Ludovic Courtès <l...@gnu.org> writes: > Hi Marius, > > Marius Bakke <mba...@fastmail.com> skribis: > >> Ludovic Courtès <l...@gnu.org> writes: > > [...] > >>> The issue that Tobias reports reminds me of the CPATH vs. C_INCLUDE_PATH >>> issue that was causing troubles with newer GCCs, and that I think Marius >>> addressed in ‘core-updates’ (?). Marius, does that ring a bell? >> >> Unfortunately there are still issues with cross-compiling C++ on >> 'core-updates'. For 'C', the workaround was to go back to "CROSS_CPATH" >> instead of "CROSS_C_INCLUDE_PATH", like with native builds. > > That should also address C++, since CPATH (and CROSS_CPATH) are for all > language front-ends, no just C, no?
Indeed. The cross-compilation problems are unrelated. >> For native builds on core-updates, GCC7 occasionally fails if the libc >> or kernel headers are not on C_INCUDE_PATH (see e.g. f90d6c3). It could >> be that cross builds need a similar workaround, but I have not found the >> magic incantation yet. > > How can it be that kernel headers are not on C_INCLUDE_PATH (or CPATH)? Sorry, this was a red herring. :-) (Kernel headers are of course on CPATH because they are propagated from glibc, but adding them on C_INCLUDE_PATH works around some corner cases because GCC disables warnings for such headers, which is expected by some build scripts.) I expected the problem with GCC not finding target libc headers to be a matter of getting it on CROSS_CPLUS_INCLUDE_PATH, just like we had to set C_INCLUDE_PATH for GCC 7's build processes to find libc. But, looking at this issue with a fresh mind I managed to locate the problem, and a one-liner fix:
From dcdedf8d8460a032c0333f6050626a41b39ff461 Mon Sep 17 00:00:00 2001
From: Marius Bakke <mba...@fastmail.com>
Date: Thu, 6 Jun 2019 19:33:05 +0200
Subject: [PATCH] gnu: cross-base: Fix C++ cross-compilation problems with GCC
7.
* gnu/packages/cross-base.scm (cross-gcc-arguments)[#:configure-flags]: Add
"--with-sysroot=/".
---
gnu/packages/cross-base.scm | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/gnu/packages/cross-base.scm b/gnu/packages/cross-base.scm
index 9fcf3bd780..0bd0cb3987 100644
--- a/gnu/packages/cross-base.scm
+++ b/gnu/packages/cross-base.scm
@@ -120,7 +120,15 @@ base compiler and using LIBC (which may be either a libc package or #f.)"
,@(if libc
`( ;; Disable libcilkrts because it is not
;; ported to GNU/Hurd.
- "--disable-libcilkrts")
+ "--disable-libcilkrts"
+ ;; When building a cross compiler, --with-sysroot is
+ ;; implicitly set to "$gcc_tooldir/sys-root". This does
+ ;; not work for us, because --with-native-system-header-dir
+ ;; is searched for relative to this location. Thus, we set
+ ;; it to "/" so GCC is able to find the target libc headers.
+ ;; This is safe because in practice GCC uses CROSS_CPATH
+ ;; & co to separate target and host libraries.
+ "--with-sysroot=/")
`( ;; Disable features not needed at this stage.
"--disable-shared" "--enable-static"
"--enable-languages=c,c++"
--
2.21.0
WDYT? Cross-compiling bootstrap-tarballs still does not work, but I think we just need to reinstate some known workarounds... Will look into it the coming days so we can get this branch rolling :-)
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