[Qemu-devel] [PATCH v4 0/4] some gdbstub fixes for debug and vcont

[Qemu-devel] [PATCH v4 0/4] some gdbstub fixes for debug and vcont

[Alex Bennée]

Hi Paolo,

I was going through my review queue and realised I had this hanging
around with an outstanding comment. Basically the only change is to
fix the bsd-user build by adding a field for the thread-id. It isn't
populated but it never was and it looks like the gdbstub for threaded
bsd-user programs has been broken forever.

Given the range of different ways of getting a thread-id and the fact
the bsd fork machinery looks like it needs updating anyway I'd left
this for a future BSD maintainer to fix up properly.

Are you happy to take this into your tree?

Alex Bennée (4):
  gdbstub: modernise DEBUG_GDB
  gdbstub: rename cpu_index -> cpu_gdb_index
  qom/cpu: remove host_tid field
  gdbstub: don't fail on vCont;C04:0;c packets

 bsd-user/qemu.h        |   2 +
 gdbstub.c              | 117 ++++++++++++++++++++++++-------------------------
 include/exec/gdbstub.h |   9 ----
 include/qom/cpu.h      |   2 -
 linux-user/syscall.c   |   1 -
 5 files changed, 59 insertions(+), 72 deletions(-)

-- 
2.13.0

[Qemu-devel] [PATCH v4 1/4] gdbstub: modernise DEBUG_GDB

[Alex Bennée]

Convert the a gdb_debug helper which compiles away to nothing when not
used but still ensures the format strings are checked. There is some
minor code motion for the incorrect checksum message to report it
before we attempt to send the reply.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Greg Kurz <groug@kaod.org>
---
 gdbstub.c | 77 +++++++++++++++++++++++++++------------------------------------
 1 file changed, 33 insertions(+), 44 deletions(-)

diff --git a/gdbstub.c b/gdbstub.c
index ec4e4b25be..31db2309aa 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -272,7 +272,20 @@ static int gdb_signal_to_target (int sig)
         return -1;
 }
 
-//#define DEBUG_GDB
+/* #define DEBUG_GDB */
+
+#ifdef DEBUG_GDB
+# define DEBUG_GDB_GATE 1
+#else
+# define DEBUG_GDB_GATE 0
+#endif
+
+#define gdb_debug(fmt, ...) do { \
+    if (DEBUG_GDB_GATE) { \
+        fprintf(stderr, "%s: " fmt, __func__, ## __VA_ARGS__); \
+    } \
+} while (0)
+
 
 typedef struct GDBRegisterState {
     int base_reg;
@@ -548,9 +561,7 @@ static int put_packet_binary(GDBState *s, const char *buf, int len)
 /* return -1 if error, 0 if OK */
 static int put_packet(GDBState *s, const char *buf)
 {
-#ifdef DEBUG_GDB
-    printf("reply='%s'\n", buf);
-#endif
+    gdb_debug("reply='%s'\n", buf);
 
     return put_packet_binary(s, buf, strlen(buf));
 }
@@ -956,9 +967,9 @@ static int gdb_handle_packet(GDBState *s, const char *line_buf)
     uint8_t *registers;
     target_ulong addr, len;
 
