artiq/soc/runtime/elf_loader.c

#include <stdio.h>
#include <string.h>

#include "elf_loader.h"

#define EI_NIDENT 16

struct elf32_ehdr {
    unsigned char ident[EI_NIDENT];    /* ident bytes */
    unsigned short type;               /* file type */
    unsigned short machine;            /* target machine */
    unsigned int version;              /* file version */
    unsigned int entry;                /* start address */
    unsigned int phoff;                /* phdr file offset */
    unsigned int shoff;                /* shdr file offset */
    unsigned int flags;                /* file flags */
    unsigned short ehsize;             /* sizeof ehdr */
    unsigned short phentsize;          /* sizeof phdr */
    unsigned short phnum;              /* number phdrs */
    unsigned short shentsize;          /* sizeof shdr */
    unsigned short shnum;              /* number shdrs */
    unsigned short shstrndx;           /* shdr string index */
} __attribute__((packed));

static const unsigned char elf_magic_header[] = {
    0x7f, 0x45, 0x4c, 0x46,  /* 0x7f, 'E', 'L', 'F' */
    0x01,                    /* Only 32-bit objects. */
    0x02,                    /* Only big-endian. */
    0x01,                    /* Only ELF version 1. */
};

#define ET_NONE         0       /* Unknown type. */
#define ET_REL          1       /* Relocatable. */
#define ET_EXEC         2       /* Executable. */
#define ET_DYN          3       /* Shared object. */
#define ET_CORE         4       /* Core file. */

#define EM_OR1K 0x005c

struct elf32_shdr {
    unsigned int name;        /* section name */
    unsigned int type;        /* SHT_... */
    unsigned int flags;       /* SHF_... */
    unsigned int addr;        /* virtual address */
    unsigned int offset;      /* file offset */
    unsigned int size;        /* section size */
    unsigned int link;        /* misc info */
    unsigned int info;        /* misc info */
    unsigned int addralign;   /* memory alignment */
    unsigned int entsize;     /* entry size if table */
} __attribute__((packed));

struct elf32_name {
    char name[12];
} __attribute__((packed));

struct elf32_rela {
    unsigned int offset;  /* Location to be relocated. */
    unsigned int info;    /* Relocation type and symbol index. */
    int addend;           /* Addend. */
} __attribute__((packed));

#define ELF32_R_SYM(info)  ((info) >> 8)
#define ELF32_R_TYPE(info) ((unsigned char)(info))

#define R_OR1K_INSN_REL_26 6

struct elf32_sym {
    unsigned int name;     /* String table index of name. */
    unsigned int value;    /* Symbol value. */
    unsigned int size;     /* Size of associated object. */
    unsigned char info;    /* Type and binding information. */
    unsigned char other;   /* Reserved (not used). */
    unsigned short shndx;  /* Section index of symbol. */
} __attribute__((packed));


#define SANITIZE_OFFSET_SIZE(offset, size) \
    if(offset > 0x10000000) { \
        printf("Incorrect offset in ELF data"); \
        return 0; \
    } \
    if((offset + size) > elf_length) { \
        printf("Attempted to access past the end of ELF data"); \
        return 0; \
    }

#define GET_POINTER_SAFE(target, target_type, offset) \
    SANITIZE_OFFSET_SIZE(offset, sizeof(target_type)); \
    target = (target_type *)((char *)elf_data + offset)

void *find_symbol(const struct symbol *symbols, const char *name)
{
    int i;

    i = 0;
    while((symbols[i].name != NULL) && (strcmp(symbols[i].name, name) != 0))
        i++;
    return symbols[i].target;
}

static int fixup(void *dest, int dest_length, struct elf32_rela *rela, void *target)
{
    int type, offset;
    unsigned int *_dest = dest;
    unsigned int *_target = target;

    type = ELF32_R_TYPE(rela->info);
    offset = rela->offset/4;
    if(type == R_OR1K_INSN_REL_26) {
        int val;

