tests/tcg/i386: add system mode Hello World test

This introduces the build framework for simple i386 system tests. The
first test is the eponymous "Hello World" which simply outputs the
text on the serial port and then exits.

I've included the framework for x86_64 but it is not in this series as
it is a work in progress.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

tests/tcg/i386/Makefile.softmmu-target

@@ -0,0 +1,46 @@
+#
+# x86 system tests
+#
+# This currently builds only for i386. The common C code is built
+# with standard compiler flags however so we can support both by
+# adding additional boot files for x86_64.
+#
+
+I386_SYSTEM_SRC=$(SRC_PATH)/tests/tcg/i386/system
+X64_SYSTEM_SRC=$(SRC_PATH)/tests/tcg/x86_64/system
+# Set search path for all sources
+VPATH+=$(I386_SYSTEM_SRC)
+
+# These objects provide the basic boot code and helper functions for all tests
+CRT_OBJS=boot.o
+
+X86_TEST_SRCS=$(wildcard $(I386_SYSTEM_SRC)/*.c)
+X86_TESTS = $(patsubst $(I386_SYSTEM_SRC)/%.c, %, $(X86_TEST_SRCS))
+
+ifeq ($(TARGET_X86_64), y)
+CRT_PATH=$(X64_SYSTEM_SRC)
+LINK_SCRIPT=$(X64_SYSTEM_SRC)/kernel.ld
+LDFLAGS=-Wl,-T$(LINK_SCRIPT) -Wl,-melf_x86_64
+else
+CRT_PATH=$(I386_SYSTEM_SRC)
+CFLAGS+=-m32
+LINK_SCRIPT=$(I386_SYSTEM_SRC)/kernel.ld
+LDFLAGS=-Wl,-T$(LINK_SCRIPT) -Wl,-melf_i386
+# FIXME: move to common once x86_64 is bootstrapped
+TESTS+=$(X86_TESTS)
+endif
+CFLAGS+=-nostdlib -ggdb -O0 $(MINILIB_INC)
+LDFLAGS+=-static -nostdlib $(CRT_OBJS) $(MINILIB_OBJS) -lgcc
+
+# building head blobs
+.PRECIOUS: $(CRT_OBJS)
+
+%.o: $(CRT_PATH)/%.S
+	$(CC) $(CFLAGS) -c $< -o $@
+
+# Build and link the tests
+%: %.c $(LINK_SCRIPT) $(CRT_OBJS) $(MINILIB_OBJS)
+	$(CC) $(CFLAGS) $< -o $@ $(LDFLAGS)
+
+# Running
+QEMU_OPTS+=-device isa-debugcon,chardev=output -device isa-debug-exit,iobase=0xf4,iosize=0x4 -kernel

