Re: [PATCH] jump_label: align jump_entry table to at least 4-bytes
From: David Daney <hidden>
Date: 2017-02-27 18:58:06
Also in:
linux-arm-kernel, linux-mips, lkml
On 02/27/2017 10:49 AM, Jason Baron wrote:
The core jump_label code makes use of the 2 lower bits of the static_key::[type|entries|next] field. Thus, ensure that the jump_entry table is at least 4-byte aligned.
[...]
quoted hunk ↗ jump to hunk
diff --git a/arch/mips/include/asm/jump_label.h b/arch/mips/include/asm/jump_label.h index e77672539e8e..243791f3ae71 100644 --- a/arch/mips/include/asm/jump_label.h +++ b/arch/mips/include/asm/jump_label.h@@ -31,6 +31,7 @@ static __always_inline bool arch_static_branch(struct static_key *key, bool bran asm_volatile_goto("1:\t" NOP_INSN "\n\t" "nop\n\t" ".pushsection __jump_table, \"aw\"\n\t" + ".balign 4\n\t" WORD_INSN " 1b, %l[l_yes], %0\n\t" ".popsection\n\t" : : "i" (&((char *)key)[branch]) : : l_yes);@@ -45,6 +46,7 @@ static __always_inline bool arch_static_branch_jump(struct static_key *key, bool asm_volatile_goto("1:\tj %l[l_yes]\n\t" "nop\n\t" ".pushsection __jump_table, \"aw\"\n\t" + ".balign 4\n\t" WORD_INSN " 1b, %l[l_yes], %0\n\t" ".popsection\n\t" : : "i" (&((char *)key)[branch]) : : l_yes);
I will speak only for the MIPS part. If the section is not already properly aligned, this change will add padding, which is probably not what we want. Have you ever seen a problem with misalignment in the real world? If so, I think a better approach might be to set properties on the __jump_table section to force the proper alignment, or do something in the linker script. David Daney