From e183914af00e15eb41ae666d44e323bfa154be13 Mon Sep 17 00:00:00 2001 From: Denys Vlasenko Date: Thu, 19 Jan 2017 22:33:04 +0100 Subject: crypto: x86 - make constants readonly, allow linker to merge them A lot of asm-optimized routines in arch/x86/crypto/ keep its constants in .data. This is wrong, they should be on .rodata. Mnay of these constants are the same in different modules. For example, 128-bit shuffle mask 0x000102030405060708090A0B0C0D0E0F exists in at least half a dozen places. There is a way to let linker merge them and use just one copy. The rules are as follows: mergeable objects of different sizes should not share sections. You can't put them all in one .rodata section, they will lose "mergeability". GCC puts its mergeable constants in ".rodata.cstSIZE" sections, or ".rodata.cstSIZE." if -fdata-sections is used. This patch does the same: .section .rodata.cst16.SHUF_MASK, "aM", @progbits, 16 It is important that all data in such section consists of 16-byte elements, not larger ones, and there are no implicit use of one element from another. When this is not the case, use non-mergeable section: .section .rodata[.VAR_NAME], "a", @progbits This reduces .data by ~15 kbytes: text data bss dec hex filename 11097415 2705840 2630712 16433967 fac32f vmlinux-prev.o 11112095 2690672 2630712 16433479 fac147 vmlinux.o Merged objects are visible in System.map: ffffffff81a28810 r POLY ffffffff81a28810 r POLY ffffffff81a28820 r TWOONE ffffffff81a28820 r TWOONE ffffffff81a28830 r PSHUFFLE_BYTE_FLIP_MASK <- merged regardless of ffffffff81a28830 r SHUF_MASK <------------- the name difference ffffffff81a28830 r SHUF_MASK ffffffff81a28830 r SHUF_MASK .. ffffffff81a28d00 r K512 <- merged three identical 640-byte tables ffffffff81a28d00 r K512 ffffffff81a28d00 r K512 Use of object names in section name suffixes is not strictly necessary, but might help if someday link stage will use garbage collection to eliminate unused sections (ld --gc-sections). Signed-off-by: Denys Vlasenko CC: Herbert Xu CC: Josh Poimboeuf CC: Xiaodong Liu CC: Megha Dey CC: linux-crypto@vger.kernel.org CC: x86@kernel.org CC: linux-kernel@vger.kernel.org Signed-off-by: Herbert Xu --- arch/x86/crypto/chacha20-ssse3-x86_64.S | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'arch/x86/crypto/chacha20-ssse3-x86_64.S') diff --git a/arch/x86/crypto/chacha20-ssse3-x86_64.S b/arch/x86/crypto/chacha20-ssse3-x86_64.S index 3a33124e9112..3f511a7d73b8 100644 --- a/arch/x86/crypto/chacha20-ssse3-x86_64.S +++ b/arch/x86/crypto/chacha20-ssse3-x86_64.S @@ -11,11 +11,14 @@ #include -.data +.section .rodata.cst16.ROT8, "aM", @progbits, 16 .align 16 - ROT8: .octa 0x0e0d0c0f0a09080b0605040702010003 +.section .rodata.cst16.ROT16, "aM", @progbits, 16 +.align 16 ROT16: .octa 0x0d0c0f0e09080b0a0504070601000302 +.section .rodata.cst16.CTRINC, "aM", @progbits, 16 +.align 16 CTRINC: .octa 0x00000003000000020000000100000000 .text -- cgit v1.2.3