mmap calls could not be restarted after being interrupted by

a signal.  The parameters on the stack were corrupted by the
signal handler.

diff --git a/sysdeps/unix/sysv/linux/arm/mmap.S b/sysdeps/unix/sysv/linux/arm/mmap.S
index f9a773f..fcff57c 100644 (file)
--- a/sysdeps/unix/sysv/linux/arm/mmap.S
+++ b/sysdeps/unix/sysv/linux/arm/mmap.S
@@ -26,10 +26,26 @@ ENTRY (__mmap)
           mmap() takes six, we need to build a parameter block and pass its    
           address instead.  The 386 port does a similar trick.  */
 
-       mov     ip, sp
-       stmdb   ip!, {a1-a4}
-       mov     a1, ip
+       /* This code previously moved sp into ip and stored the args using
+          stmdb ip!, {a1-a4}.  It did not modify sp, so the stack never had 
+          to be restored after the syscall completed.  It saved an 
+          instruction and meant no stack cleanup work was required.
+
+          This will not work in the case of a mmap call being interrupted
+          by a signal.  If the signal handler uses any stack the arguments
+          to mmap will be trashed.  The results of a restart of mmap are
+          then unpredictable. */
+
+       /* store args on the stack */
+       stmdb   sp!, {a1-a4}
+
+       /* do the syscall */
+       mov     a1, sp
        swi     SYS_ify (mmap)
+
+       /* pop args off the stack. */
+       add     sp, sp, #16
+
        cmn     r0, $4096
        bhs     PLTJMP(syscall_error);
        ret