Re: [gentoo-soc] Gentoo on Android, Summary for 2013.6.28-7.1

[heroxbd]

Dear Luca,

Picking up gcc again.

Luca Barbato <lu_zero@g.o> writes:

> Upstream can be difficult, supporting multiple c runtime is _quite_
> problematic and requires pointless patching in too many part of the
> codebase nowadays =/

Yes, for example, the *link section of gcc amd64:

*link:

%{!static:--eh-frame-hdr} %{m32|mx32:;:-m elf_x86_64} %{m32:-m elf_i386}
%{ mx32:-m elf32_x86_64} %{shared:-shared} %{!shared: %{!static:
%{rdynamic:-export-dynamic} %{m 32:-dynamic-linker
%{muclibc:/lib/ld-uClibc.so.0;:%{mbionic:/system/bin/linker;:/opt/gentoo/lib/ld-linux.so.2}}}
%{m32|mx32:;:-dynamic-linker
%{muclibc:/lib/ld64-uClibc.so.0;:%{mbionic:/system/bin/linker64;:/opt/gentoo/l
ib64/ld-linux-x86-64.so.2}}} %{mx32:-dynamic-linker
%{muclibc:/lib/ldx32-uClibc.so.0;:%{mbionic:/system/bin
/linkerx32;:/opt/gentoo/libx32/ld-linux-x32.so.2}}}} %{static:-static}}

>> An alternative: Given the similar situation in binutils, I am thinking
>> of another switch (like --{enable,with}-native-sysroot) to turn
>> --with-sysroot into a native (non-cross) version for our purpose. (GLEP
>> draft follows) What do you say?
>
> Worth a try, sadly you need to coordinate with upstream.

I spent a whole day trying to get a solution to specify dynamic
linker via configure.

The plan was:

1. let all the ports of gcc have dynamic_linker section in specs,
like that of x86.

2. add a configure option, --with-extra-specs to specify an
additional EXTRA_SPECS to gcc.c.

3. use toolchain-funcs.eclass to generate dynamic linker specs, as

+# Returns location of dynamic linker
+gcc-specs-gen-dynamic-linker() {
+       echo '*dynamic_linker:'
+
+       local dlinkers
+       case $(tc-arch)-${CTARGET##*-} in
+       amd64-gnu*)
+               for abi in ${MULTILIB_ABIS}; do
+                       case ${abi} in
+                       amd64) dlinkers+=( "m32|mx32:;:/lib64/ld-linux-x86-64.so.2" ) ;;
+                       x86) dlinkers+=( m32:/lib/ld-linux.so.2 ) ;;
+                       x32) dlinkers+=( mx32:/libx32/ld-linux-x32.so.2 ) ;;
+                       esac
+               done
+               ;;
+       x86-gnu*) dlinkers=( /lib/ld-linux.so.2 ) ;;
+       arm-gnu*)
+               case ${CTARGET//_/-} in
+               *-hardfloat-*) dlinkers=( /lib/ld-linux-armhf.so.3 ) ;;
+               *-softfloat-*) dlinkers=( /lib/ld-linux.so.3 ) ;;
+               esac
+               ;;
+       esac
+
+       for dlinker in ${dlinkers[@]}; do
+               local ldso=${dlinker##*:}
+               if [[ ${ldso} == ${dlinker} ]]; then
+                       echo -n "${EPREFIX}"${ldso}
+               else
+                       local switch=${dlinker%:*}
+                       echo -n "%{${switch}:${EPREFIX}${ldso}}"
+               fi
+       done
+}

But there are intrinsic difficulties. The default specs of gcc
are all preprocessed as C macros, which means we cannot pass a
specs file to make it default. Furthermore, I could not find a
way to pass a customized specs file for building (which is
necessary that we have to build gcc against glibc from
RAP). Therefore, we have to pass raw C into configure options,
like,

econf --with-extra-specs='{ "dynamic-linker", "/opt/gentoo/lib/ld-linux.so.2" }'

However, GNU autoconf/automake system automatically quote this to
a string, while we want to pass an array of structures.

Another solution is to prepend sysroot to dynamic linker, which is
indifferent to the runtime-prefix patch from Google, criticized by you
earlier.

Up to this point, the solution becomes complex and artificial. I
would rather use the present patch'n'prefixify method, as we used
in many ebuild, like:

--- gcc/config/i386/linux.h     2011-06-04 03:30:39.000000000 +0900
+++ gcc/config/i386/linux.h.new 2013-07-16 19:55:09.610399047 +0900
@@ -21,4 +21,4 @@ along with GCC; see the file COPYING3.
 <http://www.gnu.org/licenses/>.  */
 
 #define GNU_USER_LINK_EMULATION "elf_i386"
-#define GLIBC_DYNAMIC_LINKER "/lib/ld-linux.so.2"
+#define GLIBC_DYNAMIC_LINKER "@GENTOO_PORTAGE_EPREFIX@/lib/ld-linux.so.2"

Cheers,
Benda