tests/tcg/i386/system/boot.S

@@ -0,0 +1,172 @@
+/*
+ * i386 boot code, based on  qemu-bmibug.
+ *
+ * Copyright 2019 Doug Gale
+ * Copyright 2019 Linaro
+ *
+ * This work is licensed under the terms of the GNU GPL, version 3 or later.
+ * See the COPYING file in the top-level directory.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+        .section .head
+
+        /* Multi-boot header */
+multiboot_st:
+        .int 0x1BADB002
+        .int 0x10000
+        .int -(0x10000+0x1BADB002)
+        // Load address
+        .int __load_st
+        .int __load_st
+        .int __load_en
+        .int __bss_en
+        .int _start
+        // mode
+        .int 0
+        // width
+        .int 0
+        // height
+        .int 0
+        // depth
+        .int 0
+
+        .code32
+        .section .text
+
+        /* Kernel Entry Point */
+.global _start
+_start:
+        // Setup stack ASAP
+        mov $stack_end,%esp
+
+        // Load GDT ASAP
+        lgdt gdtr
+        ljmp $0x8,$.Lloadcs
+.Lloadcs:
+        mov $0x10,%eax
+        mov %eax,%ds
+        mov %eax,%es
+        mov %eax,%fs
+        mov %eax,%gs
+        mov %eax,%ss
+
+        // Fixup the IDT to the ridiculous i386 layout
+        xor %ebx,%ebx
+.Lnextidt:
+        mov idt_00(,%ebx,8),%eax
+        shr $16,%eax
+        movw $0x8,idt_00+2(,%ebx,8)
+        movw $0x8E00,idt_00+4(,%ebx,8)
+        movw %ax,idt_00+6(,%ebx,8)
+        add $1,%ebx
+        cmp $32,%ebx
+        jl .Lnextidt
+
+        // Load IDTR
+        push $idt_00
+        push $((32 * 8 - 1) << 16)
+        lidt 2(%esp)
+        add $8,%esp
+
+        /*
+         * Don't worry about stack frame, assume everthing
+         * is garbage when we return, we won't need it.
+         */
+        call main
+
+        /* output any non-zero result in eax to isa-debug-exit device */
+        test %al, %al
+        jz 1f
+        out %ax, $0xf4
+
+1:      /* QEMU ACPI poweroff */
+        mov $0x604,%edx
+        mov $0x2000,%eax
+        out %ax,%dx
+        hlt
+        jmp 1b
+
+        /*
+         * Helper Functions
+         */
+
+        /* Output a single character to serial port */
+        .global __sys_outc
+__sys_outc:
+        pushl %ebp
+        movl %esp, %ebp
+        out %al,$0xE9
+        movl %ebp, %esp
+        popl %ebp
+        ret
+
+
+        /* Interrupt Descriptor Table */
+
+        .section .data
+        .align 16
+
+idt_00: .int 0, 0
+idt_01: .int 0, 0
+idt_02: .int 0, 0
+idt_03: .int 0, 0
+idt_04: .int 0, 0
+idt_05: .int 0, 0
+idt_06: .int 0, 0 /* intr_6_opcode, Invalid Opcode */
+idt_07: .int 0, 0
+idt_08: .int 0, 0
+idt_09: .int 0, 0
+idt_0A: .int 0, 0
+idt_0B: .int 0, 0
+idt_0C: .int 0, 0
+idt_0D: .int 0, 0
+idt_0E: .int 0, 0
+idt_0F: .int 0, 0
+idt_10: .int 0, 0
+idt_11: .int 0, 0
+idt_12: .int 0, 0
+idt_13: .int 0, 0
+idt_14: .int 0, 0
+idt_15: .int 0, 0
+idt_16: .int 0, 0
+idt_17: .int 0, 0
+idt_18: .int 0, 0
+idt_19: .int 0, 0
+idt_1A: .int 0, 0
+idt_1B: .int 0, 0
+idt_1C: .int 0, 0
+idt_1D: .int 0, 0
+idt_1E: .int 0, 0
+idt_1F: .int 0, 0
+
+gdt:
+        .short 0
+gdtr:
+        .short gdt_en - gdt - 1
+        .int gdt
+
+        // Code
+        .short 0xFFFF
+        .short 0
+        .byte 0
+        .byte 0x9b
+        .byte 0xCF
+        .byte 0
+
+        // Data
+        .short 0xFFFF
+        .short 0
+        .byte 0
+        .byte 0x93
+        .byte 0xCF
+        .byte 0
+
+gdt_en:
+
+        .section .bss
+        .align 16
+
+stack: .space 65536
+stack_end:

tests/tcg/i386/system/hello.c

@@ -0,0 +1,14 @@
+/*
+ * Hello World, system test version
+ *
+ * We don't have the benefit of libc, just builtin C primitives and
+ * whatever is in minilib.
+ */
+
+#include <minilib.h>
+
+int main(void)
+{
+    ml_printf("Hello World\n");
+    return 0;
+}

tests/tcg/i386/system/kernel.ld

@@ -0,0 +1,23 @@
+SECTIONS {
+	. = 0x100000;
+
+	.text : {
+		__load_st = .;
+		*(.head)
+		*(.text)
+	}
+
+	.rodata : {
+		*(.rodata)
+	}
+
+	.data : {
+		*(.data)
+		__load_en = .;
+	}
+
+	.bss : {
+		*(.bss)
+		__bss_en = .;
+	}
+}