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 --- programs/winedbg/gdbproxy.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-)
diff --git a/programs/winedbg/gdbproxy.c b/programs/winedbg/gdbproxy.c index 55c970c1d1e..19ad76910af 100644 --- a/programs/winedbg/gdbproxy.c +++ b/programs/winedbg/gdbproxy.c @@ -2173,13 +2173,24 @@ 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);
- vl_empty(&gdbctx->qxfer_buffer); + if (off > 0 && + gdbctx->qxfer_buffer.len > 0 && + gdbctx->qxfer_object_idx == i && + strncmp(gdbctx->qxfer_object_annex, annex, MAX_QX_ANNEX_LEN) == 0) + { + result = packet_send_buffer; + TRACE("qXfer read result = %d (cached)\n", result); + } + else + { + vl_empty(&gdbctx->qxfer_buffer);
- gdbctx->qxfer_object_idx = i; - memcpy(gdbctx->qxfer_object_annex, annex, MAX_QX_ANNEX_LEN); + gdbctx->qxfer_object_idx = i; + memcpy(gdbctx->qxfer_object_annex, annex, MAX_QX_ANNEX_LEN);
- 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); + }
if ((result & ~packet_last_f) == packet_send_buffer) {