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Re: [PATCH v6] Avoid crash calling PrintErrMesg from efi_multiboot2
- To: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 18 Feb 2025 12:10:53 +0000
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- Cc: "Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>, Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 18 Feb 2025 12:11:03 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 18/02/2025 12:05 pm, Frediano Ziglio wrote:
> On Mon, Feb 17, 2025 at 4:56 PM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>> On 17.02.2025 17:52, Frediano Ziglio wrote:
>>> On Mon, Feb 17, 2025 at 4:41 PM Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
>>> wrote:
>>>> On 17/02/2025 4:31 pm, Jan Beulich wrote:
>>>>> On 17.02.2025 17:26, Frediano Ziglio wrote:
>>>>>> --- a/xen/common/efi/efi-common.mk
>>>>>> +++ b/xen/common/efi/efi-common.mk
>>>>>> @@ -2,6 +2,7 @@ EFIOBJ-y := boot.init.o pe.init.o ebmalloc.o runtime.o
>>>>>> EFIOBJ-$(CONFIG_COMPAT) += compat.o
>>>>>>
>>>>>> CFLAGS-y += -fshort-wchar
>>>>>> +CFLAGS-y += -fno-jump-tables
>>>>>> CFLAGS-y += -iquote $(srctree)/common/efi
>>>>>> CFLAGS-y += -iquote $(srcdir)
>>>>> Do source files other than boot.c really need this? Do any other files
>>>>> outside
>>>>> of efi/ maybe also need this (iirc this point was made along with the v5
>>>>> comment
>>>>> you got)?
>>>> Every TU reachable from efi_multiboot2() needs this, because all of
>>>> those have logic executed at an incorrect virtual address.
>>>>
>>>> ~Andrew
>>> I assume all the files in efi directory will deal with EFI boot so
>>> it's good to have the option enabled for the files inside the
>>> directory. The only exception seems runtime.c file.
>> And compat.c, being a wrapper around runtime.c.
>>
>>> About external dependencies not sure how to detect them (beside
>>> looking at all symbols).
>> Which raises the question whether we don't need to turn on that option
>> globally, without (as we have it now) any condition.
>>
>> Jan
> Are you saying enabling that option for all Xen? That potentially
> would decrease performances, we have a lot of switches in the code.
-fno-switch-tables is active by default whenever INDIRECT_THUNK is
enabled, and when CET-IBT is enabled to work around a GCC bug/misfeature.
With speculation protections active, indirect branches are *far* slower
than alternative ways of expressing a switch statement.
~Andrew
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