Re: Linux 6.2-rc2

Ard Biesheuvel
2023-01-03T10:59:21Z

On Tue, 3 Jan 2023 at 03:13, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Mon, Jan 2, 2023 at 5:45 PM Guenter Roeck <linux@roeck-us.net> wrote:
> >
> > ... and reverting commit 99cb0d917ff indeed fixes the problem.
>
> Hmm. My gut feel is that this just exposes some bug in binutils.
>
> That said, maybe that commit should not have added its own /DISCARDS/
> thing, and instead just added that "*(.note.GNU-stack)" to the general
> /DISCARDS/ thing that is defined by the
>
> #define DISCARDS ..
>
> a little bit later, so that we only end up with one single DISCARD
> list. Something like this (broken patch on purpose):
>
> --- a/include/asm-generic/vmlinux.lds.h
> +++ b/include/asm-generic/vmlinux.lds.h
> @@ -897,5 +897,4 @@
> */
> #define NOTES \
> - /DISCARD/ : { *(.note.GNU-stack) } \
> .notes : AT(ADDR(.notes) - LOAD_OFFSET) { \
> BOUNDED_SECTION_BY(.note.*, _notes) \
> @@ -1016,4 +1015,5 @@
> #define DISCARDS \
> /DISCARD/ : { \
> + *(.note.GNU-stack) \
> EXIT_DISCARDS \
> EXIT_CALL \
>
> But maybe that DISCARDS macrop ends up being used too late?
>

Masahiro's v1 did something like this, and it caused an issue on
RISC-V, which is why we ended up with this approach instead.

> It really shouldn't matter, but here we are, with a build problem with
> some random old binutils on an odd platform..
>

AIUI, the way ld.bfd used to combine output sections may also affect
the /DISCARD/ pseudo-section, and so introducing it much earlier
results in these discards to be interpreted in a different order.

The purpose of this change is to prevent .note.GNU-stack from deciding
the section type of the .notes output section, and so keeping it in
its own section should be sufficient. E.g.,

--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -896,7 +896,7 @@
* Otherwise, the type of .notes section would become PROGBITS
instead of NOTES.
*/
#define NOTES \
- /DISCARD/ : { *(.note.GNU-stack) } \
+ .note.GNU-stack : { *(.note.GNU-stack) } \
.notes : AT(ADDR(.notes) - LOAD_OFFSET) { \
BOUNDED_SECTION_BY(.note.*, _notes) \
} NOTES_HEADERS \

The .note.GNU-stack has zero size, so the result should be the same.