userland: support arch specific examples

README.adoc

@@ -10396,6 +10396,20 @@ help architecture
 
 shows ARM version up to `armv6`, so maybe `armv6` is not implemented?
 
+=== ARM EL
+
+Find the ARM EL: https://stackoverflow.com/questions/31787617/what-is-the-current-execution-mode-exception-level-etc
+
+Prints the EL at the beginning of a baremetal simulation:
+
+....
+./run --arch aarch64 --baremetal arch/aarch64/el
+....
+
+Source: link:baremetal/arch/aarch64/el.c[]
+
+The lower ELs are not mandatory, and in gem5 at least you can configure the lowest EL with configuration options TODO which, example.
+
 === How we got some baremetal stuff to work
 
 It is nice when thing just work.

baremetal/arch/aarch64/el.c

@@ -0,0 +1,9 @@
+#include <stdio.h>
+#include <inttypes.h>
+
+int main(void) {
+    register uint64_t x0 __asm__ ("x0");
+    __asm__ ("mrs x0, CurrentEL;" : : : "%x0");
+	printf("%" PRIu64 "\n", x0);
+	return 0;
+}

build-userland

@@ -58,6 +58,7 @@ has the OpenBLAS libraries and headers installed.
                 [
                     'make', common.Newline,
                     '-j', str(args.nproc), common.Newline,
+                    'ARCH={}'.format(args.arch), common.Newline,
                     'CCFLAGS_SCRIPT={} {}'.format('-I', common.userland_src_dir), common.Newline,
                     'COMMON_DIR={}'.format(common.root_dir), common.Newline,
                     'CC={}'.format(cc), common.Newline,

userland/Makefile

@@ -1,5 +1,6 @@
 .PHONY: all clean mkdir
 
+ARCH = $(shell uname -m)
 CCFLAGS = -ggdb3 -I$(COMMON_DIR) -O0 -Wall -Werror -Wextra -Wno-unused-function $(CCFLAGS_EXTRA) $(CCFLAGS_SCRIPT)
 CFLAGS = -fopenmp -std=c99 $(CCFLAGS) $(CFLAGS_EXTRA)
 CXXFLAGS = -std=c++17 $(CCFLAGS) $(CXXFLAGS_EXTRA)
@@ -8,6 +9,7 @@ CXXFLAGS = -std=c++17 $(CCFLAGS) $(CXXFLAGS_EXTRA)
 COMMON_DIR = $(CURDIR)/..
 COMMON_BASENAME = common
 COMMON_OBJ = $(OUT_DIR)/$(COMMON_BASENAME)$(OBJ_EXT)
+IN_EXT_ASM = .S
 IN_EXT_C = .c
 IN_EXT_CXX = .cpp
 LIBS = -lm
@@ -17,7 +19,7 @@ OUT_DIR = $(CURDIR)
 
 -include params.mk
 
-OUTS := $(foreach IN_EXT,$(IN_EXT_C) $(IN_EXT_CXX),$(addsuffix $(OUT_EXT), $(basename $(wildcard *$(IN_EXT)))))
+OUTS := $(foreach IN_EXT,$(IN_EXT_ASM) $(IN_EXT_C) $(IN_EXT_CXX),$(addsuffix $(OUT_EXT), $(basename $(wildcard *$(IN_EXT)))))
 ifeq ($(HAS_EIGEN),y)
 	CXXFLAGS_EXTRA += -I$(STAGING_DIR)/usr/include/eigen3
 	# TODO: was failing with:
@@ -50,6 +52,9 @@ all: mkdir $(OUTS)
 $(COMMON_OBJ): $(COMMON_DIR)/$(COMMON_BASENAME)$(IN_EXT_C)
 	$(CC) $(CFLAGS) -c -o '$@' '$<' $(LIBS)
 
+$(OUT_DIR)/%$(OUT_EXT): %$(IN_EXT_ASM) $(COMMON_OBJ)
+	$(CC) $(CFLAGS) $(COMMON_OBJ) -o '$@' '$<' $(LIBS)
+
 $(OUT_DIR)/%$(OUT_EXT): %$(IN_EXT_C) $(COMMON_OBJ)
 	$(CC) $(CFLAGS) $(COMMON_OBJ) -o '$@' '$<' $(LIBS)
 

userland/arch/aarch64/Makefile

@@ -0,0 +1 @@
+../../Makefile

userland/arch/aarch64/asm_hello.c

@@ -0,0 +1,8 @@
+#include <assert.h>
+#include <inttypes.h>
+
+int main(void) {
+    register uint32_t x0 __asm__ ("x0");
+    __asm__ ("mov x0, #1;" : : : "%x0");
+    assert(x0 == 1);
+}

userland/arch/aarch64/params.mk

@@ -0,0 +1 @@
+COMMON_DIR = ../../..

userland/arch/x86_64/Makefile

@@ -0,0 +1 @@
+../../Makefile

userland/arch/x86_64/asm_hello.c

@@ -0,0 +1,16 @@
+#include <assert.h>
+#include <inttypes.h>
+
+int main(void) {
+	uint32_t in = 1;
+	uint32_t out = 0;
+	__asm__ (
+		"movl %1, %%eax;"
+		"inc %%eax;"
+		"movl %%eax, %0"
+		: "=m" (out)
+		: "m" (in)
+		: "%eax"
+	);
+	assert(out == in + 1);
+}

userland/arch/x86_64/freestanding/hello.S

@@ -0,0 +1,19 @@
+.data
+    s:
+        .ascii "hello\n"
+        len = . - s
+.text
+    .global _start
+    _start:
+
+    /* Write. */
+    mov $1, %rax
+    mov $1, %rdi
+    mov $s, %rsi
+    mov $len, %rdx
+    syscall
+
+    /* Exit. */
+    mov $60, %rax
+    mov $0, %rdi
+    syscall

userland/arch/x86_64/params.mk

@@ -0,0 +1 @@
+COMMON_DIR = ../../..

userland/params.mk

@@ -1 +1 @@
-SUBDIRS := interactive
+SUBDIRS := interactive arch/$(ARCH)/