gdbstub: Add support for info proc mappings

Currently the GDB's generate-core-file command doesn't work well with
qemu-user: the resulting dumps are huge [1] and at the same time
incomplete (argv and envp are missing). The reason is that GDB has no
access to proc mappings and therefore has to fall back to using
heuristics for discovering them. This is, in turn, because qemu-user
does not implement the Host I/O feature of the GDB Remote Serial
Protocol.

Implement vFile:{open,close,pread,readlink} and also
qXfer:exec-file:read+. With that, generate-core-file begins to work on
aarch64 and s390x.

[1] https://sourceware.org/pipermail/gdb-patches/2023-May/199432.html

Co-developed-by: Dominik 'Disconnect3d' Czarnota <dominik.b.czarnota@gmail.com>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20230621203627.1808446-7-iii@linux.ibm.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230630180423.558337-37-alex.bennee@linaro.org>

1 files changed, 43 insertions, 2 deletions

diff --git a/gdbstub/gdbstub.c b/gdbstub/gdbstub.c
index 697dd4b..6911b73 100644
--- a/gdbstub/gdbstub.c
+++ b/gdbstub/gdbstub.c
@@ -1327,6 +1327,36 @@ static const GdbCmdParseEntry gdb_v_commands_table[] = {
         .cmd = "Kill;",
         .cmd_startswith = 1
     },
+#ifdef CONFIG_USER_ONLY
+    /*
+     * Host I/O Packets. See [1] for details.
+     * [1] https://sourceware.org/gdb/onlinedocs/gdb/Host-I_002fO-Packets.html
+     */
+    {
+        .handler = gdb_handle_v_file_open,
+        .cmd = "File:open:",
+        .cmd_startswith = 1,
+        .schema = "s,L,L0"
+    },
+    {
+        .handler = gdb_handle_v_file_close,
+        .cmd = "File:close:",
+        .cmd_startswith = 1,
+        .schema = "l0"
+    },
+    {
+        .handler = gdb_handle_v_file_pread,
+        .cmd = "File:pread:",
+        .cmd_startswith = 1,
+        .schema = "l,L,L0"
+    },
+    {
+        .handler = gdb_handle_v_file_readlink,
+        .cmd = "File:readlink:",
+        .cmd_startswith = 1,
+        .schema = "s0"
+    },
+#endif
 };
 
 static void handle_v_commands(GArray *params, void *user_ctx)
@@ -1472,11 +1502,14 @@ static void handle_query_supported(GArray *params, void *user_ctx)
             ";ReverseStep+;ReverseContinue+");
     }
 
-#if defined(CONFIG_USER_ONLY) && defined(CONFIG_LINUX)
+#if defined(CONFIG_USER_ONLY)
+#if defined(CONFIG_LINUX)
     if (gdbserver_state.c_cpu->opaque) {
         g_string_append(gdbserver_state.str_buf, ";qXfer:auxv:read+");
     }
 #endif
+    g_string_append(gdbserver_state.str_buf, ";qXfer:exec-file:read+");
+#endif
 
     if (params->len &&
         strstr(get_param(params, 0)->data, "multiprocess+")) {
@@ -1615,7 +1648,8 @@ static const GdbCmdParseEntry gdb_gen_query_table[] = {
         .cmd_startswith = 1,
         .schema = "s:l,l0"
     },
-#if defined(CONFIG_USER_ONLY) && defined(CONFIG_LINUX)
+#if defined(CONFIG_USER_ONLY)
+#if defined(CONFIG_LINUX)
     {
         .handler = gdb_handle_query_xfer_auxv,
         .cmd = "Xfer:auxv:read::",
@@ -1624,6 +1658,13 @@ static const GdbCmdParseEntry gdb_gen_query_table[] = {
     },
 #endif
     {
+        .handler = gdb_handle_query_xfer_exec_file,
+        .cmd = "Xfer:exec-file:read:",
+        .cmd_startswith = 1,
+        .schema = "l:l,l0"
+    },
+#endif
+    {
         .handler = gdb_handle_query_attached,
         .cmd = "Attached:",
         .cmd_startswith = 1