source: mainline/uspace/srv/loader/elf_load.c@ bae7bdc

/*
 * Copyright (c) 2006 Sergey Bondari
 * Copyright (c) 2006 Jakub Jermar
 * Copyright (c) 2011 Jiri Svoboda
 * 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.
 */

/** @addtogroup generic 
 * @{
 */

/**
 * @file
 * @brief       Userspace ELF loader.
 *
 * This module allows loading ELF binaries (both executables and
 * shared objects) from VFS. The current implementation allocates
 * anonymous memory, fills it with segment data and then adjusts
 * the memory areas' flags to the final value. In the future,
 * the segments will be mapped directly from the file.
 */

#include <stdio.h>
#include <sys/types.h>
#include <align.h>
#include <assert.h>
#include <as.h>
#include <unistd.h>
#include <fcntl.h>
#include <smc.h>
#include <loader/pcb.h>
#include <entry_point.h>

#include "elf.h"
#include "elf_load.h"

#define DPRINTF(...)

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

static unsigned int elf_load(elf_ld_t *elf, size_t so_bias);
static int segment_header(elf_ld_t *elf, elf_segment_header_t *entry);
static int section_header(elf_ld_t *elf, elf_section_header_t *entry);
static int load_segment(elf_ld_t *elf, elf_segment_header_t *entry);

/** Read until the buffer is read in its entirety. */
static int my_read(int fd, void *buf, size_t len)
{
        int cnt = 0;
        do {
                buf += cnt;
                len -= cnt;
                cnt = read(fd, buf, len);
        } while ((cnt > 0) && ((len - cnt) > 0));

        return cnt;
}

/** Load ELF binary from a file.
 *
 * Load an ELF binary from the specified file. If the file is
 * an executable program, it is loaded unbiased. If it is a shared
 * object, it is loaded with the bias @a so_bias. Some information
 * extracted from the binary is stored in a elf_info_t structure
 * pointed to by @a info.
 *
 * @param file_name Path to the ELF file.
 * @param so_bias   Bias to use if the file is a shared object.
 * @param info      Pointer to a structure for storing information
 *                  extracted from the binary.
 *
 * @return EOK on success or negative error code.
 *
 */
int elf_load_file(const char *file_name, size_t so_bias, elf_info_t *info)
{
        elf_ld_t elf;

        int fd;
        int rc;
        
        fd = open(file_name, O_RDONLY);
        if (fd < 0) {
                DPRINTF("failed opening file\n");
                return -1;
        }

        elf.fd = fd;
        elf.info = info;

        rc = elf_load(&elf, so_bias);

        close(fd);

        return rc;
}

/** Run an ELF executable.
 *
 * Transfers control to the entry point of an ELF executable loaded
 * earlier with elf_load_file(). This function does not return.
 *
 * @param info Info structure filled earlier by elf_load_file()
 *
 */
void elf_run(elf_info_t *info, pcb_t *pcb)
{
        entry_point_jmp(info->entry, pcb);

        /* not reached */
}

/** Create the program control block (PCB).
 *
 * Fills the program control block @a pcb with information from
 * @a info.
 *
 * @param info  Program info structure
 * @return EOK on success or negative error code
 */
void elf_create_pcb(elf_info_t *info, pcb_t *pcb)
{
        pcb->entry = info->entry;
        pcb->dynamic = info->dynamic;
}


/** Load an ELF binary.
 *
 * The @a elf structure contains the loader state, including
 * an open file, from which the binary will be loaded,
 * a pointer to the @c info structure etc.
 *
 * @param elf           Pointer to loader state buffer.
 * @param so_bias       Bias to use if the file is a shared object.
 * @return EE_OK on success or EE_xx error code.
 */
static unsigned int elf_load(elf_ld_t *elf, size_t so_bias)
{
        elf_header_t header_buf;
        elf_header_t *header = &header_buf;
        int i, rc;

        rc = my_read(elf->fd, header, sizeof(elf_header_t));
        if (rc < 0) {
                DPRINTF("Read error.\n"); 
                return EE_INVALID;
        }

        elf->header = header;

