[PATCH] MIPS: improve -march=native arch detection

[YunQiang Su]

If we cannot get info from options and cpuinfo, we try to get from:
  1. getauxval(AT_BASE_PLATFORM), introduced since Linux 5.7
  2. _MIPS_ARCH from host compiler.

This can fix the wrong loader usage on r5/r6 platform with
 -march=native.

gcc/ChangeLog:
        * config/mips/driver-native.cc (host_detect_local_cpu):
          try getauxval(AT_BASE_PLATFORM) and _MIPS_ARCH, too.
---
 gcc/config/mips/driver-native.cc | 22 +++++++++++++++++++---
 1 file changed, 19 insertions(+), 3 deletions(-)

diff --git a/gcc/config/mips/driver-native.cc b/gcc/config/mips/driver-native.cc
index 47627f85ce1..9aa7044c0b8 100644
--- a/gcc/config/mips/driver-native.cc
+++ b/gcc/config/mips/driver-native.cc
@@ -19,6 +19,7 @@ along with GCC; see the file COPYING3.  If not see
 
 #define IN_TARGET_CODE 1
 
+#include <sys/auxv.h>
 #include "config.h"
 #include "system.h"
 #include "coretypes.h"
@@ -46,15 +47,15 @@ host_detect_local_cpu (int argc, const char **argv)
   bool arch;
 
   if (argc < 1)
-    return NULL;
+    goto fallback_cpu;
 
   arch = strcmp (argv[0], "arch") == 0;
   if (!arch && strcmp (argv[0], "tune"))
-    return NULL;
+    goto fallback_cpu;
 
   f = fopen ("/proc/cpuinfo", "r");
   if (f == NULL)
-    return NULL;
+    goto fallback_cpu;
 
   while (fgets (buf, sizeof (buf), f) != NULL)
     if (startswith (buf, "cpu model"))
@@ -84,8 +85,23 @@ host_detect_local_cpu (int argc, const char **argv)
 
   fclose (f);
 
+fallback_cpu:
+/*FIXME: how about other OSes, like FreeBSD? */
+#ifdef __linux__
+  /*Note: getauxval may return NULL as:
+   * AT_BASE_PLATFORM is supported since Linux 5.7
+   * Or from older version of qemu-user
+   * */
+  if (cpu == NULL)
+    cpu = (const char *) getauxval (AT_BASE_PLATFORM);
+#endif
+
   if (cpu == NULL)
+#if defined (_MIPS_ARCH)
+    cpu = _MIPS_ARCH;
+#else
     return NULL;
+#endif
 
   return concat ("-m", argv[0], "=", cpu, NULL);
 }
-- 
2.30.2