-#ifdef DEBUG_GDB
-    printf("command='%s'\n", line_buf);
-#endif
+
+    gdb_debug("command='%s'\n", line_buf);
+
     p = line_buf;
     ch = *p++;
     switch(ch) {
@@ -1519,17 +1530,14 @@ static void gdb_read_byte(GDBState *s, int ch)
         /* Waiting for a response to the last packet.  If we see the start
            of a new command then abandon the previous response.  */
         if (ch == '-') {
-#ifdef DEBUG_GDB
-            printf("Got NACK, retransmitting\n");
-#endif
+            gdb_debug("Got NACK, retransmitting\n");
             put_buffer(s, (uint8_t *)s->last_packet, s->last_packet_len);
+        } else if (ch == '+') {
+            gdb_debug("Got ACK\n");
+        } else {
+            gdb_debug("Got '%c' when expecting ACK/NACK\n", ch);
         }
-#ifdef DEBUG_GDB
-        else if (ch == '+')
-            printf("Got ACK\n");
-        else
-            printf("Got '%c' when expecting ACK/NACK\n", ch);
-#endif
+
         if (ch == '+' || ch == '$')
             s->last_packet_len = 0;
         if (ch != '$')
@@ -1550,9 +1558,7 @@ static void gdb_read_byte(GDBState *s, int ch)
                 s->line_sum = 0;
                 s->state = RS_GETLINE;
             } else {
-#ifdef DEBUG_GDB
-                printf("gdbstub received garbage between packets: 0x%x\n", ch);
-#endif
+                gdb_debug("received garbage between packets: 0x%x\n", ch);
             }
             break;
         case RS_GETLINE:
@@ -1568,9 +1574,7 @@ static void gdb_read_byte(GDBState *s, int ch)
                 /* end of command, start of checksum*/
                 s->state = RS_CHKSUM1;
             } else if (s->line_buf_index >= sizeof(s->line_buf) - 1) {
-#ifdef DEBUG_GDB
-                printf("gdbstub command buffer overrun, dropping command\n");
-#endif
+                gdb_debug("command buffer overrun, dropping command\n");
                 s->state = RS_IDLE;
             } else {
                 /* unescaped command character */
@@ -1584,9 +1588,7 @@ static void gdb_read_byte(GDBState *s, int ch)
                 s->state = RS_CHKSUM1;
             } else if (s->line_buf_index >= sizeof(s->line_buf) - 1) {
                 /* command buffer overrun */
-#ifdef DEBUG_GDB
-                printf("gdbstub command buffer overrun, dropping command\n");
-#endif
+                gdb_debug("command buffer overrun, dropping command\n");
                 s->state = RS_IDLE;
             } else {
                 /* parse escaped character and leave escape state */
@@ -1598,25 +1600,18 @@ static void gdb_read_byte(GDBState *s, int ch)
         case RS_GETLINE_RLE:
             if (ch < ' ') {
                 /* invalid RLE count encoding */
-#ifdef DEBUG_GDB
-                printf("gdbstub got invalid RLE count: 0x%x\n", ch);
-#endif
+                gdb_debug("got invalid RLE count: 0x%x\n", ch);
                 s->state = RS_GETLINE;
             } else {
                 /* decode repeat length */
                 int repeat = (unsigned char)ch - ' ' + 3;
                 if (s->line_buf_index + repeat >= sizeof(s->line_buf) - 1) {
                     /* that many repeats would overrun the command buffer */
-#ifdef DEBUG_GDB
-                    printf("gdbstub command buffer overrun,"
-                           " dropping command\n");
-#endif
+                    gdb_debug("command buffer overrun, dropping command\n");
                     s->state = RS_IDLE;
                 } else if (s->line_buf_index < 1) {
                     /* got a repeat but we have nothing to repeat */
-#ifdef DEBUG_GDB
-                    printf("gdbstub got invalid RLE sequence\n");
-#endif
+                    gdb_debug("got invalid RLE sequence\n");
                     s->state = RS_GETLINE;
                 } else {
                     /* repeat the last character */
@@ -1631,9 +1626,7 @@ static void gdb_read_byte(GDBState *s, int ch)
         case RS_CHKSUM1:
             /* get high hex digit of checksum */
             if (!isxdigit(ch)) {
-#ifdef DEBUG_GDB
-                printf("gdbstub got invalid command checksum digit\n");
-#endif
+                gdb_debug("got invalid command checksum digit\n");
                 s->state = RS_GETLINE;
                 break;
             }
@@ -1644,21 +1637,17 @@ static void gdb_read_byte(GDBState *s, int ch)
         case RS_CHKSUM2:
             /* get low hex digit of checksum */
             if (!isxdigit(ch)) {
-#ifdef DEBUG_GDB
-                printf("gdbstub got invalid command checksum digit\n");
-#endif
+                gdb_debug("got invalid command checksum digit\n");
                 s->state = RS_GETLINE;
                 break;
             }
             s->line_csum |= fromhex(ch);
 
             if (s->line_csum != (s->line_sum & 0xff)) {
+                gdb_debug("got command packet with incorrect checksum\n");
                 /* send NAK reply */
                 reply = '-';
                 put_buffer(s, &reply, 1);
-#ifdef DEBUG_GDB
-                printf("gdbstub got command packet with incorrect checksum\n");
-#endif
                 s->state = RS_IDLE;
             } else {
                 /* send ACK reply */
-- 
2.13.0

