[Qemu-devel] [PATCH] gdbstub: Support AUXV packet for debugging PIE executables.

["Wei-cheng, Wang" <cole945@gmail.com>]

Hi,

This patch adds support for sending AUXV packet.
This is required for debugging Linux position independent executables.
Otherwise, gdb client cannot find out where the executable is loaded.

Signed-off-by: Wei-cheng, Wang <cole945@gmail.com>
---
  gdbstub.c | 41 +++++++++++++++++++++++++++++++++++++++++
  1 file changed, 41 insertions(+)

diff --git a/gdbstub.c b/gdbstub.c
index d1b5afd..30f3bbc 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -1127,6 +1127,7 @@ static int gdb_handle_packet(GDBState *s, const char *line_buf)
              if (cc->gdb_core_xml_file != NULL) {
                  pstrcat(buf, sizeof(buf), ";qXfer:features:read+");
              }
+            pstrcat(buf, sizeof(buf), ";qXfer:auxv:read+");
              put_packet(s, buf);
              break;
          }
@@ -1173,6 +1174,46 @@ static int gdb_handle_packet(GDBState *s, const char *line_buf)
              put_packet_binary(s, buf, len + 1);
              break;
          }
+#ifdef CONFIG_USER_ONLY
+        if (strncmp(p, "Xfer:auxv:read:", 15) == 0) {
+            TaskState *ts = s->c_cpu->opaque;
+            target_ulong auxv = ts->info->saved_auxv;
+            target_ulong auxv_len = ts->info->auxv_len;
+            char *ptr;
+
+            p += 15;
+            while (*p && *p != ':')
+                p++;
+            p++;
+
+            addr = strtoul(p, (char **)&p, 16);
+            if (*p == ',')
+                p++;
+            len = strtoul(p, (char **)&p, 16);
+
+            ptr = lock_user(VERIFY_READ, auxv, auxv_len, 0);
+            if (ptr == NULL) {
+                break;
+            }
+
+            if (addr > len) {
+                snprintf(buf, sizeof(buf), "E00");
+                put_packet(s, buf);
+                break;
+            }
+            if (len > (MAX_PACKET_LENGTH - 5) / 2)
+                len = (MAX_PACKET_LENGTH - 5) / 2;
+            if (len < auxv_len - addr) {
+                buf[0] = 'm';
+                len = memtox(buf + 1, ptr + addr, len);
+            } else {
+                buf[0] = 'l';
+                len = memtox(buf + 1, ptr + addr, auxv_len - addr);
+            }
+            put_packet_binary(s, buf, len + 1);
+            unlock_user(ptr, auxv, len);
+        }
+#endif /* !CONFIG_USER_ONLY */
          /* Unrecognised 'q' command.  */
          goto unknown_command;

-- 
1.9.1