        /* 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) {
                DPRINTF("Invalid header.\n");
                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) {
                DPRINTF("Incompatible data/version/class.\n");
                return EE_INCOMPATIBLE;
        }

        if (header->e_phentsize != sizeof(elf_segment_header_t)) {
                DPRINTF("e_phentsize:%d != %d\n", header->e_phentsize,
                    sizeof(elf_segment_header_t));
                return EE_INCOMPATIBLE;
        }

        if (header->e_shentsize != sizeof(elf_section_header_t)) {
                DPRINTF("e_shentsize:%d != %d\n", header->e_shentsize,
                    sizeof(elf_section_header_t));
                return EE_INCOMPATIBLE;
        }

        /* Check if the object type is supported. */
        if (header->e_type != ET_EXEC && header->e_type != ET_DYN) {
                DPRINTF("Object type %d is not supported\n", header->e_type);
                return EE_UNSUPPORTED;
        }

        /* Shared objects can be loaded with a bias */
        if (header->e_type == ET_DYN)
                elf->bias = so_bias;
        else
                elf->bias = 0;

        elf->info->interp = NULL;
        elf->info->dynamic = NULL;

        /* Walk through all segment headers and process them. */
        for (i = 0; i < header->e_phnum; i++) {
                elf_segment_header_t segment_hdr;

                /* Seek to start of segment header */
                lseek(elf->fd, header->e_phoff
                        + i * sizeof(elf_segment_header_t), SEEK_SET);

                rc = my_read(elf->fd, &segment_hdr,
                    sizeof(elf_segment_header_t));
                if (rc < 0) {
                        DPRINTF("Read error.\n");
                        return EE_INVALID;
                }

                rc = segment_header(elf, &segment_hdr);
                if (rc != EE_OK)
                        return rc;
        }

        DPRINTF("Parse sections.\n");

        /* Inspect all section headers and proccess them. */
        for (i = 0; i < header->e_shnum; i++) {
                elf_section_header_t section_hdr;

                /* Seek to start of section header */
                lseek(elf->fd, header->e_shoff
                    + i * sizeof(elf_section_header_t), SEEK_SET);

                rc = my_read(elf->fd, &section_hdr,
                    sizeof(elf_section_header_t));
                if (rc < 0) {
                        DPRINTF("Read error.\n");
                        return EE_INVALID;
                }

                rc = section_header(elf, &section_hdr);
                if (rc != EE_OK)
                        return rc;
        }

        elf->info->entry =
            (entry_point_t)((uint8_t *)header->e_entry + elf->bias);

        DPRINTF("Done.\n");

        return EE_OK;
}

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

        return error_codes[rc];
}

/** Process segment header.
 *
 * @param entry Segment header.
 *
 * @return EE_OK on success, error code otherwise.
 */
static int segment_header(elf_ld_t *elf, elf_segment_header_t *entry)
{
        switch (entry->p_type) {
        case PT_NULL:
        case PT_PHDR:
        case PT_NOTE:
                break;
        case PT_LOAD:
                return load_segment(elf, entry);
                break;
        case PT_INTERP:
                /* Assume silently interp == "/rtld.so" */
                elf->info->interp = "/rtld.so";
                break;
        case PT_DYNAMIC:
        case PT_SHLIB:
        case PT_LOPROC:
        case PT_HIPROC:
        default:
                DPRINTF("Segment p_type %d unknown.\n", entry->p_type);
                return EE_UNSUPPORTED;
                break;
        }
        return EE_OK;
}

/** Load segment described by program header entry.
 *
 * @param elf   Loader state.
 * @param entry Program header entry describing segment to be loaded.
 *
 * @return EE_OK on success, error code otherwise.
 */
int load_segment(elf_ld_t *elf, elf_segment_header_t *entry)
{
        void *a;
        int flags = 0;
        uintptr_t bias;
        uintptr_t base;
        void *seg_ptr;
        uintptr_t seg_addr;
        size_t mem_sz;
        int rc;

        bias = elf->bias;

        seg_addr = entry->p_vaddr + bias;
        seg_ptr = (void *) seg_addr;

