Commit 8f243af42ade ("sections: fix const sections for crc32 table")
removed the compile-time generated crc32 tables from the RO sections,
because it conflicts with the definition of __cacheline_aligned
which puts all such aligned data into .data..cacheline_aligned section
optimized for wasting less space, and can cause alignment issues when
used in combination with const with some gcc versions like 4.7.0 due
to a gcc bug [1].Given that most gcc versions should have the fix by now, we can just use ____cacheline_aligned, which only aligns the data but doesn't move it into specific sections as opposed to __cacheline_aligned. In case of gcc versions having the mentioned bug, the alignment attribute will have no effect, but the data will still be made RO. After patch tables are in RO: $ nm -v lib/crc32.o | grep -1 -E "crc32c?table" 0000000000000000 t arch_local_irq_enable 0000000000000000 r crc32ctable_le 0000000000000000 t crc32_exit -- 0000000000000960 t test_buf 0000000000002000 r crc32table_be 0000000000004000 r crc32table_le 000000001d1056e5 A __crc_crc32_be [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=52181 Signed-off-by: Daniel Borkmann <dbork...@redhat.com> Cc: Joe Mario <jma...@redhat.com> --- v1 -> v2: - Removed gcc test case. lib/gen_crc32table.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/lib/gen_crc32table.c b/lib/gen_crc32table.c index 71fcfcd..d83a372 100644 --- a/lib/gen_crc32table.c +++ b/lib/gen_crc32table.c @@ -109,7 +109,7 @@ int main(int argc, char** argv) if (CRC_LE_BITS > 1) { crc32init_le(); - printf("static u32 __cacheline_aligned " + printf("static const u32 ____cacheline_aligned " "crc32table_le[%d][%d] = {", LE_TABLE_ROWS, LE_TABLE_SIZE); output_table(crc32table_le, LE_TABLE_ROWS, @@ -119,7 +119,7 @@ int main(int argc, char** argv) if (CRC_BE_BITS > 1) { crc32init_be(); - printf("static u32 __cacheline_aligned " + printf("static const u32 ____cacheline_aligned " "crc32table_be[%d][%d] = {", BE_TABLE_ROWS, BE_TABLE_SIZE); output_table(crc32table_be, LE_TABLE_ROWS, @@ -128,7 +128,7 @@ int main(int argc, char** argv) } if (CRC_LE_BITS > 1) { crc32cinit_le(); - printf("static u32 __cacheline_aligned " + printf("static const u32 ____cacheline_aligned " "crc32ctable_le[%d][%d] = {", LE_TABLE_ROWS, LE_TABLE_SIZE); output_table(crc32ctable_le, LE_TABLE_ROWS, -- 1.7.11.7 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
