API/ABI change: XCBSendRequest callers must pad to 4-byte boundaries now. When not in RAW mode, a null pointer for iov_base is replaced by up to 3 padding bytes.

configure.ac

@@ -45,7 +45,6 @@ AC_MSG_RESULT($XCBPROTO_XCBINCLUDEDIR)
 AC_SUBST(XCBPROTO_XCBINCLUDEDIR)
 
 AC_HEADER_STDC
-AC_FUNC_ALLOCA
 AC_SEARCH_LIBS(gethostbyname, nsl)
 AC_SEARCH_LIBS(connect, socket)
 

src/c-client.xsl

@@ -567,7 +567,7 @@ authorization from the authors.
     <xsl:variable name="struct"
                   select="$pass1/xcb/struct[@name=current()/@ref]" />
 
-    <xsl:variable name="num-parts" select="1+count($struct/list)" />
+    <xsl:variable name="num-parts" select="1+count($struct/list)*2" />
 
     <l>static const XCBProtocolRequest xcb_req = {</l>
     <indent>
@@ -586,7 +586,7 @@ authorization from the authors.
     <l>};</l>
 
     <l />
-    <l>struct iovec xcb_parts[<xsl:value-of select="$num-parts" />];</l>
+    <l>struct iovec xcb_parts[<xsl:value-of select="$num-parts+2" />];</l>
     <l><xsl:value-of select="../@type" /> xcb_ret;</l>
     <l><xsl:value-of select="@ref" /> xcb_out;</l>
 
@@ -598,17 +598,21 @@ authorization from the authors.
     <l />
     <l>xcb_parts[0].iov_base = &amp;xcb_out;</l>
     <l>xcb_parts[0].iov_len = sizeof(xcb_out);</l>
+    <l>xcb_parts[1].iov_base = 0;</l>
+    <l>xcb_parts[1].iov_len = -xcb_parts[0].iov_len &amp; 3;</l>
 
     <xsl:for-each select="$struct/list">
-      <l>xcb_parts[<xsl:number />].iov_base = (void *) <!--
+      <l>xcb_parts[<xsl:number /> * 2].iov_base = (void *) <!--
       --><xsl:value-of select="@name" />;</l>
-      <l>xcb_parts[<xsl:number />].iov_len = <!--
+      <l>xcb_parts[<xsl:number /> * 2].iov_len = <!--
       --><xsl:apply-templates mode="output-expression" /><!--
       --><xsl:if test="not(@type = 'void')">
         <xsl:text> * sizeof(</xsl:text>
         <xsl:value-of select="@type" />
         <xsl:text>)</xsl:text>
       </xsl:if>;</l>
+      <l>xcb_parts[<xsl:number /> * 2 + 1].iov_base = 0;</l>
+      <l>xcb_parts[<xsl:number /> * 2 + 1].iov_len = -xcb_parts[<xsl:number /> * 2].iov_len &amp; 3;</l>
     </xsl:for-each>
 
     <l>XCBSendRequest(c, &amp;xcb_ret.sequence, <!--

src/xcb_out.c

@@ -31,16 +31,6 @@
 #include <string.h>
 #include <errno.h>
 
-#ifndef __GNUC__
-# if HAVE_ALLOCA_H
-#  include <alloca.h>
-# else
-#  ifdef _AIX
- #pragma alloca
-#  endif
-# endif
-#endif
-
 #include "xcb.h"
 #include "xcbext.h"
 #include "xcbint.h"
@@ -81,12 +71,9 @@ CARD32 XCBGetMaximumRequestLength(XCBConnection *c)
 
 int XCBSendRequest(XCBConnection *c, unsigned int *request, int flags, struct iovec *vector, const XCBProtocolRequest *req)
 {
-    static const char pad[3];
     int ret;
-    int i;
     CARD32 prefix[2];
-    struct iovec *padded;
+    int veclen = req->count;
-    int padlen = 0;
     enum workarounds workaround = WORKAROUND_NONE;
 
     assert(c != 0);
@@ -94,18 +81,12 @@ int XCBSendRequest(XCBConnection *c, unsigned int *request, int flags, struct io
     assert(vector != 0);
     assert(req->count > 0);
 
