source: mainline/generic/src/lib/elf.c@ baafe71

/*
 * Copyright (C) 2006 Sergey Bondari
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/**
 * @file        elf.c
 * @brief       Kernel ELF loader.
 */

#include <elf.h>
#include <debug.h>
#include <arch/types.h>
#include <typedefs.h>
#include <mm/as.h>
#include <mm/frame.h>
#include <mm/slab.h>
#include <align.h>
#include <memstr.h>
#include <macros.h>
#include <arch.h>

static char *error_codes[] = {
        "no error",
        "invalid image",
        "address space error",
        "incompatible image",
        "unsupported image type",
        "irrecoverable error"
};

static int segment_header(elf_segment_header_t *entry, elf_header_t *elf, as_t *as);
static int section_header(elf_section_header_t *entry, elf_header_t *elf, as_t *as);
static int load_segment(elf_segment_header_t *entry, elf_header_t *elf, as_t *as);

static int elf_page_fault(as_area_t *area, __address addr, pf_access_t access);
static void elf_frame_free(as_area_t *area, __address page, __address frame);

mem_backend_t elf_backend = {
        .backend_page_fault = elf_page_fault,
        .backend_frame_free = elf_frame_free
};

/** ELF loader
 *
 * @param header Pointer to ELF header in memory
 * @param as Created and properly mapped address space
 * @return EE_OK on success
 */
int elf_load(elf_header_t *header, as_t * as)
{
        int i, rc;

        /* Identify ELF */
        if (header->e_ident[EI_MAG0] != ELFMAG0 || header->e_ident[EI_MAG1] != ELFMAG1 || 
            header->e_ident[EI_MAG2] != ELFMAG2 || header->e_ident[EI_MAG3] != ELFMAG3) {
                return EE_INVALID;
        }
        
        /* Identify ELF compatibility */
        if (header->e_ident[EI_DATA] != ELF_DATA_ENCODING || header->e_machine != ELF_MACHINE || 
            header->e_ident[EI_VERSION] != EV_CURRENT || header->e_version != EV_CURRENT ||
            header->e_ident[EI_CLASS] != ELF_CLASS) {
                return EE_INCOMPATIBLE;
        }

        if (header->e_phentsize != sizeof(elf_segment_header_t))
                return EE_INCOMPATIBLE;

        if (header->e_shentsize != sizeof(elf_section_header_t))
                return EE_INCOMPATIBLE;

        /* Check if the object type is supported. */
        if (header->e_type != ET_EXEC)
                return EE_UNSUPPORTED;

        /* Walk through all segment headers and process them. */
        for (i = 0; i < header->e_phnum; i++) {
                rc = segment_header(&((elf_segment_header_t *)(((__u8 *) header) + header->e_phoff))[i], header, as);
                if (rc != EE_OK)
                        return rc;
        }

        /* Inspect all section headers and proccess them. */
        for (i = 0; i < header->e_shnum; i++) {
                rc = section_header(&((elf_section_header_t *)(((__u8 *) header) + header->e_shoff))[i], header, as);
                if (rc != EE_OK)
                        return rc;
        }

        return EE_OK;
}

/** Print error message according to error code.
 *
 * @param rc Return code returned by elf_load().
 *
 * @return NULL terminated description of error.
 */
char *elf_error(int rc)
{
        ASSERT(rc < sizeof(error_codes)/sizeof(char *));

        return error_codes[rc];
}

/** Process segment header.
 *
 * @param entry Segment header.
 * @param elf ELF header.
 * @param as Address space into wich the ELF is being loaded.
 *
 * @return EE_OK on success, error code otherwise.
 */
static int segment_header(elf_segment_header_t *entry, elf_header_t *elf, as_t *as)
{
        switch (entry->p_type) {
            case PT_NULL:
            case PT_PHDR:
                break;
            case PT_LOAD:
                return load_segment(entry, elf, as);
                break;
            case PT_DYNAMIC:
            case PT_INTERP:
            case PT_SHLIB:
            case PT_NOTE:
            case PT_LOPROC:
            case PT_HIPROC:
            default:
                return EE_UNSUPPORTED;
                break;
        }
        return EE_OK;
}

/** Load segment described by program header entry.
 *
 * @param entry Program header entry describing segment to be loaded.
 * @param elf ELF header.
 * @param as Address space into wich the ELF is being loaded.
 *
 * @return EE_OK on success, error code otherwise.
 */
int load_segment(elf_segment_header_t *entry, elf_header_t *elf, as_t *as)
{
        as_area_t *a;
        int flags = 0;
        void *backend_data[2] = { elf, entry };

        if (entry->p_align > 1) {
                if ((entry->p_offset % entry->p_align) != (entry->p_vaddr % entry->p_align)) {
                        return EE_INVALID;
                }
        }

        if (entry->p_flags & PF_X)
                flags |= AS_AREA_EXEC;
        if (entry->p_flags & PF_W)
                flags |= AS_AREA_WRITE;
        if (entry->p_flags & PF_R)
                flags |= AS_AREA_READ;

        /*
         * Check if the virtual address starts on page boundary.
         */
        if (ALIGN_UP(entry->p_vaddr, PAGE_SIZE) != entry->p_vaddr)
                return EE_UNSUPPORTED;

        a = as_area_create(as, flags, entry->p_memsz, entry->p_vaddr, AS_AREA_ATTR_NONE, &elf_backend, backend_data);
        if (!a)
                return EE_MEMORY;
        
