[PATCH 3/6] xen/efi: Make efi-boot.h compile with -Wwrite-strings

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

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.

Lie to the compiler using a union.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Julien Grall <julien@xxxxxxx>
CC: Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
CC: Bertrand Marquis <bertrand.marquis@xxxxxxx>
CC: Michal Orzel <michal.orzel@xxxxxxx>
CC: Roberto Bagnara <roberto.bagnara@xxxxxxxxxxx>
CC: Nicola Vetrini <nicola.vetrini@xxxxxxxxxxx>

I *really* don't like this, but it's the only suggestion given.
---
 xen/arch/arm/efi/efi-boot.h | 2 +-
 xen/arch/x86/efi/efi-boot.h | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/xen/arch/arm/efi/efi-boot.h b/xen/arch/arm/efi/efi-boot.h
index 1c3640bb65fd..c26bf18b68b9 100644
--- 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,
diff --git a/xen/arch/x86/efi/efi-boot.h b/xen/arch/x86/efi/efi-boot.h
index eebc54180bf7..e2d256e0517b 100644
--- 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);
 
     if ( mbi.cmdline )
-- 
2.30.2