI_LIBC_COMPAT_H if that works for all kernel > > versions. It seems to; see: > > > > https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/include/uapi/linux/libc-compat.h?id=cfd280c91253cc28e4919e349fa7a813b63e71e8 > > > > where the file was introduced. > > Note that for the actually installed kernel headers the "_UAPI" prefix > is stripped from the include guard. For example "_UAPI__LINUX_KEYBOARD" > becomes "__LINUX_KEYBOARD". > > Second, defining the include guard in <netinet/in.h> would prevent > <linux/libc-compat.h> from defining __UAPI_* constants for things > actually missing from musl. For example, a recent <linux/ipx.h> would > no longer define struct sockaddr_ipx when included after > <netinet/in.h>. Uhg. So there's really no fix except for the kernel to put #ifndef around its definitions of individual macros, is there? Would you be willing to propose such a patch? I'd ack it. Rich
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