--without-headers and --with-newlib configure options

--without-headers and --with-newlib configure options

[booleandomain]

Hello,

I have some doubts about the --without-headers and --with-newlib options 
when configuring a cross-compiler.

The only source of informations about these options I'm aware of is 
http://gcc.gnu.org/install/configure.html. There it is written:

--without-headers: Tells GCC not use any target headers from a libc when 
building a cross compiler.
--with-newlib: Specifies that `newlib' is being used as the target C 
library.

In other words --without-headers means not to use any libc headers, 
while --with-newlib means to use newlib headers. So in my opinion 
--without-headers --with-newlib doesn't make any sense. Despite of this, 
I have often seen in the web both options used at the same time. Why?

Thanks.

Re: --without-headers and --with-newlib configure options

[Ian Lance Taylor]

booleandomain <booleandomain@gmail.com> writes:

> I have some doubts about the --without-headers and --with-newlib
> options when configuring a cross-compiler.
>
> The only source of informations about these options I'm aware of is
> http://gcc.gnu.org/install/configure.html. There it is written:
>
> --without-headers: Tells GCC not use any target headers from a libc
> when building a cross compiler.
> --with-newlib: Specifies that `newlib' is being used as the target C
> library.
>
> In other words --without-headers means not to use any libc headers,
> while --with-newlib means to use newlib headers. So in my opinion
> --without-headers --with-newlib doesn't make any sense. Despite of
> this, I have often seen in the web both options used at the same
> time. Why?

Normally if you use --with-newlib the compiler will build the gcc
support library, libgcc, without requiring any external support from the
C library.  Using --without-headers will disable that, and the gcc
support library will be built without requiring any library support.
This disables a few features which are generally uninteresting for
embedded systems.

--with-newlib is still useful even when using --without-headers, because
the newlib header files will be used for libraries other than libgcc,
such as libstdc++.

Ian

Re: --without-headers and --with-newlib configure options

[booleandomain]

Ian Lance Taylor wrote:
> Normally if you use --with-newlib the compiler will build the gcc
> support library, libgcc, without requiring any external support from the
> C library.  Using --without-headers will disable that, and the gcc
> support library will be built without requiring any library support.
> This disables a few features which are generally uninteresting for
> embedded systems.
> 
> --with-newlib is still useful even when using --without-headers, because
> the newlib header files will be used for libraries other than libgcc,
> such as libstdc++.
> 
> Ian

Let me see if I understood correctly.

--with-newlib tells the compiler to use newlib headers wherever possible 
(also for other libraries than libgcc). --without-headers tells the 
compiler to build libgcc (only it) without any headers at all.

So if I use --without-headers --with-newlib, libgcc will be built 
without requiring the presence of any header, and other libraries will 
be built with newlib headers.

If I use --without-headers alone, libgcc will be built without requiring 
the presence of any headers, and other libraries will be built with libc 
headers.

If I use --with-newlib alone, libgcc and other libraries will be built 
with newlib headers.

If I use nothing, libgcc and other libraries will be built with libc 
headers.

So I think I can use either --without-headers --with-newlib or 
--with-newlib alone for bootstrapping a cross-compiler.

Re: --without-headers and --with-newlib configure options

[Ian Lance Taylor]

booleandomain <booleandomain@gmail.com> writes:

> --with-newlib tells the compiler to use newlib headers wherever
> possible (also for other libraries than libgcc). --without-headers
> tells the compiler to build libgcc (only it) without any headers at
> all.

Yes.  Note that --without-headers is the default for a cross-compiler.

> So if I use --without-headers --with-newlib, libgcc will be built
> without requiring the presence of any header, and other libraries will
> be built with newlib headers.

Yes.

> If I use --without-headers alone, libgcc will be built without
> requiring the presence of any headers, and other libraries will be
> built with libc headers.

When building a cross-compiler, in practice what will happen is that
libgcc will build and the other libraries will fail to build.

> If I use --with-newlib alone, libgcc and other libraries will be built
> with newlib headers.

Yes.

> If I use nothing, libgcc and other libraries will be built with libc
> headers.

When building a cross-compiler, you do need to provide some headers for
the libraries other than libgcc.  In other words, at build time, the
compiler needs to be able to find the libc headers.  This is typically
done using one of --with-newlib, --with-sysroot, or
--with-build-sysroot.

> So I think I can use either --without-headers --with-newlib or
> --with-newlib alone for bootstrapping a cross-compiler.

Yes.

Ian

Re: --without-headers and --with-newlib configure options

[booleandomain]

Thank you very much Ian for your explanation!