[Qemu-devel] [PATCH 5/5] tcg-arm: Use AT_PLATFORM to detect the host ISA

[Richard Henderson <rth@twiddle.net>]

With this we can generate armv7 insns even when the OS compiles for a
lower common denominator.  The macros are arranged so that when we do
compile for a given ISA, all of the runtime checks for that ISA are
optimized away.

Signed-off-by: Richard Henderson <rth@twiddle.net>
---
 tcg/arm/tcg-target.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/tcg/arm/tcg-target.c b/tcg/arm/tcg-target.c
index 202f1fc..243dedd 100644
--- a/tcg/arm/tcg-target.c
+++ b/tcg/arm/tcg-target.c
@@ -41,9 +41,11 @@
 # endif
 #endif
 
-#define use_armv5_instructions  (__ARM_ARCH >= 5)
-#define use_armv6_instructions  (__ARM_ARCH >= 6)
-#define use_armv7_instructions  (__ARM_ARCH >= 7)
+static int arm_arch = __ARM_ARCH;
+
+#define use_armv5_instructions  (__ARM_ARCH >= 5 || arm_arch >= 5)
+#define use_armv6_instructions  (__ARM_ARCH >= 6 || arm_arch >= 6)
+#define use_armv7_instructions  (__ARM_ARCH >= 7 || arm_arch >= 7)
 
 #ifndef use_idiv_instructions
 bool use_idiv_instructions;
@@ -2036,12 +2038,22 @@ static const TCGTargetOpDef arm_op_defs[] = {
 
 static void tcg_target_init(TCGContext *s)
 {
-#if defined(CONFIG_GETAUXVAL) && !defined(use_idiv_instructions)
+#if defined(CONFIG_GETAUXVAL)
+    /* Only probe for the platform and capabilities if we havn't already
+       determined maximum values at compile time.  */
+# if !defined(use_idiv_instructions)
     {
         unsigned long hwcap = getauxval(AT_HWCAP);
         use_idiv_instructions = hwcap & (HWCAP_ARM_IDIVA | HWCAP_ARM_IDIVT);
     }
-#endif
+# endif
+    if (__ARM_ARCH < 7) {
+        const char *pl = (const char *)getauxval(AT_PLATFORM);
+        if (pl != NULL && pl[0] == 'v' && pl[1] >= '4' && pl[1] <= '9') {
+            arm_arch = pl[1] - '0';
+        }
+    }
+#endif /* GETAUXVAL */
 
 #if !defined(CONFIG_USER_ONLY)
     /* fail safe */
-- 
1.8.1.4