Re: [PATCH] memory: fix build with COVERAGE but !HVM

[Wei Liu <wl@xxxxxxx>]

On Mon, Feb 01, 2021 at 05:20:54PM +0100, Jan Beulich wrote:
> Xen is heavily relying on the DCE stage to remove unused code so the
> linker doesn't throw an error because a function is not implemented
> yet we defined a prototype for it.
> 
> On some GCC versions (such as 9.4 provided by Debian sid), the compiler
> DCE stage will not manage to figure that out for
> xenmem_add_to_physmap_batch():
> 
> ld: ld: prelink.o: in function `xenmem_add_to_physmap_batch':
> /xen/xen/common/memory.c:942: undefined reference to 
> `xenmem_add_to_physmap_one'
> /xen/xen/common/memory.c:942:(.text+0x22145): relocation truncated
> to fit: R_X86_64_PLT32 against undefined symbol `xenmem_add_to_physmap_one'
> prelink-efi.o: in function `xenmem_add_to_physmap_batch':
> /xen/xen/common/memory.c:942: undefined reference to 
> `xenmem_add_to_physmap_one'
> make[2]: *** [Makefile:215: /root/xen/xen/xen.efi] Error 1
> make[2]: *** Waiting for unfinished jobs....
> ld: /xen/xen/.xen-syms.0: hidden symbol `xenmem_add_to_physmap_one' isn't 
> defined
> ld: final link failed: bad value
> 
> It is not entirely clear why the compiler DCE is not detecting the
> unused code. However, cloning the check introduced by the commit below
> into xenmem_add_to_physmap_batch() does the trick.
> 
> No functional change intended.
> 
> Fixes: d4f699a0df6c ("x86/mm: p2m_add_foreign() is HVM-only")
> Reported-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
> Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> Release-Acked-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>

Reviewed-by: Wei Liu <wl@xxxxxxx>