linux-kernel - Re: [PATCH v4] MIPS: Truncate link address into 32bit for 32bit kernel

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Date:   Mon, 13 Apr 2020 21:08:46 +0100 (BST)
From:   "Maciej W. Rozycki" <macro@...ux-mips.org>
To:     Fangrui Song <maskray@...gle.com>
cc:     Jiaxun Yang <jiaxun.yang@...goat.com>, linux-mips@...r.kernel.org,
        clang-built-linux@...glegroups.com,
        Nathan Chancellor <natechancellor@...il.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Borislav Petkov <bp@...e.de>,
        Kees Cook <keescook@...omium.org>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] MIPS: Truncate link address into 32bit for 32bit
 kernel

On Mon, 13 Apr 2020, Fangrui Song wrote:

> >> > diff --git a/arch/mips/kernel/vmlinux.lds.S
> >> > b/arch/mips/kernel/vmlinux.lds.S index a5f00ec73ea6..5226cd8e4bee
> >> > 100644 --- a/arch/mips/kernel/vmlinux.lds.S
> >> > +++ b/arch/mips/kernel/vmlinux.lds.S
> >> > @@ -55,7 +55,7 @@ SECTIONS
> >> >   /* . = 0xa800000000300000; */
> >> >   . = 0xffffffff80300000;
> >> > #endif
> >> > -	. = VMLINUX_LOAD_ADDRESS;
> >> > +	. = VMLINUX_LINK_ADDRESS;
> >>
> >> The CONFIG_BOOT_ELF64 cruft right above it looks interesting to me,
> >> never have ever been used.  We have had the current arrangement since:
> >
> >It confused me either.
> >It's only used by SGI so probably it's time to rename it as
> >BOOT_SEG_ELF64.
> >
> >Wish someone could clarify what is it.
> >
> >Thanks.
> 
> Agreed that -Ttext in
> 
> arch/mips/boot/compressed/Makefile
> 100:      cmd_zld = $(LD) $(KBUILD_LDFLAGS) -Ttext $(VMLINUZ_LOAD_ADDRESS) -T
> $< $(vmlinuzobjs-y) -o $@
> 
> and a few other places are brittle. They need to be replaced with Output
> Section Address:
> (https://sourceware.org/binutils/docs/ld/Output-Section-Address.html
> https://github.com/llvm/llvm-project/blob/master/lld/docs/ELF/linker_script.rst#output-section-address)
> 
> -Ttext changes the address of .text . This can lead to the change of the
> address of the text segment (RX), but this is not guaranteed (many
> sections can be placed before .text and they are not affected).

 That is unrelated, but you're free to clean it up of course.

  Maciej