target/riscv: remove fixed numbering from GDB xml feature files

The fixed register numbering in the various GDB feature files for
RISC-V only exists because these files were originally copied from the
GDB source tree.

However, the fixed numbering only exists in the GDB source tree so
that GDB, when it connects to a target that doesn't provide a target
description, will use a specific numbering scheme.

That numbering scheme is designed to be compatible with the first
versions of QEMU (for RISC-V), that didn't send a target description,
and relied on a fixed numbering scheme.

Because of the way that QEMU manages its target descriptions,
recording the number of registers in each feature, and just relying on
GDB's numbering starting from 0, then I propose that we remove all the
fixed numbering from the RISC-V feature xml files, and just rely on
the standard numbering scheme.  Plenty of other targets manage their
xml files this way, e.g. ARM, AArch64, Loongarch, m68k, rx, and s390.

Signed-off-by: Andrew Burgess <aburgess@redhat.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Palmer Dabbelt <palmer@rivosinc.com>
Message-Id: <6069395f90e6fc24dac92197be815fedf42f5974.1661934573.git.aburgess@redhat.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>

gdb-xml/riscv-32bit-cpu.xml

@@ -5,13 +5,9 @@
      are permitted in any medium without royalty provided the copyright
      notice and this notice are preserved.  -->
 
-<!-- Register numbers are hard-coded in order to maintain backward
-     compatibility with older versions of tools that didn't use xml
-     register descriptions.  -->
-
 <!DOCTYPE feature SYSTEM "gdb-target.dtd">
 <feature name="org.gnu.gdb.riscv.cpu">
-  <reg name="zero" bitsize="32" type="int" regnum="0"/>
+  <reg name="zero" bitsize="32" type="int"/>
   <reg name="ra" bitsize="32" type="code_ptr"/>
   <reg name="sp" bitsize="32" type="data_ptr"/>
   <reg name="gp" bitsize="32" type="data_ptr"/>

gdb-xml/riscv-32bit-fpu.xml

@@ -5,13 +5,9 @@
      are permitted in any medium without royalty provided the copyright
      notice and this notice are preserved.  -->
 
-<!-- Register numbers are hard-coded in order to maintain backward
-     compatibility with older versions of tools that didn't use xml
-     register descriptions.  -->
-
 <!DOCTYPE feature SYSTEM "gdb-target.dtd">
 <feature name="org.gnu.gdb.riscv.fpu">
-  <reg name="ft0" bitsize="32" type="ieee_single" regnum="33"/>
+  <reg name="ft0" bitsize="32" type="ieee_single"/>
   <reg name="ft1" bitsize="32" type="ieee_single"/>
   <reg name="ft2" bitsize="32" type="ieee_single"/>
   <reg name="ft3" bitsize="32" type="ieee_single"/>

gdb-xml/riscv-64bit-cpu.xml

@@ -5,13 +5,9 @@
      are permitted in any medium without royalty provided the copyright
      notice and this notice are preserved.  -->
 
-<!-- Register numbers are hard-coded in order to maintain backward
-     compatibility with older versions of tools that didn't use xml
-     register descriptions.  -->
-
 <!DOCTYPE feature SYSTEM "gdb-target.dtd">
 <feature name="org.gnu.gdb.riscv.cpu">
-  <reg name="zero" bitsize="64" type="int" regnum="0"/>
+  <reg name="zero" bitsize="64" type="int"/>
   <reg name="ra" bitsize="64" type="code_ptr"/>
   <reg name="sp" bitsize="64" type="data_ptr"/>
   <reg name="gp" bitsize="64" type="data_ptr"/>

gdb-xml/riscv-64bit-fpu.xml

@@ -5,10 +5,6 @@
      are permitted in any medium without royalty provided the copyright
      notice and this notice are preserved.  -->
 
-<!-- Register numbers are hard-coded in order to maintain backward
-     compatibility with older versions of tools that didn't use xml
-     register descriptions.  -->
-
 <!DOCTYPE feature SYSTEM "gdb-target.dtd">
 <feature name="org.gnu.gdb.riscv.fpu">
 
@@ -17,7 +13,7 @@
     <field name="double" type="ieee_double"/>
   </union>
 
-  <reg name="ft0" bitsize="64" type="riscv_double" regnum="33"/>
+  <reg name="ft0" bitsize="64" type="riscv_double"/>
   <reg name="ft1" bitsize="64" type="riscv_double"/>
   <reg name="ft2" bitsize="64" type="riscv_double"/>
   <reg name="ft3" bitsize="64" type="riscv_double"/>