>
> Thanks Terry (and everyone else) for explaining why we want to do this in the 
> driver.  The substance of the patch looks good to me, and below are some 
> comments and nit-picks.  (Also, I'm not an ARM maintainer, so this is a 
> review, not an approval to commit).
>
> Please make sure to update changelog before committing.
>

Thanks Maxim, your comments are great. I accepted all of them and
commented two of them that I am not clear.

<<snapped>>
>> +
>> +struct arm_arch_core_flag
>> +{
>> +  const char *const name;
>> +  const unsigned long flags;
>> +};
>> +
>> +static const struct arm_arch_core_flag arm_arch_core_flags[] =
>> +{
>> +#undef ARM_CORE
>> +#define ARM_CORE(NAME, X, IDENT, ARCH, FLAGS, COSTS) \
>> +  {NAME, FLAGS | FL_FOR_ARCH##ARCH},
>> +#include "arm-cores.def"
>> +#undef ARM_CORE
>> +#undef ARM_ARCH
>> +#define ARM_ARCH(NAME, CORE, ARCH, FLAGS) \
>> +  {NAME, FLAGS},
>> +#include "arm-arches.def"
>> +#undef ARM_ARCH
>> +  {NULL, 0}
>> +};
>
> Did you consider implications from mixing ARCHes and CPUs in the same array?  
> It should not be a problem, but would you please double-check that cases like 
> "-march=cortex-a15" are properly caught as errors elsewhere in the driver?
>

Not sure I follow you correctly here. This array is just used for my
new arm_target_thumb_only function. It isn't used by any another code
in gcc. So I don't think mixing them will break gcc option check
mechanism. I tried below command and I can get error message:

$ ./install-native/bin/arm-none-eabi-gcc -march=cortex-a15 x.c -S -mthumb
arm-none-eabi-gcc: error: unrecognized argument in option '-march=cortex-a15'

>>  #endif
>> diff --git a/gcc/config/arm/arm-protos.h b/gcc/config/arm/arm-protos.h
>> index 28ffe52..325a81c 100644
>> --- a/gcc/config/arm/arm-protos.h
>> +++ b/gcc/config/arm/arm-protos.h
>> @@ -325,75 +325,6 @@ extern const char *arm_rewrite_selected_cpu (const char 
>> *name);
>>
>>  extern bool arm_is_constant_pool_ref (rtx);
>>
>> -/* Flags used to identify the presence of processor capabilities.  */
>
> You've lost this comment in the new file.  Was it intentional?
>

The line is used as first line in new file arm-flags.h.

BR,
Terry

Here is updated ChangeLog:

gcc/ChangeLog:

2015-03-05  Terry Guo  <terry....@arm.com>

      * common/config/arm/arm-common.c (arm_target_thumb_only): New function.
      * config/arm/arm-protos.h: Move FL_* stuff into below file and
then include it.
      * config/arm/arm-flags.h: New file for FL_* stuff.
      * config/arm/arm-opts.h (struct arm_arch_core_flag): New struct.
      (arm_arch_core_flags): New array for arch/core and flag map.
      * config/arm/arm.h (TARGET_MODE_SPEC_FUNCTIONS): New SPEC function.
      (EXTRA_SPEC_FUNCTIONS): Include new SPEC function.
      (TARGET_MODE_SPECS): New SPEC.
      (DRIVER_SELF_SPECS): Include new SPEC.
diff --git a/gcc/common/config/arm/arm-common.c 
b/gcc/common/config/arm/arm-common.c
index 86673b7..5efb55e 100644
--- a/gcc/common/config/arm/arm-common.c
+++ b/gcc/common/config/arm/arm-common.c
@@ -97,6 +97,28 @@ arm_rewrite_mcpu (int argc, const char **argv)
   return arm_rewrite_selected_cpu (argv[argc - 1]);
 }
 
