imx233: fix app.lds to properly support INIT_ATTR

Original fix by Marcin: it had a problem because crt0 on imx233 is more
complicated than many targets: since we use virtual memory, we first disable
the MMU, then move the entire image (including init and itext stuff), then
setup a temporary stack to setup the MMU. Only when the MMU is enabled, can
we move the init and itext stuff to its right location and finally boot.
This requires some trickery because:
- the initial move copies everything, including init and itext
- the stack overlaps with init and itext to reclaim space
- the temporary stack cannot be the same as the main stack to avoid trashing
  the init and itext code, also it needs to be a physical address

Change-Id: Ibaf331c7d90b61f99225d93c9e621eb0f3f8f2dc

3 files changed, 16 insertions, 9 deletions

diff --git a/firmware/target/arm/imx233/app.lds b/firmware/target/arm/imx233/app.lds
index b378f9ea16..335aa4fcc3 100644
--- a/firmware/target/arm/imx233/app.lds
+++ b/firmware/target/arm/imx233/app.lds
@@ -39,7 +39,7 @@ SECTIONS
     {
         _dramcopystart = .;
     } > DRAM
-        
+
     .text :
     {
         *(.text*)
@@ -47,6 +47,8 @@ SECTIONS
         *(.rodata*)
     } > DRAM
 
+    _dramtextend = .;
+
     .itext :
     {
         _iramstart = .; // always 0
@@ -77,12 +79,17 @@ SECTIONS
 
     _initcopy = LOADADDR(.init);
 
+    /* crt0 needs a temporary stack which does not overlap with init and itext
+     * and is in physical memory: put it *after* init and itext. A small one suffices */
+    crt0_tmpstack_phys = _dramcopyend + 0x200 - CACHED_DRAM_ADDR + UNCACHED_DRAM_ADDR;
+
     .dramcopyend (NOLOAD) :
     {
         _dramcopyend = .;
     } > DRAM
 
-    .stack (NOLOAD) :
+    /* the stack overlaps the init and itext region, to reclaim space */
+    .stack _dramtextend (NOLOAD) :
     {
         *(.stack)
         stackbegin = .;
@@ -90,9 +97,6 @@ SECTIONS
         stackend = .;
     } > DRAM
 
-    /* physical address of the stack */
-    stackend_phys = stackend - CACHED_DRAM_ADDR + UNCACHED_DRAM_ADDR;
-
     /* treat .bss and .ncbss as a single section */
     .bss (NOLOAD) :
     {
diff --git a/firmware/target/arm/imx233/boot.lds b/firmware/target/arm/imx233/boot.lds
index 68472d129c..ca455b47ca 100644
--- a/firmware/target/arm/imx233/boot.lds
+++ b/firmware/target/arm/imx233/boot.lds
@@ -74,7 +74,7 @@ SECTIONS
     } > DRAM
 
     /* physical address of the stack */
-    stackend_phys = stackend - CACHED_DRAM_ADDR + UNCACHED_DRAM_ADDR;
+    crt0_tmpstack_phys = stackend - CACHED_DRAM_ADDR + UNCACHED_DRAM_ADDR;
 
     /* treat .bss and .ncbss as a single section */
     .bss (NOLOAD) :
diff --git a/firmware/target/arm/imx233/crt0.S b/firmware/target/arm/imx233/crt0.S
index 0a71da5d08..5e1720c7c9 100644
--- a/firmware/target/arm/imx233/crt0.S
+++ b/firmware/target/arm/imx233/crt0.S
@@ -56,9 +56,12 @@ start:
     bic     r0, r1
     mcr     p15, 0, r0, c1, c0, 0
 
-    /* To call the C code we need a stack, since the stack is in virtual memory
-     * use the stack's physical address */
-    ldr     sp, =stackend_phys
+    /* To call the C code we need a stack, since the loader's stack might be
+     * in virtual memory, we need a physical address for the stack. Furthermore,
+     * we cannot use the main firmware stack yet because it overlaps with the
+     * init code which will be moved later. We rely on the linker to provide
+     * a safe, temporary stack */
+    ldr     sp, =crt0_tmpstack_phys
 
     /* Enable MMU */
     bl      memory_init