Re: Hello

[orc <orc@sibserver.ru>]

On Fri, 6 Jul 2012 02:26:14 -0400
Rich Felker <dalias@aerifal.cx> wrote:

> On Fri, Jul 06, 2012 at 02:06:01PM +0800, orc wrote:
> > Here a patch, attached. It contains both missing syscalls and weak
> > aliases. It does not contain glibc-specific stuff (if you want, I
> > can send it too, but it looks ugly, intended only for 'run it
> > successfully'). Some notes about:
> > - rawmemchr() was taken from uClibc
> > - ioperm() and iopl() were not necessary to make glxgears work, just
> >   added them because Xorg will want them
> > - I don't think libc even needs xattr stuff, but glibc includes
> > them. On many systems they are usually duplicated, libattr provides
> > same interface
> > - It seems that every function in src/locale needs it's __underscore
> >   alias, to match glibc api
> > - there some ugly __funcname_internal aliases, don't know why glibc
> >   defines them in that way
> 
> I think most of this is an artifact of some hacks they do in the glibc
> headers for inlining/optimization and/or _FORTIFY_SOURCE support.
> The functions it creates references to are not (AFAIK) in the LSB ABI
> and thus binaries using them are non-LSB-conforming...
> 
> > Probably you will want to add:
> > - weak_aliases for __underscores
> 
> Except most of them should be in the opposite direction. Especially
> for functions like strxfrm_l where we'll eventually want the ISO C
> "foo" function to depend on the POSIX "foo_l" function, the latter
> will need its real name to be the __-prefixed version.
> 
> > - weak_aliases __funcname_internal
> 
> These are rather ugly and stupid, but seem harmless.
> 
> > - rawmemchr() (probably your own implementation, not uClibc one)
> 
> Indeed, I'll want to copy the existing fast code from strchr.
> 
> > - some missing syscalls (I really misguessed number of needed
> > syscalls, seems that this was a number of aliases, not syscalls)
> 
> These look mostly fine, but the header changes are all wrong (the
> declarations are not under _GNU_SOURCE control).

Of course adapt the patch to be correct here. My local manpages did not
say much about feature test macros.

> 
> > glibc-specific functions and objects required to make glxgears work:
> > - dlvsym() (wrapper around dlsym(), we don't need ugly symvers)
> 
> Ugly because it needs to be written in asm and adds a useless per-arch
> asm function. Perhaps we could just have dlvsym be a weak alias to
> dlsym in the existing asm files...
> 
> > - gnu_get_libc_*()
> 
> return "not glibc";
> 
> > - malloc_usable_size() (returns 0 always, probably there is no code
> > in musl to make it work. Definition in eglibc was cryptic for me,
> > but it clearly seems to be the glibc/ptmalloc feature)
> 
> return (*((size_t *)ptr - 1) & -2) - 2*sizeof(size_t);

It will be nice to see correct implementation instead of 'always-fail',
cool.

> 
> 
> > - 4 function-wrappers in math code: __isnan(), __isnanf(),
> > __isinf(), __isinff()
> 
> Reasonable to add; perhaps even more efficient than the current
> approach.
> 
> There's also that function named "finite" whose name violates the
> namespace and thus it cannot be in a common source file with other
> stuff that could be needed by conformant code.

Yes, I also did not sure about it.

> 
> > - __xmknod()
> 
> Ugly but this should be added; it's analogous to the __xstat junk.
> 
> > - _IO_2_1_stdout_ -> stdout
> 
> Very ugly, but shouldn't break anything...


*looking in glibc-compat patch*
I forgot this one:
- A _*_chk versions of common functions like memcpy, *printf, etc. and
  longjmp. They are nearly same as their non-chk versions (additional
  arg) except that they do additional buffer overflow checks. I did
  quick weak_alias to non-chk versions to test that it will work. It
  worked, but what do you think about them?

> 
> > gtk2 will not work that way, I checked. One library in chain
> > requires libstdc++, libstdc++ defines 'unique' symbols (see manual
> > page of binutils nm) which musl linker cannot handle. Additionally,
> > there is much more missing symbols including missing functions. But
> > plain X11 apps worked (I checked xfontsel and xlogo).
> 
> Have you looked into building the apps/libs natively against musl
> except for the nvidia binary blob, to see if the blob works under that
> usage? I think that's a usage case that's a lot more applicable to
> real-world usage of musl, and in fact it's probably the first real
> reason anybody would be interested in having musl work with code that
> was built against glibc...

I mostly do building in KVM now to test how applications are portable
and collect the patches that will be needed when transiting to
musl-enabled system. I was busy with patching old gcc and binutils these
days, since I found that musl systems by default are built with
executable stack (GNU_STACK thing) enabled (binutils issue). I will try
that on host of course, but I generally dislike cross-compiling even to
same arch because of autotools and pkg-config (will be required by
gtk2 stuff).

> 
> Rich