+/* Called by driver to check whether the target denoted by current
+   command line options is thumb-only target.  If -march present,
+   check the last -march option.  If no -march, check the last -mcpu
+   option.  */
+const char *
+arm_target_thumb_only (int argc, const char **argv)
+{
+  unsigned int opt;
+
+  if (argc)
+    {
+      for (opt = 0; opt < (ARRAY_SIZE (arm_arch_core_flags) - 1); opt++)
+       if ((strcmp (argv[argc - 1], arm_arch_core_flags[opt].name) == 0)
+           && ((arm_arch_core_flags[opt].flags & FL_NOTM) == 0))
+         return "-mthumb";
+
+      return NULL;
+    }
+  else
+    return NULL;
+}
+
 #undef ARM_CPU_NAME_LENGTH
 
 
diff --git a/gcc/config/arm/arm-flags.h b/gcc/config/arm/arm-flags.h
new file mode 100644
index 0000000..e206ad1
--- /dev/null
+++ b/gcc/config/arm/arm-flags.h
@@ -0,0 +1,92 @@
+/* Flags used to identify the presence of processor capabilities.
+
+   Copyright (C) 2015 Free Software Foundation, Inc.
+   Contributed by ARM Ltd.
+
+   This file is part of GCC.
+
+   GCC is free software; you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published
+   by the Free Software Foundation; either version 3, or (at your
+   option) any later version.
+
+   GCC is distributed in the hope that it will be useful, but WITHOUT
+   ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+   or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
+   License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with GCC; see the file COPYING3.  If not see
+   <http://www.gnu.org/licenses/>.  */
+
+#ifndef GCC_ARM_FLAGS_H
+#define GCC_ARM_FLAGS_H
+
+/* Bit values used to identify processor capabilities.  */
+#define FL_CO_PROC    (1 << 0)        /* Has external co-processor bus */
+#define FL_ARCH3M     (1 << 1)        /* Extended multiply */
+#define FL_MODE26     (1 << 2)        /* 26-bit mode support */
+#define FL_MODE32     (1 << 3)        /* 32-bit mode support */
+#define FL_ARCH4      (1 << 4)        /* Architecture rel 4 */
+#define FL_ARCH5      (1 << 5)        /* Architecture rel 5 */
+#define FL_THUMB      (1 << 6)        /* Thumb aware */
+#define FL_LDSCHED    (1 << 7)       /* Load scheduling necessary */
+#define FL_STRONG     (1 << 8)       /* StrongARM */
+#define FL_ARCH5E     (1 << 9)        /* DSP extensions to v5 */
+#define FL_XSCALE     (1 << 10)              /* XScale */
+/* spare             (1 << 11) */
+#define FL_ARCH6      (1 << 12)       /* Architecture rel 6.  Adds
+                                        media instructions.  */
+#define FL_VFPV2      (1 << 13)       /* Vector Floating Point V2.  */
+#define FL_WBUF              (1 << 14)       /* Schedule for write buffer ops.
+                                        Note: ARM6 & 7 derivatives only.  */
+#define FL_ARCH6K     (1 << 15)       /* Architecture rel 6 K extensions.  */
+#define FL_THUMB2     (1 << 16)              /* Thumb-2.  */
+#define FL_NOTM              (1 << 17)       /* Instructions not present in 
the 'M'
+                                        profile.  */
+#define FL_THUMB_DIV  (1 << 18)              /* Hardware divide (Thumb mode).  
*/
+#define FL_VFPV3      (1 << 19)       /* Vector Floating Point V3.  */
+#define FL_NEON       (1 << 20)       /* Neon instructions.  */
+#define FL_ARCH7EM    (1 << 21)              /* Instructions present in the 
ARMv7E-M
+                                        architecture.  */
+#define FL_ARCH7      (1 << 22)       /* Architecture 7.  */
+#define FL_ARM_DIV    (1 << 23)              /* Hardware divide (ARM mode).  */
+#define FL_ARCH8      (1 << 24)       /* Architecture 8.  */
+#define FL_CRC32      (1 << 25)              /* ARMv8 CRC32 instructions.  */
+
+#define FL_SMALLMUL   (1 << 26)       /* Small multiply supported.  */
+#define FL_NO_VOLATILE_CE   (1 << 27) /* No volatile memory in IT block.  */
+
+#define FL_IWMMXT     (1 << 29)              /* XScale v2 or "Intel Wireless 
MMX technology".  */
+#define FL_IWMMXT2    (1 << 30)       /* "Intel Wireless MMX2 technology".  */
+
+/* Flags that only effect tuning, not available instructions.  */
+#define FL_TUNE                (FL_WBUF | FL_VFPV2 | FL_STRONG | FL_LDSCHED \
+                        | FL_CO_PROC)
+
+#define FL_FOR_ARCH2   FL_NOTM
+#define FL_FOR_ARCH3   (FL_FOR_ARCH2 | FL_MODE32)
+#define FL_FOR_ARCH3M  (FL_FOR_ARCH3 | FL_ARCH3M)
+#define FL_FOR_ARCH4   (FL_FOR_ARCH3M | FL_ARCH4)
+#define FL_FOR_ARCH4T  (FL_FOR_ARCH4 | FL_THUMB)
+#define FL_FOR_ARCH5   (FL_FOR_ARCH4 | FL_ARCH5)
+#define FL_FOR_ARCH5T  (FL_FOR_ARCH5 | FL_THUMB)
+#define FL_FOR_ARCH5E  (FL_FOR_ARCH5 | FL_ARCH5E)
+#define FL_FOR_ARCH5TE (FL_FOR_ARCH5E | FL_THUMB)
+#define FL_FOR_ARCH5TEJ        FL_FOR_ARCH5TE
+#define FL_FOR_ARCH6   (FL_FOR_ARCH5TE | FL_ARCH6)
+#define FL_FOR_ARCH6J  FL_FOR_ARCH6
+#define FL_FOR_ARCH6K  (FL_FOR_ARCH6 | FL_ARCH6K)
+#define FL_FOR_ARCH6Z  FL_FOR_ARCH6
+#define FL_FOR_ARCH6ZK FL_FOR_ARCH6K
+#define FL_FOR_ARCH6T2 (FL_FOR_ARCH6 | FL_THUMB2)
+#define FL_FOR_ARCH6M  (FL_FOR_ARCH6 & ~FL_NOTM)
+#define FL_FOR_ARCH7   ((FL_FOR_ARCH6T2 & ~FL_NOTM) | FL_ARCH7)
+#define FL_FOR_ARCH7A  (FL_FOR_ARCH7 | FL_NOTM | FL_ARCH6K)
+#define FL_FOR_ARCH7VE (FL_FOR_ARCH7A | FL_THUMB_DIV | FL_ARM_DIV)
+#define FL_FOR_ARCH7R  (FL_FOR_ARCH7A | FL_THUMB_DIV)
+#define FL_FOR_ARCH7M  (FL_FOR_ARCH7 | FL_THUMB_DIV)
+#define FL_FOR_ARCH7EM  (FL_FOR_ARCH7M | FL_ARCH7EM)
+#define FL_FOR_ARCH8A  (FL_FOR_ARCH7VE | FL_ARCH8)
+
+#endif /* GCC_ARM_FLAGS_H */
diff --git a/gcc/config/arm/arm-opts.h b/gcc/config/arm/arm-opts.h
index 039e333..dd727cf 100644
--- a/gcc/config/arm/arm-opts.h
+++ b/gcc/config/arm/arm-opts.h
@@ -25,6 +25,8 @@
 #ifndef ARM_OPTS_H
 #define ARM_OPTS_H
 
