Re: [PATCH v4 08/17] arm64/mm: Remove needless section quotes

Arvind Sankar
2020-06-29T21:06:23Z

On Mon, Jun 29, 2020 at 04:54:48PM -0400, Arvind Sankar wrote:
> On Mon, Jun 29, 2020 at 01:04:31PM -0700, Kees Cook wrote:
> > On Mon, Jun 29, 2020 at 12:53:47PM -0700, Nick Desaulniers wrote:
> > > On Sun, Jun 28, 2020 at 11:18 PM Kees Cook <keescook@chromium.org> wrote:
> > > >
> > > > Fix a case of needless quotes in __section(), which Clang doesn't like.
> > > >
> > > > Acked-by: Will Deacon <will@kernel.org>
> > > > Signed-off-by: Kees Cook <keescook@chromium.org>
> > >
> > > Yep, I remember bugs from this. Probably should scan the kernel for
> > > other instances of this. +Joe for checkpatch.pl validation.
> >
> > I think the others are safe because they're in macros:
>
> Why does that make it safe -- the commit msg is a bit sparse, but I
> assume the problem is that it generates
> __attribute__((__section__("\".foo\"")))
> from
> __section(".foo")
> after preprocessing, and clang keeps the quotes in the section name when
> generating assembly, while gcc appears to strip them off.
>
> It does that even if nested in another macro, no?

Yep, I can see things like:
[25] ".discard.ksym" PROGBITS 0000000000000000 0000217c
0000000000000000 0000000000000000 WA 0 0 4

Doesn't seem to cause a build error, but that can't be good.

>
> >
> > $ git grep -4 '__section("'
> > include/linux/compiler.h-# define KENTRY(sym) \
>
> Am I missing something, or is KENTRY unused in the tree?
>
> > include/linux/compiler.h- extern typeof(sym) sym; \
> > include/linux/compiler.h- static const unsigned long __kentry_##sym \
> > include/linux/compiler.h- __used \
> > include/linux/compiler.h: __section("___kentry" "+" #sym ) \
> > include/linux/compiler.h- = (unsigned long)&sym;
> > --
> > include/linux/export.h-#define __ksym_marker(sym) \
> > include/linux/export.h: static int __ksym_marker_##sym[0] __section(".discard.ksym") __used
> > --
> > include/linux/srcutree.h-# define __DEFINE_SRCU(name, is_static) \
> > include/linux/srcutree.h- is_static struct srcu_struct name; \
> > include/linux/srcutree.h- struct srcu_struct * const __srcu_struct_##name \
> > include/linux/srcutree.h: __section("___srcu_struct_ptrs") = &name
> >
> >
> > > Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
> >
> > Thanks!
> >
> > --
> > Kees Cook