Re: [Qemu-devel] [PATCH 12/12 v14] introduce a new monitor command 'dump-guest-memory' to dump guest's memory

[Luiz Capitulino]

On Tue, 24 Apr 2012 12:10:07 +0800
Wen Congyang <address@hidden> wrote:

> The command's usage:
>    dump [-p] protocol [begin] [length]
> The supported protocol can be file or fd:
> 1. file: the protocol starts with "file:", and the following string is
>    the file's path.
> 2. fd: the protocol starts with "fd:", and the following string is the
>    fd's name.
> 
> Note:
>   1. If you want to use gdb to process the core, please specify -p option.
>      The reason why the -p option is not default is:
>        a. guest machine in a catastrophic state can have corrupted memory,
>           which we cannot trust.
>        b. The guest machine can be in read-mode even if paging is enabled.
>           For example: the guest machine uses ACPI to sleep, and ACPI sleep
>           state goes in real-mode.
>   2. If you don't want to dump all guest's memory, please specify the start
>      physical address and the length.
> 
> Signed-off-by: Wen Congyang <address@hidden>
> ---
>  Makefile.target  |    2 +
>  dump.c           |  883 
> ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  elf.h            |    5 +
>  hmp-commands.hx  |   28 ++
>  hmp.c            |   22 ++
>  hmp.h            |    1 +
>  memory_mapping.c |   27 ++
>  memory_mapping.h |    3 +
>  qapi-schema.json |   33 ++
>  qmp-commands.hx  |   36 +++
>  10 files changed, 1040 insertions(+), 0 deletions(-)
>  create mode 100644 dump.c
> 
> diff --git a/Makefile.target b/Makefile.target
> index 2e32c75..2020990 100644
> --- a/Makefile.target
> +++ b/Makefile.target
> @@ -440,6 +440,8 @@ obj-y += $(addprefix ../, $(trace-obj-y))
>  
>  endif # CONFIG_SOFTMMU
>  
> +obj-y += dump.o
> +
>  ifndef CONFIG_LINUX_USER
>  ifndef CONFIG_BSD_USER
>  # libcacard needs qemu-thread support, and besides is only needed by devices
> diff --git a/dump.c b/dump.c
> new file mode 100644
> index 0000000..0ca14f8
> --- /dev/null
> +++ b/dump.c
> @@ -0,0 +1,883 @@
> +/*
> + * QEMU dump
> + *
> + * Copyright Fujitsu, Corp. 2011, 2012
> + *
> + * Authors:
> + *     Wen Congyang <address@hidden>
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2.  See
> + * the COPYING file in the top-level directory.
> + *
> + */
> +
> +#include "qemu-common.h"
> +#include <unistd.h>
> +#include "elf.h"
> +#include <sys/procfs.h>
> +#include <glib.h>
> +#include "cpu.h"
> +#include "cpu-all.h"
> +#include "targphys.h"
> +#include "monitor.h"
> +#include "kvm.h"
> +#include "dump.h"
> +#include "sysemu.h"
> +#include "bswap.h"
> +#include "memory_mapping.h"
> +#include "error.h"
> +#include "qmp-commands.h"
> +#include "gdbstub.h"
> +
> +#if defined(CONFIG_HAVE_CORE_DUMP)
> +static uint16_t cpu_convert_to_target16(uint16_t val, int endian)
> +{
> +    if (endian == ELFDATA2LSB) {
> +        val = cpu_to_le16(val);
> +    } else {
> +        val = cpu_to_be16(val);
> +    }
> +
> +    return val;
> +}
> +
> +static uint32_t cpu_convert_to_target32(uint32_t val, int endian)
> +{
> +    if (endian == ELFDATA2LSB) {
> +        val = cpu_to_le32(val);
> +    } else {
> +        val = cpu_to_be32(val);
> +    }
> +
> +    return val;
> +}
> +
> +static uint64_t cpu_convert_to_target64(uint64_t val, int endian)
> +{
> +    if (endian == ELFDATA2LSB) {
> +        val = cpu_to_le64(val);
> +    } else {
> +        val = cpu_to_be64(val);
> +    }
> +
> +    return val;
> +}
> +
> +typedef struct DumpState {
> +    ArchDumpInfo dump_info;
> +    MemoryMappingList list;
> +    uint16_t phdr_num;
> +    uint32_t sh_info;