+#include "arm-flags.h"
+
 /* The various ARM cores.  */
 enum processor_type
 {
@@ -77,4 +79,25 @@ enum arm_tls_type {
   TLS_GNU,
   TLS_GNU2
 };
+
+struct arm_arch_core_flag
+{
+  const char *const name;
+  const unsigned long flags;
+};
+
+static const struct arm_arch_core_flag arm_arch_core_flags[] =
+{
+#undef ARM_CORE
+#define ARM_CORE(NAME, X, IDENT, ARCH, FLAGS, COSTS) \
+  {NAME, FLAGS | FL_FOR_ARCH##ARCH},
+#include "arm-cores.def"
+#undef ARM_CORE
+#undef ARM_ARCH
+#define ARM_ARCH(NAME, CORE, ARCH, FLAGS) \
+  {NAME, FLAGS},
+#include "arm-arches.def"
+#undef ARM_ARCH
+  {NULL, 0}
+};
 #endif
diff --git a/gcc/config/arm/arm-protos.h b/gcc/config/arm/arm-protos.h
index 28ffe52..0d5f61f 100644
--- a/gcc/config/arm/arm-protos.h
+++ b/gcc/config/arm/arm-protos.h
@@ -22,6 +22,8 @@
 #ifndef GCC_ARM_PROTOS_H
 #define GCC_ARM_PROTOS_H
 
+#include "arm-flags.h"
+
 extern enum unwind_info_type arm_except_unwind_info (struct gcc_options *);
 extern int use_return_insn (int, rtx);
 extern bool use_simple_return_p (void);
@@ -325,75 +327,6 @@ extern const char *arm_rewrite_selected_cpu (const char 
*name);
 
 extern bool arm_is_constant_pool_ref (rtx);
 
