[Qemu-devel] [PATCH 0/3] ppc/gdbstub: Expose SPRs to GDB

[Qemu-devel] [PATCH 0/3] ppc/gdbstub: Expose SPRs to GDB

[Fabiano Rosas]

This series implements the reading and writing of Special Purpose
Registers in PPC's gdbstub.

* How it works generally [1]:

GDB asks for the target.xml file which contains the target description
along with the list of available feature XMLs. GDB then asks for each
of the XML files in sequence.

The XML files contain a list of registers descriptions:

  <reg name="msr" bitsize="64" type="uint64"/>

When the user tries to access a register, GDB looks for the register
name in the XML file and sends QEMU the index of the register. This
index is sequential across all feature files.

The index provided by GDB must be converted by QEMU to match QEMU's
internal representation.

A set of callbacks are implemented to read/write the register.

* In this series:

The first patch implements the dynamic generation of the power-spr.xml
file. Making it dynamically facilitates converting the GDB index to an
index useful for addressing the env->spr array.

The second patch implements the gdb_{get,set}_spr_reg callbacks along
with the convertion from GDB index to QEMU index.

The third patch enables the functionality.

1- https://sourceware.org/gdb/current/onlinedocs/gdb/Target-Descriptions.html


Fabiano Rosas (3):
  target/ppc: Add SPRs XML generation code for gdbstub
  target/ppc: Add GDB callbacks for SPRs
  target/ppc: Enable reporting of SPRs to GDB

 target/ppc/cpu.h                |  7 ++++
 target/ppc/gdbstub.c            | 45 +++++++++++++++++++++++++
 target/ppc/translate_init.inc.c | 59 +++++++++++++++++++++++++++++++--
 3 files changed, 109 insertions(+), 2 deletions(-)

--
2.17.1

[Qemu-devel] [PATCH 1/3] target/ppc: Add SPRs XML generation code for gdbstub

[Fabiano Rosas]

A following patch will add support for handling the Special Purpose
Registers (SPR) in GDB via gdbstub. For that purpose, GDB needs to be
provided with an XML description of the registers (see gdb-xml
directory).

This patch adds the code that generates the XML dynamically based on
the SPRs already defined in the machine. This eliminates the need for
several XML files to match each possible ppc machine.

A "group" is defined so that the GDB command `info registers spr` can
be used.

Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
---
 target/ppc/cpu.h     |  7 +++++++
 target/ppc/gdbstub.c | 45 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+)

diff --git a/target/ppc/cpu.h b/target/ppc/cpu.h
index d5f99f1fc7..365bca2248 100644
--- a/target/ppc/cpu.h
+++ b/target/ppc/cpu.h
@@ -1052,6 +1052,9 @@ struct CPUPPCState {
     /* Special purpose registers */
     target_ulong spr[1024];
     ppc_spr_t spr_cb[1024];
+#if !defined(CONFIG_USER_ONLY)
+    const char *gdb_spr_xml;
+#endif
     /* Altivec registers */
     ppc_avr_t avr[32];
     uint32_t vscr;
@@ -1264,6 +1267,10 @@ int ppc_cpu_gdb_read_register(CPUState *cpu, uint8_t *buf, int reg);
 int ppc_cpu_gdb_read_register_apple(CPUState *cpu, uint8_t *buf, int reg);
 int ppc_cpu_gdb_write_register(CPUState *cpu, uint8_t *buf, int reg);
 int ppc_cpu_gdb_write_register_apple(CPUState *cpu, uint8_t *buf, int reg);
+#ifndef CONFIG_USER_ONLY
+int ppc_gdb_gen_spr_xml(CPUState *cpu);
+const char *ppc_gdb_get_dynamic_xml(CPUState *cs, const char *xml_name);
+#endif
 int ppc64_cpu_write_elf64_note(WriteCoreDumpFunction f, CPUState *cs,
                                int cpuid, void *opaque);
 int ppc32_cpu_write_elf32_note(WriteCoreDumpFunction f, CPUState *cs,
diff --git a/target/ppc/gdbstub.c b/target/ppc/gdbstub.c
index b6f6693583..82db500457 100644
--- a/target/ppc/gdbstub.c
+++ b/target/ppc/gdbstub.c
@@ -319,3 +319,48 @@ int ppc_cpu_gdb_write_register_apple(CPUState *cs, uint8_t *mem_buf, int n)
     }
     return r;
 }
+
+#ifndef CONFIG_USER_ONLY
+int ppc_gdb_gen_spr_xml(CPUState *cs)
+{
+    PowerPCCPU *cpu = POWERPC_CPU(cs);
+    CPUPPCState *env = &cpu->env;
+    GString *s = g_string_new(NULL);
+    int num_regs = 0;
+    int i;
+
+    g_string_printf(s, "<?xml version=\"1.0\"?>");
+    g_string_append_printf(s, "<!DOCTYPE target SYSTEM \"gdb-target.dtd\">");
+    g_string_append_printf(s, "<feature name=\"org.qemu.power.spr\">");
+
+    for (i = 0; i < ARRAY_SIZE(env->spr_cb); i++) {
+        ppc_spr_t *spr = &env->spr_cb[i];
+
+        if (!spr->name) {
+            continue;
+        }
+
+        g_string_append_printf(s, "<reg name=\"%s\"",
+                               g_ascii_strdown(spr->name, -1));
+        g_string_append_printf(s, " bitsize=\"%d\"", TARGET_LONG_BITS);
+        g_string_append_printf(s, " group=\"spr\"/>");
+
+        num_regs++;
+    }
+
+    g_string_append_printf(s, "</feature>");
+    env->gdb_spr_xml = g_string_free(s, false);
+    return num_regs;
+}
+
+const char *ppc_gdb_get_dynamic_xml(CPUState *cs, const char *xml_name)
+{
+    PowerPCCPU *cpu = POWERPC_CPU(cs);
+    CPUPPCState *env = &cpu->env;
+
+    if (strcmp(xml_name, "power-spr.xml") == 0) {
+        return env->gdb_spr_xml;
+    }
+    return NULL;
+}
+#endif
--
2.17.1

