[Buildroot] [PATCH v2 1/3] toolchain: workaround musl/kernel headers conflict

[Arnout Vandecappelle]

On 10-11-16 14:27, Baruch Siach wrote:
> Rick Felker suggested[1] this hack as a workaround to musl libc conflict with
> kernel headers:
> 
>   The problem is linux/libc-compat.h, which should fix this, only works
>   on glibc, by design. See:
> 
>   #ifndef _LIBC_COMPAT_H
>   #define _LIBC_COMPAT_H
> 
>   /* We have included glibc headers... */
>   #if defined(__GLIBC__)
> 
>   /* Coordinate with glibc netinet/in.h header. */
>   #if defined(_NETINET_IN_H)
> 
>   If you patch it like this:
> 
>   -#if defined(__GLIBC__)
>   +#if 1
> 
>   then it should mostly work but it's still all a big hack. I think
>   that's what distros are doing. The problem is that the same header is
>   trying to do two different things:
> 
>   1. Provide extra linux-kernel-API stuff that's not in the
>      libc/userspace headers.
> 
>   2. Provide definitions of the standard types and constants for uClibc
>      and klibc, which don't have complete libc headers and rely on the
>      kernel headers for definitions.
> 
>   These two uses really should be separated out into separate headers so
>   that the latter only get included explicitly by uClibc and klibc and
>   otherwise remain completely unused. But that would require coordinated
>   changes/upgrades which are unlikely to happen. :(
> 
> Upstream musl still evaluates[2][3] a permanent solution.
> 
> With this in place we can revert (at least) commits a167081c5d (bridge-utils:
> fix build with musl) and e74d4fc4932 (norm: add patch to fix musl build).
> 
> [1] http://www.openwall.com/lists/musl/2015/10/08/2
> [2] http://git.musl-libc.org/cgit/musl/commit/?id=04983f2272382af92eb8f8838964ff944fbb8258
> [3] http://www.openwall.com/lists/musl/2016/11/09/2
> 
> Signed-off-by: Baruch Siach <baruch at tkos.co.il>

Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout at mind.be>

 As mentioned in response to v1, I really would prefer this to be part of
musl-compat-headers, so that we have one place to collect all musl hacks.
However, that would be a bit more intricate, because it would require
musl-compat-headers to be built _after_ musl or the external toolchain, which
makes for some complicated dependency chains. So I'm fine with this solution.

 However, if bridge-utils and norm are really the only packages that suffer from
this problem, is it really worthwhile to apply this workaround?

 Regards,
 Arnout

> ---
> v2:
>   * Add Rick's explanation in the commit log (Arnout)
>   * Link to more recent upstream changes
> ---
>  toolchain/toolchain/toolchain.mk | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/toolchain/toolchain/toolchain.mk b/toolchain/toolchain/toolchain.mk
> index c22713bfe349..d317e917d032 100644
> --- a/toolchain/toolchain/toolchain.mk
> +++ b/toolchain/toolchain/toolchain.mk
> @@ -12,6 +12,20 @@ endif
>  
>  TOOLCHAIN_ADD_TOOLCHAIN_DEPENDENCY = NO
>  
> +# Apply a hack that Rick Felker suggested[1] to avoid conflicts between libc
> +# headers and kernel headers. This is a temporary measure until musl finds a
> +# better solution.
> +#
> +# [1] http://www.openwall.com/lists/musl/2015/10/08/2
> +ifeq ($(BR2_TOOLCHAIN_USES_MUSL),y)
> +define TOOLCHAIN_MUSL_KERNEL_HEADERS_COMPATIBILITY_HACK
> +	$(SED) 's/^#if defined(__GLIBC__)$$/#if 1/' \
> +		$(STAGING_DIR)/usr/include/linux/libc-compat.h
> +endef
> +TOOLCHAIN_POST_INSTALL_STAGING_HOOKS += TOOLCHAIN_MUSL_KERNEL_HEADERS_COMPATIBILITY_HACK
> +TOOLCHAIN_INSTALL_STAGING = YES
> +endif
> +
>  $(eval $(virtual-package))
>  
>  toolchain: $(HOST_DIR)/usr/share/buildroot/toolchainfile.cmake
> 

-- 
Arnout Vandecappelle                          arnout at mind be
Senior Embedded Software Architect            +32-16-286500
Essensium/Mind                                http://www.mind.be
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