[newlib-cygwin] Don't rely on size argument in shmget call

Corinna Vinschen corinna@sourceware.org
Fri May 29 13:58:00 GMT 2015


https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=023be4aedbd5bfb0a56164a2803c9c24a0d546f5

commit 023be4aedbd5bfb0a56164a2803c9c24a0d546f5
Author: Corinna Vinschen <corinna@vinschen.de>
Date:   Sun Apr 12 14:05:12 2015 +0200

    Don't rely on size argument in shmget call
    
    	* shm.cc (shmget): Fetch segment size from server rather than using
    	size argument to accommodate existing segments.  Add comment to explain
    	why.
    
    Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

Diff:
---
 winsup/cygwin/ChangeLog     | 6 ++++++
 winsup/cygwin/release/2.0.0 | 3 +++
 winsup/cygwin/shm.cc        | 9 ++++++++-
 3 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/winsup/cygwin/ChangeLog b/winsup/cygwin/ChangeLog
index 9a48131..a75810f 100644
--- a/winsup/cygwin/ChangeLog
+++ b/winsup/cygwin/ChangeLog
@@ -1,3 +1,9 @@
+2015-04-12  Corinna Vinschen  <corinna@vinschen.de>
+
+	* shm.cc (shmget): Fetch segment size from server rather than using
+	size argument to accommodate existing segments.  Add comment to explain
+	why.
+
 2015-04-10  Corinna Vinschen  <corinna@vinschen.de>
 
 	* include/cygwin/version.h (CYGWIN_VERSION_DLL_MAJOR): Bump to 2000.
diff --git a/winsup/cygwin/release/2.0.0 b/winsup/cygwin/release/2.0.0
index f01e497..6c89819 100644
--- a/winsup/cygwin/release/2.0.0
+++ b/winsup/cygwin/release/2.0.0
@@ -40,3 +40,6 @@ Bug Fixes
 
 - Fix UTF-16 surrogate handling in wctomb and friends.
   Addresses: https://cygwin.com/ml/cygwin/2015-03/msg00452.html
+
+- Fix shmget usage of size parameter for already existing segments.
+  Addresses: https://cygwin.com/ml/cygwin/2015-04/msg00105.html
diff --git a/winsup/cygwin/shm.cc b/winsup/cygwin/shm.cc
index c5ab708..e209346 100644
--- a/winsup/cygwin/shm.cc
+++ b/winsup/cygwin/shm.cc
@@ -377,7 +377,14 @@ shmget (key_t key, size_t size, int shmflg)
      shmid and hdl value to the list. */
   ssh_new_entry->shmid = shmid;
   ssh_new_entry->hdl = hdl;
-  ssh_new_entry->size = size;
+  /* Fetch segment size from server.  If this is an already existing segment,
+     the size value in this shmget call is supposed to be meaningless. */
+  struct shmid_ds stat;
+  client_request_shm stat_req (shmid, IPC_STAT, &stat);
+  if (stat_req.make_request () == -1 || stat_req.retval () == -1)
+    ssh_new_entry->size = size;
+  else
+    ssh_new_entry->size = stat.shm_segsz;
   ssh_new_entry->ref_count = 0;
   SLIST_INSERT_HEAD (&ssh_list, ssh_new_entry, ssh_next);
   SLIST_UNLOCK ();



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