[OE-core] musl thoughts

[Andreas Müller]

On Mon, Mar 25, 2019 at 5:26 PM Andreas Müller <schnitzeltony at gmail.com> wrote:
>
> On Mon, Mar 25, 2019 at 5:10 PM Adrian Bunk <bunk at stusta.de> wrote:
> >
> > On Mon, Mar 25, 2019 at 04:36:44PM +0100, Andrea Adami wrote:
> > > On Sat, Mar 23, 2019 at 11:00 PM Andreas Müller <schnitzeltony at gmail.com> wrote:
> > > >
> > > > On Sat, Mar 23, 2019 at 10:53 PM Adrian Bunk <bunk at stusta.de> wrote:
> > > > >
> > > > > On Sat, Mar 23, 2019 at 10:22:15PM +0100, Andreas Müller wrote:
> > > > > > On Sat, Mar 23, 2019 at 10:16 PM Adrian Bunk <bunk at stusta.de> wrote:
> > > > > > >
> > > > > > > On Fri, Mar 22, 2019 at 03:18:01PM -0700, Khem Raj wrote:
> > > > > > > >...
> > > > > > > > There are certain design aspects of musl which are actually turning
> > > > > > > > out to be good
> > > > > > > > e.g. there is no __MUSL__ define, so non-portable code can not be
> > > > > > > > hidden which is a good thing,
> > > > > > > >...
> > > > > > >
> > > > > > > Please take a closer look at some of the musl changes to NM that made
> > > > > > > upgrading NM so hard for Andreas.
> > > > > > >
> > > > > > > +#if defined(__GLIBC__)
> > > > > > >  #include <net/ethernet.h>
> > > > > > > +#else /* musl libc */
> > > > > > > +#define ETH_ALEN       6               /* Octets in one ethernet addr   */
> > > > > > > +#endif
> > >...
> > >
> > > Hi,
> >
> > Hi Andrea,
> >
> > > I am jumping in a little late to take side with Khem :)
> > >
> > > What happens now is that more 'bad' sources (written to suit glibc and
> > > thus not portable) are discovered by the wider base of developers and
> > > autobuilders.
> > >...
> >
> > but this does not apply to this example, which is a problem between
> > musl itself and the kernel headers.
> >
> > Code can expect #include <foo.h> to work for any headers, and with any
> > order of these headers. If it does not, the 'bad' sources are whatever
> > sources provide the headers in question.
> >
> > musl does provide net/ethernet.h, but including it causes a compile
> > error here.
> Out of curiosity: you have some log?
>
Looked into this. Found an old musl build failure of networkmanager
[1] but I think the issue has not changed:

| In file included from
TOPDIR/build/tmp/work/mips32r2-yoe-linux-musl/networkmanager/1.14.4-r0/recipe-sysroot/usr/include/net/ethernet.h:10,
|                  from ../NetworkManager-1.14.4/shared/n-acd/src/n-acd.c:28:
| TOPDIR/build/tmp/work/mips32r2-yoe-linux-musl/networkmanager/1.14.4-r0/recipe-sysroot/usr/include/netinet/if_ether.h:111:8:
error: redefinition of 'struct ethhdr'
|  struct ethhdr {
|         ^~~~~~
| In file included from ../NetworkManager-1.14.4/shared/n-acd/src/n-acd.c:26:
| TOPDIR/build/tmp/work/mips32r2-yoe-linux-musl/networkmanager/1.14.4-r0/recipe-sysroot/usr/include/linux/if_ether.h:167:8:
note: originally defined here
| struct ethhdr {
|         ^~~~~~

glibc does not fail because it does include linux header
| /* Get definitions from kernel header file.  */
| #include <linux/if_ether.h>
and does not define struct ethhdr

linux/if_ether.h says:
/* allow libcs like musl to deactivate this, glibc does not implement this. */
#ifndef __UAPI_DEF_ETHHDR
#define __UAPI_DEF_ETHHDR        1
#endif

#if __UAPI_DEF_ETHHDR
struct ethhdr {
    unsigned char    h_dest[ETH_ALEN];    /* destination eth addr    */
    unsigned char    h_source[ETH_ALEN];    /* source ether addr    */
    __be16        h_proto;        /* packet type ID field    */
} __attribute__((packed));
#endif

musl does not include linux header but defines which is differen from
what linux does:
struct ethhdr {
    uint8_t h_dest[ETH_ALEN];
    uint8_t h_source[ETH_ALEN];
    uint16_t h_proto;
};
and later
#define __UAPI_DEF_ETHHDR       0

So for networkmanager there is either some wrong sequence or it
includes linux headers.

And I am still not confident that it is our job to teach umpteen
projects written for linux how to write portable code (oe-core has 147
musl related patches and meta-openembedded has 140)...

[1] http://errors.yoctoproject.org/Errors/Details/198239/

Andreas