From: Tom Lane <tgl@sss.pgh.pa.us>
To: YunQiang Su <wzssyqa@gmail.com>
cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #15844: MIPS: remove .set mips2 in s_lock.h to fix r6 build
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Comments: In-reply-to YunQiang Su <wzssyqa@gmail.com>
	message dated "Sun, 16 Jun 2019 11:52:54 +0800"
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Date: Sun, 16 Jun 2019 00:28:02 -0400
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YunQiang Su <wzssyqa@gmail.com> writes:
> Tom Lane <tgl@sss.pgh.pa.us> =E4=BA=8E2019=E5=B9=B46=E6=9C=8816=E6=97=A5=
=E5=91=A8=E6=97=A5 =E4=B8=8A=E5=8D=8811:32=E5=86=99=E9=81=93=EF=BC=9A
>> experimentation that NetBSD as of 7.0.2 doesn't default to assuming

> I have no idea about NetBSD. Can you run gcc -v on it?

$ gcc -v
Using built-in specs.
COLLECT_GCC=3Dgcc
COLLECT_LTO_WRAPPER=3D/usr/libexec/lto-wrapper
Target: mipsel--netbsd
Configured with: /usr/7/src/tools/gcc/../../external/gpl3/gcc/dist/configu=
re --target=3Dmipsel--netbsd --enable-long-long --enable-threads --with-bu=
gurl=3Dhttp://www.NetBSD.org/Misc/send-pr.html --with-pkgversion=3D'NetBSD=
 nb2 20150115' --with-system-zlib --enable-__cxa_atexit --enable-libstdcxx=
-threads --enable-libstdcxx-time=3Drt --enable-lto --with-mpc-lib=3D/var/o=
bj/mknative/pmax-mipsel/usr/7/src/external/lgpl3/mpc/lib/libmpc --with-mpf=
r-lib=3D/var/obj/mknative/pmax-mipsel/usr/7/src/external/lgpl3/mpfr/lib/li=
bmpfr --with-gmp-lib=3D/var/obj/mknative/pmax-mipsel/usr/7/src/external/lg=
pl3/gmp/lib/libgmp --with-mpc-include=3D/usr/7/src/external/lgpl3/mpc/dist=
/src --with-mpfr-include=3D/usr/7/src/external/lgpl3/mpfr/dist/src --with-=
gmp-include=3D/usr/7/src/external/lgpl3/gmp/lib/libgmp/arch/mipsel --enabl=
e-tls --disable-multilib --disable-symvers --disable-libstdcxx-pch --build=
=3Dx86_64-unknown-netbsd6.0. --host=3Dmipsel--netbsd --with-sysroot=3D/var=
/obj/mknative/pmax-mipsel/usr/7/src/destdir.pmax
Thread model: posix
gcc version 4.8.4 (nb2 20150115) =


I found that specifying -march=3Dmips2 gets it to accept the s_lock.h
code without ".set mips2".  Given that we don't make any pretense of
actually running on MIPS-I hardware, I wonder if some hack involving
forcing -march would be sane?  You'd get better code quality across
the board, presumably.

Also, checking the predefined symbols on this gcc, I don't see
anything about __mips_isa_rev, but I do see that "__mips" is defined
and -march=3Dmips2 changes it from "1" to "2".  So I'm wondering about
some test along the lines of

#if __mips_isa_rev > 0 || __mips =3D=3D 1
#define FORCE_MIPS2_ARCHITECTURE
#endif

or alternatively, teach configure to force -march=3Dmips2 if it sees
that "__mips" is predefined as 1.

(BTW, have you got any recommendations for booting recent Debian/MIPS
under qemu?  I can't get anything newer than wheezy to work.)

			regards, tom lane