On Thu, Aug 25, 2022 at 9:21 PM Yann Sionneau <ysionneau@xxxxxxxxx> wrote: > > Hello Ard, > > On 25/08/2022 14:12, Ard Biesheuvel wrote: > > On Thu, 25 Aug 2022 at 14:10, Yann Sionneau <ysionneau@xxxxxxxxx> wrote: > >> Forwarding also the actual patch to linux-kbuild and linux-arch > >> > >> -------- Forwarded Message -------- > >> Subject: [RFC PATCH 1/1] Fix __kcrctab+* sections alignment > >> Date: Wed, 17 Aug 2022 18:14:38 +0200 > >> From: Yann Sionneau <ysionneau@xxxxxxxxx> > >> To: linux-kernel@xxxxxxxxxxxxxxx > >> CC: Nicolas Schier <nicolas@xxxxxxxxx>, Masahiro Yamada > >> <masahiroy@xxxxxxxxxx>, Jules Maselbas <jmaselbas@xxxxxxxxx>, Julian > >> Vetter <jvetter@xxxxxxxxx>, Yann Sionneau <ysionneau@xxxxxxxxx> > >> > >> > >> > > What happened to the commit log? > > This is a forward of this thread: https://lkml.org/lkml/2022/8/17/868 > > Either I did something wrong with my email agent or maybe the email > containing the cover letter is taking some time to reach you? > > > > >> Signed-off-by: Yann Sionneau <ysionneau@xxxxxxxxx> > >> --- > >> include/linux/export-internal.h | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/include/linux/export-internal.h > >> b/include/linux/export-internal.h > >> index c2b1d4fd5987..d86bfbd7fa6d 100644 > >> --- a/include/linux/export-internal.h > >> +++ b/include/linux/export-internal.h > >> @@ -12,6 +12,6 @@ > >> /* __used is needed to keep __crc_* for LTO */ > >> #define SYMBOL_CRC(sym, crc, sec) \ > >> - u32 __section("___kcrctab" sec "+" #sym) __used __crc_##sym = crc > >> + u32 __section("___kcrctab" sec "+" #sym) __used __aligned(4) > > __aligned(4) is the default for u32 so this should not be needed. > > Well, I am not completely sure about that. See my cover letter, previous > mechanism for symbol CRC was actually enforcing the section alignment to > 4 bytes boundary as well. I do not think so. I do not see such alignment in for __CRC_SYMBOL() in include/linux/export.h If you are talking about KCRC_ALIGN in include/asm-generic/export.h, it is only used by *.S. Most of EXPORT_SYMBOL's are defined in *.c files, which include <linux/export.h> If I am missing something, please point me to the code. > > Also, I'm not sure it is forbidden for an architecture/compiler > implementation to actually enforce a stronger alignment on u32, which in > theory would not break anything. It seems like an interesting compiler. Does it also enforce 8 byte alignment to u8? (that is, 7-byte padding for u8 ?) > > But in this precise case it does break something since it will cause > "gaps" in the end result vmlinux binary segment. For this to work I > think we really want to enforce a 4 bytes alignment on the section. My best guess it, it was previously working for the kvm compiler because include/linux/export.h previously used an inline assembler. The kvm toolchain presumably gives natural alignment/padding to '.long' assembly directive, but enforces 8-byte to u32. -- Best Regards Masahiro Yamada
