[rtems commit] bsp/tms570: ensure that linker symbol comparison to NULL is not optimized out.

[Gedare Bloom]

Module:    rtems
Branch:    master
Commit:    4a02a74154f40850d4a8fd99b6d25c23ee9bb46a
Changeset: http://git.rtems.org/rtems/commit/?id=4a02a74154f40850d4a8fd99b6d25c23ee9bb46a

Author:    Pavel Pisa <pisa at cmp.felk.cvut.cz>
Date:      Sat Nov 28 12:01:36 2015 +0100

bsp/tms570: ensure that linker symbol comparison to NULL is not optimized out.

Signed-off-by: Pavel Pisa <pisa at cmp.felk.cvut.cz>

---

 c/src/lib/libbsp/arm/tms570/startup/bspstart.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/c/src/lib/libbsp/arm/tms570/startup/bspstart.c b/c/src/lib/libbsp/arm/tms570/startup/bspstart.c
index b7e2b62..7c1e9a1 100644
--- a/c/src/lib/libbsp/arm/tms570/startup/bspstart.c
+++ b/c/src/lib/libbsp/arm/tms570/startup/bspstart.c
@@ -32,6 +32,9 @@
 
 void bsp_start( void )
 {
+  void *need_remap_ptr;
+  unsigned int need_remap_int;
+
   #if BYTE_ORDER == BIG_ENDIAN
     /*
      * If CPU is big endian (TMS570 family variant)
@@ -65,9 +68,16 @@ void bsp_start( void )
    * SRAM then it leads to CPU error halt.
    *
    * So use of POM to replace jumps to vectors target
-   * addresses seems to be the best option.
+   * addresses seems to be the best option for now.
+   *
+   * The passing of linker symbol (represented as start address
+   * of global array) through dummy asm block ensures that C compiler
+   * cannot optimize comparison out on premise that reference cannot
+   * evaluate to NULL definition in standard.
    */
-  if ( (uintptr_t)bsp_start_vector_table_begin != 0 ) {
+  need_remap_ptr = bsp_start_vector_table_begin;
+  asm volatile ("\n": "=r" (need_remap_int): "0" (need_remap_ptr));
+  if ( need_remap_int != 0 ) {
     tms570_pom_remap();
   }