[Qemu-devel] [PATCH 2/3] target/ppc: Add GDB callbacks for SPRs

[Fabiano Rosas]

These will be used to let GDB know about PPC's Special Purpose
Registers (SPR).

They take an index based on the order the registers appear in the XML
file sent by QEMU to GDB. This index does not match the actual
location of the registers in the env->spr array so the
gdb_find_spr_idx function does that conversion.

Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
---
 target/ppc/translate_init.inc.c | 50 +++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/target/ppc/translate_init.inc.c b/target/ppc/translate_init.inc.c
index 03f1d34a97..f10a3637d9 100644
--- a/target/ppc/translate_init.inc.c
+++ b/target/ppc/translate_init.inc.c
@@ -9483,6 +9483,56 @@ static bool avr_need_swap(CPUPPCState *env)
 #endif
 }
 
+#if !defined(CONFIG_USER_ONLY)
+static int gdb_find_spr_idx(CPUPPCState *env, int n)
+{
+    int idx = -1;
+    int i;
+
+    for (i = 0; i < ARRAY_SIZE(env->spr_cb); i++) {
+        ppc_spr_t *spr = &env->spr_cb[i];
+
+        if (spr->name && ++idx == n) {
+            break;
+        }
+    }
+    return i;
+}
+
+static int gdb_get_spr_reg(CPUPPCState *env, uint8_t *mem_buf, int n)
+{
+    int reg;
+    int len;
+
+    reg = gdb_find_spr_idx(env, n);
+    if (!reg) {
+        return 0;
+    }
+
+    len = TARGET_LONG_SIZE;
+    stn_p(mem_buf, len, env->spr[reg]);
+    ppc_maybe_bswap_register(env, mem_buf, len);
+    return len;
+}
+
+static int gdb_set_spr_reg(CPUPPCState *env, uint8_t *mem_buf, int n)
+{
+    int reg;
+    int len;
+
+    reg = gdb_find_spr_idx(env, n);
+    if (!reg) {
+        return 0;
+    }
+
+    len = TARGET_LONG_SIZE;
+    ppc_maybe_bswap_register(env, mem_buf, len);
+    env->spr[reg] = ldn_p(mem_buf, len);
+
+    return len;
+}
+#endif
+
 static int gdb_get_float_reg(CPUPPCState *env, uint8_t *mem_buf, int n)
 {
     if (n < 32) {
-- 
2.17.1

[Qemu-devel] [PATCH 3/3] target/ppc: Enable reporting of SPRs to GDB

[Fabiano Rosas]

This allows reading and writing of SPRs via GDB:

(gdb) p/x $srr1
$1 = 0x8000000002803033

(gdb) p/x $pvr
$2 = 0x4b0201
(gdb) set $pvr=0x4b0000
(gdb) p/x $pvr
$3 = 0x4b0000

