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Re: [PATCH 3/6] xen/efi: Make efi-boot.h compile with -Wwrite-strings
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Tue, 21 Nov 2023 18:03:22 +0000
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Roberto Bagnara <roberto.bagnara@xxxxxxxxxxx>, Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Tue, 21 Nov 2023 18:03:34 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 21/11/2023 8:40 am, Jan Beulich wrote:
> On 20.11.2023 23:49, Andrew Cooper wrote:
>> GCC complains:
>>
>> In file included from arch/arm/efi/boot.c:700:
>> arch/arm/efi/efi-boot.h: In function 'efi_arch_handle_cmdline':
>> arch/arm/efi/efi-boot.h:482:16: error: assignment discards 'const'
>> qualifier from pointer target type [-Werror=discarded-qualifiers]
>> 482 | name.s = "xen";
>> | ^
>>
>> There's no easy option. .rodata is really read-only, so the fact Xen doesn't
>> crash means these strings aren't written to.
> And the consuming sites confirm this being the case. Hence ...
>
>> Lie to the compiler using a union.
> ... to at least slightly limit the lying, how about ...
>
>> --- a/xen/arch/arm/efi/efi-boot.h
>> +++ b/xen/arch/arm/efi/efi-boot.h
>> @@ -479,7 +479,7 @@ static void __init efi_arch_handle_cmdline(CHAR16
>> *image_name,
>> w2s(&name);
>> }
>> else
>> - name.s = "xen";
>> + name.cs = "xen"; /* TODO, find a better way of doing this. */
>>
>> prop_len = 0;
>> prop_len += snprintf(buf + prop_len,
> ... you also switch to using name.cs down below here and ...
>
>> --- a/xen/arch/x86/efi/efi-boot.h
>> +++ b/xen/arch/x86/efi/efi-boot.h
>> @@ -324,7 +324,8 @@ static void __init efi_arch_handle_cmdline(CHAR16
>> *image_name,
>> w2s(&name);
>> }
>> else
>> - name.s = "xen";
>> + name.cs = "xen"; /* TODO, find a better way of doing this. */
>> +
>> place_string(&mbi.cmdline, name.s);
> ... here?
>
> An alternative would be to introduce 'char xen[4] = "xen";' in both
> cases, and use them instead of plain string literals.
They'd have to be static, or dynamically allocated or they'll end up out
of scope, wont they?
I have to admit I find this logic very hard to follow.
Furthermore, I note:
mbi.boot_loader_name = (long)"EFI";
which is exactly the kind of pointer which is liable to end up being
edited via kextra in the other patch.
~Andrew
|