        /*
         * The segment will be mapped on demand by elf_page_fault().
         */

        return EE_OK;
}

/** Process section header.
 *
 * @param entry Segment header.
 * @param elf ELF header.
 * @param as Address space into wich the ELF is being loaded.
 *
 * @return EE_OK on success, error code otherwise.
 */
static int section_header(elf_section_header_t *entry, elf_header_t *elf, as_t *as)
{
        switch (entry->sh_type) {
            default:
                break;
        }
        
        return EE_OK;
}

/** Service a page fault in the ELF backend address space area.
 *
 * The address space area and page tables must be already locked.
 *
 * @param area Pointer to the address space area.
 * @param addr Faulting virtual address.
 * @param access Access mode that caused the fault (i.e. read/write/exec).
 *
 * @return AS_PF_FAULT on failure (i.e. page fault) or AS_PF_OK on success (i.e. serviced).
 */
int elf_page_fault(as_area_t *area, __address addr, pf_access_t access)
{
        elf_header_t *elf = (elf_header_t *) area->backend_data[0];
        elf_segment_header_t *entry = (elf_segment_header_t *) area->backend_data[1];
        __address base, frame;
        index_t i;

        ASSERT((addr >= entry->p_vaddr) && (addr < entry->p_vaddr + entry->p_memsz));
        i = (addr - entry->p_vaddr) >> PAGE_WIDTH;
        base = (__address) (((void *) elf) + entry->p_offset);
        ASSERT(ALIGN_UP(base, FRAME_SIZE) == base);
        
        if (ALIGN_DOWN(addr, PAGE_SIZE) + PAGE_SIZE < entry->p_vaddr + entry->p_filesz) {
                /*
                 * Initialized portion of the segment. The memory is backed
                 * directly by the content of the ELF image. Pages are
                 * only copied if the segment is writable so that there
                 * can be more instantions of the same memory ELF image
                 * used at a time. Note that this could be later done
                 * as COW.
                 */
                if (entry->p_flags & PF_W) {
                        frame = PFN2ADDR(frame_alloc(ONE_FRAME, 0));
                        memcpy((void *) PA2KA(frame), (void *) (base + i*FRAME_SIZE), FRAME_SIZE);
                } else {
                        frame = KA2PA(base + i*FRAME_SIZE);
                }       
        } else if (ALIGN_DOWN(addr, PAGE_SIZE) >= ALIGN_UP(entry->p_vaddr + entry->p_filesz, PAGE_SIZE)) {
                /*
                 * This is the uninitialized portion of the segment.
                 * It is not physically present in the ELF image.
                 * To resolve the situation, a frame must be allocated
                 * and cleared.
                 */
                frame = PFN2ADDR(frame_alloc(ONE_FRAME, 0));
                memsetb(PA2KA(frame), FRAME_SIZE, 0);
        } else {
                size_t size;
                /*
                 * The mixed case.
                 * The lower part is backed by the ELF image and
                 * the upper part is anonymous memory.
                 */
                size = entry->p_filesz - (i<<PAGE_WIDTH);
                frame = PFN2ADDR(frame_alloc(ONE_FRAME, 0));
                memsetb(PA2KA(frame) + size, FRAME_SIZE - size, 0);
                memcpy((void *) PA2KA(frame), (void *) (base + i*FRAME_SIZE), size);
        }
        
        page_mapping_insert(AS, addr, frame, as_area_get_flags(area));
        if (!used_space_insert(area, ALIGN_DOWN(addr, PAGE_SIZE), 1))
                panic("Could not insert used space.\n");

        return AS_PF_OK;
}

/** Free a frame that is backed by the ELF backend.
 *
 * The address space area and page tables must be already locked.
 *
 * @param area Pointer to the address space area.
 * @param page Page that is mapped to frame. Must be aligned to PAGE_SIZE.
 * @param frame Frame to be released.
 *
 */
void elf_frame_free(as_area_t *area, __address page, __address frame)
{
        elf_header_t *elf = (elf_header_t *) area->backend_data[0];
        elf_segment_header_t *entry = (elf_segment_header_t *) area->backend_data[1];
        __address base;
        index_t i;
        
        ASSERT((page >= entry->p_vaddr) && (page < entry->p_vaddr + entry->p_memsz));
        i = (page - entry->p_vaddr) >> PAGE_WIDTH;
        base = (__address) (((void *) elf) + entry->p_offset);
        ASSERT(ALIGN_UP(base, FRAME_SIZE) == base);
        
        if (page + PAGE_SIZE < ALIGN_UP(entry->p_vaddr + entry->p_filesz, PAGE_SIZE)) {
                if (entry->p_flags & PF_W) {
                        /*
                         * Free the frame with the copy of writable segment data.
                         */
                        frame_free(ADDR2PFN(frame));
                }
        } else {
                /*
                 * The frame is either anonymous memory or the mixed case (i.e. lower
                 * part is backed by the ELF image and the upper is anonymous).
                 * In any case, a frame needs to be freed.
                 */
                frame_free(ADDR2PFN(frame)); 
        }
}