[PATCH] gdbstub: add support to Xfer:auxv:read: packet

[Lirong Yuan]

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 <yua...@google.com>
---
 gdbstub.c | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)

diff --git a/gdbstub.c b/gdbstub.c
index 22a2d630cd..c2865ea873 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -2105,6 +2105,12 @@ static void handle_query_supported(GdbCmdContext 
*gdb_ctx, void *user_ctx)
         pstrcat(gdb_ctx->str_buf, sizeof(gdb_ctx->str_buf),
                 ";qXfer:features:read+");
     }
+#ifdef CONFIG_USER_ONLY
+    if (gdb_ctx->s->c_cpu->opaque) {
+        pstrcat(gdb_ctx->str_buf, sizeof(gdb_ctx->str_buf),
+                ";qXfer:auxv:read+");
+    }
+#endif
 
     if (gdb_ctx->num_params &&
         strstr(gdb_ctx->params[0].data, "multiprocess+")) {
@@ -2166,6 +2172,42 @@ static void handle_query_xfer_features(GdbCmdContext 
*gdb_ctx, void *user_ctx)
     put_packet_binary(gdb_ctx->s, gdb_ctx->str_buf, len + 1, true);
 }
 
+#ifdef CONFIG_USER_ONLY
+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(gdb_ctx->s, "E22");
+        return;
+    }
+
+    offset = gdb_ctx->params[0].val_ul;
+    len = gdb_ctx->params[1].val_ul;
+
+    ts = gdb_ctx->s->c_cpu->opaque;
+    saved_auxv = ts->info->saved_auxv;
+    auxv_len = ts->info->auxv_len;
+    mem = (const char *)(saved_auxv + offset);
+
+    if (len > (MAX_PACKET_LENGTH - 5) / 2) {
+        len = (MAX_PACKET_LENGTH - 5) / 2;
+    }
+
+    if (len < auxv_len - offset) {
+        gdb_ctx->str_buf[0] = 'm';
+        len = memtox(gdb_ctx->str_buf + 1, mem, len);
+    } else {
+        gdb_ctx->str_buf[0] = 'l';
+        len = memtox(gdb_ctx->str_buf + 1, mem, auxv_len - offset);
+    }
+
+    put_packet_binary(gdb_ctx->s, gdb_ctx->str_buf, len + 1, true);
+}
+#endif
+
 static void handle_query_attached(GdbCmdContext *gdb_ctx, void *user_ctx)
 {
     put_packet(gdb_ctx->s, GDB_ATTACHED);
@@ -2271,6 +2313,14 @@ static GdbCmdParseEntry gdb_gen_query_table[] = {
         .cmd_startswith = 1,
         .schema = "s:l,l0"
     },
+#ifdef CONFIG_USER_ONLY
+    {
+        .handler = handle_query_xfer_auxv,
+        .cmd = "Xfer:auxv:read:",
+        .cmd_startswith = 1,
+        .schema = "l,l0"
+    },
+#endif
     {
         .handler = handle_query_attached,
         .cmd = "Attached:",
-- 
2.25.1.481.gfbce0eb801-goog