| Message ID | 20200107122501.15511-1-andrew.cooper3@citrix.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | x86/vmx: Shrink TASK_SWITCH's hvm_task_switch_reason reasons[] | expand |
On 07.01.2020 13:25, Andrew Cooper wrote: > No need to use 4-byte integers to store two bits of information. > > Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> In principle Reviewed-by: Jan Beulich <jbeulich@suse.com> But ... > --- a/xen/arch/x86/hvm/vmx/vmx.c > +++ b/xen/arch/x86/hvm/vmx/vmx.c > @@ -3978,7 +3978,7 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs) > vmx_update_cpu_exec_control(v); > break; > case EXIT_REASON_TASK_SWITCH: { > - static const enum hvm_task_switch_reason reasons[] = { > + static const int8_t reasons[] = { > TSW_call_or_int, TSW_iret, TSW_jmp, TSW_call_or_int > }; ... given our general preference of unsigned types when values can't become negative, why not uint8_t? As an aside, elsewhere I saw people starting to convert code because apparently gcc 10 will warn about enum type mismatches. I didn't investigate yet whether that's just for enum -> enum conversions, or also for enum <- / -> integer ones. Of course it wouldn't be the end of the world if we had to revert the change above; did you consider the alternative of making the enum a __packed one (which would avoid potential issues like the one named)? Jan
> From: Andrew Cooper <andrew.cooper3@citrix.com> > Sent: Tuesday, January 7, 2020 8:25 PM > > No need to use 4-byte integers to store two bits of information. > > Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c index f83f102638..b79bca71ad 100644 --- a/xen/arch/x86/hvm/vmx/vmx.c +++ b/xen/arch/x86/hvm/vmx/vmx.c @@ -3978,7 +3978,7 @@ void vmx_vmexit_handler(struct cpu_user_regs *regs) vmx_update_cpu_exec_control(v); break; case EXIT_REASON_TASK_SWITCH: { - static const enum hvm_task_switch_reason reasons[] = { + static const int8_t reasons[] = { TSW_call_or_int, TSW_iret, TSW_jmp, TSW_call_or_int }; unsigned int inst_len, source;
No need to use 4-byte integers to store two bits of information. Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> --- CC: Jan Beulich <JBeulich@suse.com> CC: Wei Liu <wl@xen.org> CC: Roger Pau Monné <roger.pau@citrix.com> CC: Jun Nakajima <jun.nakajima@intel.com> CC: Kevin Tian <kevin.tian@intel.com> --- xen/arch/x86/hvm/vmx/vmx.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)