Re: [patch] Add support for ARMv7M devices.

[Jonathan Larmour <jifl@eCosCentric.com>]

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On 03/11/10 13:17, Daniel Jacobowitz wrote:
> On Wed, Nov 03, 2010 at 03:21:24AM +0000, Jonathan Larmour wrote:
>> I think there's a more general issue here about whether it's expected to
>> maintain support for existing working stub implementations such that they
>> can be used as they have been used even when GDB is upgraded. Changing the
>> interface with GDB remote stubs used to be a big no-no for GDB.
> 
> In general, I want to keep existing stubs working.  But someone who
> has access to an affected stub needs to lend a hand here; I don't and
> can't test anything.

I believe I've now worked out a solution, and it's not that complicated in
fact. See the attached patch. The key seems to be to let remote.c choose
the tdesc.

2010-11-09  Jonathan Larmour  <jifl@eCosCentric.com>

	* arm-tdep.c (arm_gdbarch_init): Allow M-profile targets' remote
	stubs to provide 'g' packets with or without FPA registers.

> With stubs out there sending both FPA-regs+fake-CPSR and
> FPA-regs+XPSR, I don't know how to make it work; in fact, I don't know
> how FPA-regs+XPSR ever worked.

It's clearly impossible to tell the difference between fake-CPSR and XPSR.
But even an XML target description can't make that case work right, so I
don't think that's too bad for us not to cope with. Unless you have some
ideas (a 'set' option seems overkill).

Jifl
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diff -x CVS -x .svn -x '*~' -x '.#*' -x autom4te.cache -urpN src.old/gdb/arm-tdep.c src/gdb/arm-tdep.c
--- src.old/gdb/arm-tdep.c	2010-11-10 01:25:08.000000000 +0000
+++ src/gdb/arm-tdep.c	2010-11-10 02:00:31.000000000 +0000
@@ -42,6 +42,7 @@
 #include "prologue-value.h"
 #include "target-descriptions.h"
 #include "user-regs.h"
+#include "remote.h"
 
 #include "arm-tdep.h"
 #include "gdb/sim-arm.h"
@@ -54,6 +55,7 @@
 #include "vec.h"
 
 #include "features/arm-with-m.c"
+#include "features/arm-with-m-fpa.c"
 
 static int arm_debug;
 
@@ -7130,7 +7132,7 @@ arm_gdbarch_init (struct gdbarch_info in
 		  && (attr_arch == TAG_CPU_ARCH_V6_M
 		      || attr_arch == TAG_CPU_ARCH_V6S_M
 		      || attr_profile == 'M'))
-		tdesc = tdesc_arm_with_m;
+		is_m = 1;
 #endif
 	    }
 
@@ -7192,6 +7194,8 @@ arm_gdbarch_init (struct gdbarch_info in
 	  else
 	    is_m = 1;
 	}
+      else
+        is_m = 0;
 
       tdesc_data = tdesc_data_alloc ();
 
@@ -7566,6 +7570,29 @@ arm_gdbarch_init (struct gdbarch_info in
     user_reg_add (gdbarch, arm_register_aliases[i].name,
 		  value_of_arm_user_reg, &arm_register_aliases[i].regnum);
 
+  if (is_m)
+    {
+      /* For backward-compatibility we allow two 'g' packet lengths with
+         the remote protocol depending on whether FPA registers are
+         supplied. M-profile targets do not have FPA registers, but some
+         stubs already exist in the wild which use a 'g' packet which
+         supplies them albeit with dummy values. The packet format which
+         includes FPA registers should be considered deprecated for
+         M-profile targets.
+
+         The register sizes are fixed for these target descriptions in the
+         XML files, so we can hard-code them: r0-12,sp,lr,pc,xpsr for
+         tdesc_arm_with_m; and additionally f0-f7 and fps for
+         tdesc_arm_with_m_fpa.  */
+      
+      register_remote_g_packet_guess (gdbarch,
+                                      17 * INT_REGISTER_SIZE,
+                                      tdesc_arm_with_m);
+      register_remote_g_packet_guess (gdbarch,
+                                      18 * INT_REGISTER_SIZE +
+                                      8 * FP_REGISTER_SIZE,
+                                      tdesc_arm_with_m_fpa);
+    }
   return gdbarch;
 }
 
@@ -7609,6 +7636,7 @@ _initialize_arm_tdep (void)
 
   /* Initialize the standard target descriptions.  */
   initialize_tdesc_arm_with_m ();
+  initialize_tdesc_arm_with_m_fpa ();
 
