llext: add support for arc

Adds compiler flag(s) and some architecture-specific relocations
for ARC. No userspace support, doesn't support all relocations.

Signed-off-by: Lauren Murphy <lauren.murphy@intel.com>

arch/arc/core/CMakeLists.txt

@@ -34,3 +34,5 @@ add_subdirectory_ifdef(CONFIG_ARC_CORE_MPU mpu)
 add_subdirectory_ifdef(CONFIG_ARC_SECURE_FIRMWARE secureshield)
 
 zephyr_linker_sources(ROM_START SORT_KEY 0x0vectors vector_table.ld)
+
+zephyr_library_sources_ifdef(CONFIG_LLEXT elf.c)

arch/arc/core/elf.c

@@ -0,0 +1,79 @@
+/*
+ * Copyright (c) 2024 Intel Corporation
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <zephyr/llext/elf.h>
+#include <zephyr/llext/llext.h>
+#include <zephyr/llext/loader.h>
+#include <zephyr/logging/log.h>
+
+LOG_MODULE_REGISTER(elf, CONFIG_LLEXT_LOG_LEVEL);
+
+#define R_ARC_32            4
+#define R_ARC_B26           5 /* AKA R_ARC_64 */
+#define R_ARC_S25W_PCREL    17
+#define R_ARC_32_ME         27
+
+/* ARCompact insns packed in memory have Middle Endian encoding */
+#define ME(x) ((x & 0xffff0000) >> 16) | ((x & 0xffff) << 16);
+
+/**
+ * @brief Architecture specific function for relocating shared elf
+ *
+ * Elf files contain a series of relocations described in multiple sections.
+ * These relocation instructions are architecture specific and each architecture
+ * supporting modules must implement this.
+ *
+ * The relocation codes are well documented:
+ * https://github.com/foss-for-synopsys-dwc-arc-processors/arc-ABI-manual/blob/master/ARCv2_ABI.pdf
+ * https://github.com/zephyrproject-rtos/binutils-gdb
+ */
+int arch_elf_relocate(elf_rela_t *rel, uintptr_t loc, uintptr_t sym_base_addr, const char *sym_name,
+		      uintptr_t load_bias)
+{
+	int ret = 0;
+	uint32_t insn = *(uint32_t *)loc;
+	uint32_t value;
+
+	sym_base_addr += rel->r_addend;
+
+	int reloc_type = ELF32_R_TYPE(rel->r_info);
+
+	switch (reloc_type) {
+	case R_ARC_32:
+	case R_ARC_B26:
+		*(uint32_t *)loc = sym_base_addr;
+		break;
+	case R_ARC_S25W_PCREL:
+		/* ((S + A) - P) >> 2
+		 * S = symbol address
+		 * A = addend
+		 * P = relative offset to PCL
+		 */
+		value = (sym_base_addr + rel->r_addend - (loc & ~0x3)) >> 2;
+
+		insn = ME(insn);
+
+		/* disp25w */
+		insn = insn & ~0x7fcffcf;
+		insn |= ((value >> 0) & 0x01ff) << 18;
+		insn |= ((value >> 9) & 0x03ff) << 6;
+		insn |= ((value >> 19) & 0x000f) << 0;
+
+		insn = ME(insn);
+
+		*(uint32_t *)loc = insn;
+		break;
+	case R_ARC_32_ME:
+		*(uint32_t *)loc = ME(sym_base_addr);
+		break;
+	default:
+		LOG_ERR("unknown relocation: %u\n", reloc_type);
+		ret = -ENOEXEC;
+		break;
+	}
+
+	return ret;
+}

cmake/compiler/gcc/target_arc.cmake

@@ -8,5 +8,16 @@ if(NOT DEFINED GCC_ARC_TUNED_CPU)
   set(GCC_ARC_TUNED_CPU ${GCC_M_CPU})
 endif()
 
+# Flags not supported by llext linker
+# (regexps are supported and match whole word)
+set(LLEXT_REMOVE_FLAGS
+  -fno-pic
+  -fno-pie
+  -ffunction-sections
+  -fdata-sections
+  -g.*
+  -Os
+)
+
 list(APPEND TOOLCHAIN_C_FLAGS -mcpu=${GCC_ARC_TUNED_CPU})
 list(APPEND TOOLCHAIN_LD_FLAGS -mcpu=${GCC_ARC_TUNED_CPU})

doc/services/llext/index.rst

@@ -21,4 +21,4 @@ and introspected to some degree, as well as unloaded when no longer needed.
 .. note::
 
    The LLEXT subsystem requires architecture-specific support. It is currently
-   available only on RISC-V, ARM, ARM64 and Xtensa cores.
+   available only on RISC-V, ARM, ARM64, ARC (experimental) and Xtensa cores.