        DPRINTF("Load segment at addr %p, size 0x%x\n", (void *) seg_addr,
                entry->p_memsz);

        if (entry->p_align > 1) {
                if ((entry->p_offset % entry->p_align) !=
                    (seg_addr % entry->p_align)) {
                        DPRINTF("Align check 1 failed offset%%align=%d, "
                            "vaddr%%align=%d\n",
                            entry->p_offset % entry->p_align,
                            seg_addr % entry->p_align
                        );
                        return EE_INVALID;
                }
        }

        /* Final flags that will be set for the memory area */

        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;
        flags |= AS_AREA_CACHEABLE;
        
        base = ALIGN_DOWN(entry->p_vaddr, PAGE_SIZE);
        mem_sz = entry->p_memsz + (entry->p_vaddr - base);

        DPRINTF("Map to seg_addr=%p-%p.\n", (void *) seg_addr,
            (void *) (entry->p_vaddr + bias +
            ALIGN_UP(entry->p_memsz, PAGE_SIZE)));

        /*
         * For the course of loading, the area needs to be readable
         * and writeable.
         */
        a = as_area_create((uint8_t *)base + bias, mem_sz,
            AS_AREA_READ | AS_AREA_WRITE | AS_AREA_CACHEABLE);
        if (a == (void *)(-1)) {
                DPRINTF("Memory mapping failed.\n");
                return EE_MEMORY;
        }

        DPRINTF("as_area_create(%p, %#zx, %d) -> %p\n",
            (void *) (base + bias), mem_sz, flags, (void *) a);

        /*
         * Load segment data
         */
        rc = lseek(elf->fd, entry->p_offset, SEEK_SET);
        if (rc < 0) {
                printf("seek error\n");
                return EE_INVALID;
        }

/*      rc = read(fd, (void *)(entry->p_vaddr + bias), entry->p_filesz);
        if (rc < 0) { printf("read error\n"); return EE_INVALID; }*/

        /* Long reads are not possible yet. Load segment piecewise. */

        unsigned left, now;
        uint8_t *dp;

        left = entry->p_filesz;
        dp = seg_ptr;

        while (left > 0) {
                now = 16384;
                if (now > left) now = left;

                rc = my_read(elf->fd, dp, now);

                if (rc < 0) { 
                        DPRINTF("Read error.\n");
                        return EE_INVALID;
                }

                left -= now;
                dp += now;
        }

        rc = as_area_change_flags(seg_ptr, flags);
        if (rc != 0) {
                DPRINTF("Failed to set memory area flags.\n");
                return EE_MEMORY;
        }

        if (flags & AS_AREA_EXEC) {
                /* Enforce SMC coherence for the segment */
                if (smc_coherence(seg_ptr, entry->p_filesz))
                        return EE_MEMORY;
        }

        return EE_OK;
}

/** Process section header.
 *
 * @param elf   Loader state.
 * @param entry Segment header.
 *
 * @return EE_OK on success, error code otherwise.
 */
static int section_header(elf_ld_t *elf, elf_section_header_t *entry)
{
        switch (entry->sh_type) {
        case SHT_PROGBITS:
                if (entry->sh_flags & SHF_TLS) {
                        /* .tdata */
                }
                break;
        case SHT_NOBITS:
                if (entry->sh_flags & SHF_TLS) {
                        /* .tbss */
                }
                break;
        case SHT_DYNAMIC:
                /* Record pointer to dynamic section into info structure */
                elf->info->dynamic =
                    (void *)((uint8_t *)entry->sh_addr + elf->bias);
                DPRINTF("Dynamic section found at %p.\n",
                    (void *) elf->info->dynamic);
                break;
        default:
                break;
        }
        
        return EE_OK;
}

/** @}
 */