On Thu, Jan 19, 2017 at 10:33:04PM +0100, Denys Vlasenko wrote: > 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.<object_name>" 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 <dvlasenk@xxxxxxxxxx> Patch applied. Thanks. -- Email: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> Home Page: http://gondor.apana.org.au/~herbert/ PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
