linux-kernel - Re: [PATCH -next] arm32: enable HAVE_LD_DEAD_CODE_DATA

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Message-Id: <f5326293-b446-49e5-9cc0-78c9009af136@app.fastmail.com>
Date: Thu, 22 Feb 2024 10:52:10 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Yuntao Liu" <liuyuntao12@...wei.com>,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc: "Russell King" <linux@...linux.org.uk>, "Andrew Davis" <afd@...com>,
 "Andrew Morton" <akpm@...ux-foundation.org>,
 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 "Geert Uytterhoeven" <geert+renesas@...der.be>,
 "Jonathan Corbet" <corbet@....net>, "Mike Rapoport" <rppt@...nel.org>,
 "Eric DeVolder" <eric.devolder@...cle.com>, "Rob Herring" <robh@...nel.org>,
 "Thomas Gleixner" <tglx@...utronix.de>,
 "Linus Walleij" <linus.walleij@...aro.org>
Subject: Re: [PATCH -next] arm32: enable HAVE_LD_DEAD_CODE_DATA_ELIMINATION

On Wed, Feb 21, 2024, at 16:51, Arnd Bergmann wrote:
> I have given your patch some build testing with random
> configurations in my build setup and it seems to work
> fine with gcc/binutils, but unfortunately I came across
> a link failure using clang/lld:

I ran into another bug now, this time with CONFIG_XIP_KERNEL=y:

no __ex_table in file: vmlinux
Failed to sort kernel tables
make[4]: *** [scripts/Makefile.vmlinux:37: vmlinux] Error 1

Essentially you have to modify arch/arm/kernel/vmlinux-xip.lds.S
the same way as vmlinux.lds.S:

--- a/arch/arm/kernel/vmlinux-xip.lds.S
+++ b/arch/arm/kernel/vmlinux-xip.lds.S
@@ -63,7 +63,7 @@ SECTIONS
        . = ALIGN(4);
        __ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) {
                __start___ex_table = .;
-               ARM_MMU_KEEP(*(__ex_table))
+               ARM_MMU_KEEP(KEEP(*(__ex_table)))
                __stop___ex_table = .;
        }

@@ -83,7 +83,7 @@ SECTIONS
        }
        .init.arch.info : {
                __arch_info_begin = .;
-               *(.arch.info.init)
+               KEEP(*(.arch.info.init))
                __arch_info_end = .;
        }
        .init.tagtable : {

The pv_table is not needed for XIP_KERNEL=y because that
requires not patching the kernel.

    Arnd