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Re: [PATCH] riscv: Separate FPU register size from core register size in

From: Palmer Dabbelt
Subject: Re: [PATCH] riscv: Separate FPU register size from core register size in gdbstub [v2]
Date: Thu, 30 Jan 2020 12:49:44 -0800 (PST)

On Tue, 28 Jan 2020 23:32:16 GMT (+0000), address@hidden wrote:
The size of the FPU registers is dictated by the 'f' and 'd' features,
not the core processor register size. Processors with the 'd' feature
have 64-bit FPU registers. Processors without the 'd' feature but with
the 'f' feature have 32-bit FPU registers.

Signed-off-by: Keith Packard <address@hidden>


    Fix checkpatch formatting complaints.
 configure              |  4 ++--
 target/riscv/gdbstub.c | 20 +++++++++++---------
 2 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/configure b/configure
index a72a5def57..c21bff8d10 100755
--- a/configure
+++ b/configure
@@ -7709,13 +7709,13 @@ case "$target_name" in
-    gdb_xml_files="riscv-32bit-cpu.xml riscv-32bit-fpu.xml riscv-32bit-csr.xml 
+    gdb_xml_files="riscv-32bit-cpu.xml riscv-32bit-fpu.xml riscv-64bit-fpu.xml 
riscv-32bit-csr.xml riscv-32bit-virtual.xml"
-    gdb_xml_files="riscv-64bit-cpu.xml riscv-64bit-fpu.xml riscv-64bit-csr.xml 
+    gdb_xml_files="riscv-64bit-cpu.xml riscv-32bit-fpu.xml riscv-64bit-fpu.xml 
riscv-64bit-csr.xml riscv-64bit-virtual.xml"
diff --git a/target/riscv/gdbstub.c b/target/riscv/gdbstub.c
index 1a7947e019..1a72f7be9c 100644
--- a/target/riscv/gdbstub.c
+++ b/target/riscv/gdbstub.c
@@ -303,7 +303,12 @@ int riscv_cpu_gdb_write_register(CPUState *cs, uint8_t 
*mem_buf, int n)
 static int riscv_gdb_get_fpu(CPURISCVState *env, uint8_t *mem_buf, int n)
     if (n < 32) {
-        return gdb_get_reg64(mem_buf, env->fpr[n]);
+        if (env->misa & RVD) {
+            return gdb_get_reg64(mem_buf, env->fpr[n]);
+        }
+        if (env->misa & RVF) {
+            return gdb_get_reg32(mem_buf, env->fpr[n]);
+        }
     /* there is hole between ft11 and fflags in fpu.xml */
     } else if (n < 36 && n > 32) {
         target_ulong val = 0;
@@ -403,23 +408,20 @@ void riscv_cpu_register_gdb_regs_for_features(CPUState 
     RISCVCPU *cpu = RISCV_CPU(cs);
     CPURISCVState *env = &cpu->env;
-#if defined(TARGET_RISCV32)
-    if (env->misa & RVF) {
+    if (env->misa & RVD) {
+        gdb_register_coprocessor(cs, riscv_gdb_get_fpu, riscv_gdb_set_fpu,
+                                 36, "riscv-64bit-fpu.xml", 0);
+    } else if (env->misa & RVF) {
         gdb_register_coprocessor(cs, riscv_gdb_get_fpu, riscv_gdb_set_fpu,
                                  36, "riscv-32bit-fpu.xml", 0);
+#if defined(TARGET_RISCV32)
     gdb_register_coprocessor(cs, riscv_gdb_get_csr, riscv_gdb_set_csr,
                              240, "riscv-32bit-csr.xml", 0);

     gdb_register_coprocessor(cs, riscv_gdb_get_virtual, riscv_gdb_set_virtual,
                              1, "riscv-32bit-virtual.xml", 0);
 #elif defined(TARGET_RISCV64)
-    if (env->misa & RVF) {
-        gdb_register_coprocessor(cs, riscv_gdb_get_fpu, riscv_gdb_set_fpu,
-                                 36, "riscv-64bit-fpu.xml", 0);
-    }
     gdb_register_coprocessor(cs, riscv_gdb_get_csr, riscv_gdb_set_csr,
                              240, "riscv-64bit-csr.xml", 0);

This isn't working for me.  When I apply it on top of my for-master (which is
very close to master), I get
   $ ./install/bin/qemu-system-riscv32 -M virt -m 256 -nographic -cpu rv32 -s -S 
-bios default -kernel vmlinux &
   $ ./install/bin/riscv32-unknown-elf-gdb --ex "target remote :1234"
   GNU gdb (GDB)
   Copyright (C) 2020 Free Software Foundation, Inc.
   License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
   This is free software: you are free to change and redistribute it.
   There is NO WARRANTY, to the extent permitted by law.
   Type "show copying" and "show warranty" for details.
   This GDB was configured as "--host=x86_64-pc-linux-gnu 
   Type "show configuration" for configuration details.
   For bug reporting instructions, please see:
   Find the GDB manual and other documentation resources online at:
For help, type "help".
   Type "apropos word" to search for commands related to "word".
   Remote debugging using :1234
   warning: while parsing target description (at line 1): Could not load XML document 
   warning: Could not load XML target description; ignoring
   warning: No executable has been specified and target does not support
   determining executable automatically.  Try using the "file" command.
   Truncated register 16 in remote 'g' packet
   (gdb) q

The same setup works (for some definition of works, as I get 32-bit D
registers) before the patch, so I don't think it's just something silly in my

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