From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <gcc-bugzilla@gcc.gnu.org>
Received: by sourceware.org (Postfix, from userid 48)
	id AED6E385734B; Fri, 18 Aug 2023 13:31:42 +0000 (GMT)
DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org AED6E385734B
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gcc.gnu.org;
	s=default; t=1692365502;
	bh=PjVXbh17+wvu7uBUeacHRMXdY8aSebllfuvW+Vp9hH0=;
	h=From:To:Subject:Date:From;
	b=IsyCi2GKXWCMg3TIGZ11BreUDcL74JwokukE6xEkuDoKvpF0+5ZVVmu5WDJ3bGYp7
	 dKZPN+ouMYyuk4ofpefYl19lOKLV0NGzHthHBSswqNr8swje34a0XSgihTlgUlS0F8
	 MwULQtzgPcjJ/ExN8zcQ9u+kSi90yxu82kW+Z6eg=
From: "tommy_murphy at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug target/111065] New: [RISCV] t-linux-multilib specifies
 incorrect multilib reuse patterns
Date: Fri, 18 Aug 2023 13:31:42 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
X-Bugzilla-Watch-Reason: None
X-Bugzilla-Product: gcc
X-Bugzilla-Component: target
X-Bugzilla-Version: og13 (devel/omp/gcc-13)
X-Bugzilla-Keywords: 
X-Bugzilla-Severity: normal
X-Bugzilla-Who: tommy_murphy at hotmail dot com
X-Bugzilla-Status: UNCONFIRMED
X-Bugzilla-Resolution: 
X-Bugzilla-Priority: P3
X-Bugzilla-Assigned-To: unassigned at gcc dot gnu.org
X-Bugzilla-Target-Milestone: ---
X-Bugzilla-Flags: 
X-Bugzilla-Changed-Fields: bug_id short_desc product version bug_status
 bug_severity priority component assigned_to reporter target_milestone
Message-ID: <bug-111065-4@http.gcc.gnu.org/bugzilla/>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
X-Bugzilla-URL: http://gcc.gnu.org/bugzilla/
Auto-Submitted: auto-generated
MIME-Version: 1.0
List-Id: <gcc-bugs.sourceware.org>

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D111065

            Bug ID: 111065
           Summary: [RISCV] t-linux-multilib specifies incorrect multilib
                    reuse patterns
           Product: gcc
           Version: og13 (devel/omp/gcc-13)
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tommy_murphy at hotmail dot com
  Target Milestone: ---

The file gcc/config/riscv/t-linux-multilib:

*
https://github.com/gcc-mirror/gcc/blob/master/gcc/config/riscv/t-linux-mult=
ilib

specifies the RISC-V multilibs to be built when --enable-multilib is passed=
 at
configuration time:

*
https://github.com/riscv-collab/riscv-gnu-toolchain#installation-newliblinu=
x-multilib

It also specifies multilib reuse patterns. These control what (if any) mult=
ilib
is (re)used when an arch/abi is specified at compile time (using -march=3D.=
..
-mabi=3D...) for which no specific multilib exists. For example:

* rv64imafdc-lp64d-rv64imafd-

This specifies that the multilib for rv64imafdc/lp64d be built at toolchain
build time, and that it also be (re)used for the arch/abi rv64imafd/lp64d w=
hen
-march=3Drv64imafd -mabi=3Dlp64d is passed at compile time.

In this case this reuse mapping will lead to problems if the target platform
(hardware, simulator etc.) strictly supports rv64imafd/lp64d but
libraries/startup code for rv64imafdc/lp64d are linked. This is because the
latter will most likely use RISC-V compressed instructions (via the RISC-V
optional C/Compressed extension) which the rv64imafd/lp64d target will not
support and will trap on.=20

Multilib reuse mappings should always be from an arch/abi "superset" to a
"subset" of extensions. For example:

* reusing rv64imafd/lp64d for a rv64imafdc/lp64d target is OK - it just doe=
sn't
take advantage of the C (Compressed) extension
* reusing rv64imafdc/lp64d for a rv64imafd/lp64d target is not OK - the
libraries will most likely use C (Compressed) instructions which the latter
target does not support and will trap on.

According to this comment:

*
https://github.com/gcc-mirror/gcc/blob/35b5762a740d4506d7acac65d0f837564036=
2492/gcc/config/riscv/t-linux-multilib#L2C1-L3C1

This is the list of multilibs/reuse patterns specified:

* rv32imac-ilp32-rv32ima,rv32imaf,rv32imafd,rv32imafc,rv32imafdc-
* rv32imafdc-ilp32d-rv32imafd-=20
* rv64imac-lp64-rv64ima,rv64imaf,rv64imafd,rv64imafc,rv64imafdc-
* rv64imafdc-lp64d-rv64imafd-

all of which seem problematic/erroneous because they specify the reuse of
libraries with compressed instructions for arch/abi's that do not support t=
he C
(Compressed) extension.

However I am loath to submit a patch because I am not sure what the
correct/authoritative list of multilibs and reuse patterns *should be* and =
what
disturbance may be caused by changing this file.

Maybe one of the seasoned RISC-V GCC contributors might be able to comment?

Thanks.=