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Message-ID: <CAK7LNARgQ0t=4dfkJXDhSzdFGbxDuN2kPGxTgDR7siCYTtGU5w@mail.gmail.com>
Date: Thu, 21 Dec 2023 22:07:54 +0900
From: Masahiro Yamada <masahiroy@...nel.org>
To: deller@...nel.org
Cc: linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
linux-modules@...r.kernel.org, linux-arch@...r.kernel.org,
Luis Chamberlain <mcgrof@...nel.org>
Subject: Re: [PATCH 3/4] vmlinux.lds.h: Fix alignment for __ksymtab*,
__kcrctab_* and .pci_fixup sections
On Thu, Nov 23, 2023 at 7:18 AM <deller@...nel.org> wrote:
>
> From: Helge Deller <deller@....de>
>
> On 64-bit architectures without CONFIG_HAVE_ARCH_PREL32_RELOCATIONS
> (e.g. ppc64, ppc64le, parisc, s390x,...) the __KSYM_REF() macro stores
> 64-bit pointers into the __ksymtab* sections.
> Make sure that the start of those sections is 64-bit aligned in the vmlinux
> executable, otherwise unaligned memory accesses may happen at runtime.
Are you solving a real problem?
1/4 already ensures the proper alignment of __ksymtab*, doesn't it?
I applied the following hack to attempt to
break the alignment intentionally.
diff --git a/include/asm-generic/vmlinux.lds.h
b/include/asm-generic/vmlinux.lds.h
index bae0fe4d499b..e2b5c9acee97 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -482,7 +482,7 @@
TRACEDATA \
\
PRINTK_INDEX \
- \
+ . = . + 1; \
/* Kernel symbol table: Normal symbols */ \
__ksymtab : AT(ADDR(__ksymtab) - LOAD_OFFSET) { \
__start___ksymtab = .; \
The __ksymtab section and __start___ksymtab symbol
are still properly aligned due to the '.balign'
in <linux/export-internal.h>
So, my understanding is this patch is unneeded.
Or, does the behaviour depend on toolchains?
> The __kcrctab* sections store 32-bit entities, so make those sections
> 32-bit aligned.
>
> The pci fixup routines want to be 64-bit aligned on 64-bit platforms
> which don't define CONFIG_HAVE_ARCH_PREL32_RELOCATIONS. An alignment
> of 8 bytes is sufficient to guarantee aligned accesses at runtime.
>
> Signed-off-by: Helge Deller <deller@....de>
> Cc: <stable@...r.kernel.org> # v6.0+
> ---
> include/asm-generic/vmlinux.lds.h | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
> index bae0fe4d499b..fa4335346e7d 100644
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -467,6 +467,7 @@
> } \
> \
> /* PCI quirks */ \
> + . = ALIGN(8); \
> .pci_fixup : AT(ADDR(.pci_fixup) - LOAD_OFFSET) { \
> BOUNDED_SECTION_PRE_LABEL(.pci_fixup_early, _pci_fixups_early, __start, __end) \
> BOUNDED_SECTION_PRE_LABEL(.pci_fixup_header, _pci_fixups_header, __start, __end) \
> @@ -484,6 +485,7 @@
> PRINTK_INDEX \
> \
> /* Kernel symbol table: Normal symbols */ \
> + . = ALIGN(8); \
> __ksymtab : AT(ADDR(__ksymtab) - LOAD_OFFSET) { \
> __start___ksymtab = .; \
> KEEP(*(SORT(___ksymtab+*))) \
> @@ -491,6 +493,7 @@
> } \
> \
> /* Kernel symbol table: GPL-only symbols */ \
> + . = ALIGN(8); \
> __ksymtab_gpl : AT(ADDR(__ksymtab_gpl) - LOAD_OFFSET) { \
> __start___ksymtab_gpl = .; \
> KEEP(*(SORT(___ksymtab_gpl+*))) \
> @@ -498,6 +501,7 @@
> } \
> \
> /* Kernel symbol table: Normal symbols */ \
> + . = ALIGN(4); \
> __kcrctab : AT(ADDR(__kcrctab) - LOAD_OFFSET) { \
> __start___kcrctab = .; \
> KEEP(*(SORT(___kcrctab+*))) \
> @@ -505,6 +509,7 @@
> } \
> \
> /* Kernel symbol table: GPL-only symbols */ \
> + . = ALIGN(4); \
> __kcrctab_gpl : AT(ADDR(__kcrctab_gpl) - LOAD_OFFSET) { \
> __start___kcrctab_gpl = .; \
> KEEP(*(SORT(___kcrctab_gpl+*))) \
> --
> 2.41.0
>
--
Best Regards
Masahiro Yamada
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