[sw/crt] Fix CRT code clobbering the first word of .bss
When this assembly was written, an incorrect assumption was made that
the _*_end pointers pointed to the final word in a section, when in
reality, they point one past. Due to how the linker laid out .data and
.bss, .data initialization would clobber the first word of .bss.
Signed-off-by: Miguel Young de la Sota <mcyoung@google.com>
diff --git a/sw/device/boot_rom/rom_crt.S b/sw/device/boot_rom/rom_crt.S
index 41ffaea..33c16e1 100644
--- a/sw/device/boot_rom/rom_crt.S
+++ b/sw/device/boot_rom/rom_crt.S
@@ -82,21 +82,21 @@
bss_zero_loop:
sw zero, 0(t0)
addi t0, t0, 0x4
- ble t0, t1, bss_zero_loop
+ blt t0, t1, bss_zero_loop
bss_zero_loop_end:
// Zero out the stack
//
// We use `t0` and `t1` to represent the start and end pointers of the stack.
// As the stack grows downwards and we zero going forwards the start pointer
- // starts as _stack_end and the end pointer at _stack_start - 4
+ // starts as _stack_end and the end pointer at _stack_start
la t0, _stack_end
- la t1, (_stack_start - 4)
+ la t1, _stack_start
bge t0, t1, stack_zero_loop_end
stack_zero_loop:
sw zero, 0(t0)
addi t0, t0, 0x4
- ble t0, t1, stack_zero_loop
+ blt t0, t1, stack_zero_loop
stack_zero_loop_end:
// Initialize the `.data` segment from the `.idata` segment.
@@ -114,7 +114,7 @@
sw t3, 0(t0)
addi t0, t0, 0x4
addi t2, t2, 0x4
- ble t0, t1, data_copy_loop
+ blt t0, t1, data_copy_loop
data_copy_loop_end:
// Re-clobber all of the registers from above.
diff --git a/sw/device/boot_rom/rom_link.ld b/sw/device/boot_rom/rom_link.ld
index cf6b334..c7b6127 100644
--- a/sw/device/boot_rom/rom_link.ld
+++ b/sw/device/boot_rom/rom_link.ld
@@ -116,6 +116,7 @@
*/
*(.data)
*(.data.*)
+ . = ALIGN(4);
_data_end = .;
} > ram_main
@@ -138,6 +139,7 @@
*(.bss)
*(.bss.*)
*(COMMON)
+ . = ALIGN(4);
_bss_end = .;
} > ram_main
diff --git a/sw/device/exts/common/flash_crt.S b/sw/device/exts/common/flash_crt.S
index 84124f3..11faeea 100644
--- a/sw/device/exts/common/flash_crt.S
+++ b/sw/device/exts/common/flash_crt.S
@@ -48,21 +48,21 @@
bss_zero_loop:
sw zero, 0(t0)
addi t0, t0, 0x4
- ble t0, t1, bss_zero_loop
+ blt t0, t1, bss_zero_loop
bss_zero_loop_end:
// Zero out the stack
//
// We use `t0` and `t1` to represent the start and end pointers of the stack.
// As the stack grows downwards and we zero going forwards the start pointer
- // starts as _stack_end and the end pointer at _stack_start - 4
+ // starts as _stack_end and the end pointer at _stack_start.
la t0, _stack_end
- la t1, (_stack_start - 4)
+ la t1, _stack_start
bge t0, t1, stack_zero_loop_end
stack_zero_loop:
sw zero, 0(t0)
addi t0, t0, 0x4
- ble t0, t1, stack_zero_loop
+ blt t0, t1, stack_zero_loop
stack_zero_loop_end:
// Initialize the `.data` segment from the `.idata` segment.
@@ -80,7 +80,7 @@
sw t3, 0(t0)
addi t0, t0, 0x4
addi t2, t2, 0x4
- ble t0, t1, data_copy_loop
+ blt t0, t1, data_copy_loop
data_copy_loop_end:
// Jump into the C program entry point. This is your standard
diff --git a/sw/device/exts/common/flash_link.ld b/sw/device/exts/common/flash_link.ld
index 59e8c2d..dfe1fde 100644
--- a/sw/device/exts/common/flash_link.ld
+++ b/sw/device/exts/common/flash_link.ld
@@ -112,6 +112,7 @@
*/
*(.data)
*(.data.*)
+ . = ALIGN(4);
_data_end = .;
} > ram_main
@@ -127,6 +128,7 @@
*(.bss)
*(.bss.*)
*(COMMON)
+ . = ALIGN(4);
_bss_end = .;
} > ram_main
