test-gdb: can now run in either userland or baremetal modes

Selection with --mode userland (default because has x86_64) or --mode baremetal.

This is the first userland tool where this choice is done on the command line,
which led to a refactor of supported_archs and is_baremetal and is_userland
into a single self.env['mode'].

userland/arch/aarch64/gdb_tests/build

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

userland/arch/aarch64/gdb_tests/test

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

userland/arch/arm/gdb_tests/build

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

userland/arch/arm/gdb_tests/test

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

userland/arch/x86_64/gdb_tests/README.adoc

@@ -0,0 +1 @@
+https://github.com/cirosantilli/linux-kernel-module-cheat#gdb-tests

userland/arch/x86_64/gdb_tests/build

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

userland/arch/x86_64/gdb_tests/integer_registers.S

@@ -0,0 +1,11 @@
+#include <lkmc.h>
+
+LKMC_PROLOGUE
+    /* 1 + 2 == 3 */
+    mov $1, %rax
+    /* test-gdb-op1 */
+    mov $2, %rbx
+    add %rax, %rbx
+    /* test-gdb-result */
+    LKMC_ASSERT_EQ(%rbx, $3)
+LKMC_EPILOGUE

userland/arch/x86_64/gdb_tests/integer_registers.py

@@ -0,0 +1,7 @@
+def test(self):
+    self.sendline('tbreak main')
+    self.sendline('continue')
+    self.continue_to('op1')
+    assert self.get_int('$rax') == 1
+    self.continue_to('result')
+    assert self.get_int('$rbx') == 3

userland/arch/x86_64/gdb_tests/set_registers.S

@@ -0,0 +1,10 @@
+/* Test that we can set registers from GDB. */
+
+#include <lkmc.h>
+
+LKMC_PROLOGUE
+    mov $1, %rax
+    /* test-gdb-rax */
+    mov $2, %rbx
+    /* test-gdb-rbx */
+LKMC_EPILOGUE

userland/arch/x86_64/gdb_tests/set_registers.py

@@ -0,0 +1,9 @@
+def test(self):
+    self.sendline('tbreak main')
+    self.sendline('continue')
+
+    self.continue_to('rax')
+    self.sendline('set $rax = 3')
+    self.continue_to('rbx')
+    assert self.get_int('$rax') == 3
+    assert self.get_int('$rbx') == 2

userland/arch/x86_64/gdb_tests/test

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