-/* Flags used to identify the presence of processor capabilities.  */
-
-/* Bit values used to identify processor capabilities.  */
-#define FL_CO_PROC    (1 << 0)        /* Has external co-processor bus */
-#define FL_ARCH3M     (1 << 1)        /* Extended multiply */
-#define FL_MODE26     (1 << 2)        /* 26-bit mode support */
-#define FL_MODE32     (1 << 3)        /* 32-bit mode support */
-#define FL_ARCH4      (1 << 4)        /* Architecture rel 4 */
-#define FL_ARCH5      (1 << 5)        /* Architecture rel 5 */
-#define FL_THUMB      (1 << 6)        /* Thumb aware */
-#define FL_LDSCHED    (1 << 7)       /* Load scheduling necessary */
-#define FL_STRONG     (1 << 8)       /* StrongARM */
-#define FL_ARCH5E     (1 << 9)        /* DSP extensions to v5 */
-#define FL_XSCALE     (1 << 10)              /* XScale */
-/* spare             (1 << 11) */
-#define FL_ARCH6      (1 << 12)       /* Architecture rel 6.  Adds
-                                        media instructions.  */
-#define FL_VFPV2      (1 << 13)       /* Vector Floating Point V2.  */
-#define FL_WBUF              (1 << 14)       /* Schedule for write buffer ops.
-                                        Note: ARM6 & 7 derivatives only.  */
-#define FL_ARCH6K     (1 << 15)       /* Architecture rel 6 K extensions.  */
-#define FL_THUMB2     (1 << 16)              /* Thumb-2.  */
-#define FL_NOTM              (1 << 17)       /* Instructions not present in 
the 'M'
-                                        profile.  */
-#define FL_THUMB_DIV  (1 << 18)              /* Hardware divide (Thumb mode).  
*/
-#define FL_VFPV3      (1 << 19)       /* Vector Floating Point V3.  */
-#define FL_NEON       (1 << 20)       /* Neon instructions.  */
-#define FL_ARCH7EM    (1 << 21)              /* Instructions present in the 
ARMv7E-M
-                                        architecture.  */
-#define FL_ARCH7      (1 << 22)       /* Architecture 7.  */
-#define FL_ARM_DIV    (1 << 23)              /* Hardware divide (ARM mode).  */
-#define FL_ARCH8      (1 << 24)       /* Architecture 8.  */
-#define FL_CRC32      (1 << 25)              /* ARMv8 CRC32 instructions.  */
-
-#define FL_SMALLMUL   (1 << 26)       /* Small multiply supported.  */
-#define FL_NO_VOLATILE_CE   (1 << 27) /* No volatile memory in IT block.  */
-
-#define FL_IWMMXT     (1 << 29)              /* XScale v2 or "Intel Wireless 
MMX technology".  */
-#define FL_IWMMXT2    (1 << 30)       /* "Intel Wireless MMX2 technology".  */
-
-/* Flags that only effect tuning, not available instructions.  */
-#define FL_TUNE                (FL_WBUF | FL_VFPV2 | FL_STRONG | FL_LDSCHED \
-                        | FL_CO_PROC)
-
-#define FL_FOR_ARCH2   FL_NOTM
-#define FL_FOR_ARCH3   (FL_FOR_ARCH2 | FL_MODE32)
-#define FL_FOR_ARCH3M  (FL_FOR_ARCH3 | FL_ARCH3M)
-#define FL_FOR_ARCH4   (FL_FOR_ARCH3M | FL_ARCH4)
-#define FL_FOR_ARCH4T  (FL_FOR_ARCH4 | FL_THUMB)
-#define FL_FOR_ARCH5   (FL_FOR_ARCH4 | FL_ARCH5)
-#define FL_FOR_ARCH5T  (FL_FOR_ARCH5 | FL_THUMB)
-#define FL_FOR_ARCH5E  (FL_FOR_ARCH5 | FL_ARCH5E)
-#define FL_FOR_ARCH5TE (FL_FOR_ARCH5E | FL_THUMB)
-#define FL_FOR_ARCH5TEJ        FL_FOR_ARCH5TE
-#define FL_FOR_ARCH6   (FL_FOR_ARCH5TE | FL_ARCH6)
-#define FL_FOR_ARCH6J  FL_FOR_ARCH6
-#define FL_FOR_ARCH6K  (FL_FOR_ARCH6 | FL_ARCH6K)
-#define FL_FOR_ARCH6Z  FL_FOR_ARCH6
-#define FL_FOR_ARCH6ZK FL_FOR_ARCH6K
-#define FL_FOR_ARCH6T2 (FL_FOR_ARCH6 | FL_THUMB2)
-#define FL_FOR_ARCH6M  (FL_FOR_ARCH6 & ~FL_NOTM)
-#define FL_FOR_ARCH7   ((FL_FOR_ARCH6T2 & ~FL_NOTM) | FL_ARCH7)
-#define FL_FOR_ARCH7A  (FL_FOR_ARCH7 | FL_NOTM | FL_ARCH6K)
-#define FL_FOR_ARCH7VE (FL_FOR_ARCH7A | FL_THUMB_DIV | FL_ARM_DIV)
-#define FL_FOR_ARCH7R  (FL_FOR_ARCH7A | FL_THUMB_DIV)
-#define FL_FOR_ARCH7M  (FL_FOR_ARCH7 | FL_THUMB_DIV)
-#define FL_FOR_ARCH7EM  (FL_FOR_ARCH7M | FL_ARCH7EM)
-#define FL_FOR_ARCH8A  (FL_FOR_ARCH7VE | FL_ARCH8)
-
 /* The bits in this mask specify which
    instructions we are allowed to generate.  */
 extern unsigned long insn_flags;
diff --git a/gcc/config/arm/arm.h b/gcc/config/arm/arm.h
index 8c10ea3..6a2dfaf 100644
--- a/gcc/config/arm/arm.h
+++ b/gcc/config/arm/arm.h
@@ -2394,13 +2394,18 @@ extern const char *arm_rewrite_mcpu (int argc, const 
char **argv);
    "   :%{march=*:-march=%*}}"                                 \
    BIG_LITTLE_SPEC
 