-    padded =
-#ifdef HAVE_ALLOCA
-        alloca
-#else
-        malloc
-#endif
-        ((req->count * 2 + 2) * sizeof(struct iovec));
-
     if(!(flags & XCB_REQUEST_RAW))
     {
+        static const char pad[3];
+        int i;
         CARD16 shortlen = 0;
-        CARD32 longlen = 0;
+        size_t longlen = 0;
         /* set the major opcode, and the minor opcode for extensions */
         if(req->ext)
         {
@@ -120,7 +101,16 @@ int XCBSendRequest(XCBConnection *c, unsigned int *request, int flags, struct io
 
         /* put together the length field, possibly using BIGREQUESTS */
         for(i = 0; i < req->count; ++i)
-            longlen += (vector[i].iov_len + 3) >> 2;
+        {
+            longlen += vector[i].iov_len;
+            if(!vector[i].iov_base)
+            {
+                vector[i].iov_base = (caddr_t) pad;
+                assert(vector[i].iov_len <= sizeof(pad));
+            }
+        }
+        assert((longlen & 3) == 0);
+        longlen >>= 2;
 
         if(longlen <= c->setup->maximum_request_length)
         {
@@ -135,29 +125,18 @@ int XCBSendRequest(XCBConnection *c, unsigned int *request, int flags, struct io
         ((CARD16 *) vector[0].iov_base)[1] = shortlen;
         if(!shortlen)
         {
-            padded[0].iov_base = prefix;
+            memmove(vector + 1, vector, veclen++ * sizeof(*vector));
-            padded[0].iov_len = sizeof(prefix);
+            ++veclen;
+            vector[0].iov_base = prefix;
+            vector[0].iov_len = sizeof(prefix);
             prefix[0] = ((CARD32 *) vector[0].iov_base)[0];
             prefix[1] = ++longlen;
-            vector[0].iov_base = ((char *) vector[0].iov_base) + sizeof(CARD32);
+            vector[1].iov_base = ((char *) vector[1].iov_base) + sizeof(CARD32);
-            vector[0].iov_len -= sizeof(CARD32);
+            vector[1].iov_len -= sizeof(CARD32);
-            padlen = 1;
         }
     }
     flags &= ~XCB_REQUEST_RAW;
 
-    for(i = 0; i < req->count; ++i)
-    {
-        if(!vector[i].iov_len)
-            continue;
-        padded[padlen].iov_base = vector[i].iov_base;
-        padded[padlen++].iov_len = vector[i].iov_len;
-        if(!XCB_PAD(vector[i].iov_len))
-            continue;
-        padded[padlen].iov_base = (caddr_t) pad;
-        padded[padlen++].iov_len = XCB_PAD(vector[i].iov_len);
-    }
-
     /* do we need to work around the X server bug described in glx.xml? */
     if(req->ext && !req->isvoid && strcmp(req->ext->name, "GLX") &&
             ((req->opcode == 17 && ((CARD32 *) vector[0].iov_base)[0] == 0x10004) ||
@@ -169,9 +148,6 @@ int XCBSendRequest(XCBConnection *c, unsigned int *request, int flags, struct io
     if(req->isvoid && !force_sequence_wrap(c))
     {
         pthread_mutex_unlock(&c->iolock);
-#ifndef HAVE_ALLOCA
-        free(padded);
-#endif
         return -1;
     }
 
@@ -183,12 +159,8 @@ int XCBSendRequest(XCBConnection *c, unsigned int *request, int flags, struct io
 
     _xcb_in_expect_reply(c, *request, workaround, flags);
 
-    ret = _xcb_out_write_block(c, padded, padlen);
+    ret = _xcb_out_write_block(c, vector, veclen);
     pthread_mutex_unlock(&c->iolock);
-#ifndef HAVE_ALLOCA
-    free(padded);
-#endif
-
     return ret;
 }