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Re: [PATCH v3 1/5] xen: define ACPI and DT device info sections macros


  • To: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Wed, 25 Sep 2024 10:36:25 +0200
  • Autocrypt: addr=jbeulich@xxxxxxxx; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL
  • Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
  • Delivery-date: Wed, 25 Sep 2024 08:36:36 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 24.09.2024 18:42, Oleksii Kurochko wrote:
> --- a/xen/include/xen/xen.lds.h
> +++ b/xen/include/xen/xen.lds.h
> @@ -114,6 +114,11 @@
>  
>  /* List of constructs other than *_SECTIONS in alphabetical order. */
>  
> +#define ADEV_INFO     \
> +      _asdevice = .;  \
> +      *(.adev.info)   \
> +      _aedevice = .;
> +
>  #define BUGFRAMES                               \
>      __start_bug_frames_0 = .;                   \
>      *(.bug_frames.0)                            \
> @@ -131,6 +136,11 @@
>      *(.bug_frames.3)                            \
>      __stop_bug_frames_3 = .;
>  
> +#define DT_DEV_INFO \
> +      _sdevice = .; \
> +      *(.dev.info)  \
> +      _edevice = .;

I have a question more to the Arm maintainers than to you, Oleksii: Section
names as well as the names of the symbols bounding the sections are overly
unspecific. There's nothing indicating DT at all, and it's solely 'a' to
indicate ACPI. I consider this a possible problem going forward, when this
is now being generalized.

In turn I wonder about ADEV_INFO when comparing with DT_DEV_INFO. The
latter makes clear it's DT. The former doesn't make clear it's ACPI; 'A'
could stand for about anything, including "a device" (of any kind).

Finally, Oleksii, looking at Arm's present uses - why is the abstraction
limited to the inner part of the section statements in the linker script?
IOW why isn't it all (or at least quite a bit more) of

  . = ALIGN(8);
  .dev.info : {
      _sdevice = .;
      *(.dev.info)
      _edevice = .;
  } :text

that moves into DT_DEV_INFO? I can see that the :text may want leaving
to the architectures (yet then perhaps as a macro argument). I could
also see a remote need for the ALIGN()'s value to be arch-controlled.
(Why is it uniformly 8 anyway on Arm?)

PPC's desire to use DECL_SECTION() can certainly be covered by providing
a (trivial) DECL_SECTION() also for Arm and RISC-V. Seeing that even x86
overrides the default to the trivial form for building xen.efi, I'm
inclined to suggest we should actually have a way for an arch to indicate
to xen.lds.h that it wants just the trivial form (avoiding a later
#undef).

When to be generalized I further wonder whether the ALIGN()s are actually
well placed. I'd have expected

  .dev.info ALIGN(POINTER_ALIGN) : {
      _sdevice = .;
      *(.dev.info)
      _edevice = .;
  } :text

Jan



 


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