spl: implement stack usage check

This implements a stack usage check in SPL.

Many boards start up SPL to run code + data from one common, rather small
SRAM. To implement a sophisticated SPL binary size limit on such boards,
the stack size (as well as malloc size and global data size) must be
subtracted from this SRAM size.

However, to do that properly, the stack size first needs to be known.

This patch adds a new Kconfig option:
- SPL_SYS_REPORT_STACK_F_USAGE: memset(0xaa) the whole area of the stack
  very early and check stack usage based on this constant later before the
  stack is switched to DRAM

Initializing the stack and checking it is implemented in weak functions,
in case a board does not use the stack as saved in gd->start_addr_sp.

Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>

1 files changed, 25 insertions, 0 deletions

diff --git a/common/spl/spl.c b/common/spl/spl.c
index c182705b3f..2c696f2a79 100644
--- a/common/spl/spl.c
+++ b/common/spl/spl.c
@@ -710,6 +710,28 @@ void preloader_console_init(void)
 #endif
 
 /**
+ * This function is called before the stack is changed from initial stack to
+ * relocated stack. It tries to dump the stack size used
+ */
+__weak void spl_relocate_stack_check(void)
+{
+#if CONFIG_IS_ENABLED(SYS_REPORT_STACK_F_USAGE)
+	ulong init_sp = gd->start_addr_sp;
+	ulong stack_bottom = init_sp - CONFIG_VAL(SIZE_LIMIT_PROVIDE_STACK);
+	u8 *ptr = (u8 *)stack_bottom;
+	ulong i;
+
+	for (i = 0; i < CONFIG_VAL(SIZE_LIMIT_PROVIDE_STACK); i++) {
+		if (*ptr != CONFIG_VAL(SYS_STACK_F_CHECK_BYTE))
+			break;
+		ptr++;
+	}
+	printf("SPL initial stack usage: %lu bytes\n",
+	       CONFIG_VAL(SIZE_LIMIT_PROVIDE_STACK) - i);
+#endif
+}
+
+/**
  * spl_relocate_stack_gd() - Relocate stack ready for board_init_r() execution
  *
  * Sometimes board_init_f() runs with a stack in SRAM but we want to use SDRAM
@@ -733,6 +755,9 @@ ulong spl_relocate_stack_gd(void)
 	gd_t *new_gd;
 	ulong ptr = CONFIG_SPL_STACK_R_ADDR;
 
+	if (CONFIG_IS_ENABLED(SYS_REPORT_STACK_F_USAGE))
+		spl_relocate_stack_check();
+
 #if defined(CONFIG_SPL_SYS_MALLOC_SIMPLE) && CONFIG_VAL(SYS_MALLOC_F_LEN)
 	if (CONFIG_SPL_STACK_R_MALLOC_SIMPLE_LEN) {
 		debug("SPL malloc() before relocation used 0x%lx bytes (%ld KB)\n",