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Re: AARCH64 configure check for gas -mabi support

From: Yufeng Zhang
Subject: Re: AARCH64 configure check for gas -mabi support
Date: Fri, 06 Dec 2013 16:18:08 +0000
User-agent: Mozilla/5.0 (X11; Linux i686 on x86_64; rv:8.0) Gecko/20111105 Thunderbird/8.0

Hi Kugan,

Thanks for working on this issue.

On 12/04/13 21:03, Kugan wrote:

gcc trunk aarch64 bootstrapping fails with gas version 2.23.2 (with
error message similar to cannot compute suffix of object files) as this
particular version does not support -mabi=lp64. It succeeds with later
versions of gas that supports -mabi.

The -mabi option was introduced to gas when the support for ILP32 was added. Initially the options were named -milp32 and -mlp64:

and later on they were change to -mabi=ilp32 and -mabi=lp64 for consistency with those in the aarch64 gcc:

The following gcc patch made the driver use the explicit option to drive gas:

It is a neglect of the backward compatibility with binutils 2.23.

Attached patch add checking for -mabi=lp64 and prompts upgradation. Is
this Ok?

I think instead of mandating the support for the -mabi option, the compiler shall be changed able to work with binutils 2.23. The 2.23 binutils have a good support for aarch64 and the main difference from 2.24 is the ILP32 support. I think it is necessary to maintain the backward compatibility, and it should be achieved by suppressing the compiler's support for ILP32 when the -mabi option is not found available in gas during the configuration time.

I had a quick look at areas need to be updated:

* multilib support

In gcc/config.gcc, the default and the only accepted value for --with-multilib-list and --with-abi shall be lp64 when -mabi is not available.

* -mabi option

I suggest we keep the -mabi option, but reject -mabi=ilp32 in gcc/config/aarch64/aarch64.c:aarch64_override_options ()

* driver spec

In gcc/config/aarch64/aarch64-elf.h, the DRIVER_SELF_SPECS and ASM_SPEC shall be updated to not pass/specify -mabi for gas.

* documentation

I think it needs to be mentioned in gcc/doc/install.texi the constraint of using pre-2.24 binutils with aarch64 gcc that is 4.9 or later.

It is a quick scouting, but hopefully it has provided provide some guidance. If you need more help, just let me know.


P.s. some minor comments on the attached patch.

diff --git a/gcc/configure b/gcc/configure
index fdf0cd0..17b6e85 100755
--- a/gcc/configure
+++ b/gcc/configure

Diff result of auto-generation is usually excluded from a patch.

diff --git a/gcc/ b/gcc/
index 91a22d5..730ada0 100644
--- a/gcc/
+++ b/gcc/
@@ -3532,6 +3532,15 @@ case "$target" in
                [Define if your assembler supports the -no-mul-bug-abort 

+ aarch64-*-*)


+    gcc_GAS_CHECK_FEATURE([-mabi option],
+      gcc_cv_as_aarch64_mabi,,
+      [-mabi=lp64], [.text],,,)
+    if test x$gcc_cv_as_aarch64_mabi = xno; then
+       AC_MSG_ERROR([Assembler support for -mabi=lp64 is required. Upgrade the 
+    fi
+    ;;
      gcc_GAS_CHECK_FEATURE([.register], gcc_cv_as_sparc_register_op,,,
        [.register %g2, #scratch],,

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