[Qemu-devel] [PATCH v4 2/4] gdbstub: rename cpu_index -> cpu_gdb_index

[Alex Bennée]

This is to make it clear the index is purely a gdbstub function and
should not be confused with the value of cpu->cpu_index. At the same
time we move the function from the header to gdbstub itself which will
help with later changes.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

---
v3
  - move cpu_gdb_index into gdbstub
---
 gdbstub.c              | 26 ++++++++++++++++++++------
 include/exec/gdbstub.h |  9 ---------
 2 files changed, 20 insertions(+), 15 deletions(-)

diff --git a/gdbstub.c b/gdbstub.c
index 31db2309aa..6b56f55eba 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -56,6 +56,20 @@ static inline int target_memory_rw_debug(CPUState *cpu, target_ulong addr,
     return cpu_memory_rw_debug(cpu, addr, buf, len, is_write);
 }
 
+/* Return the GDB index for a given vCPU state.
+ *
+ * For user mode this is simply the thread id. In system mode GDB
+ * numbers CPUs from 1 as 0 is reserved as an "any cpu" index.
+ */
+static inline int cpu_gdb_index(CPUState *cpu)
+{
+#if defined(CONFIG_USER_ONLY)
+    return cpu->host_tid;
+#else
+    return cpu->cpu_index + 1;
+#endif
+}
+
 enum {
     GDB_SIGNAL_0 = 0,
     GDB_SIGNAL_INT = 2,
@@ -838,7 +852,7 @@ static CPUState *find_cpu(uint32_t thread_id)
     CPUState *cpu;
 
     CPU_FOREACH(cpu) {
-        if (cpu_index(cpu) == thread_id) {
+        if (cpu_gdb_index(cpu) == thread_id) {
             return cpu;
         }
     }
@@ -926,7 +940,7 @@ static int gdb_handle_vcont(GDBState *s, const char *p)
             idx = tmp;
             /* 0 means any thread, so we pick the first valid CPU */
             if (!idx) {
-                idx = cpu_index(first_cpu);
+                idx = cpu_gdb_index(first_cpu);
             }
 
             /*
@@ -976,7 +990,7 @@ static int gdb_handle_packet(GDBState *s, const char *line_buf)
     case '?':
         /* TODO: Make this return the correct value for user-mode.  */
         snprintf(buf, sizeof(buf), "T%02xthread:%02x;", GDB_SIGNAL_TRAP,
-                 cpu_index(s->c_cpu));
+                 cpu_gdb_index(s->c_cpu));
         put_packet(s, buf);
         /* Remove all the breakpoints when this query is issued,
          * because gdb is doing and initial connect and the state
@@ -1244,7 +1258,7 @@ static int gdb_handle_packet(GDBState *s, const char *line_buf)
         } else if (strcmp(p,"sThreadInfo") == 0) {
         report_cpuinfo:
             if (s->query_cpu) {
-                snprintf(buf, sizeof(buf), "m%x", cpu_index(s->query_cpu));
+                snprintf(buf, sizeof(buf), "m%x", cpu_gdb_index(s->query_cpu));
                 put_packet(s, buf);
                 s->query_cpu = CPU_NEXT(s->query_cpu);
             } else
@@ -1401,7 +1415,7 @@ static void gdb_vm_state_change(void *opaque, int running, RunState state)
             }
             snprintf(buf, sizeof(buf),
                      "T%02xthread:%02x;%swatch:" TARGET_FMT_lx ";",
-                     GDB_SIGNAL_TRAP, cpu_index(cpu), type,
+                     GDB_SIGNAL_TRAP, cpu_gdb_index(cpu), type,
                      (target_ulong)cpu->watchpoint_hit->vaddr);
             cpu->watchpoint_hit = NULL;
             goto send_packet;
@@ -1435,7 +1449,7 @@ static void gdb_vm_state_change(void *opaque, int running, RunState state)
         break;
     }
     gdb_set_stop_cpu(cpu);
-    snprintf(buf, sizeof(buf), "T%02xthread:%02x;", ret, cpu_index(cpu));
+    snprintf(buf, sizeof(buf), "T%02xthread:%02x;", ret, cpu_gdb_index(cpu));
 
 send_packet:
     put_packet(s, buf);
diff --git a/include/exec/gdbstub.h b/include/exec/gdbstub.h
index f9708bbcd6..9aa7756d92 100644
--- a/include/exec/gdbstub.h
+++ b/include/exec/gdbstub.h
@@ -58,15 +58,6 @@ void gdb_register_coprocessor(CPUState *cpu,
                               gdb_reg_cb get_reg, gdb_reg_cb set_reg,
                               int num_regs, const char *xml, int g_pos);
 
