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

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Sat, 6 Mar 2021, Julien Grall 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 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>

For the ARM part:

Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>


> ---
> 
> I don't have a strong opinion on the minimum version for GCC on x86.
> So this is following Andrew's suggestion and the minimum from Linux.
> 
> 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 everyone else). Xen will stop
> building for anyone using older compiler. But it is better than fighting
> with codegen issues.
> ---
>  README                     |  9 ++++++---
>  xen/include/xen/compiler.h | 13 +++++++++++++
>  2 files changed, 19 insertions(+), 3 deletions(-)
> 
> diff --git a/README b/README
> index 8c99c30986c1..5c32c03f2ea1 100644
> --- a/README
> +++ b/README
> @@ -38,12 +38,15 @@ provided by your OS distributor:
>      * GNU Make v3.80 or later
>      * C compiler and linker:
>        - For x86:
> -        - GCC 4.1.2_20070115 or later
> +        - GCC 4.9 or later
>          - 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..46779660cc8f 100644
> --- a/xen/include/xen/compiler.h
> +++ b/xen/include/xen/compiler.h
> @@ -5,6 +5,19 @@
>  #error Sorry, your compiler is too old/not recognized.
>  #endif
>  
> +#if CONFIG_CC_IS_GCC
> +# if CONFIG_GCC_VERSION < 40900
> +/* https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145 */
> +#  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")
>  
>  #define likely(x)     __builtin_expect(!!(x),1)