support elfloader for shared object and relocatable object

1. elfloader for shared object
example: TencentOS-tiny\examples\elfloader_shared_object
keil: TencentOS-tiny\board\TencentOS_tiny_EVB_MX_Plus\KEIL\elfloader_shared_object

2. elfloader for relocatable object:
example: TencentOS-tiny\examples\elfloader_relocatable_object
keil: TencentOS-tiny\board\TencentOS_tiny_EVB_MX_Plus\KEIL\elfloader_relocatable_object

3. TODO:
- add icache/dcache flush when module is loaded
- support more relocation type in elfloader_arch_relocate

examples/elfloader_shared_object/elfloader_shared_object.c

@@ -0,0 +1,103 @@
+#include "tos_k.h"
+#include "tos_hal.h"
+#include "ff.h"
+#include "tos_vfs.h"
+#include "tos_fatfs_drv.h"
+#include "tos_fatfs_vfs.h"
+
+#include "tos_elfloader.h"
+
+int d_e_a = 9;
+
+int f_e_a(int a)
+{
+    /* a = d_e_a + d_g_a = d_e_a + 15 = 24 */
+    printf("f_e_a:  %d\n", a);
+    return 0;
+}
+
+const el_symbol_t el_symbols[] = {
+    { "d_e_a", &d_e_a },
+    { "f_e_a", f_e_a },
+    { K_NULL, K_NULL },
+};
+
+/*
+ step1: create 1.c
+
+ extern int d_e_a;
+
+ int d_g_a = 3;
+
+ static int d_s_a = 5;
+
+ extern int f_e_a(int);
+
+ static int f_s_a(void) {
+     d_s_a += 7; // d_s_a = 12
+ }
+
+ int f_g_a(void) {
+     f_s_a();
+
+     d_g_a += d_s_a; // d_g_a = 15
+
+     d_e_a += d_g_a; // + 15
+
+     f_e_a(d_e_a);
+ }
+
+ step2: compile 1.c to 1.o
+ arm-linux-gnueabihf-gcc -fno-builtin -nostdlib -mthumb -mthumb-interwork -fPIC -mcpu=cortex-m4 -c 1.c -o 1.o
+
+ step3: ld 1.o to 1.so
+ arm-linux-gnueabihf-ld -fno-builtin -nostdlib -fPIC -shared -z max-page-size=0x4 1.o -o 1.so
+ */
+
+void application_entry(void *arg)
+{
+    int fd;
+    el_module_t module;
+
+    extern vfs_blkdev_ops_t sd_dev;
+    extern vfs_fs_ops_t fatfs_ops;
+
+    if (tos_vfs_block_device_register("/dev/sd", &sd_dev) != VFS_ERR_NONE) {
+        return;
+    }
+
+    if (tos_vfs_fs_register("fatfs_sd", &fatfs_ops) != VFS_ERR_NONE) {
+        return;
+    }
+
+    if (tos_vfs_fs_mount("/dev/sd", "/fs/fatfs_sd", "fatfs_sd") != VFS_ERR_NONE) {
+        printf("mount failed!\n");
+        return;
+    }
+
+    fd = tos_vfs_open("/fs/fatfs_sd/1.so", VFS_OFLAG_READ | VFS_OFLAG_EXISTING);
+    if (fd < 0) {
+        return;
+    }
+
+    if (tos_elfloader_load(&module, fd) != ELFLOADER_ERR_NONE) {
+        return;
+    }
+
+    void *addr = tos_elfloader_find_symbol(&module, "f_g_a");
+    if (!addr) {
+        printf("symbol NOT FOUND: %s\n", "f_g_a");
+        return;
+    }
+
+    printf("addr: %x\n", addr);
+
+    typedef int (*fp_t)(void);
+    /* call f_g_a in 1.so */
+    ((fp_t)addr)();
+
+    tos_elfloader_unload(&module);
+
+    tos_vfs_close(fd);
+}
+