(cc Arnd) On Thu, 25 Aug 2022 at 14:21, 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? > Never mind, i see the other thread as well. Exec summary: out-of-tree port for kvx architecture appears to impose 8 byte alignment for u32 types in some cases. > > > >> 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. > > 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. > u32 is a Linux type, and Linux expects natural alignment (and padding). So if your toolchain/architecture violates this rule, I suggest you typedef u32 to 'unsigned int __aligned(4)' explicitly. so that things don't break in other places. However, even then, I am highly skeptical. This really seems like an issue in your toolchain that could cause problems all over the place. > 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. > You are addressing one of many potential issues that could be caused by this, so I don't think this patch is a good idea tbh. > > > > > >> __crc_##sym = crc > >> #endif /* __LINUX_EXPORT_INTERNAL_H__ */ > >> > >> -- > >> 2.37.2 > > Thanks for your review :) > > -- > > Yann > > > > >
