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Re: GCCFLAGS for gcc 3.3.x (-march and _MIPS_ISA)

To: linux-mips@linux-mips.org
Subject: Re: GCCFLAGS for gcc 3.3.x (-march and _MIPS_ISA)
From: Kumba <kumba@gentoo.org>
Date: Tue, 12 Aug 2003 02:49:48 -0400
In-reply-to: <20030812.152654.74756131.nemoto@toshiba-tops.co.jp>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20030812.152654.74756131.nemoto@toshiba-tops.co.jp>
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Atsushi Nemoto wrote:

I'm trying to compile kernel with gcc 3.3.1 and binutils 2.14.  I
found this report on this ML:


On Tue, 13 May 2003 13:33:16 +0200, Guido Guenther <agx@sigxcpu.org> said:

Guido> Just for completeness: I had to use:
Guido>  GCCFLAGS += -mabi=32 -march=r4600 -mtune=r4600 -Wa,--trap
Guido> to make gcc-3.3 happy (note the 32 instead of o32). gcc-3.2
Guido> doesn't seem to handle these options correctly at all.

It can compile the kernel, but handle_adel_int (and handle_ades_int)
contain wrong codes.

8002630c <handle_adel_int> 40284000       dmfc0   t0,$8
80026310 <handle_adel_int+0x4> 00000000   nop
80026314 <handle_adel_int+0x8> ffa800a4   sd      t0,164(sp)

The source code for this instructions are:

#define __BUILD_clear_ade(exception)                                    \
                .set    reorder;                                        \
                MFC0    t0,CP0_BADVADDR;                                \
                .set    noreorder;                                      \
                REG_S   t0,PT_BVADDR(sp);                               \
                KMODE

The macro MFC0 and REG_S are defined asm.h and depend on _MIPS_ISA.

#if (_MIPS_ISA == _MIPS_ISA_MIPS1) || (_MIPS_ISA == _MIPS_ISA_MIPS2) || \
    (_MIPS_ISA == _MIPS_ISA_MIPS32)
#define MFC0            mfc0
#define MTC0            mtc0
#endif
#if (_MIPS_ISA == _MIPS_ISA_MIPS3) || (_MIPS_ISA == _MIPS_ISA_MIPS4) || \
    (_MIPS_ISA == _MIPS_ISA_MIPS5) || (_MIPS_ISA == _MIPS_ISA_MIPS64)
#define MFC0            dmfc0
#define MTC0            dmtc0
#endif

The option -march=r4600 seems to make gcc 3.3.x choose MIPS_ISA_MIPS3.

So, the right options is:

        GCCFLAGS += -mabi=32 -march=mips2 -mtune=r4600 -Wa,--trap
(or     GCCFLAGS += $(call check_gcc, -mcpu=r4600 -mips2, -mabi=32 -march=mips2 
-mtune=r4600) -Wa,--trap)

Isn't it?

---
Atsushi Nemoto


I don't claim to be an expert on all things mips yet, but If I recall correctly, the R4K processor line is a MIPS III capable processor. So -mips3 -mabi=32 should be safe for it. I've been building kernels off linux-mips.org CVS using "-mips3 -mabi=32 -Wa,--trap" in the arch/mips/Makefile, and it works great.

Several people I know using Indy's with R5000 processors use "-mips4 -mabi=32 -Wa,--trap" (cause R5K is MIPS IV). I know with gcc-3.3.x, -mipsX is just a synonym for the appropriate -march specifier, so it doesn't seem to make a different whether one uses -march or -mipsX.

I'm slowly working on building a Gentoo install using "-mips3 -mabi=32" code on my Indigo2 (Right now, it's a mix of -mips2 and -mips3 with a random -mips1 binary scattered around). Quite a fun, albeit slow, experiment.


--Kumba

--
"Such is oft the course of deeds that move the wheels of the world: small hands do them because they must, while the eyes of the great are elsewhere." --Elrond


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