Skip to content

Commit

Permalink
linux/export: use inline assembler to populate symbol CRCs
Browse files Browse the repository at this point in the history
Since commit 7b45371 ("kbuild: link symbol CRCs at final link,
removing CONFIG_MODULE_REL_CRCS"), the module versioning on the
(non-upstreamed-yet) kvx Linux port is broken due to unexpected padding
for __crc_* symbols. The kvx GCC adds padding so u32 gets 8-byte
alignment instead of 4.

I do not know if this happens for upstream architectures in general,
but any compiler has the freedom to insert padding for faster access.

Use the inline assembler to directly specify the wanted data layout.
This is how we previously did before the breakage.

Link: https://lore.kernel.org/lkml/20220817161438.32039-1-ysionneau@kalray.eu/
Link: https://lore.kernel.org/linux-kbuild/31ce5305-a76b-13d7-ea55-afca82c46cf2@kalray.eu/
Fixes: 7b45371 ("kbuild: link symbol CRCs at final link, removing CONFIG_MODULE_REL_CRCS")
Reported-by: Yann Sionneau <ysionneau@kalray.eu>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Tested-by: Yann Sionneau <ysionneau@kalray.eu>
  • Loading branch information
masahir0y committed Sep 28, 2022
1 parent 9ec6ab6 commit f3304ec
Showing 1 changed file with 4 additions and 2 deletions.
6 changes: 4 additions & 2 deletions include/linux/export-internal.h
Original file line number Diff line number Diff line change
Expand Up @@ -10,8 +10,10 @@
#include <linux/compiler.h>
#include <linux/types.h>

/* __used is needed to keep __crc_* for LTO */
#define SYMBOL_CRC(sym, crc, sec) \
u32 __section("___kcrctab" sec "+" #sym) __used __crc_##sym = crc
asm(".section \"___kcrctab" sec "+" #sym "\",\"a\"" "\n" \
"__crc_" #sym ":" "\n" \
".long " #crc "\n" \
".previous" "\n")

#endif /* __LINUX_EXPORT_INTERNAL_H__ */

0 comments on commit f3304ec

Please sign in to comment.