Re: [PATCH] doc: add Creating a New Cross Target.
Hi Jan!
Thanks for looking into it, and thanks for coping with the latency!
Jan Nieuwenhuizen skribis:
> From e887762bd07d77b68ff19b0ced3ab41c15faa1ac Mon Sep 17 00:00:00 2001
> From: Jan Nieuwenhuizen
> Date: Wed, 7 Dec 2016 17:45:29 +0100
> Subject: [PATCH] doc: add Creating a New Cross Target.
>
> * doc/guix.texi: Add Creating a New Cross Target.
[...]
> +@node Creating a New Cross Target
> +@section Creating a New Cross Target
> +
> +As a first step of making a full port, you may want to start by creating
> +a cross target. A cross target in essence is a cross compiler
> +@code{cross-gcc-@var{}}, which depends on
> +@code{cross-binutils-@var{}} a @code{libc-@var{}} and
> +possibly @code{kernel-headers-@var{}}. Several cross targets
> +are available, such as @code{i586-pc-hurd}, @code{armhf-linux},
> +@code{avr}, @code{i686-w64-mingw32} and @code{mips64el-linux}.
> +
> +Building a full gcc cross compiler depends on a c-library for the
> +target. We can build a c-library for the target once we have a cross
> +compiler. To break this loop a minimal gcc compiler can be built
> +without a c-library; we call this
> +@code{gcc-cross-sans-libc-@var{}}. With this minimal gcc
> +compiler we cross compile the c-library and then we build the full cross
> +gcc.
> +
> +In @code{gnu/packages/cross-base.scm} are functions to create these
> +cross packages. Also, Guix needs to know the name of the dynamic
> +linker, see @var{glibc-dynamic-linker} in
> +@code{gnu/packages/bootstrap.scm}.
I feel that some of it is redundant with, or should be added to
the “Porting” node. WDYT?
> +@menu
> +* Rebuilding My World:: How to avoid rebuilding too often.
> +* GCC and Cross Environment Paths:: Details on the cross build setup.
> +* The MinGW Cross Target:: Some notes on MinGW.
> +@end menu
> +
> +@node Rebuilding My World
> +@subsection Rebuilding My World
> +
> +Why is it that we all tend love to rebuild our world, yet like it
> +somewhat less when others decide do it for us? One of the great things
> +of Guix is that it tracks all dependencies and will rebuild any package
> +that is out of date: We never have to worry that doing a fresh, clean
> +build does not reproduce.
[...]
> +Now it is time to check what the impact of our changes in @var{ncurses}
> +
> +@smallexample
> +$ ./pre-inst-env guix refresh -l ncurses
> +Building the following 1056 packages would ensure 2658 dependent packages
> are rebuilt: @dots{}
> +@end smallexample
My gut feeling is that an explanation of why something gets rebuilt does
not belong here (it is not specific to cross-compilation). So I would
suggest putting it elsewhere; maybe we need a new “Developing with Guix”
section or similar, that would include this as well as “Defining
Packages” and “Programming Interface”, though I understand this goes
beyond this patch.
Another though is that we should provide a command to make it easier to
understand why something is rebuilt (we discussed this in Berlin last
week). I’m not sure exactly what that command’s output would look like,
but I would welcome mockups of what people would like to see, and we can
work from there.
WDYT?
> +@node GCC and Cross Environment Paths
> +@subsection GCC and Cross Environment Paths
> +
> +@c See <http://gcc.gnu.org/ml/gcc/2013-02/msg00124.html>
> +@c <http://bugs.gnu.org/22186> and
> +@c <https://lists.gnu.org/archive/html/guix-devel/2016-04/msg00533.html>
> +@c for a discussion of what follows.
> +Some build systems compile and run programs at build time to generate
> +host-specific data. This means we usually have two compilers installed:
> +@code{gcc} and @code{-gcc}. Guix does not use
> +@file{/usr/include} and @file{/usr/lib} to install additional headers
> +and libraries, instead it adds to environment path variables such as
> +@var{C_INCLUDE_PATH} and @var{LIBRARY_PATH}.
> +
> +To distinguish between native build-time headers and libraries and
> +cross-built target system headers and libraries, we use a patched gcc as
> +cross compiler. The cross compiler instead looks at
> +@var{CROSS_C_INCLUDE_PATH} and @var{CROSS_LIBRARY_PATH}.
> +
> +@node The MinGW Cross Target
> +@subsection The MinGW Cross Target
> +
> +The MinGW target is somewhat special in that it does not support
> +@var{glibc}. @var{Gcc} needs to be passed the @code{--with-newlib} flag
> +and instead we use the combined c-library and free reïmplementation of
> +Windows kernel-headers and system-libraries provided by the MinGW-w64
> +project. Also, it's not POSIX so it often needs explicit support,
> +sometimes we need to create a patch ourselves.
> +
> +For standard libc headers and libraries that are missing in MinGW such
> +as @var{libiconv} and
[PATCH] doc: add Creating a New Cross Target.
Hi,
Here's my doc draft on the cross build system. Suggestions/additions
welcome!
