Now that we zero all registers early on all entry paths, use that to
avoid a couple of immediates here.
Signed-off-by: Jan Beulich <jbeul...@suse.com>
Acked-by: Andrew Cooper <andrew.coop...@citrix.com>
---
v4: Add comments about the %r12 being zero
---
We may want to consider eliminating a few more $0 this way. But
especially for byte ones I'm not sure it's worth it, due to the REX
prefix the use of %r12 would incur.
--- a/xen/arch/x86/x86_64/compat/entry.S
+++ b/xen/arch/x86/x86_64/compat/entry.S
@@ -216,7 +216,8 @@ ENTRY(cstar_enter)
mov %rcx, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
neg %rcx
mov %rcx, %cr3
- movq $0, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
+ /* %r12 is still zero at this point. */
+ mov %r12, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
.Lcstar_cr3_okay:
ALTERNATIVE_NOP .Lcstar_cr3_start, .Lcstar_cr3_okay,
X86_FEATURE_NO_XPTI
sti
--- a/xen/arch/x86/x86_64/entry.S
+++ b/xen/arch/x86/x86_64/entry.S
@@ -185,7 +185,8 @@ ENTRY(lstar_enter)
mov %rcx, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
neg %rcx
mov %rcx, %cr3
- movq $0, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
+ /* %r12 is still zero at this point. */
+ mov %r12, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
.Llstar_cr3_okay:
ALTERNATIVE_NOP .Llstar_cr3_start, .Llstar_cr3_okay,
X86_FEATURE_NO_XPTI
sti
@@ -296,7 +297,8 @@ GLOBAL(sysenter_eflags_saved)
mov %rcx, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
neg %rcx
mov %rcx, %cr3
- movq $0, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
+ /* %r12 is still zero at this point. */
+ mov %r12, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
.Lsyse_cr3_okay:
ALTERNATIVE_NOP .Lsyse_cr3_start, .Lsyse_cr3_okay, X86_FEATURE_NO_XPTI
sti
@@ -348,7 +350,8 @@ ENTRY(int80_direct_trap)
mov %rcx, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
neg %rcx
mov %rcx, %cr3
- movq $0, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
+ /* %r12 is still zero at this point. */
+ mov %r12, STACK_CPUINFO_FIELD(xen_cr3)(%rbx)
.Lint80_cr3_okay:
ALTERNATIVE_NOP .Lint80_cr3_start, .Lint80_cr3_okay,
X86_FEATURE_NO_XPTI
sti
@@ -561,10 +564,10 @@ ENTRY(common_interrupt)
neg %rcx
.Lintr_cr3_load:
mov %rcx, %cr3
- xor %ecx, %ecx
- mov %rcx, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
+ /* %r12 is still zero at this point. */
+ mov %r12, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
testb $3, UREGS_cs(%rsp)
- cmovnz %rcx, %r15
+ cmovnz %r12, %r15
.Lintr_cr3_okay:
ALTERNATIVE_NOP .Lintr_cr3_start, .Lintr_cr3_okay, X86_FEATURE_NO_XPTI
@@ -605,10 +608,10 @@ GLOBAL(handle_exception)
neg %rcx
.Lxcpt_cr3_load:
mov %rcx, %cr3
- xor %ecx, %ecx
- mov %rcx, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
+ /* %r12 is still zero at this point. */
+ mov %r12, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
testb $3, UREGS_cs(%rsp)
- cmovnz %rcx, %r15
+ cmovnz %r12, %r15
.Lxcpt_cr3_okay:
ALTERNATIVE_NOP .Lxcpt_cr3_start, .Lxcpt_cr3_okay, X86_FEATURE_NO_XPTI
@@ -824,7 +827,8 @@ handle_ist_exception:
neg %rcx
.List_cr3_load:
mov %rcx, %cr3
- movq $0, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
+ /* %r12 is still zero at this point. */
+ mov %r12, STACK_CPUINFO_FIELD(xen_cr3)(%r14)
.List_cr3_okay:
ALTERNATIVE_NOP .List_cr3_start, .List_cr3_okay, X86_FEATURE_NO_XPTI
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