Compiling libpcap from source using musl and clang

Compiling libpcap from source using musl and clang

[Hamed Ghavamnia]

[-- Attachment #1: Type: text/plain, Size: 500 bytes --]

Hi to all,

I'm trying to compile the libpcap library from source using musl and clang.
It compiles if I only use clang with libc, but using musl it dies.
The problem I'm currently facing is that the source codes require header
files such as linux/types.h, but there isn't any linux sub folder in the
include folder of my compiled musl library. Is that normal? Should I be
able to compile libpcap using musl, or does it require any features which
haven't been implemented in musl yet?

Thanks,
Hamed

[-- Attachment #2: Type: text/html, Size: 604 bytes --]

Re: Compiling libpcap from source using musl and clang

[Rich Felker]

On Mon, Nov 20, 2017 at 02:02:43PM -0500, Hamed Ghavamnia wrote:
> Hi to all,
> 
> I'm trying to compile the libpcap library from source using musl and clang.
> It compiles if I only use clang with libc, but using musl it dies.
> The problem I'm currently facing is that the source codes require header
> files such as linux/types.h, but there isn't any linux sub folder in the
> include folder of my compiled musl library. Is that normal? Should I be
> able to compile libpcap using musl, or does it require any features which
> haven't been implemented in musl yet?

To get the linux/* headers you need to install them. If you're using a
cross toolchain built with musl-cross-make, they're installed for you
in its sysroot. Otherwise you can install them yourself from the
kernel sources or if you're using compiler wrappers on a glibc-based
system you can make symlinks to the copies of the Linux headers in the
glibc include dir (/usr/include/linux, etc.). Do NOT add
-I/usr/include though to get them; this will use glibc headers and
badly break things.

Rich

Linux headers for musl (was: Compiling libpcap from source using musl and clang)

[Assaf Gordon]

Hello Rich and all,

Regarding this:

On 2017-11-20 12:31 PM, Rich Felker wrote:
> On Mon, Nov 20, 2017 at 02:02:43PM -0500, Hamed Ghavamnia wrote:
>> [...]
>> The problem I'm currently facing is that the source codes require header
>> files such as linux/types.h, but there isn't any linux sub folder in the
>> include folder of my compiled musl library.
 >
> [...] Otherwise you can install them yourself from the
> kernel sources or if you're using compiler wrappers on a glibc-based
> system you can make symlinks to the copies of the Linux headers in the
> glibc include dir (/usr/include/linux, etc.). 

I encountered a similar issue when building libreSSL with musl
(on standard ubuntu 16.04 x86_64 machine).

The solution I've found is:

      apt-get install -y linux-libc-dev
      ln -s /usr/include/linux            $MUSLROOT/include
      ln -s /usr/include/asm-generic      $MUSLROOT/include
      ln -s /usr/include/x86_64-linux-gnu $MUSLROOT/include

And then there was one more strange issue:
Somewhere during compilation of libressl-portable
the file <asm/types.h> is included.

With gcc+glibc, this automatically resolves to
   "/usr/include/x86_64-linux-gnu/asm/types.h".

With musl-gcc, it didn't "just work",
and adding "-I$MUSLROOT/include/x86_64-linux-gnu" seemed to have made 
things worse (headers from <bits/XXX> failed to compile).

This issue can be reproduced with:

    echo "#include <asm/types.h>" > 1.c

Then gcc/clang "just work":

     $ gcc -E 1.c | head
     # 1 "1.c"
     # 1 "<built-in>"
     # 1 "<command-line>"
     # 1 "/usr/include/stdc-predef.h" 1 3 4
     # 1 "<command-line>" 2
     # 1 "1.c"
     # 1 "/usr/include/x86_64-linux-gnu/asm/types.h" 1 3 4


     $ clang -E 1.c | head
     # 1 "1.c"
     # 1 "<built-in>" 1
     # 1 "<built-in>" 3
     # 317 "<built-in>" 3
     # 1 "<command line>" 1
     # 1 "<built-in>" 2
     # 1 "1.c" 2
     # 1 "/usr/include/x86_64-linux-gnu/asm/types.h" 1 3 4

While musl does not:

     $ musl-gcc -E 1.c | head
     1.c:1:23: fatal error: asm/types.h: No such file or directory
     compilation terminated.
     # 1 "1.c"
     # 1 "<built-in>"
     # 1 "<command-line>"
     # 1 "1.c"

My ugly work-around was:

    cd $muslroot/include
    ln -s x86_64-linux-gnu/asm asm


Is this the recommended way?
It seemed symlink'ing /usr/include/linux alone was not sufficient.

Comments very welcomed,
  - assaf

Re: Linux headers for musl (was: Compiling libpcap from source using musl and clang)

[Szabolcs Nagy]

* Assaf Gordon <assafgordon@gmail.com> [2017-11-23 01:03:21 -0700]:
> On 2017-11-20 12:31 PM, Rich Felker wrote:
> > On Mon, Nov 20, 2017 at 02:02:43PM -0500, Hamed Ghavamnia wrote:
> > > [...]
> > > The problem I'm currently facing is that the source codes require header
> > > files such as linux/types.h, but there isn't any linux sub folder in the
> > > include folder of my compiled musl library.
> >
> > [...] Otherwise you can install them yourself from the
> > kernel sources or if you're using compiler wrappers on a glibc-based
> > system you can make symlinks to the copies of the Linux headers in the
> > glibc include dir (/usr/include/linux, etc.).
> 
> I encountered a similar issue when building libreSSL with musl
> (on standard ubuntu 16.04 x86_64 machine).
> 
> The solution I've found is:
> 
>      apt-get install -y linux-libc-dev
>      ln -s /usr/include/linux            $MUSLROOT/include
>      ln -s /usr/include/asm-generic      $MUSLROOT/include
>      ln -s /usr/include/x86_64-linux-gnu $MUSLROOT/include
> 
...
> My ugly work-around was:
> 
>    cd $muslroot/include
>    ln -s x86_64-linux-gnu/asm asm
> 
> 
> Is this the recommended way?

no, the recommended way is to use a cross toolchain that
is built for musl (and has the linux headers installed),
instead of using your platform toolchain with various hacks
(like the musl-gcc wrapper around gcc)

in case you prefer musl-gcc then you should install your
deps to $MUSLROOT instead of trying to use platform components,
this includes library and header deps as well, so get linux
sources and install the headers yourself

make ARCH=x86 INSTALL_HDR_PATH=staging O=builddir headers_install
cp -a -n staging/include $MUSLROOT
(not tested)

(note that the ubuntu toolchain uses 'multi-arch' layout for
the include and library paths, but musl-gcc drops all platform
specific include paths and uses its own (standard) layout,
so symlinking stuff from ubuntu include path like
'x86_64-linux-gnu' wont work)