Greetings,
Jan
>From e887762bd07d77b68ff19b0ced3ab41c15faa1ac Mon Sep 17 00:00:00 2001
From: Jan Nieuwenhuizen
Date: Wed, 7 Dec 2016 17:45:29 +0100
Subject: [PATCH] doc: add Creating a New Cross Target.
* doc/guix.texi: Add Creating a New Cross Target.
---
doc/guix.texi | 170 +
gnu/packages/mingw.scm | 6 +-
2 files changed, 171 insertions(+), 5 deletions(-)
diff --git a/doc/guix.texi b/doc/guix.texi
index 738b7fb..91a83e9 100644
--- a/doc/guix.texi
+++ b/doc/guix.texi
@@ -182,6 +182,7 @@ GNU Distribution
* Packaging Guidelines::Growing the distribution.
* Bootstrapping:: GNU/Linux built from scratch.
* Porting:: Targeting another platform or kernel.
+* Creating a New Cross Target::
System Installation
@@ -259,6 +260,12 @@ Coding Style
* Data Types and Pattern Matching:: Implementing data structures.
* Formatting Code:: Writing conventions.
+Creating a New Cross Target
+
+* Rebuilding My World:: How to avoid rebuilding too often.
+* GCC and Cross Environment Paths:: Details on the cross build setup.
+* The MinGW Cross Target:: Some notes on MinGW.
+
@end detailmenu
@end menu
@@ -6457,6 +6464,7 @@ For information on porting to other architectures or kernels,
* Packaging Guidelines::Growing the distribution.
* Bootstrapping:: GNU/Linux built from scratch.
* Porting:: Targeting another platform or kernel.
+* Creating a New Cross Target::
@end menu
Building this distribution is a cooperative effort, and you are invited
@@ -14361,6 +14369,168 @@ Second, some of the required packages could fail to build for that
platform. Lastly, the generated binaries could be broken for some
reason.
+@node Creating a New Cross Target
+@section Creating a New Cross Target
+
+As a first step of making a full port, you may want to start by creating
+a cross target. A cross target in essence is a cross compiler
+@code{cross-gcc-@var{}}, which depends on
+@code{cross-binutils-@var{}} a @code{libc-@var{}} and
+possibly @code{kernel-headers-@var{}}. Several cross targets
+are available, such as @code{i586-pc-hurd}, @code{armhf-linux},
+@code{avr}, @code{i686-w64-mingw32} and @code{mips64el-linux}.
+
+Building a full gcc cross compiler depends on a c-library for the
+target. We can build a c-library for the target once we have a cross
+compiler. To break this loop a minimal gcc compiler can be built
+without a c-library; we call this
+@code{gcc-cross-sans-libc-@var{}}. With this minimal gcc
+compiler we cross compile the c-library and then we build the full cross
+gcc.
+
+In @code{gnu/packages/cross-base.scm} are functions to create these
+cross packages. Also, Guix needs to know the name of the dynamic
+linker, see @var{glibc-dynamic-linker} in
+@code{gnu/packages/bootstrap.scm}.
+
+@menu
+* Rebuilding My World:: How to avoid rebuilding too often.
+* GCC and Cross Environment Paths:: Details on the cross build setup.
+* The MinGW Cross Target:: Some notes on MinGW.
+@end menu
+
+@node Rebuilding My World
+@subsection Rebuilding My World
+
+Why is it that we all tend love to rebuild our world, yet like it
+somewhat less when others decide do it for us? One of the great things
+of Guix is that it tracks all dependencies and will rebuild any package
+that is out of date: We never have to worry that doing a fresh, clean
+build does not reproduce.
+
+However, if we make the tiniest change for our cross build to the
+@var{ncurses} package then Guix will first rebuild world before starting
+the cross-build. If we made a silly typo in the cross-build recipe, it
+takes a long time to get feedback on that.
+
+Say our target is to cross-build @var{Guile} which needs a cross-built
+@var{readline} which requires making a change to the @var{ncurses}
+package. What we can do is create a temporary alternative package
+hierarchy. We copy @var{ncurses} to @var{cross-ncurses}
+
+@example
+(define-public cross-ncurses
+ @dots{}
+ (name "cross-ncurses")
+ @dots{})
+@end example
+
+@noindent
+and because we are really aiming for @var{readline}, we copy that too
+
+@example
+(define-public cross-readline
+ @dots{}
+ (name "cross-readline")
+ @dots{}
+ (propagated-inputs `(("ncurses" ,cross-ncurses)))
+ @dots{})
+@end example
+
+@noindent
+which we then use in our copied @var{cross-guile} package. We replace
+the original packages descriptions with the @var{cross-} variants and
+remove the @var{cross-} prefixes.
+
+Now it is time to check what the impact of our changes in @var{ncurses}
+
+@smallexample
+$ ./pre-inst-env guix refresh -l ncurses
+Building the following 1056 packages would ensure 2658 dependent packages are rebuilt: @dots{}
+@end smallexample
+
+When we are satisfied with
