[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[Help-smalltalk] Re: GNU Smalltalk crashes when calling xcb_create_windo

From: Paolo Bonzini
Subject: [Help-smalltalk] Re: GNU Smalltalk crashes when calling xcb_create_window via cCall
Date: Wed, 30 Sep 2009 14:59:42 +0200
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20090814 Fedora/3.0-2.6.b3.fc11 Lightning/1.0pre Thunderbird/3.0b3

On 09/29/2009 09:14 PM, Dmitry Matveev wrote:

New gdb log is attacted.
GNU Smalltalk is build from git (2-3 days ago).

Aha, got it.

I tried using gdb to print the stack in xcb_create_window from both the failing and the succeeding call.

Here is the failing call to xcb_create_window. We have first the next stack frame, then the return address, then the arguments (this is 32-bit, which does not pass arguments in registers):

(gdb) p/x *(uint32_t **) address@hidden
$6 = {0xffffb2a8, 0x427c27, 0x80c92b8, 0x0, 0x4400000, 0x10b, 0x0, 0x0,
  0x96,  0x96, 0xa, 0x1, 0x21, 0x0, 0x0}

Here is the succeeding call to gst_xcb_create_window:

(gdb) p/x *(uint32_t **)address@hidden
$4 = {0xffffb298, 0x37bc27, 0x80c92b8, 0x0, 0x4600000, 0x10b, 0x0, 0x0,
  0x96, 0x96, 0xa, 0x1, 0x21, 0x0, 0x0, 0xffffb2d8, 0x37ba3e, 0x37bab0,
  0xffffb2c4, 0x34}

This looks the same---correct, since the cCall pragma was the same.

Now here is the succeeding call to xcb_create_window

(gdb) down
#0  0x001946a5 in xcb_create_window () from /usr/lib/
(gdb) p/x *(uint32_t **)address@hidden
$5 = {0xffffb25c, 0x110618, 0xffffb224, 0x80c92b8, 0x0, 0x4600000,
  0x10b, 0x0, 0x0, 0x96, 0x96, 0xa, 0x1, 0x21, 0x0, 0x0, 0x8074540,
  0xffffb2c0, 0xffffb438, 0xe3c3eb22}

Notice the "0xffffb224" after the return address? That is the place where the callee can store the return value, which is not a "void" but an "xcb_void_cookie_t" -- which is a struct.

So, you have to wrap all the function calls of XCB that are asynchronous (like xcb_create_window and xcb_map_window). However, note that big parts of libxcb, in particular these very functions, are automatically generated from XML, for example:

  <request name="CreateWindow" opcode="1">
    <field type="CARD8" name="depth" />
    <field type="WINDOW" name="wid" />
    <field type="WINDOW" name="parent" />
    <field type="INT16" name="x" />
    <field type="INT16" name="y" />
    <field type="CARD16" name="width" />
    <field type="CARD16" name="height" />
    <field type="CARD16" name="border_width" />
    <field type="CARD16" name="class" />
    <field type="VISUALID" name="visual" />
    <valueparam value-mask-type="CARD32"
                value-list-name="value_list" />


Unfortunately I could not find the generator, also because is down. But if there is one, generating the XCB request functions (i.e. not the whole bindings, only the requests) from GNU Smalltalk may be a viable path.

BTW, your code has a small memory leak.  You can say

  iter := XcbScreenIterator gcNew.

instead of "new".


reply via email to

[Prev in Thread] Current Thread [Next in Thread]