linux-kernel - Re: Build regressions/improvements in v6.4-rc7

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Date:   Mon, 19 Jun 2023 11:10:38 +0200 (CEST)
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>
cc:     linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Build regressions/improvements in v6.4-rc7

On Mon, 19 Jun 2023, Geert Uytterhoeven wrote:
> JFYI, when comparing v6.4-rc7[1] to v6.4-rc6[3], the summaries are:
>  - build errors: +1/-5

   + {standard input}: Error: branch to a symbol in another ISA mode: 5023, 5028 => 5017, 5023, 5028, 5012

mips-gcc1[12]/micro32r2{,el}_defconfig

Not exactly a new problem, but we got two new of these while compiling
arch/mips/kernel/smp-cps.o, due to the addition of two gcc12 builds.

I could reproduce this with micro32r2_defconfig on next-20230691 using
gcc-12.3.0 from kernel.org crosstool.

In arch/mips/kernel/smp-cps.c:

     static void cps_init_secondary(void)
     {
 	    int core = cpu_core(&current_cpu_data);

 	    /* Disable MT - we only want to run 1 TC per VPE */
 	    if (cpu_has_mipsmt)
 		    dmt();

 	    ...
     }

"make arch/mips/kernel/smp-cps.s" shows cps_init_secondary() is compiled
with the following ISA settings:

         .set    nomips16
         .set    micromips

while arch/mips/include/asm/mipsmtregs.h has:

     static inline unsigned int dmt(void)
     {
 	    int res;

 	    __asm__ __volatile__(
 	    "       .set    push                                            \n"
 	    "       .set    mips32r2                                        \n"
 	    "       .set    noat                                            \n"
 	    "       .word   0x41610BC1                      # dmt $1        \n"
 	    "       ehb                                                     \n"
 	    "       move    %0, $1                                          \n"
 	    "       .set    pop                                             \n"
 	    : "=r" (res));

 	    instruction_hazard();

 	    return res;
     }

> [1] http://kisskb.ellerman.id.au/kisskb/branch/linus/head/45a3e24f65e90a047bef86f927ebdc4c710edaa1/ (all 160 configs)
> [3] http://kisskb.ellerman.id.au/kisskb/branch/linus/head/858fd168a95c5b9669aac8db6c14a9aeab446375/ (151 out of 160 configs)

Gr{oetje,eeting}s,

 						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
 							    -- Linus Torvalds