From ed13fc33f763035a7c290f11c7111877c3a5daab Mon Sep 17 00:00:00 2001 From: Matthias Maennich Date: Fri, 6 Sep 2019 11:32:26 +0100 Subject: [PATCH] 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 Signed-off-by: Martijn Coenen Reviewed-by: Greg Kroah-Hartman Signed-off-by: Matthias Maennich Signed-off-by: Jessica Yu --- arch/m68k/include/asm/export.h | 1 - include/asm-generic/export.h | 12 +++++------- include/linux/export.h | 3 ++- 3 files changed, 7 insertions(+), 9 deletions(-) diff --git a/arch/m68k/include/asm/export.h b/arch/m68k/include/asm/export.h index 0af20f48bd07..b53008b67ce1 100644 --- a/arch/m68k/include/asm/export.h +++ b/arch/m68k/include/asm/export.h @@ -1,3 +1,2 @@ -#define KSYM_ALIGN 2 #define KCRC_ALIGN 2 #include diff --git a/include/asm-generic/export.h b/include/asm-generic/export.h index 294d6ae785d4..63f54907317b 100644 --- a/include/asm-generic/export.h +++ b/include/asm-generic/export.h @@ -4,14 +4,12 @@ #ifndef KSYM_FUNC #define KSYM_FUNC(x) x #endif -#ifdef CONFIG_64BIT -#ifndef KSYM_ALIGN -#define KSYM_ALIGN 8 -#endif -#else -#ifndef KSYM_ALIGN +#ifdef CONFIG_HAVE_ARCH_PREL32_RELOCATIONS +#define KSYM_ALIGN 4 +#elif defined(CONFIG_64BIT) +#define KSYM_ALIGN 8 +#else #define KSYM_ALIGN 4 -#endif #endif #ifndef KCRC_ALIGN #define KCRC_ALIGN 4 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 {