-static inline int cpu_index(CPUState *cpu)
-{
-#if defined(CONFIG_USER_ONLY)
-    return cpu->host_tid;
-#else
-    return cpu->cpu_index + 1;
-#endif
-}
-
 /* The GDB remote protocol transfers values in target byte order.  This means
  * we can use the raw memory access routines to access the value buffer.
  * Conveniently, these also handle the case where the buffer is mis-aligned.
-- 
2.13.0

[Qemu-devel] [PATCH v4 3/4] qom/cpu: remove host_tid field

[Alex Bennée]

This was only used by the gdbstub and even then was only being set for
subsequent threads. Rather the continue duplicating the number just
make the gdbstub get the information from TaskState structure.

Now the tid is correctly reported for all threads the bug I was seeing
with "vCont;C04:0;c" packets is fixed as the correct tid is reported
to gdb.

I moved cpu_gdb_index into the gdbstub to facilitate easy access to
the TaskState which is used elsewhere in gdbstub.

To prevent BSD failing to build I've included ts_tid into its
TaskStruct but not populated it - which was the same state as the old
cpu->host_tid. I'll leave it up to the BSD maintainers to actually
populate this properly if they want a working gdbstub with
user-threads.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Laurent Vivier <laurent@vivier.eu>

---
v4
  - add host_tid field for BSD (but don't populate it)
v3
  - fix merge, did move of function in previous commit
---
 bsd-user/qemu.h      | 2 ++
 gdbstub.c            | 3 ++-
 include/qom/cpu.h    | 2 --
 linux-user/syscall.c | 1 -
 4 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/bsd-user/qemu.h b/bsd-user/qemu.h
index b550cee0cb..19b2b8fecb 100644
--- a/bsd-user/qemu.h
+++ b/bsd-user/qemu.h
@@ -85,6 +85,8 @@ struct emulated_sigtable {
 /* NOTE: we force a big alignment so that the stack stored after is
    aligned too */
 typedef struct TaskState {
+    pid_t ts_tid;     /* tid (or pid) of this task */
+
     struct TaskState *next;
     int used; /* non zero if used */
     struct image_info *info;
diff --git a/gdbstub.c b/gdbstub.c
index 6b56f55eba..484e96dbd9 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -64,7 +64,8 @@ static inline int target_memory_rw_debug(CPUState *cpu, target_ulong addr,
 static inline int cpu_gdb_index(CPUState *cpu)
 {
 #if defined(CONFIG_USER_ONLY)
-    return cpu->host_tid;
+    TaskState *ts = (TaskState *) cpu->opaque;
+    return ts->ts_tid;
 #else
     return cpu->cpu_index + 1;
 #endif
diff --git a/include/qom/cpu.h b/include/qom/cpu.h
index 7bfd50cc32..d3c783b4b5 100644
--- a/include/qom/cpu.h
+++ b/include/qom/cpu.h
@@ -265,7 +265,6 @@ struct qemu_work_item;
  * @cpu_index: CPU index (informative).
  * @nr_cores: Number of cores within this CPU package.
  * @nr_threads: Number of threads within this CPU.
- * @host_tid: Host thread ID.
  * @running: #true if CPU is currently running (lockless).
  * @has_waiter: #true if a CPU is currently waiting for the cpu_exec_end;
  * valid under cpu_list_lock.
@@ -319,7 +318,6 @@ struct CPUState {
     HANDLE hThread;
 #endif
     int thread_id;
-    uint32_t host_tid;
     bool running, has_waiter;
     struct QemuCond *halt_cond;
     bool thread_kicked;
diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 925ae11ea6..003943b736 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -6219,7 +6219,6 @@ static void *clone_func(void *arg)
     thread_cpu = cpu;
     ts = (TaskState *)cpu->opaque;
     info->tid = gettid();
-    cpu->host_tid = info->tid;
     task_settid(ts);
     if (info->child_tidptr)
         put_user_u32(info->tid, info->child_tidptr);
-- 
2.13.0

[Qemu-devel] [PATCH v4 4/4] gdbstub: don't fail on vCont; C04:0; c packets

[Alex Bennée]

The thread-id of 0 means any CPU but we then ignore the fact we find
the first_cpu in this case who can have an index of 0. Instead of
bailing out just test if we have managed to match up thread-id to a
CPU.

