Hi! In a toolchain where GCC has been configured for --target=i686-pc-linux-gnu, and where an x86_64 multilib has also been configured, by default GCC will generate code for 32-bit mode, and for 64-bit mode only when -m64 is passed. Per ASM_SPEC definition, the -m64 option is translated to --64 when invoking the assembler. This is working fine.
What however is not working fine is GCC's very own configure testing. When using said toolchain for building on/for x86_64-linux-gnu by configuring a native GCC build with CC='gcc -m64' CXX='g++ -m64', I'm seeing the following happen in [GCC]/gcc/configure: configure:23559: checking assembler for thread-local storage support configure:23572: [...]/bin/as --fatal-warnings -o conftest.o conftest.s >&5 conftest.s: Assembler messages: conftest.s:5: Error: bad register name `%rax' [...] configure: failed program was .section ".tdata","awT",@progbits foo: .long 25 .text movq %fs:0, %rax [...] configure:23586: result: no In this toolchain, an unadorned invocation of as will default to 32-bit mode, and enter 64-bit mode only when an explicit --64 is passed -- which is not done here. This is, from a quick glance, the "inverse" thing as has once been discussed in <http://gcc.gnu.org/PR42345>, <http://news.gmane.org/find-root.php?message_id=%3C20091210175824.GA32242%40lucon.org%3E>. Wanting to use this toolchain, do I have to configure GCC pointing to an assembler that defaults to 64-bit mode, or use something like --with-as='as --64' (not checked whether that works), or should the GCC configure system deduce from $CXX' -m64 that it needs to pass --64 to the assembler (à la ASM_SPEC as indicated above), or is the following patch the way to go, or something else? H.J., the gnux32 change is just a guess; please comment if that's not right. (And, of course, this is not a problem specific to *-*-linux*, but changing that is for another day.) gcc/ * acinclude.m4 (gcc_GAS_FLAGS): Add more gcc_cv_as_flags overrides. * configure: Regenerate. --- gcc/acinclude.m4 +++ gcc/acinclude.m4 @@ -444,8 +444,16 @@ AC_DEFUN([gcc_GAS_FLAGS], [AC_CACHE_CHECK([assembler flags], gcc_cv_as_flags, [ case "$target" in i[]86-*-linux*) - dnl Always pass --32 to ia32 Linux assembler. - gcc_cv_as_flags="--32" + dnl Override the default, which may be incompatible. + gcc_cv_as_flags=--32 + ;; + x86_64-*-linux-gnux32) + dnl Override the default, which may be incompatible. + gcc_cv_as_flags=--x32 + ;; + x86_64-*-linux*) + dnl Override the default, which may be incompatible. + gcc_cv_as_flags=--64 ;; powerpc*-*-darwin*) dnl Always pass -arch ppc to assembler. Grüße, Thomas
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