PowerPC makecontext

http://sourceware.org/ml/libc-alpha/2013-08/msg00092.html

Use conditional form of branch and link to avoid destroying the cpu
link stack used to predict blr return addresses.

	* sysdeps/unix/sysv/linux/powerpc/powerpc32/makecontext.S: Use
	conditional form of branch and link when obtaining pc.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/makecontext.S: Likewise.

diff --git a/ChangeLog b/ChangeLog
index ec81a6b..07aaa25 100644 (file)
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,11 @@
 2013-10-04  Alan Modra  <amodra@gmail.com>
 
+       * sysdeps/unix/sysv/linux/powerpc/powerpc32/makecontext.S: Use
+       conditional form of branch and link when obtaining pc.
+       * sysdeps/unix/sysv/linux/powerpc/powerpc64/makecontext.S: Likewise.
+
+2013-10-04  Alan Modra  <amodra@gmail.com>
+
        * sysdeps/unix/sysv/linux/powerpc/powerpc32/getcontext-common.S: Use
        HIWORD/LOWORD.
        * sysdeps/unix/sysv/linux/powerpc/powerpc32/setcontext-common.S: Ditto.

diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc32/makecontext.S b/sysdeps/unix/sysv/linux/powerpc/powerpc32/makecontext.S
index 95902b1..70e3c97 100644 (file)
--- a/sysdeps/unix/sysv/linux/powerpc/powerpc32/makecontext.S
+++ b/sysdeps/unix/sysv/linux/powerpc/powerpc32/makecontext.S
@@ -47,7 +47,9 @@ ENTRY(__makecontext)
 #ifdef PIC
        mflr    r0
        cfi_register(lr,r0)
-       bl      1f
+       /* Use this conditional form of branch and link to avoid destroying
+          the cpu link stack used to predict blr return addresses.  */
+       bcl     20,31,1f
 1:     mflr    r6
        addi    r6,r6,L(exitcode)-1b
        mtlr    r0
@@ -136,7 +138,9 @@ ENTRY(__novec_makecontext)
 #ifdef PIC
        mflr    r0
        cfi_register(lr,r0)
-       bl      1f
+       /* Use this conditional form of branch and link to avoid destroying
+          the cpu link stack used to predict blr return addresses.  */
+       bcl     20,31,1f
 1:     mflr    r6
        addi    r6,r6,L(novec_exitcode)-1b
        mtlr    r0

diff --git a/sysdeps/unix/sysv/linux/powerpc/powerpc64/makecontext.S b/sysdeps/unix/sysv/linux/powerpc/powerpc64/makecontext.S
index 4a16669..32fc47c 100644 (file)
--- a/sysdeps/unix/sysv/linux/powerpc/powerpc64/makecontext.S
+++ b/sysdeps/unix/sysv/linux/powerpc/powerpc64/makecontext.S
@@ -124,8 +124,10 @@ L(noparms):
 
   /* If the target function returns we need to do some cleanup.  We use a
      code trick to get the address of our cleanup function into the link
-     register.  Do not add any code between here and L(exitcode).  */
-  bl  L(gotexitcodeaddr);
+     register.  Do not add any code between here and L(exitcode).
+     Use this conditional form of branch and link to avoid destroying
+     the cpu link stack used to predict blr return addresses.  */
+  bcl  20,31,L(gotexitcodeaddr);
 
        /* This is the helper code which gets called if a function which
           is registered with 'makecontext' returns.  In this case we