        val = _target - (_dest + offset);
        _dest[offset] = (_dest[offset] & 0xfc000000) | (val & 0x03ffffff);
    } else
        printf("Unsupported relocation type: %d\n", type);
    return 1;
}

int load_elf(symbol_resolver resolver, void *elf_data, int elf_length, void *dest, int dest_length)
{
    struct elf32_ehdr *ehdr;
    struct elf32_shdr *strtable;
    unsigned int shdrptr;
    int i;

    unsigned int textoff, textsize;
    unsigned int textrelaoff, textrelasize;
    unsigned int symtaboff, symtabsize;
    unsigned int strtaboff, strtabsize;


    /* validate ELF */
    GET_POINTER_SAFE(ehdr, struct elf32_ehdr, 0);
    if(memcmp(ehdr->ident, elf_magic_header, sizeof(elf_magic_header)) != 0) {
        printf("Incorrect ELF header\n");
        return 0;
    }
    if(ehdr->type != ET_REL) {
        printf("ELF is not relocatable\n");
        return 0;
    }
    if(ehdr->machine != EM_OR1K) {
        printf("ELF is for a different machine\n");
        return 0;
    }

    /* extract section info */
    GET_POINTER_SAFE(strtable, struct elf32_shdr, ehdr->shoff + ehdr->shentsize*ehdr->shstrndx);
    textoff = textsize = 0;
    textrelaoff = textrelasize = 0;
    symtaboff = symtabsize = 0;
    strtaboff = strtabsize = 0;
    shdrptr = ehdr->shoff;
    for(i=0;i<ehdr->shnum;i++) {
        struct elf32_shdr *shdr;
        struct elf32_name *name;

        GET_POINTER_SAFE(shdr, struct elf32_shdr, shdrptr);
        GET_POINTER_SAFE(name, struct elf32_name, strtable->offset + shdr->name);
        
        if(strncmp(name->name, ".text", 5) == 0) {
            textoff = shdr->offset;
            textsize = shdr->size;
        } else if(strncmp(name->name, ".rela.text", 10) == 0) {
            textrelaoff = shdr->offset;
            textrelasize = shdr->size;
        } else if(strncmp(name->name, ".symtab", 7) == 0) {
            symtaboff = shdr->offset;
            symtabsize = shdr->size;
        } else if(strncmp(name->name, ".strtab", 7) == 0) {
            strtaboff = shdr->offset;
            strtabsize = shdr->size;
        }

        shdrptr += ehdr->shentsize;
    }
    SANITIZE_OFFSET_SIZE(textoff, textsize);
    SANITIZE_OFFSET_SIZE(textrelaoff, textrelasize);
    SANITIZE_OFFSET_SIZE(symtaboff, symtabsize);
    SANITIZE_OFFSET_SIZE(strtaboff, strtabsize);

    /* load .text section */
    if(textsize > dest_length) {
        printf(".text section is too large\n");
        return 0;
    }
    memcpy(dest, (char *)elf_data + textoff, textsize);

    /* process .text relocations */
    for(i=0;i<textrelasize;i+=sizeof(struct elf32_rela)) {
        struct elf32_rela *rela;
        struct elf32_sym *sym;
        char *name;

        GET_POINTER_SAFE(rela, struct elf32_rela, textrelaoff + i);
        GET_POINTER_SAFE(sym, struct elf32_sym, symtaboff + sizeof(struct elf32_sym)*ELF32_R_SYM(rela->info));
        if(sym->name != 0) {
            void *target;

            name = (char *)elf_data + strtaboff + sym->name;
            target = resolver(name);
            if(target == NULL) {
                printf("Undefined symbol: %s\n", name);
                return 0;
            }
            if(!fixup(dest, dest_length, rela, target))
                return 0;
        } else {
            printf("Unsupported relocation\n");
            return 0;
        }
    }

    return 1;
}