gdbstub: add support to Xfer:auxv:read: packet

This allows gdb to access the target’s auxiliary vector,
which can be helpful for telling system libraries important details
about the hardware, operating system, and process.

Signed-off-by: Lirong Yuan <yuanzi@google.com>
[AJB: minor tweaks to test case, update MAINTAINERS, restrict to Linux]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20200730193932.3654677-1-yuanzi@google.com>
Message-Id: <20210108224256.2321-7-alex.bennee@linaro.org>

1 files changed, 54 insertions, 0 deletions

diff --git a/gdbstub.c b/gdbstub.c
index d99bc0bf2e..aeffdaf06f 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -2172,6 +2172,12 @@ static void handle_query_supported(GdbCmdContext *gdb_ctx, void *user_ctx)
             ";ReverseStep+;ReverseContinue+");
     }
 
+#ifdef CONFIG_USER_ONLY
+    if (gdbserver_state.c_cpu->opaque) {
+        g_string_append(gdbserver_state.str_buf, ";qXfer:auxv:read+");
+    }
+#endif
+
     if (gdb_ctx->num_params &&
         strstr(gdb_ctx->params[0].data, "multiprocess+")) {
         gdbserver_state.multiprocess = true;
@@ -2233,6 +2239,46 @@ static void handle_query_xfer_features(GdbCmdContext *gdb_ctx, void *user_ctx)
                       gdbserver_state.str_buf->len, true);
 }
 
+#if defined(CONFIG_USER_ONLY) && defined(CONFIG_LINUX_USER)
+static void handle_query_xfer_auxv(GdbCmdContext *gdb_ctx, void *user_ctx)
+{
+    TaskState *ts;
+    unsigned long offset, len, saved_auxv, auxv_len;
+    const char *mem;
+
+    if (gdb_ctx->num_params < 2) {
+        put_packet("E22");
+        return;
+    }
+
+    offset = gdb_ctx->params[0].val_ul;
+    len = gdb_ctx->params[1].val_ul;
+    ts = gdbserver_state.c_cpu->opaque;
+    saved_auxv = ts->info->saved_auxv;
+    auxv_len = ts->info->auxv_len;
+    mem = (const char *)(saved_auxv + offset);
+    if (offset > auxv_len) {
+        put_packet("E00");
+        return;
+    }
+
+    if (len > (MAX_PACKET_LENGTH - 5) / 2) {
+        len = (MAX_PACKET_LENGTH - 5) / 2;
+    }
+
+    if (len < auxv_len - offset) {
+        g_string_assign(gdbserver_state.str_buf, "m");
+        memtox(gdbserver_state.str_buf, mem, len);
+    } else {
+        g_string_assign(gdbserver_state.str_buf, "l");
+        memtox(gdbserver_state.str_buf, mem, auxv_len - offset);
+    }
+
+    put_packet_binary(gdbserver_state.str_buf->str,
+                      gdbserver_state.str_buf->len, true);
+}
+#endif
+
 static void handle_query_attached(GdbCmdContext *gdb_ctx, void *user_ctx)
 {
     put_packet(GDB_ATTACHED);
@@ -2338,6 +2384,14 @@ static GdbCmdParseEntry gdb_gen_query_table[] = {
         .cmd_startswith = 1,
         .schema = "s:l,l0"
     },
+#if defined(CONFIG_USER_ONLY) && defined(CONFIG_LINUX_USER)
+    {
+        .handler = handle_query_xfer_auxv,
+        .cmd = "Xfer:auxv:read::",
+        .cmd_startswith = 1,
+        .schema = "l,l0"
+    },
+#endif
     {
         .handler = handle_query_attached,
         .cmd = "Attached:",