linux-hardening - Re: mainline build failure of powerpc allmodconfig for prom_init

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Message-ID: <CADVatmO9XzFnX+N0TuOtr0FYyxKr1oe5RAhCEJjmnvjteT5QNw@mail.gmail.com>
Date:   Sun, 17 Jul 2022 10:12:42 +0100
From:   Sudip Mukherjee <sudipm.mukherjee@...il.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Kees Cook <keescook@...omium.org>
Cc:     linuxppc-dev@...ts.ozlabs.org,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-hardening@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: mainline build failure of powerpc allmodconfig for prom_init_check

On Thu, Jul 14, 2022 at 9:55 AM Sudip Mukherjee (Codethink)
<sudipm.mukherjee@...il.com> wrote:
>
> Hi All,
>
> Not sure if it has been reported before but the latest mainline kernel
> branch fails to build for powerpc allmodconfig with gcc-12 and the error is:
>
> Error: External symbol 'memset' referenced from prom_init.c
> make[2]: *** [arch/powerpc/kernel/Makefile:204: arch/powerpc/kernel/prom_init_check] Error 1

I was trying to check it. With gcc-11 the assembly code generated is
not using memset, but using __memset.
But with gcc-12, I can see the assembly code is using memset. One
example from the assembly:

call_prom:
        .quad   .call_prom,.TOC.@...base,0
        .previous
        .size   call_prom,24
        .type   .call_prom,@function
.call_prom:
        mflr 0           #,
        std 29,-24(1)    #,
        std 30,-16(1)    #,
        std 31,-8(1)     #,
        mr 29,3          # tmp166, service
        mr 31,4          # nargs, tmp167
        mr 30,5          # tmp168, nret
 # arch/powerpc/kernel/prom_init.c:396:         struct prom_args args;
        li 4,254                 #,
        li 5,52          #,
 # arch/powerpc/kernel/prom_init.c:394: {
        std 0,16(1)      #,
        stdu 1,-208(1)   #,,
 # arch/powerpc/kernel/prom_init.c:396:         struct prom_args args;
        addi 3,1,112     # tmp174,,
 # arch/powerpc/kernel/prom_init.c:394: {
        std 9,304(1)     #,
        std 10,312(1)    #,
        std 6,280(1)     #,
        std 7,288(1)     #,
        std 8,296(1)     #,
 # arch/powerpc/kernel/prom_init.c:396:         struct prom_args args;
        bl .memset       #
        nop
        rldicl 9,31,0,32         # nargs, nargs
        addi 9,9,1       # tmp163, nargs,
        mtctr 9          # tmp163, tmp163



-- 
Regards
Sudip