tests/subsys/llext/simple/boards/qemu_arc_qemu_arc_em.conf

@@ -0,0 +1,6 @@
+CONFIG_FILE_SYSTEM=y
+CONFIG_FILE_SYSTEM_LITTLEFS=y
+CONFIG_FS_LITTLEFS_FMP_DEV=y
+CONFIG_FLASH_MAP=y
+CONFIG_FLASH=y
+CONFIG_FLASH_SIMULATOR=y

tests/subsys/llext/simple/boards/qemu_arc_qemu_arc_em.overlay

@@ -0,0 +1,28 @@
+/ {
+	sim_flash_controller: sim_flash_controller {
+		compatible = "zephyr,sim-flash";
+
+		#address-cells = <1>;
+		#size-cells = <1>;
+		erase-value = <0x00>;
+
+		flash_sim0: flash_sim@0 {
+			compatible = "soc-nv-flash";
+			reg = <0x00000000 0x2000>;
+
+			erase-block-size = <1024>;
+			write-block-size = <4>;
+
+			partitions {
+				compatible = "fixed-partitions";
+				#address-cells = <1>;
+				#size-cells = <1>;
+
+				storage_partition: partition@0 {
+					label = "storage_partition";
+					reg = <0x00000000 0x2000>;
+				};
+			};
+		};
+	};
+};

tests/subsys/llext/simple/no_mem_protection.conf

@@ -6,3 +6,4 @@
 CONFIG_ARM_MPU=n
 CONFIG_ARM_AARCH32_MMU=n
 CONFIG_RISCV_PMP=n
+CONFIG_ARC_MPU_ENABLE=n

tests/subsys/llext/simple/testcase.yaml

@@ -6,11 +6,6 @@ common:
     - s32z2xxdc2/s32z270/rtu0 # See commit 18a0660
     - s32z2xxdc2/s32z270/rtu1 # See commit 18a0660
     # platforms that are always skipped by the runtime filter
-    - qemu_arc/qemu_arc_em
-    - qemu_arc/qemu_arc_hs
-    - qemu_arc/qemu_arc_hs/xip
-    - qemu_arc/qemu_arc_hs5x
-    - qemu_arc/qemu_arc_hs6x
     - qemu_cortex_m0
     - qemu_xtensa/dc233c/mmu
   integration_platforms:
@@ -36,7 +31,7 @@ tests:
   # most tests include no_mem_protection.conf, which disables memory protection
   # hardware completely.
   llext.simple.readonly:
-    arch_allow: arm riscv # Xtensa needs writable storage
+    arch_allow: arm riscv arc # Xtensa needs writable storage
     filter: not CONFIG_MPU and not CONFIG_MMU
     extra_conf_files: ['no_mem_protection.conf']
     extra_configs:
@@ -57,7 +52,7 @@ tests:
       - CONFIG_LLEXT_HEAP_SIZE=128 # qemu_cortex_a9 requires larger heap
       - CONFIG_LLEXT_STORAGE_WRITABLE=n
   llext.simple.writable:
-    arch_allow: arm xtensa riscv
+    arch_allow: arm xtensa riscv arc
     integration_platforms:
       - qemu_xtensa/dc233c      # Xtensa ISA
     filter: not CONFIG_MPU and not CONFIG_MMU
@@ -65,7 +60,9 @@ tests:
     extra_configs:
       - CONFIG_LLEXT_STORAGE_WRITABLE=y
   llext.simple.writable_relocatable:
-    arch_allow: arm xtensa riscv
+    arch_allow: arm xtensa riscv arc
+    platform_exclude:
+      - qemu_arc/qemu_arc_hs5x  # See #80949
     integration_platforms:
       - qemu_xtensa/dc233c      # Xtensa ISA
     filter: not CONFIG_MPU and not CONFIG_MMU
@@ -77,7 +74,7 @@ tests:
   # Test the Symbol Link Identifier (SLID) linking feature on writable
   # storage to cover both ARM and Xtensa architectures on the same test.
   llext.simple.writable_slid_linking:
-    arch_allow: arm xtensa riscv
+    arch_allow: arm xtensa riscv arc
     integration_platforms:
       - qemu_xtensa/dc233c      # Xtensa ISA
     filter: not CONFIG_MPU and not CONFIG_MMU
@@ -86,7 +83,9 @@ tests:
       - CONFIG_LLEXT_STORAGE_WRITABLE=y
       - CONFIG_LLEXT_EXPORT_BUILTINS_BY_SLID=y
   llext.simple.writable_relocatable_slid_linking:
-    arch_allow: arm xtensa riscv
+    arch_allow: arm xtensa riscv arc
+    platform_exclude:
+      - qemu_arc/qemu_arc_hs5x  # See #80949
     integration_platforms:
       - qemu_xtensa/dc233c      # Xtensa ISA
     filter: not CONFIG_MPU and not CONFIG_MMU