[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-changelog] [xen master] x86emul: VEX.B is ignored in compatibility mode
commit 89c76ee7f60777b81c8fd0475a6af7c84e72a791 Author: Jan Beulich <jbeulich@xxxxxxxx> AuthorDate: Tue Jan 17 10:32:25 2017 +0100 Commit: Jan Beulich <jbeulich@xxxxxxxx> CommitDate: Tue Jan 17 10:32:25 2017 +0100 x86emul: VEX.B is ignored in compatibility mode While VEX.R and VEX.X are guaranteed to be 1 in compatibility mode (and hence a respective mode_64bit() check can be dropped), VEX.B can be encoded as zero, but would be ignored by the processor. Since we emulate instructions in 64-bit mode (except possibly in the test harness), we need to force the bit to 1 in order to not act on the wrong {X,Y,Z}MM register (which has no bad effect on 32-bit test harness builds, as there the bit would again be ignored by the hardware, and would by default be expected to be 1 anyway). We must not, however, fiddle with the high bit of VEX.VVVV in the decode phase, as that would undermine the checking of instructions requiring the field to be all ones independent of mode. This is being enforced in copy_REX_VEX() instead. Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx> Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx> --- xen/arch/x86/x86_emulate/x86_emulate.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-) diff --git a/xen/arch/x86/x86_emulate/x86_emulate.c b/xen/arch/x86/x86_emulate/x86_emulate.c index de239b6..20285b2 100644 --- a/xen/arch/x86/x86_emulate/x86_emulate.c +++ b/xen/arch/x86/x86_emulate/x86_emulate.c @@ -332,7 +332,11 @@ union vex { #define copy_REX_VEX(ptr, rex, vex) do { \ if ( (vex).opcx != vex_none ) \ + { \ + if ( !mode_64bit() ) \ + vex.reg |= 8; \ ptr[0] = 0xc4, ptr[1] = (vex).raw[0], ptr[2] = (vex).raw[1]; \ + } \ else if ( mode_64bit() ) \ ptr[1] = rex | REX_PREFIX; \ } while (0) @@ -2309,6 +2313,8 @@ x86_decode( op_bytes = 8; } } + else + vex.b = 1; switch ( b ) { case 0x62: @@ -2327,7 +2333,7 @@ x86_decode( break; } } - if ( mode_64bit() && !vex.r ) + if ( !vex.r ) rex_prefix |= REX_R; ext = vex.opcx; -- generated by git-patchbot for /home/xen/git/xen.git#master _______________________________________________ Xen-changelog mailing list Xen-changelog@xxxxxxxxxxxxx https://lists.xenproject.org/xen-changelog
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