winedbg: Cache GDB qXfer command result for chunked fetching.

GDB does not retrieve the result of a qXfer command at once; instead, it issues a series of requests to obtain the result one "chunk" at a time, and concatenates those chunks internally. Each request contains offset and length variables that specify which portion of the result shall be retrieved. Today, Winedbg handles this by generating the entire result data each time a request is received and slicing out the requested range for the response. This is not only inefficient due to repeated computation, but also prone to race condition since the result may change between successive chunk requests due to the dynamic nature of some commands such as "libraries" and "threads." Fix this by cacheing the result into a buffer at the first request, and use the buffer to serve successive chunk requests. The cache is invalidated when the remote requests a different object, or the debugger reaches the end of the result cache buffer. Signed-off-by: Jinoh Kang <jinoh.kang.kr@gmail.com> Signed-off-by: Rémi Bernon <rbernon@codeweavers.com> Signed-off-by: Alexandre Julliard <julliard@winehq.org>

winedbg: Cache GDB qXfer command result for chunked fetching.
f18c0db3 · Jinoh Kang · Alexandre Julliard · 595bfdee · f18c0db3
Commit f18c0db3 authored Nov 24, 2021 by Jinoh Kang Committed by Alexandre Julliard Nov 23, 2021
Hide whitespace changes
Inline Side-by-side

Showing with 32 additions and 10 deletions

gdbproxy.c programs/winedbg/gdbproxy.c +32 -10

No files found.
--- a/programs/winedbg/gdbproxy.c
+++ b/programs/winedbg/gdbproxy.c
@@ -931,15 +931,17 @@ static inline void packet_reply_register_hex_to(struct gdb_context* gdbctx, dbg_
    packet_reply_hex_to(gdbctx, cpu_register_ptr(gdbctx, ctx, idx), cpu_register_map[idx].length);
 }

-static void packet_reply_xfer(struct gdb_context* gdbctx, size_t off, size_t len)
+static void packet_reply_xfer(struct gdb_context* gdbctx, size_t off, size_t len, BOOL* more_p)
 {
+    BOOL more;
    size_t data_len, trunc_len;

    packet_reply_open(gdbctx);
    data_len = gdbctx->qxfer_buffer.len;

    /* check if off + len would overflow */
-    if (off < data_len && off + len < data_len)
+    more = off < data_len && off + len < data_len;
+    if (more)
        packet_reply_add(gdbctx, "m");
    else
        packet_reply_add(gdbctx, "l");
@@ -951,6 +953,8 @@ static void packet_reply_xfer(struct gdb_context* gdbctx, size_t off, size_t len
    }

    packet_reply_close(gdbctx);
+
+    *more_p = more;
 }

 /* =============================================== *
@@ -2071,6 +2075,7 @@ static enum packet_return packet_query(struct gdb_context* gdbctx)
        {
            enum packet_return result;
            int i;
+            BOOL more;

            for (i = 0; i < ARRAY_SIZE(qxfer_handlers); i++)
            {
@@ -2086,21 +2091,38 @@ static enum packet_return packet_query(struct gdb_context* gdbctx)

            TRACE("qXfer %s read %s %u,%u\n", debugstr_a(object_name), debugstr_a(annex), off, len);

-            gdbctx->qxfer_object_idx = i;
-            strcpy(gdbctx->qxfer_object_annex, annex);
+            if (off > 0 &&
+                gdbctx->qxfer_buffer.len > 0 &&
+                gdbctx->qxfer_object_idx == i &&
+                strcmp(gdbctx->qxfer_object_annex, annex) == 0)
+            {
+                result = packet_send_buffer;
+                TRACE("qXfer read result = %d (cached)\n", result);
+            }
+            else
+            {
+                reply_buffer_clear(&gdbctx->qxfer_buffer);
+
+                gdbctx->qxfer_object_idx = i;
+                strcpy(gdbctx->qxfer_object_annex, annex);

-            result = (*qxfer_handlers[i].handler)(gdbctx);
-            TRACE("qXfer read result = %d\n", result);
+                result = (*qxfer_handlers[i].handler)(gdbctx);
+                TRACE("qXfer read result = %d\n", result);
+            }

+            more = FALSE;
            if ((result & ~packet_last_f) == packet_send_buffer)
            {
-                packet_reply_xfer(gdbctx, off, len);
+                packet_reply_xfer(gdbctx, off, len, &more);
                result = (result & packet_last_f) | packet_done;
            }

-            gdbctx->qxfer_object_idx = -1;
-            gdbctx->qxfer_object_annex[0] = '\0';
-            reply_buffer_clear(&gdbctx->qxfer_buffer);
+            if (!more)
+            {
+                gdbctx->qxfer_object_idx = -1;
+                gdbctx->qxfer_object_annex[0] = '\0';
+                reply_buffer_clear(&gdbctx->qxfer_buffer);
+            }

            return result;
        }