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| author |   Matthias Maennich <maennich@google.com> | 2019-09-06 11:32:26 +0100 |
|---|---|---|
| committer |   Jessica Yu <jeyu@kernel.org> | 2019-09-10 10:30:09 +0200 |
| commit | ed13fc33f763035a7c290f11c7111877c3a5daab (patch) | |
| tree | 40cc79e8871ff027f7063ba38dd9f25790feace0 /include/linux/export.h | |
| parent | module: support reading multiple values per modinfo tag (diff) | |
| download | wireguard-linux-ed13fc33f763035a7c290f11c7111877c3a5daab.tar.xz wireguard-linux-ed13fc33f763035a7c290f11c7111877c3a5daab.zip | |
export: explicitly align struct kernel_symbol
This change allows growing struct kernel_symbol without wasting bytes to
alignment. It also concretized the alignment of ksymtab entries if
relative references are used for ksymtab entries.
struct kernel_symbol was already implicitly being aligned to the word
size, except on x86_64 and m68k, where it is aligned to 16 and 2 bytes,
respectively.
As far as I can tell there is no requirement for aligning struct
kernel_symbol to 16 bytes on x86_64, but gcc aligns structs to their
size, and the linker aligns the custom __ksymtab sections to the largest
data type contained within, so setting KSYM_ALIGN to 16 was necessary to
stay consistent with the code generated for non-ASM EXPORT_SYMBOL(). Now
that non-ASM EXPORT_SYMBOL() explicitly aligns to word size (8),
KSYM_ALIGN is no longer necessary.
In case of relative references, the alignment has been changed
accordingly to not waste space when adding new struct members.
As for m68k, struct kernel_symbol is aligned to 2 bytes even though the
structure itself is 8 bytes; using a 4-byte alignment shouldn't hurt.
I manually verified the output of the __ksymtab sections didn't change
on x86, x86_64, arm, arm64 and m68k. As expected, the section contents
didn't change, and the ELF section alignment only changed on x86_64 and
m68k. Feedback from other archs more than welcome.
Co-developed-by: Martijn Coenen <maco@android.com>
Signed-off-by: Martijn Coenen <maco@android.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Matthias Maennich <maennich@google.com>
Signed-off-by: Jessica Yu <jeyu@kernel.org>
Diffstat (limited to 'include/linux/export.h')
| -rw-r--r-- | include/linux/export.h | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/include/linux/export.h b/include/linux/export.h index fd8711ed9ac4..28a4d2150689 100644 --- a/include/linux/export.h +++ b/include/linux/export.h @@ -52,7 +52,7 @@ extern struct module __this_module; #define __KSYMTAB_ENTRY(sym, sec) \ __ADDRESSABLE(sym) \ asm(" .section \"___ksymtab" sec "+" #sym "\", \"a\" \n" \ - " .balign 8 \n" \ + " .balign 4 \n" \ "__ksymtab_" #sym ": \n" \ " .long " #sym "- . \n" \ " .long __kstrtab_" #sym "- . \n" \ @@ -66,6 +66,7 @@ struct kernel_symbol { #define __KSYMTAB_ENTRY(sym, sec) \ static const struct kernel_symbol __ksymtab_##sym \ __attribute__((section("___ksymtab" sec "+" #sym), used)) \ + __aligned(sizeof(void *)) \ = { (unsigned long)&sym, __kstrtab_##sym } struct kernel_symbol { |