From d86b0601b9cad839225dcd786a5c341ff54f44c8 Mon Sep 17 00:00:00 2001
From: Daniel Pouzzner <douzzer@wolfssl.com>
Date: Sat, 22 Aug 2020 01:10:28 -0500
Subject: [PATCH] lkm: tweak Kbuild to work on 4.x (hardcoded fallback stack
 size); add linuxkm/get_thread_size.c.

---
 linuxkm/Kbuild            |  7 ++++++-
 linuxkm/get_thread_size.c | 13 +++++++++++++
 2 files changed, 19 insertions(+), 1 deletion(-)
 create mode 100644 linuxkm/get_thread_size.c

diff --git a/linuxkm/Kbuild b/linuxkm/Kbuild
index b7b37845c..f8509c83d 100644
--- a/linuxkm/Kbuild
+++ b/linuxkm/Kbuild
@@ -20,11 +20,16 @@ ifeq "$(WOLFSSL_CFLAGS)" ""
 $(error $$WOLFSSL_CFLAGS is unset.)
 endif
 
+# this mechanism only works in kernel 5.x+ (fallback to hardcoded value)
 hostprogs := linuxkm/get_thread_size
 always-y := $(hostprogs)
 HOST_EXTRACFLAGS += $(NOSTDINC_FLAGS) $(LINUXINCLUDE) $(KBUILD_CFLAGS) -static
+
+# this rule is needed to get build to succeed in 4.x (get_thread_size still doesn't get built)
+$(obj)/linuxkm/get_thread_size: $(src)/linuxkm/get_thread_size.c
+
 $(patsubst %, $(obj)/%, $(WOLFSSL_OBJ_FILES)): $(obj)/linuxkm/get_thread_size
-KERNEL_THREAD_STACK_SIZE=$(shell $(obj)/linuxkm/get_thread_size)
+KERNEL_THREAD_STACK_SIZE=$(shell test -x $(obj)/linuxkm/get_thread_size && $(obj)/linuxkm/get_thread_size || echo 16384)
 MAX_STACK_FRAME_SIZE=$(shell echo $$(( $(KERNEL_THREAD_STACK_SIZE) / 4)))
 
 libwolfssl-y := $(WOLFSSL_OBJ_FILES)
diff --git a/linuxkm/get_thread_size.c b/linuxkm/get_thread_size.c
new file mode 100644
index 000000000..cad1c0c61
--- /dev/null
+++ b/linuxkm/get_thread_size.c
@@ -0,0 +1,13 @@
+#ifndef __KERNEL__
+#define __KERNEL__
+#endif
+#include <linux/kconfig.h>
+#include <linux/kernel.h>
+#include <linux/kthread.h>
+
+extern int dprintf(int fd, const char *format, ...);
+
+int main(__maybe_unused int argc, __maybe_unused char **argv) {
+  dprintf(1, "%lu\n",THREAD_SIZE);
+  return 0;
+}