source: mainline/generic/src/mm/backend_elf.c@ 1ec1fd8

/*
 * Copyright (C) 2006 Jakub Jermar
 * 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        backend_elf.c
 * @brief       Backend for address space areas backed by an ELF image.
 */

#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 <mm/page.h>
#include <genarch/mm/page_pt.h>
#include <genarch/mm/page_ht.h>
#include <align.h>
#include <memstr.h>
#include <macros.h>
#include <arch.h>

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);
static void elf_share(as_area_t *area);

mem_backend_t elf_backend = {
        .page_fault = elf_page_fault,
        .frame_free = elf_frame_free,
        .share = elf_share
};

/** 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 = area->backend_data.elf;
        elf_segment_header_t *entry = area->backend_data.segment;
        btree_node_t *leaf;
        __address base, frame;
        index_t i;

        if (!as_area_check_access(area, access))
                return AS_PF_FAULT;

        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 (area->sh_info) {
                bool found = false;

                /*
                 * The address space area is shared.
                 */
                 
                mutex_lock(&area->sh_info->lock);
                frame = (__address) btree_search(&area->sh_info->pagemap,
                        ALIGN_DOWN(addr, PAGE_SIZE) - area->base, &leaf);
                if (!frame) {
                        int i;

                        /*
                         * Workaround for valid NULL address.
                         */

                        for (i = 0; i < leaf->keys; i++) {
                                if (leaf->key[i] == ALIGN_DOWN(addr, PAGE_SIZE)) {
                                        found = true;
                                        break;
                                }
                        }
                }
                if (frame || found) {
                        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");
                        mutex_unlock(&area->sh_info->lock);
                        return AS_PF_OK;
                }
        }
        
        /*
         * The area is either not shared or the pagemap does not contain the mapping.
         */
        
        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);
                        
                        if (area->sh_info) {
                                btree_insert(&area->sh_info->pagemap, ALIGN_DOWN(addr, PAGE_SIZE) - area->base,
                                        (void *) frame, leaf);
                        }

                } 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);

                if (area->sh_info) {
                        btree_insert(&area->sh_info->pagemap, ALIGN_DOWN(addr, PAGE_SIZE) - area->base,
                                (void *) frame, leaf);
                }

        } 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);

                if (area->sh_info) {
                        btree_insert(&area->sh_info->pagemap, ALIGN_DOWN(addr, PAGE_SIZE) - area->base,
                                (void *) frame, leaf);
                }

        }
        
        if (area->sh_info)
                mutex_unlock(&area->sh_info->lock);
        
        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 = area->backend_data.elf;
        elf_segment_header_t *entry = area->backend_data.segment;
        __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)); 
        }
}

/** Share ELF image backed address space area.
 *
 * If the area is writable, then all mapped pages are duplicated in the pagemap.
 * Otherwise only portions of the area that are not backed by the ELF image
 * are put into the pagemap.
 *
 * The address space and address space area must be locked prior to the call.
 *
 * @param area Address space area.
 */
void elf_share(as_area_t *area)
{
        elf_segment_header_t *entry = area->backend_data.segment;
        link_t *cur;
        btree_node_t *leaf, *node;
        __address start_anon = entry->p_vaddr + entry->p_filesz;

        /*
         * Find the node in which to start linear search.
         */
        if (area->flags & AS_AREA_WRITE) {
                node = list_get_instance(area->used_space.leaf_head.next, btree_node_t, leaf_link);
        } else {
                (void) btree_search(&area->sh_info->pagemap, start_anon, &leaf);
                node = btree_leaf_node_left_neighbour(&area->sh_info->pagemap, leaf);
                if (!node)
                        node = leaf;
        }

        /*
         * Copy used anonymous portions of the area to sh_info's page map.
         */
        mutex_lock(&area->sh_info->lock);
        for (cur = &node->leaf_link; cur != &area->used_space.leaf_head; cur = cur->next) {
                int i;
                
                node = list_get_instance(cur, btree_node_t, leaf_link);
                
                for (i = 0; i < node->keys; i++) {
                        __address base = node->key[i];
                        count_t count = (count_t) node->value[i];
                        int j;
                        
                        /*
                         * Skip read-only areas of used space that are backed
                         * by the ELF image.
                         */
                        if (!(area->flags & AS_AREA_WRITE))
                                if (base + count*PAGE_SIZE <= start_anon)
                                        continue;
                        
                        for (j = 0; j < count; j++) {
                                pte_t *pte;
                        
                                /*
                                 * Skip read-only pages that are backed by the ELF image.
                                 */
                                if (!(area->flags & AS_AREA_WRITE))
                                        if (base + (j + 1)*PAGE_SIZE <= start_anon)
                                                continue;
                                
                                page_table_lock(area->as, false);
                                pte = page_mapping_find(area->as, base + j*PAGE_SIZE);
                                ASSERT(pte && PTE_VALID(pte) && PTE_PRESENT(pte));
                                btree_insert(&area->sh_info->pagemap, (base + j*PAGE_SIZE) - area->base,
                                        (void *) PTE_GET_FRAME(pte), NULL);
                                page_table_unlock(area->as, false);
                        }
                                
                }
        }
        mutex_unlock(&area->sh_info->lock);
}