[Minios-devel] [UNIKRAFT PATCH v4 7/8] arch/x86: Introduce NO_X86_EXTREGS_FLAGS

[Florian Schmidt <florian.schmidt@xxxxxxxxx>]

This set of flags disables the use of extended registers: FP, MMX/XMM,
YMM, and hence should be used on files that implement
trap/exception/interrupt handler functions, because we do not save the
extended x86 register state when those events happen.

Signed-off-by: Florian Schmidt <florian.schmidt@xxxxxxxxx>
Reviewed-by: Yuri Volchkov <yuri.volchkov@xxxxxxxxx>
---
 arch/x86/x86_64/Makefile.uk | 3 +++
 plat/kvm/Makefile.uk        | 1 +
 plat/kvm/x86/time.c         | 4 ++++
 3 files changed, 8 insertions(+)

diff --git a/arch/x86/x86_64/Makefile.uk b/arch/x86/x86_64/Makefile.uk
index 8cd2f8be..8ec7d6b9 100644
--- a/arch/x86/x86_64/Makefile.uk
+++ b/arch/x86/x86_64/Makefile.uk
@@ -9,6 +9,9 @@ CINCLUDES   += -I$(CONFIG_UK_BASE)/arch/x86/x86_64/include
 ASINCLUDES  += -I$(CONFIG_UK_BASE)/arch/x86/x86_64/include
 CXXINCLUDES += -I$(CONFIG_UK_BASE)/arch/x86/x86_64/include
 
+# compiler flags to prevent use of extended (FP, SSE, AVX) registers.
+# This is for files that contain trap/exception/interrupt handlers
+NO_X86_EXTREGS_FLAGS := -mno-80387 -mno-fp-ret-in-387 -mno-mmx -mno-sse 
-mno-avx
 
 ASFLAGS-$(CONFIG_MARCH_X86_64_GENERIC)     += -mtune=generic
 CFLAGS-$(CONFIG_MARCH_X86_64_GENERIC)      += -mtune=generic
diff --git a/plat/kvm/Makefile.uk b/plat/kvm/Makefile.uk
index 5fb56ee9..19ad3d67 100644
--- a/plat/kvm/Makefile.uk
+++ b/plat/kvm/Makefile.uk
@@ -27,6 +27,7 @@ LIBKVMPLAT_CXXFLAGS            += -DKVMPLAT
 ##
 LIBKVMPLAT_SRCS-$(CONFIG_ARCH_X86_64) += 
$(UK_PLAT_COMMON_BASE)/x86/trace.c|common
 LIBKVMPLAT_SRCS-$(CONFIG_ARCH_X86_64) += 
$(UK_PLAT_COMMON_BASE)/x86/traps.c|common
+LIBKVMPLAT_TRAPS_COMMON_FLAGS += $(NO_X86_EXTREGS_FLAGS)
 LIBKVMPLAT_SRCS-$(CONFIG_ARCH_X86_64) += 
$(UK_PLAT_COMMON_BASE)/x86/cpu_features.c|common
 LIBKVMPLAT_SRCS-$(CONFIG_ARCH_X86_64) += 
$(UK_PLAT_COMMON_BASE)/x86/cpu_native.c|common
 ifeq ($(CONFIG_HAVE_SCHED),y)
diff --git a/plat/kvm/x86/time.c b/plat/kvm/x86/time.c
index 3d8a8421..d62142ff 100644
--- a/plat/kvm/x86/time.c
+++ b/plat/kvm/x86/time.c
@@ -58,6 +58,10 @@ __nsec ukplat_clock_wall(void)
        return tscclock_monotonic() + tscclock_epochoffset();
 }
 
+/* NB: If this ever does more than an immediate return, it will need to be
+ * compiled with NO_X86_EXTREGS_FLAGS to prevent potential clobbering of
+ * registers that are not saved on interrupt handling.
+ */
 static int timer_handler(void *arg __unused)
 {
        /* Yes, we handled the irq. */
-- 
2.20.1


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