[PATCH v2 4/5] gdbstub: Add Xfer:siginfo:read stub

[Gustavo Romero <gustavo.romero@linaro.org>]

Add stub to handle Xfer:siginfo:read packet query that requests the
machine's siginfo data.

This is used when GDB user executes 'print $_siginfo' and when the
machine stops due to a signal, for instance, on SIGSEGV. The information
in siginfo allows GDB to determiner further details on the signal, like
the fault address/insn when the SIGSEGV is caught.

Signed-off-by: Gustavo Romero <gustavo.romero@linaro.org>
---
 gdbstub/gdbstub.c     |  8 ++++++++
 gdbstub/internals.h   |  1 +
 gdbstub/user-target.c | 23 +++++++++++++++++++++++
 3 files changed, 32 insertions(+)

diff --git a/gdbstub/gdbstub.c b/gdbstub/gdbstub.c
index 2909bc8c69..ab38cea46b 100644
--- a/gdbstub/gdbstub.c
+++ b/gdbstub/gdbstub.c
@@ -1651,6 +1651,8 @@ static void handle_query_supported(GArray *params, void *user_ctx)
         g_string_append(gdbserver_state.str_buf, ";qXfer:auxv:read+");
     }
     g_string_append(gdbserver_state.str_buf, ";QCatchSyscalls+");
+
+    g_string_append(gdbserver_state.str_buf, ";qXfer:siginfo:read+");
 #endif
     g_string_append(gdbserver_state.str_buf, ";qXfer:exec-file:read+");
 #endif
@@ -1799,6 +1801,12 @@ static const GdbCmdParseEntry gdb_gen_query_table[] = {
         .cmd_startswith = 1,
         .schema = "l,l0"
     },
+    {
+        .handler = gdb_handle_query_xfer_siginfo,
+        .cmd = "Xfer:siginfo:read::",
+        .cmd_startswith = 1,
+        .schema = "l,l0"
+     },
 #endif
     {
         .handler = gdb_handle_query_xfer_exec_file,
diff --git a/gdbstub/internals.h b/gdbstub/internals.h
index a7cc69dab3..15c01c525a 100644
--- a/gdbstub/internals.h
+++ b/gdbstub/internals.h
@@ -193,6 +193,7 @@ typedef union GdbCmdVariant {
 void gdb_handle_query_rcmd(GArray *params, void *user_ctx); /* softmmu */
 void gdb_handle_query_offsets(GArray *params, void *user_ctx); /* user */
 void gdb_handle_query_xfer_auxv(GArray *params, void *user_ctx); /*user */
+void gdb_handle_query_xfer_siginfo(GArray *params, void *user_ctx); /*user */
 void gdb_handle_v_file_open(GArray *params, void *user_ctx); /* user */
 void gdb_handle_v_file_close(GArray *params, void *user_ctx); /* user */
 void gdb_handle_v_file_pread(GArray *params, void *user_ctx); /* user */
diff --git a/gdbstub/user-target.c b/gdbstub/user-target.c
index 215bf33ab3..93739852b0 100644
--- a/gdbstub/user-target.c
+++ b/gdbstub/user-target.c
@@ -285,6 +285,29 @@ void gdb_handle_query_xfer_auxv(GArray *params, void *user_ctx)
     gdb_put_packet_binary(gdbserver_state.str_buf->str,
                       gdbserver_state.str_buf->len, true);
 }
+
+void gdb_handle_query_xfer_siginfo(GArray *params, void *user_ctx)
+{
+    unsigned long offset, len;
+    uint8_t *siginfo_offset;
+
+    offset = get_param(params, 0)->val_ul;
+    len = get_param(params, 1)->val_ul;
+
+    if (offset + len > sizeof(target_siginfo_t)) {
+        /* Invalid offset and/or requested length. */
+        gdb_put_packet("E01");
+        return;
+    }
+
+    siginfo_offset = (uint8_t *)gdbserver_state.siginfo + offset;
+
+    /* Reply */
+    g_string_assign(gdbserver_state.str_buf, "l");
+    gdb_memtox(gdbserver_state.str_buf, (const char *)siginfo_offset, len);
+    gdb_put_packet_binary(gdbserver_state.str_buf->str,
+                          gdbserver_state.str_buf->len, true);
+}
 #endif
 
 static const char *get_filename_param(GArray *params, int i)
-- 
2.34.1