multiple changes: BL1/BL2/kernel separation (build system, etc.) BL2 implementation. BL documentation

bootloader/stage2_load.c

@@ -0,0 +1,118 @@
+#include <stdint.h>
+
+// ELF Ident indexes
+#define EI_NIDENT 16
+
+// Program header types
+#define PT_NULL    0
+#define PT_LOAD    1
+
+// ELF Header (32-bit)
+typedef struct {
+    uint8_t  e_ident[EI_NIDENT];
+    uint16_t e_type;
+    uint16_t e_machine;
+    uint32_t e_version;
+    uint32_t e_entry;     // Entry point
+    uint32_t e_phoff;     // Program header table offset
+    uint32_t e_shoff;     // Section header table offset
+    uint32_t e_flags;
+    uint16_t e_ehsize;
+    uint16_t e_phentsize;
+    uint16_t e_phnum;
+    uint16_t e_shentsize;
+    uint16_t e_shnum;
+    uint16_t e_shstrndx;
+} __attribute__((packed)) Elf32_Ehdr;
+
+// Program Header (32-bit)
+typedef struct {
+    uint32_t p_type;
+    uint32_t p_offset;
+    uint32_t p_vaddr;
+    uint32_t p_paddr;
+    uint32_t p_filesz;
+    uint32_t p_memsz;
+    uint32_t p_flags;
+    uint32_t p_align;
+} __attribute__((packed)) Elf32_Phdr;
+
+// Load an ELF executable into memory.
+static int elf_load(const void* data, void (*load_segment)(uint8_t *vaddr, uint32_t src, uint32_t size)) {
+    const Elf32_Ehdr* header = (const Elf32_Ehdr*)data;
+    const Elf32_Phdr* ph = (const Elf32_Phdr*)((uint8_t*)data + header->e_phoff);
+
+    for (int i = 0; i < header->e_phnum; i++) {
+        if (ph[i].p_type != PT_LOAD)
+            continue;
+
+        uint32_t offset = ph[i].p_offset;
+        uint32_t vaddr = ph[i].p_vaddr;
+        uint32_t filesz = ph[i].p_filesz;
+        uint32_t memsz = ph[i].p_memsz;
+
+        // Copy data segment
+        //load_segment((uint8_t *)vaddr, offset, filesz);
+        load_segment((uint8_t *)vaddr, offset, filesz);
+
+        // Zero remaining BSS (if any)
+        if (memsz > filesz) {
+            uint8_t* bss_start = (uint8_t*)(vaddr + filesz);
+            for (uint32_t j = 0; j < memsz - filesz; j++) {
+                bss_start[j] = 0;
+            }
+        }
+    }
+
+    return header->e_entry;
+}
+
+#define KERN_START_SECT 5
+#define MAX(a, b) ((a)>(b) ? (a) : (b))
+
+extern void ata_lba_read(uint32_t lba, uint8_t nsect, void *addr);
+extern uint8_t read_buf[];
+
+static uint32_t
+total_header_size(const Elf32_Ehdr *header) {
+    uint32_t phend = header->e_phoff + header->e_phentsize*header->e_phnum;
+
+    // Align to 512
+    return (phend + 511) & ~511;
+}
+
+static void read_sectors(uint8_t *vaddr, uint32_t offset, uint32_t size) {
+    // # of sectors to read
+    uint32_t rem_nsect = ((size + 511) & ~511) / 512;
+
+    // Current lba address, offset by the first sector already read
+    uint32_t lba = KERN_START_SECT + offset / 512;
+
+    // Max 255 sectors at a time
+    while (rem_nsect) {
+        uint8_t nsect = rem_nsect > 255 ? 255 : rem_nsect;
+        ata_lba_read(lba, nsect, vaddr);
+
+        vaddr += nsect * 512;
+        rem_nsect -= nsect;
+        lba += nsect;
+    }
+}
+
+void *load_kernel(void) {
+    // Read the first sector
+    ata_lba_read(KERN_START_SECT, 1, read_buf);
+
+    const Elf32_Ehdr* header = (const Elf32_Ehdr*)read_buf;
+
+    // Remaining data size, subtract the first 512B already read
+    uint32_t rem = total_header_size(header) - 512;
+
+    // Read the rest if necessary
+    if (rem)
+        read_sectors(read_buf+512, 512, rem);
+
+    elf_load(read_buf, read_sectors);
+
+    return (void *)header->e_entry;
+}