They can also be shown as a group:
(gdb) info reg spr

Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
---
 target/ppc/translate_init.inc.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/target/ppc/translate_init.inc.c b/target/ppc/translate_init.inc.c
index f10a3637d9..5771ef5386 100644
--- a/target/ppc/translate_init.inc.c
+++ b/target/ppc/translate_init.inc.c
@@ -9760,7 +9760,10 @@ static void ppc_cpu_realize(DeviceState *dev, Error **errp)
         gdb_register_coprocessor(cs, gdb_get_vsx_reg, gdb_set_vsx_reg,
                                  32, "power-vsx.xml", 0);
     }
-
+#ifndef CONFIG_USER_ONLY
+    gdb_register_coprocessor(cs, gdb_get_spr_reg, gdb_set_spr_reg,
+                             ppc_gdb_gen_spr_xml(cs), "power-spr.xml", 0);
+#endif
     qemu_init_vcpu(cs);
 
     pcc->parent_realize(dev, errp);
@@ -10523,7 +10526,9 @@ static void ppc_cpu_class_init(ObjectClass *oc, void *data)
 #endif
 
     cc->gdb_num_core_regs = 71;
-
+#ifndef CONFIG_USER_ONLY
+    cc->gdb_get_dynamic_xml = ppc_gdb_get_dynamic_xml;
+#endif
 #ifdef USE_APPLE_GDB
     cc->gdb_read_register = ppc_cpu_gdb_read_register_apple;
     cc->gdb_write_register = ppc_cpu_gdb_write_register_apple;
-- 
2.17.1

Re: [Qemu-devel] [PATCH 2/3] target/ppc: Add GDB callbacks for SPRs

[David Gibson]

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On Fri, Jan 04, 2019 at 05:56:53PM -0200, Fabiano Rosas wrote:
> These will be used to let GDB know about PPC's Special Purpose
> Registers (SPR).
> 
> They take an index based on the order the registers appear in the XML
> file sent by QEMU to GDB. This index does not match the actual
> location of the registers in the env->spr array so the
> gdb_find_spr_idx function does that conversion.
> 
> Signed-off-by: Fabiano Rosas <farosas@linux.ibm.com>
> ---
>  target/ppc/translate_init.inc.c | 50 +++++++++++++++++++++++++++++++++
>  1 file changed, 50 insertions(+)
> 
> diff --git a/target/ppc/translate_init.inc.c b/target/ppc/translate_init.inc.c
> index 03f1d34a97..f10a3637d9 100644
> --- a/target/ppc/translate_init.inc.c
> +++ b/target/ppc/translate_init.inc.c
> @@ -9483,6 +9483,56 @@ static bool avr_need_swap(CPUPPCState *env)
>  #endif
>  }
>  
> +#if !defined(CONFIG_USER_ONLY)
> +static int gdb_find_spr_idx(CPUPPCState *env, int n)
> +{
> +    int idx = -1;
> +    int i;
> +
> +    for (i = 0; i < ARRAY_SIZE(env->spr_cb); i++) {
> +        ppc_spr_t *spr = &env->spr_cb[i];
> +
> +        if (spr->name && ++idx == n) {
> +            break;
> +        }
> +    }
> +    return i;
> +}

This is very subtle - it relies on the fact that you also generate the
XML in sequence, which makes for a very non-obvious dependency between
different parts of the code.  At the very least this needs a big fat
comment explaining how the gdb ids are allocated.

I think better would be to explicitly put a gdb_id into the spr_cb
structure - that would be filled in at the same time you generate the
XML, then referenced here.

> +static int gdb_get_spr_reg(CPUPPCState *env, uint8_t *mem_buf, int n)
> +{
> +    int reg;
> +    int len;
> +
> +    reg = gdb_find_spr_idx(env, n);
> +    if (!reg) {
> +        return 0;
> +    }
> +
> +    len = TARGET_LONG_SIZE;
> +    stn_p(mem_buf, len, env->spr[reg]);
> +    ppc_maybe_bswap_register(env, mem_buf, len);
> +    return len;
> +}
> +
> +static int gdb_set_spr_reg(CPUPPCState *env, uint8_t *mem_buf, int n)
> +{
> +    int reg;
> +    int len;
> +
> +    reg = gdb_find_spr_idx(env, n);
> +    if (!reg) {
> +        return 0;
> +    }
> +
> +    len = TARGET_LONG_SIZE;
> +    ppc_maybe_bswap_register(env, mem_buf, len);
> +    env->spr[reg] = ldn_p(mem_buf, len);
> +
> +    return len;
> +}
> +#endif
> +
>  static int gdb_get_float_reg(CPUPPCState *env, uint8_t *mem_buf, int n)
>  {
>      if (n < 32) {

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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