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1424 jermar 1 
/*
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 * Copyright (C) 2006 Jakub Jermar
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 * All rights reserved.
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 *
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 * Redistribution and use in source and binary forms, with or without
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 * modification, are permitted provided that the following conditions
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 * are met:
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 *
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 * - Redistributions of source code must retain the above copyright
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 *   notice, this list of conditions and the following disclaimer.
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 * - Redistributions in binary form must reproduce the above copyright
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 *   notice, this list of conditions and the following disclaimer in the
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 *   documentation and/or other materials provided with the distribution.
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 * - The name of the author may not be used to endorse or promote products
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 *   derived from this software without specific prior written permission.
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 *
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 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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 */
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/**
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 * @file    backend_elf.c
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 * @brief   Backend for address space areas backed by an ELF image.
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 */
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#include <elf.h>
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#include <debug.h>
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#include <arch/types.h>
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#include <typedefs.h>
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#include <mm/as.h>
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#include <mm/frame.h>
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#include <mm/slab.h>
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#include <align.h>
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#include <memstr.h>
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#include <macros.h>
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#include <arch.h>
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static int elf_page_fault(as_area_t *area, __address addr, pf_access_t access);
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static void elf_frame_free(as_area_t *area, __address page, __address frame);
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mem_backend_t elf_backend = {
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    .page_fault = elf_page_fault,
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    .frame_free = elf_frame_free,
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    .share = NULL
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};
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/** Service a page fault in the ELF backend address space area.
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 *
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 * The address space area and page tables must be already locked.
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 *
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 * @param area Pointer to the address space area.
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 * @param addr Faulting virtual address.
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 * @param access Access mode that caused the fault (i.e. read/write/exec).
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 *
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 * @return AS_PF_FAULT on failure (i.e. page fault) or AS_PF_OK on success (i.e. serviced).
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 */
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int elf_page_fault(as_area_t *area, __address addr, pf_access_t access)
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{
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    elf_header_t *elf = area->backend_data.elf;
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    elf_segment_header_t *entry = area->backend_data.segment;
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    __address base, frame;
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    index_t i;
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    if (!as_area_check_access(area, access))
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        return AS_PF_FAULT;
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    ASSERT((addr >= entry->p_vaddr) && (addr < entry->p_vaddr + entry->p_memsz));
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    i = (addr - entry->p_vaddr) >> PAGE_WIDTH;
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    base = (__address) (((void *) elf) + entry->p_offset);
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    ASSERT(ALIGN_UP(base, FRAME_SIZE) == base);
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    if (ALIGN_DOWN(addr, PAGE_SIZE) + PAGE_SIZE < entry->p_vaddr + entry->p_filesz) {
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        /*
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         * Initialized portion of the segment. The memory is backed
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         * directly by the content of the ELF image. Pages are
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         * only copied if the segment is writable so that there
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         * can be more instantions of the same memory ELF image
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         * used at a time. Note that this could be later done
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         * as COW.
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         */
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        if (entry->p_flags & PF_W) {
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            frame = PFN2ADDR(frame_alloc(ONE_FRAME, 0));
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            memcpy((void *) PA2KA(frame), (void *) (base + i*FRAME_SIZE), FRAME_SIZE);
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        } else {
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            frame = KA2PA(base + i*FRAME_SIZE);
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        }  
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    } else if (ALIGN_DOWN(addr, PAGE_SIZE) >= ALIGN_UP(entry->p_vaddr + entry->p_filesz, PAGE_SIZE)) {
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        /*
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         * This is the uninitialized portion of the segment.
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         * It is not physically present in the ELF image.
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         * To resolve the situation, a frame must be allocated
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         * and cleared.
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         */
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        frame = PFN2ADDR(frame_alloc(ONE_FRAME, 0));
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        memsetb(PA2KA(frame), FRAME_SIZE, 0);
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    } else {
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        size_t size;
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        /*
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         * The mixed case.
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         * The lower part is backed by the ELF image and
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         * the upper part is anonymous memory.
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         */
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        size = entry->p_filesz - (i<<PAGE_WIDTH);
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        frame = PFN2ADDR(frame_alloc(ONE_FRAME, 0));
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        memsetb(PA2KA(frame) + size, FRAME_SIZE - size, 0);
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        memcpy((void *) PA2KA(frame), (void *) (base + i*FRAME_SIZE), size);
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    }
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    page_mapping_insert(AS, addr, frame, as_area_get_flags(area));
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        if (!used_space_insert(area, ALIGN_DOWN(addr, PAGE_SIZE), 1))
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                panic("Could not insert used space.\n");
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    return AS_PF_OK;
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}
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/** Free a frame that is backed by the ELF backend.
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 *
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 * The address space area and page tables must be already locked.
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 *
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 * @param area Pointer to the address space area.
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 * @param page Page that is mapped to frame. Must be aligned to PAGE_SIZE.
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 * @param frame Frame to be released.
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 *
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 */
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void elf_frame_free(as_area_t *area, __address page, __address frame)
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{
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    elf_header_t *elf = area->backend_data.elf;
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    elf_segment_header_t *entry = area->backend_data.segment;
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    __address base;
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    index_t i;
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    ASSERT((page >= entry->p_vaddr) && (page < entry->p_vaddr + entry->p_memsz));
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    i = (page - entry->p_vaddr) >> PAGE_WIDTH;
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    base = (__address) (((void *) elf) + entry->p_offset);
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    ASSERT(ALIGN_UP(base, FRAME_SIZE) == base);
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    if (page + PAGE_SIZE < ALIGN_UP(entry->p_vaddr + entry->p_filesz, PAGE_SIZE)) {
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        if (entry->p_flags & PF_W) {
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            /*
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             * Free the frame with the copy of writable segment data.
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             */
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            frame_free(ADDR2PFN(frame));
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        }
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    } else {
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        /*
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         * The frame is either anonymous memory or the mixed case (i.e. lower
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         * part is backed by the ELF image and the upper is anonymous).
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         * In any case, a frame needs to be freed.
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         */
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        frame_free(ADDR2PFN(frame));
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    }
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}