Re: [PATCH for-4.15 v2] xen: Bump the minimum version of GCC supported to 4.9 for arm32 and 5.1 on arm64

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi Julien,

> On 13 Mar 2021, at 13:41, Julien Grall <julien@xxxxxxx> wrote:
> 
> From: Julien Grall <jgrall@xxxxxxxxxx>
> 
> Compilers older than 4.8 have known codegen issues which can lead to
> silent miscompilation:
> 
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145
> 
> Furthermore, pre-4.9 GCC have known bugs (including things like
> internal compiler errors on Arm) which would require workaround (I
> haven't checked if we have any in Xen).
> 
> The minimum version of GCC to build the hypervisor on arm is now
> raised to 4.9.
> 
> In addition to that, on arm64, GCC version >= 4.9 and < 5.1 have been
> shown to emit memory references beyond the stack pointer, resulting in
> memory corruption if an interrupt is taken after the stack pointer has
> been adjusted but before the reference has been executed.
> 
> Therefore, the minimum for arm64 is raised to 5.1.
> 
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>

Cheers
Bertrand


> 
> ---
> 
> This patch is candidate to 4.15 and backport.
> 
> This is only a build change and will be low-risk for anyone using newer
> compiler (5.1+ for arm64 and 4.9+ for arm32). Xen will stop building
> for anyone using older compiler. But it is better than fighting
> with codegen issues.
> 
> Changes in v2:
>    - Only bump the GCC version for Arm.
> ---
> README                     |  7 +++++--
> xen/include/xen/compiler.h | 10 ++++++++++
> 2 files changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/README b/README
> index 8c99c30986c1..aa8b4fe126a8 100644
> --- a/README
> +++ b/README
> @@ -42,8 +42,11 @@ provided by your OS distributor:
>         - GNU Binutils 2.16.91.0.5 or later
>         or
>         - Clang/LLVM 3.5 or later
> -      - For ARM:
> -        - GCC 4.8 or later
> +      - For ARM 32-bit:
> +        - GCC 4.9 or later
> +        - GNU Binutils 2.24 or later
> +      - For ARM 64-bit:
> +        - GCC 5.1 or later
>         - GNU Binutils 2.24 or later
>     * Development install of zlib (e.g., zlib-dev)
>     * Development install of Python 2.6 or later (e.g., python-dev)
> diff --git a/xen/include/xen/compiler.h b/xen/include/xen/compiler.h
> index 0ec0b4698ea7..17cf00e1ec92 100644
> --- a/xen/include/xen/compiler.h
> +++ b/xen/include/xen/compiler.h
> @@ -3,6 +3,16 @@
> 
> #if !defined(__GNUC__) || (__GNUC__ < 4)
> #error Sorry, your compiler is too old/not recognized.
> +#elif CONFIG_CC_IS_GCC
> +# if defined(CONFIG_ARM_32) && CONFIG_GCC_VERSION < 40900
> +#  error Sorry, your version of GCC is too old - please use 4.9 or newer.
> +# elif defined(CONFIG_ARM_64) && CONFIG_GCC_VERSION < 50100
> +/*
> + * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63293
> + * https://lore.kernel.org/r/20210107111841.GN1551@xxxxxxxxxxxxxxxxxxxxx
> + */
> +#  error Sorry, your version of GCC is too old - please use 5.1 or newer.
> +# endif
> #endif
> 
> #define barrier()     __asm__ __volatile__("": : :"memory")
> -- 
> 2.17.1
>