Re: [Xen-devel] [PATCH v6 09/15] x86: add multiboot2 protocol support for EFI platforms

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

On Mon, Sep 19, 2016 at 06:29:55AM -0600, Jan Beulich wrote:
> >>> On 12.09.16 at 22:18, <daniel.kiper@xxxxxxxxxx> wrote:
> > --- a/xen/arch/x86/efi/stub.c
> > +++ b/xen/arch/x86/efi/stub.c
> > @@ -3,6 +3,43 @@
> >  #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)
>
> Long line.
>
> > +{
> > +    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 is not
> > +     * directly supported by C compiler and/or linker.
>
> So how can lack of calling convention support be due to missing
> functionality in the linker? Please avoid such misleading comments:
> Linker capabilities get probed solely for PE32+ output format
> support. With the linker part dropped here,

The problem here is that we are not able to tell why stub.c is build.
There is a chance that C compiler does not support MS x64 calling
convention or linker is not able to emit PE32+ output or both. So,
I think that we should say so. However, I can agree that comment
can be improved.

Daniel

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