On 1 April 2023 12:57:33 BST, Michael Tokarev <mjt@tls.msk.ru> wrote:
01.04.2023 14:45, Joao Martins пишет:
On 01/04/2023 09:40, Michael Tokarev wrote:
After bringing in xen guest support, qemu fails to build on x32:
Adding the folks who added the feature too
target/i386/kvm/xen-emu.c:876:5: note: in expansion of macro ‘qemu_build_assert’
876 | qemu_build_assert(sizeof(struct vcpu_info) == 64);
| ^~~~~~~~~~~~~~~~~
This one should be easy to fix, but I wonder if there are other issues
with x32 exists..
Not sure.
struct vcpu_info is supposed to be 64bytes on both 32-bit and 64-bit builds.
If anything maybe arch_vcpu_info struct is different on 32-bit and 64-bit...
David, Paul, any ideas?
Yes, it is arch_vcpu_info. I assumed it is a trivial thing, but let me explain
if it's not the case.
include/hw/xen/interface/arch-x86/xen.h :
#if defined(__i386__)
#include "xen-x86_32.h"
#elif defined(__x86_64__)
#include "xen-x86_64.h"
#endif
(I wonder if it ever possible to have none of the two defined).
Now, xen-x86_32.h has:
struct arch_vcpu_info {
unsigned long cr2;
unsigned long pad[5]; /* sizeof(vcpu_info_t) == 64 */
};
Assuming sizeof(long)==32bits. But actually it is 64bits on x32.
While xen-x86_64.h has:
struct arch_vcpu_info {
unsigned long cr2;
unsigned long pad; /* sizeof(vcpu_info_t) == 64 */
};
It looks like for x32, the test in arch-x86/xen.h should be:
#if defined(__x86_64__)
#include "xen-x86_64.h"
#else
#include "xen-x86_32.h"
#endif
since x32 is almost like x86_64. The only difference from x86_64
is sizeof(pointer), which is 32bits.
Hm, doesn't x32 also align uint64_t to 64 bits (unlike i386 which only aligns
it to 32 bits)?
Well. Maybe xen support should be disabled entirely on x32.
Or maybe x32 should be declared as unsupported entirely.
I dunno.
We rely heavily on the struct layouts being precisely the same, since these are
ABI for the Xen guests. Wherever there was some 32/64 compatibility issue — and
often where there wasn't — that's why I littered it with those build assertions.
But while there are enough in there to sanity check the i386 vs. x86_64 ABI differences,
I wouldn't swear that I've put in enough checks for x32. So "it builds without
hitting an assertion" does not necessarily mean it'll be *correct*. Let's disable it
on x32.