   /* Get the number of possible sets of register names defined in opcodes.  */
   num_disassembly_options = get_arm_regname_num_options ();
diff -x CVS -x .svn -x '*~' -x '.#*' -x autom4te.cache -urpN src.old/gdb/features/arm-with-m-fpa.c src/gdb/features/arm-with-m-fpa.c
--- src.old/gdb/features/arm-with-m-fpa.c	1970-01-01 01:00:00.000000000 +0100
+++ src/gdb/features/arm-with-m-fpa.c	2010-11-10 02:00:31.000000000 +0000
@@ -0,0 +1,46 @@
+/* THIS FILE IS GENERATED.  Original: arm-with-m-fpa.xml */
+
+#include "defs.h"
+#include "osabi.h"
+#include "target-descriptions.h"
+
+struct target_desc *tdesc_arm_with_m_fpa;
+static void
+initialize_tdesc_arm_with_m_fpa (void)
+{
+  struct target_desc *result = allocate_target_description ();
+  struct tdesc_feature *feature;
+  struct tdesc_type *field_type, *type;
+
+  feature = tdesc_create_feature (result, "org.gnu.gdb.arm.m-profile");
+  tdesc_create_reg (feature, "r0", 0, 1, NULL, 32, "int");
+  tdesc_create_reg (feature, "r1", 1, 1, NULL, 32, "int");
+  tdesc_create_reg (feature, "r2", 2, 1, NULL, 32, "int");
+  tdesc_create_reg (feature, "r3", 3, 1, NULL, 32, "int");
+  tdesc_create_reg (feature, "r4", 4, 1, NULL, 32, "int");
+  tdesc_create_reg (feature, "r5", 5, 1, NULL, 32, "int");
+  tdesc_create_reg (feature, "r6", 6, 1, NULL, 32, "int");
+  tdesc_create_reg (feature, "r7", 7, 1, NULL, 32, "int");
+  tdesc_create_reg (feature, "r8", 8, 1, NULL, 32, "int");
+  tdesc_create_reg (feature, "r9", 9, 1, NULL, 32, "int");
+  tdesc_create_reg (feature, "r10", 10, 1, NULL, 32, "int");
+  tdesc_create_reg (feature, "r11", 11, 1, NULL, 32, "int");
+  tdesc_create_reg (feature, "r12", 12, 1, NULL, 32, "int");
+  tdesc_create_reg (feature, "sp", 13, 1, NULL, 32, "data_ptr");
+  tdesc_create_reg (feature, "lr", 14, 1, NULL, 32, "int");
+  tdesc_create_reg (feature, "pc", 15, 1, NULL, 32, "code_ptr");
+  tdesc_create_reg (feature, "xpsr", 25, 1, NULL, 32, "int");
+
+  feature = tdesc_create_feature (result, "org.gnu.gdb.arm.fpa");
+  tdesc_create_reg (feature, "f0", 16, 1, NULL, 96, "arm_fpa_ext");
+  tdesc_create_reg (feature, "f1", 17, 1, NULL, 96, "arm_fpa_ext");
+  tdesc_create_reg (feature, "f2", 18, 1, NULL, 96, "arm_fpa_ext");
+  tdesc_create_reg (feature, "f3", 19, 1, NULL, 96, "arm_fpa_ext");
+  tdesc_create_reg (feature, "f4", 20, 1, NULL, 96, "arm_fpa_ext");
+  tdesc_create_reg (feature, "f5", 21, 1, NULL, 96, "arm_fpa_ext");
+  tdesc_create_reg (feature, "f6", 22, 1, NULL, 96, "arm_fpa_ext");
+  tdesc_create_reg (feature, "f7", 23, 1, NULL, 96, "arm_fpa_ext");
+  tdesc_create_reg (feature, "fps", 24, 1, NULL, 32, "int");
+
+  tdesc_arm_with_m_fpa = result;
+}
diff -x CVS -x .svn -x '*~' -x '.#*' -x autom4te.cache -urpN src.old/gdb/features/arm-with-m-fpa.xml src/gdb/features/arm-with-m-fpa.xml
--- src.old/gdb/features/arm-with-m-fpa.xml	1970-01-01 01:00:00.000000000 +0100
+++ src/gdb/features/arm-with-m-fpa.xml	2010-11-10 02:00:31.000000000 +0000
@@ -0,0 +1,12 @@
+<?xml version="1.0"?>
+<!-- Copyright (C) 2010 Free Software Foundation, Inc.
+
+     Copying and distribution of this file, with or without modification,
+     are permitted in any medium without royalty provided the copyright
+     notice and this notice are preserved.  -->
+
+<!DOCTYPE target SYSTEM "gdb-target.dtd">
+<target>
+  <xi:include href="arm-m-profile.xml"/>
+  <xi:include href="arm-fpa.xml"/>
+</target>