Re: [Xen-devel] [PATCH v11 07/13] x86: add multiboot2 protocol support for EFI platforms

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 05/12/16 22:25, Daniel Kiper wrote:
> diff --git a/xen/arch/x86/efi/stub.c b/xen/arch/x86/efi/stub.c
> index 4158124..6ea6aa1 100644
> --- a/xen/arch/x86/efi/stub.c
> +++ b/xen/arch/x86/efi/stub.c
> @@ -3,6 +3,44 @@
>  #include <xen/init.h>
>  #include <xen/lib.h>
>  #include <asm/page.h>
> +#include <asm/efibind.h>
> +#include <efi/efidef.h>
> +#include <efi/eficapsule.h>
> +#include <efi/eficon.h>
> +#include <efi/efidevp.h>
> +#include <efi/efiapi.h>
> +
> +/*
> + * Here we are in EFI stub. EFI calls are not supported due to lack
> + * of relevant functionality in compiler and/or linker.
> + *
> + * efi_multiboot2() is an exception. Please look below for more details.
> + */
> +
> +paddr_t __init noreturn efi_multiboot2(EFI_HANDLE ImageHandle,
> +                                       EFI_SYSTEM_TABLE *SystemTable)
> +{
> +    CHAR16 *err = L"Xen does not have EFI code build in!!!\r\nSystem 
> halted!!!\r\n";
> +    SIMPLE_TEXT_OUTPUT_INTERFACE *StdErr;
> +
> +    StdErr = SystemTable->StdErr ? SystemTable->StdErr : SystemTable->ConOut;
> +
> +    /*
> +     * Print error message and halt the system.
> +     *
> +     * We have to open code MS x64 calling convention
> +     * in assembly because here this convention may
> +     * not be directly supported by C compiler.
> +     */
> +    asm volatile(
> +    "    call %2                      \n"

This should be `call *%2`, because otherwise gcc complains with:

stub.c: Assembler messages:
stub.c:35: Warning: indirect call without `*'

Interestingly, it isn't fatal to the build which is why I didn't spot it
earlier.  I also can't work out why it isn't fatal to the build, because
I'd have thought the -Werror should have been enough.

~Andrew

> +    "0:  hlt                          \n"
> +    "    jmp  0b                      \n"
> +       : "+c" (StdErr), "+d" (err) : "g" (StdErr->OutputString)
> +       : "rax", "r8", "r9", "r10", "r11", "memory");
> +
> +    unreachable();
> +}
>  
>  bool efi_enabled(unsigned int feature)
>  {


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