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Re: [PATCH] x86: make hypervisor build with gcc11
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Date: Thu, 27 May 2021 10:48:16 +0200
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- Cc: "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, "Andrew Cooper" <andrew.cooper3@xxxxxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, "Stefano Stabellini" <sstabellini@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>
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On Wed, May 19, 2021 at 05:39:50PM +0200, Jan Beulich wrote:
> Gcc 11 looks to make incorrect assumptions about valid ranges that
> pointers may be used for addressing when they are derived from e.g. a
> plain constant. See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100680.
>
> Utilize RELOC_HIDE() to work around the issue, which for x86 manifests
> in at least
> - mpparse.c:efi_check_config(),
> - tboot.c:tboot_probe(),
> - tboot.c:tboot_gen_frametable_integrity(),
> - x86_emulate.c:x86_emulate() (at -O2 only).
> The last case is particularly odd not just because it only triggers at
> higher optimization levels, but also because it only affects one of at
> least three similar constructs. Various "note" diagnostics claim the
> valid index range to be [0, 2⁶³-1].
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
This is all quite ugly, but I don't have any recommendation short of
getting gcc fixed (or being able to disable those heuristics).
>
> --- a/tools/tests/x86_emulator/x86-emulate.c
> +++ b/tools/tests/x86_emulator/x86-emulate.c
> @@ -8,6 +8,13 @@
>
> #define ERR_PTR(val) NULL
>
> +/* See gcc bug 100680, but here don't bother making this version dependent.
> */
Might be worth also referencing 99578 which seems to be the parent
bug? (as 100680 has been closed as a duplicate)
Thanks, Roger.
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