boards: qemu_x86_tiny: enabled for general demand paging testing

This enables qemu_x86_tiny to be used for more general demand
paging testing where non-pinned code and data is not available
in physical memory at boot. This adds a custom linker script to
qemu_x86_tiny for pinning code and data. In the process, a new
kconfig CONFIG_BOARD_QEMU_X86_TINY has to be introduced to
distinguish from other qemu_x86* boards. This linker script
is based on the generic x86-32 one in
include/arch/x86/ia32/linker.ld, with additions to
put symbols into boot and pinned sections.

Signed-off-by: Daniel Leung <[email protected]>

Author: dcpleung

boards/x86/qemu_x86/Kconfig.board

@@ -20,3 +20,9 @@ config BOARD_QEMU_X86_LAKEMONT
 	select QEMU_TARGET
 	select CPU_HAS_FPU
 	select HAS_COVERAGE_SUPPORT
+
+config BOARD_QEMU_X86_TINY
+	bool "QEMU x86 (tiny memory)"
+	depends on SOC_IA32
+	select QEMU_TARGET
+	select CPU_HAS_FPU

boards/x86/qemu_x86/Kconfig.defconfig

@@ -56,3 +56,38 @@ config X86_PC_COMPATIBLE
 	default y
 
 endif # BOARD_QEMU_X86_LAKEMONT
+
+if BOARD_QEMU_X86_TINY
+
+config BUILD_OUTPUT_BIN
+	default n
+
+config BOARD
+	default "qemu_x86_tiny"
+
+config KERNEL_VM_SIZE
+	default 0x400000
+
+config MULTIBOOT
+	# This is needed for QEMU to load the ELF image
+	default y
+
+config X86_PC_COMPATIBLE
+	# QEMU presents a PC-compatible machine
+	default y
+
+config HAVE_CUSTOM_LINKER_SCRIPT
+	default y
+
+config CUSTOM_LINKER_SCRIPT
+	default "${ZEPHYR_BASE}/boards/x86/qemu_x86/qemu_x86_tiny.ld"
+
+config X86_EXTRA_PAGE_TABLE_PAGES
+	# This is needed for gen_mmu.py to map the flash into memory
+	default 2 if DEMAND_PAGING && !LINKER_GENERIC_SECTIONS_PRESENT_AT_BOOT
+
+config DEMAND_PAGING_PAGE_FRAMES_RESERVE
+	# Need to accommodate the heap for newlib in libc-hook.c
+	default 6 if NEWLIB_LIBC
+
+endif # BOARD_QEMU_X86_TINY

boards/x86/qemu_x86/board.cmake

@@ -22,6 +22,10 @@ endif()
 if(CONFIG_XIP)
   # Extra 4MB to emulate flash area
   math(EXPR QEMU_MEMORY_SIZE_MB "${CONFIG_SRAM_SIZE} / 1024 + 4")
+elseif(CONFIG_BOARD_QEMU_X86_TINY AND CONFIG_DEMAND_PAGING
+       AND NOT CONFIG_LINKER_GENERIC_SECTIONS_PRESENT_AT_BOOT)
+  # Flash is at 4MB-8MB, so need this to be large enough
+  math(EXPR QEMU_MEMORY_SIZE_MB "8")
 else()
   math(EXPR QEMU_MEMORY_SIZE_MB "${CONFIG_SRAM_SIZE} / 1024")
 endif()
@@ -69,3 +73,11 @@ endif()
 # board_set_debugger_ifnset(qemu)
 # debugserver: QEMU_EXTRA_FLAGS += -s -S
 # debugserver: qemu
+
+if(CONFIG_BOARD_QEMU_X86_TINY AND CONFIG_DEMAND_PAGING
+   AND NOT CONFIG_LINKER_GENERIC_SECTIONS_PRESENT_AT_BOOT)
+  # This is to map the flash so it is accessible.
+  math(EXPR QEMU_FLASH_SIZE_KB "${CONFIG_FLASH_SIZE} * 1024")
+  set(X86_EXTRA_GEN_MMU_ARGUMENTS
+      --map ${CONFIG_FLASH_BASE_ADDRESS},${QEMU_FLASH_SIZE_KB},W)
+endif()