Hello,
I'd like to PING this patch in that it's been two weeks since I sent the
patch.
Kind regards,
Zero Tang
On Wed, Aug 6, 2025 at 3:58 PM Zero Tang <zero.tang...@gmail.com> wrote:
> Replaces "long" with "int64_t" during canonicalization.
>
> ---
> In Linux GCC, "long" has 8 bytes. However, in msys2 GCC, "long" has 4
> bytes. In this case, canonicalization would set all high bits to 1 when
> the segment base is bigger than 0x7FFF (assuming 48-bit linear address).
>
> This is why QEMU-TCG in Windows cannot boot a bluepill-like hypervisor
> in UEFI, in that the guest IDT and GDT bases are above 0x7FFF, thereby
> resulting in incorrect bases. When an interrupt arrives, it would
> trigger a #PF exception; the #PF would trigger again, resulting in a #DF
> exception; the #PF would trigger for the third time, resulting in
> triple-fault, and eventually causes the shutdown VM-Exit to the
> bluepill hypervisor right after it boots.
>
> In summary, this patch replaces "long" with "int64_t" in order to enforce
> the canonicalization with 64-bit signed integers.
>
> Signed-off-by: Zero Tang <zero.tang...@gmail.com>
> ---
> target/i386/tcg/system/svm_helper.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/target/i386/tcg/system/svm_helper.c
> b/target/i386/tcg/system/svm_helper.c
> index b27049b9ed..1ccfccf419 100644
> --- a/target/i386/tcg/system/svm_helper.c
> +++ b/target/i386/tcg/system/svm_helper.c
> @@ -49,7 +49,7 @@ static void svm_save_seg(CPUX86State *env, int mmu_idx,
> hwaddr addr,
> static inline void svm_canonicalization(CPUX86State *env, target_ulong
> *seg_base)
> {
> uint16_t shift_amt = 64 - cpu_x86_virtual_addr_width(env);
> - *seg_base = ((((long) *seg_base) << shift_amt) >> shift_amt);
> + *seg_base = ((((int64_t) *seg_base) << shift_amt) >> shift_amt);
> }
>
> static void svm_load_seg(CPUX86State *env, int mmu_idx, hwaddr addr,
>
> ---
> base-commit: e0006a86615baa70bc9d8b183e528aed91c1ac90
> change-id: 20250806-fix-tcg-svm-canon-adbea9508073
>
> Best regards,
> --
> Zero Tang <zero.tang...@gmail.com>
>