Otherwise you get:
  gdb_handle_packet: command='vCont;C04:0;c'
  put_packet: reply='E22'

The actual reason for gdb sending vCont;C04:0;c was fixed in a
previous commit where we ensure the first_cpu's tid is correctly
reported to gdb however we should still behave correctly next time it
does send 0.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Greg Kurz <groug@kaod.org>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.vnet.ibm.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

---
v4
  - one more r-b
v2
  - used Greg's less convoluted suggestion
  - expand commit message
---
 gdbstub.c | 15 ++++-----------
 1 file changed, 4 insertions(+), 11 deletions(-)

diff --git a/gdbstub.c b/gdbstub.c
index 484e96dbd9..a576585638 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -938,23 +938,16 @@ static int gdb_handle_vcont(GDBState *s, const char *p)
             if (res) {
                 goto out;
             }
-            idx = tmp;
+
             /* 0 means any thread, so we pick the first valid CPU */
-            if (!idx) {
-                idx = cpu_gdb_index(first_cpu);
-            }
+            cpu = tmp ? find_cpu(tmp) : first_cpu;
 
-            /*
-             * If we are in user mode, the thread specified is actually a
-             * thread id, and not an index. We need to find the actual
-             * CPU first, and only then we can use its index.
-             */
-            cpu = find_cpu(idx);
             /* invalid CPU/thread specified */
-            if (!idx || !cpu) {
+            if (!cpu) {
                 res = -EINVAL;
                 goto out;
             }
+
             /* only use if no previous match occourred */
             if (newstates[cpu->cpu_index] == 1) {
                 newstates[cpu->cpu_index] = cur_action;
-- 
2.13.0

Re: [Qemu-devel] [PATCH v4 0/4] some gdbstub fixes for debug and vcont

[Philippe Mathieu-Daudé]

CC'ed Kamil Rytarowski (new NetBSD maintainer)

On 07/12/2017 07:52 AM, Alex Bennée wrote:
> Hi Paolo,
> 
> I was going through my review queue and realised I had this hanging
> around with an outstanding comment. Basically the only change is to
> fix the bsd-user build by adding a field for the thread-id. It isn't
> populated but it never was and it looks like the gdbstub for threaded
> bsd-user programs has been broken forever.
> 
> Given the range of different ways of getting a thread-id and the fact
> the bsd fork machinery looks like it needs updating anyway I'd left
> this for a future BSD maintainer to fix up properly.
> 
> Are you happy to take this into your tree?
> 
> Alex Bennée (4):
>    gdbstub: modernise DEBUG_GDB
>    gdbstub: rename cpu_index -> cpu_gdb_index
>    qom/cpu: remove host_tid field
>    gdbstub: don't fail on vCont;C04:0;c packets
> 
>   bsd-user/qemu.h        |   2 +
>   gdbstub.c              | 117 ++++++++++++++++++++++++-------------------------
>   include/exec/gdbstub.h |   9 ----
>   include/qom/cpu.h      |   2 -
>   linux-user/syscall.c   |   1 -
>   5 files changed, 59 insertions(+), 72 deletions(-)
> 

Re: [Qemu-devel] [PATCH v4 0/4] some gdbstub fixes for debug and vcont

[Paolo Bonzini]

On 12/07/2017 12:52, Alex Bennée wrote:
> Hi Paolo,
> 
> I was going through my review queue and realised I had this hanging
> around with an outstanding comment. Basically the only change is to
> fix the bsd-user build by adding a field for the thread-id. It isn't
> populated but it never was and it looks like the gdbstub for threaded
> bsd-user programs has been broken forever.
> 
> Given the range of different ways of getting a thread-id and the fact
> the bsd fork machinery looks like it needs updating anyway I'd left
> this for a future BSD maintainer to fix up properly.
> 
> Are you happy to take this into your tree?

Yes, I will include it in my pull request.

Paolo