cpukit/libdebugger: Add support for TLS variables

This adds support for the "vGetTLSAddr" GDB query which retrieves the
address of a TLS variable by offset from the beginning of the TLS memory
space for the given thread. This offset does not include the size of the
thread control block which is at the beginning of every TLS area as used
by RTEMS. Notably, the returned address is big-endian rather than the
little-endian typical with other responses.

This functionality does not include retrieval of addresses for TLS
variables hosted in loadable modules, only TLS variables in the host
binary.

Closes #5271

cpukit/libdebugger/rtems-debugger-server.c

@@ -33,6 +33,7 @@
 
 #include <rtems/bspIo.h>
 #include <rtems/score/smp.h>
+#include <rtems/score/tls.h>
 
 #include <rtems/rtems-debugger.h>
 #include <rtems/debugger/rtems-debugger-server.h>
@@ -696,6 +697,25 @@ remote_packet_out_append_hex(const uint8_t* data, size_t size)
   return 0;
 }
 
+/* output data in big-endian instead of little-endian */
+static int
+remote_packet_out_append_hex_be(const uint8_t* data, size_t size)
+{
+  size_t ol = rtems_debugger->output_level;
+  size_t i = size;
+  while (i > 0) {
+    uint8_t byte = data[--i];
+    if (rtems_debugger->output_level >= (RTEMS_DEBUGGER_BUFFER_SIZE - 2)) {
+      rtems_debugger->output_level = ol;
+      rtems_debugger_printf("rtems-db: output overflow\n");
+      return -1;
+    }
+    rtems_debugger->output[rtems_debugger->output_level++] = hex_encode(byte >> 4);
+    rtems_debugger->output[rtems_debugger->output_level++] = hex_encode(byte);
+  }
+  return 0;
+}
+
 static int
 remote_packet_out_append_str(const char* str)
 {
@@ -1019,6 +1039,115 @@ remote_gq_attached(uint8_t* buffer, int size)
   return 0;
 }
 
+static rtems_debugger_thread* get_debugger_thread_from_id(const char* thread_id)
+{
+  int r;
+  DB_UINT pid = 0;
+  DB_UINT tid = 0;
+  bool    extended;
+  rtems_debugger_threads* threads = rtems_debugger->threads;
+  rtems_debugger_thread* current;
+
+  extended = thread_id_decode(thread_id, &pid, &tid);
+  if (!extended && !check_pid(pid)) {
+    return NULL;
+  }
+
+  r = rtems_debugger_thread_find_index(tid);
+  if (r < 0) {
+    return NULL;
+  }
+
+  current = rtems_debugger_thread_current(threads);
+  return &current[r];
+}
+
+static int
+parse_get_tls_addr(
+  uint8_t* buffer,
+  int size,
+  const char** thread_id_str,
+  const char** offset_str,
+  const char** lm_str
+)
+{
+  if (thread_id_str == NULL || offset_str == NULL || lm_str == NULL) {
+    return 1;
+  }
+
+  *thread_id_str = strchr((const char*) buffer, ':') + 1;
+  if (*thread_id_str == NULL || *thread_id_str - (char*)buffer > size) {
+    /* malformed packet */
+    return 1;
+  }
+
+  *offset_str = strchr(*thread_id_str, ',') + 1;
+  if (*offset_str == NULL || *offset_str - (char*)buffer > size) {
+    /* malformed packet */
+    return 1;
+  }
+
+  *lm_str = strchr(*offset_str, ',') + 1;
+  if (*lm_str == NULL || *lm_str - (char*)buffer > size) {
+    /* malformed packet */
+    return 1;
+  }
+
+  return 0;
+}
+
+static int
+remote_gq_get_tls_addr(uint8_t* buffer, int size)
+{
+  const char* thread_id_str;
+  const char* offset_str;
+  const char* lm_str;
+  uint64_t target_address;
+  int r;
+  rtems_debugger_thread* thread;
+  DB_UINT offset;
+  DB_UINT lm;
+
+  if (parse_get_tls_addr(buffer, size, &thread_id_str, &offset_str, &lm_str)) {
+    /* malformed packet */
+    remote_packet_out_str(r_E01);
+    remote_packet_out_send();
+    return 0;
+  }
+
+  offset = hex_decode_uint((const uint8_t*) offset_str);
+  lm = hex_decode_uint((const uint8_t*) lm_str);
+  if (lm != 0) {
+    /*
+     * TODO(kmoore) lm is the load module identifier. It is ignored and expected
+     * to be 0 until TLS support for dynamically loaded modules is added.
+     */
+    remote_packet_out_str(r_E01);
+    remote_packet_out_send();
+    return 0;
+  }
+
+  thread = get_debugger_thread_from_id(thread_id_str);
+  if (thread == NULL) {
+    remote_packet_out_str(r_E01);
+    remote_packet_out_send();
+    return 0;
+  }
+
+  target_address = thread->tcb->Registers.thread_id;
+  target_address += sizeof(TLS_Thread_control_block) + offset;
+
+  remote_packet_out_reset();
+  r = remote_packet_out_append_hex_be((const uint8_t*) &target_address,
+                                   sizeof(target_address));
+
+  if (r < 0) {
+    remote_packet_out_str(r_E01);
+  }
+  remote_packet_out_send();
+  return 0;
+}
+
 static const rtems_debugger_packet general_query[] = {
   { .label   = "qfThreadInfo",
     .command = remote_gq_thread_info_first },
@@ -1032,6 +1161,8 @@ static const rtems_debugger_packet general_query[] = {
     .command = remote_gq_attached },
   { .label   = "qXfer",
     .command = remote_gq_uninterpreted_transfer },
+  { .label   = "qGetTLSAddr",
+    .command = remote_gq_get_tls_addr },
 };
 
 #define REMOTE_GENERAL_QUERIES RTEMS_DEBUGGER_NUMOF(general_query)