+extern const char *arm_target_thumb_only (int argc, const char **argv);
+#define TARGET_MODE_SPEC_FUNCTIONS                                     \
+  { "target_mode_check", arm_target_thumb_only },
+
 /* -mcpu=native handling only makes sense with compiler running on
    an ARM chip.  */
 #if defined(__arm__)
 extern const char *host_detect_local_cpu (int argc, const char **argv);
 # define EXTRA_SPEC_FUNCTIONS                                          \
   { "local_cpu_detect", host_detect_local_cpu },                       \
-  BIG_LITTLE_CPU_SPEC_FUNCTIONS
+  BIG_LITTLE_CPU_SPEC_FUNCTIONS                                                
\
+  TARGET_MODE_SPEC_FUNCTIONS
 
 # define MCPU_MTUNE_NATIVE_SPECS                                       \
    " %{march=native:%<march=native %:local_cpu_detect(arch)}"          \
@@ -2408,9 +2413,19 @@ extern const char *host_detect_local_cpu (int argc, 
const char **argv);
    " %{mtune=native:%<mtune=native %:local_cpu_detect(tune)}"
 #else
 # define MCPU_MTUNE_NATIVE_SPECS ""
-# define EXTRA_SPEC_FUNCTIONS BIG_LITTLE_CPU_SPEC_FUNCTIONS
+# define EXTRA_SPEC_FUNCTIONS                                          \
+  BIG_LITTLE_CPU_SPEC_FUNCTIONS                                                
\
+  TARGET_MODE_SPEC_FUNCTIONS
 #endif
 
-#define DRIVER_SELF_SPECS MCPU_MTUNE_NATIVE_SPECS
+/* Automatically add -mthumb for thumb-only target if mode isn't specified
+   via configuration option --with-mode and command line.
+   If -march present, we collect just -march options.  Otherwise we
+   collect just -mcpu options.  The last one of them will be used to
+   decide target mode.  */
+#define TARGET_MODE_SPECS                                                      
\
+  " %{!marm:%{!mthumb:%:target_mode_check(%{march=*:%*;mcpu=*:%*})}}"
+
+#define DRIVER_SELF_SPECS MCPU_MTUNE_NATIVE_SPECS TARGET_MODE_SPECS
 #define TARGET_SUPPORTS_WIDE_INT 1
 #endif /* ! GCC_ARM_H */

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