store .data section directly in RAM area

Since the use of a elf binary is anyway required, we can place
sections freely in memory. Therefor it is not necessary to store
the variable initialization section (.data) after the code (.text)
section and copy it in the firmwares startup code. Instead, just
let the elf loader load the .data section directly to its final
place. With that the program header look like this:

  Program Header:
    LOAD off    0x00001000 vaddr 0x00000000 paddr 0x00000000 align 2**12
         filesz 0x00000240 memsz 0x00000240 flags r--
    LOAD off    0x00002000 vaddr 0x1fff8000 paddr 0x1fff8000 align 2**12
         filesz 0x00006534 memsz 0x00006534 flags rwx
    LOAD off    0x00009000 vaddr 0x20000000 paddr 0x20000000 align 2**12
         filesz 0x000001d0 memsz 0x00005dc8 flags rw-

Note the additional program header which loads the .data section
directly to the data region at 0x20000000.

This safes space in the code region and slightly improves the
startup time since the copy loop is not required.

Signed-off-by: Stefan Agner <stefan.agner@toradex.com>

2 files changed, 1 insertions, 42 deletions

diff --git a/platform/devices/MCIMX7D/linker/gcc/MCIMX7D_M4.ld b/platform/devices/MCIMX7D/linker/gcc/MCIMX7D_M4.ld
index 2feebd8..6699153 100644
--- a/platform/devices/MCIMX7D/linker/gcc/MCIMX7D_M4.ld
+++ b/platform/devices/MCIMX7D/linker/gcc/MCIMX7D_M4.ld
@@ -142,25 +142,15 @@ SECTIONS
     PROVIDE_HIDDEN (__fini_array_end = .);
   } > m_text
 
-  __etext = .;    /* define a global symbol at end of code */
-  __DATA_ROM = .; /* Symbol is used by startup for data initialization */
-
-  .data : AT(__DATA_ROM)
+  .data :
   {
     . = ALIGN(4);
-    __DATA_RAM = .;
-    __data_start__ = .;      /* create a global symbol at data start */
     *(.data)                 /* .data sections */
     *(.data*)                /* .data* sections */
     KEEP(*(.jcr*))
     . = ALIGN(4);
-    __data_end__ = .;        /* define a global symbol at data end */
   } > m_data
 
-  __DATA_END = __DATA_ROM + (__data_end__ - __data_start__);
-  text_end = ORIGIN(m_text) + LENGTH(m_text);
-  ASSERT(__DATA_END <= text_end, "region m_text overflowed with text and data")
-
   /* Uninitialized data section */
   .bss :
   {
diff --git a/platform/devices/MCIMX7D/startup/gcc/startup_MCIMX7D_M4.S b/platform/devices/MCIMX7D/startup/gcc/startup_MCIMX7D_M4.S
index 2a97408..a518a15 100644
--- a/platform/devices/MCIMX7D/startup/gcc/startup_MCIMX7D_M4.S
+++ b/platform/devices/MCIMX7D/startup/gcc/startup_MCIMX7D_M4.S
@@ -219,37 +219,6 @@ Reset_Handler:
 #ifndef __NO_SYSTEM_INIT
     bl SystemInit
 #endif
-/*     Loop to copy data from read only memory to RAM. The ranges
- *      of copy from/to are specified by following symbols evaluated in
- *      linker script.
- *      __etext: End of code section, i.e., begin of data sections to copy from.
- *      __data_start__/__data_end__: RAM address range that data should be
- *      copied to. Both must be aligned to 4 bytes boundary.  */
-
-    ldr    r1, =__etext
-    ldr    r2, =__data_start__
-    ldr    r3, =__data_end__
-
-#if 1
-/* Here are two copies of loop implemenations. First one favors code size
- * and the second one favors performance. Default uses the first one.
- * Change to "#if 0" to use the second one */
-.LC0:
-    cmp     r2, r3
-    ittt    lt
-    ldrlt   r0, [r1], #4
-    strlt   r0, [r2], #4
-    blt    .LC0
-#else
-    subs    r3, r2
-    ble    .LC1
-.LC0:
-    subs    r3, #4
-    ldr    r0, [r1, r3]
-    str    r0, [r2, r3]
-    bgt    .LC0
-.LC1:
-#endif
 
 #ifdef __STARTUP_CLEAR_BSS
 /*     This part of work usually is done in C library startup code. Otherwise,