The following patch comes from the upstream 0.4.2 distribution and

addresses the stated problem. It will be removed here once we update to

a later version of greenlet.

commit 3b03825089384f86842032ec1476ad3031908d43

Author: Floris Bruynooghe <[email protected]>

Date:   Mon Sep 2 10:25:14 2013 +0100

    Fix slp_switch on SPARC for multi-threaded environments

    The CLEAN_WINDOWS trap was wrongly removed previously.  It is not

    required in a single-threaded environment but does need to be present

    for the switching code to not mess up the register windows in a multi-

    threaded environment.

diff --git a/platform/switch_sparc_sun_gcc.h b/platform/switch_sparc_sun_gcc.h

index 1f701a2..5c67205 100644

--- a/platform/switch_sparc_sun_gcc.h

+++ b/platform/switch_sparc_sun_gcc.h

@@ -2,6 +2,11 @@

  * this is the internal transfer function.

  *

  * HISTORY

+ * 30-Aug-13  Floris Bruynooghe <[email protected]>

+        Clean the register windows again before returning.

+        This does not clobber the PIC register as it leaves

+        the current window intact and is required for multi-

+        threaded code to work correctly.

  * 08-Mar-11  Floris Bruynooghe <[email protected]>

  *      No need to set return value register explicitly

  *      before the stack and framepointer are adjusted

@@ -28,7 +33,8 @@

 #define STACK_MAGIC 0

-#define ST_FLUSH_WINDOWS 3

+#define ST_FLUSH_WINDOWS 0x03

+#define ST_CLEAN_WINDOWS 0x04

 static int

 slp_switch(void)

@@ -37,7 +43,17 @@ slp_switch(void)

     /* Flush SPARC register windows onto the stack, so they can be used to

      * restore the registers after the stack has been switched out and

-     * restored.  Then put the stack pointer into stackref. */

+     * restored.  This also ensures the current window (pointed at by

+     * the CWP register) is the only window left in the registers

+     * (CANSAVE=0, CANRESTORE=0), that means the registers of our

+     * caller are no longer there and when we return they will always

+     * be loaded from the stack by a window underflow/fill trap.

+     *

+     * On SPARC v9 and above it might be more efficient to use the

+     * FLUSHW instruction instead of TA ST_FLUSH_WINDOWS.  But that

+     * requires the correct -mcpu flag to gcc.

+     *

+     * Then put the stack pointer into stackref. */

     __asm__ volatile (

         "ta %1\n\t"

         "mov %%sp, %0"

@@ -57,11 +73,13 @@ slp_switch(void)

         /* Copy new stack from it's save store on the heap */

         SLP_RESTORE_STATE();

-        /* No need to restore any registers from the stack nor clear them: the

-         * frame pointer has just been set and the return value register is

-         * also being set by the return statement below.  After returning a

-         * restore instruction is given and the frame below us will load all

-         * it's registers using a fill_trap if required. */

+        /* No need to set the return value register, the return

+         * statement below does this just fine.  After returning a restore

+         * instruction is given and a fill-trap will load all the registers

+         * from the stack if needed.  However in a multi-threaded environment

+         * we can't guarantee the other register windows are fine to use by

+         * their threads anymore, so tell the CPU to clean them. */

+        __asm__ volatile ("ta %0" : : "i" (ST_CLEAN_WINDOWS));

         return 0;

     }