> +    bool have_section;
> +    bool resume;
> +    size_t note_size;
> +    target_phys_addr_t memory_offset;
> +    int fd;
> +
> +    RAMBlock *block;
> +    ram_addr_t start;
> +    bool has_filter;
> +    int64_t begin;
> +    int64_t length;
> +    Error **errp;
> +} DumpState;
> +
> +static int dump_cleanup(DumpState *s)
> +{
> +    int ret = 0;
> +
> +    memory_mapping_list_free(&s->list);
> +    if (s->fd != -1) {
> +        close(s->fd);
> +    }
> +    if (s->resume) {
> +        vm_start();
> +    }
> +
> +    return ret;
> +}
> +
> +static void dump_error(DumpState *s, const char *reason)
> +{
> +    dump_cleanup(s);
> +}
> +
> +static int fd_write_vmcore(void *buf, size_t size, void *opaque)
> +{
> +    DumpState *s = opaque;
> +    int fd = s->fd;
> +    size_t writen_size;
> +
> +    /* The fd may be passed from user, and it can be non-blocked */
> +    while (size) {
> +        writen_size = qemu_write_full(fd, buf, size);
> +        if (writen_size != size && errno != EAGAIN) {
> +            return -1;
> +        }
> +
> +        buf += writen_size;
> +        size -= writen_size;
> +    }
> +
> +    return 0;
> +}
> +
> +static int write_elf64_header(DumpState *s)
> +{
> +    Elf64_Ehdr elf_header;
> +    int ret;
> +    int endian = s->dump_info.d_endian;
> +
> +    memset(&elf_header, 0, sizeof(Elf64_Ehdr));
> +    memcpy(&elf_header, ELFMAG, SELFMAG);
> +    elf_header.e_ident[EI_CLASS] = ELFCLASS64;
> +    elf_header.e_ident[EI_DATA] = s->dump_info.d_endian;
> +    elf_header.e_ident[EI_VERSION] = EV_CURRENT;
> +    elf_header.e_type = cpu_convert_to_target16(ET_CORE, endian);
> +    elf_header.e_machine = cpu_convert_to_target16(s->dump_info.d_machine,
> +                                                   endian);
> +    elf_header.e_version = cpu_convert_to_target32(EV_CURRENT, endian);
> +    elf_header.e_ehsize = cpu_convert_to_target16(sizeof(elf_header), 
> endian);
> +    elf_header.e_phoff = cpu_convert_to_target64(sizeof(Elf64_Ehdr), endian);
> +    elf_header.e_phentsize = cpu_convert_to_target16(sizeof(Elf64_Phdr),
> +                                                     endian);
> +    elf_header.e_phnum = cpu_convert_to_target16(s->phdr_num, endian);
> +    if (s->have_section) {
> +        uint64_t shoff = sizeof(Elf64_Ehdr) + sizeof(Elf64_Phdr) * 
> s->sh_info;
> +
> +        elf_header.e_shoff = cpu_convert_to_target64(shoff, endian);
> +        elf_header.e_shentsize = cpu_convert_to_target16(sizeof(Elf64_Shdr),
> +                                                         endian);
> +        elf_header.e_shnum = cpu_convert_to_target16(1, endian);
> +    }
> +
> +    ret = fd_write_vmcore(&elf_header, sizeof(elf_header), s);
> +    if (ret < 0) {
> +        dump_error(s, "dump: failed to write elf header.\n");
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
> +static int write_elf32_header(DumpState *s)
> +{
> +    Elf32_Ehdr elf_header;
> +    int ret;
> +    int endian = s->dump_info.d_endian;
> +
> +    memset(&elf_header, 0, sizeof(Elf32_Ehdr));
> +    memcpy(&elf_header, ELFMAG, SELFMAG);
> +    elf_header.e_ident[EI_CLASS] = ELFCLASS32;
> +    elf_header.e_ident[EI_DATA] = endian;
> +    elf_header.e_ident[EI_VERSION] = EV_CURRENT;
> +    elf_header.e_type = cpu_convert_to_target16(ET_CORE, endian);
> +    elf_header.e_machine = cpu_convert_to_target16(s->dump_info.d_machine,
> +                                                   endian);
> +    elf_header.e_version = cpu_convert_to_target32(EV_CURRENT, endian);
> +    elf_header.e_ehsize = cpu_convert_to_target16(sizeof(elf_header), 
> endian);
> +    elf_header.e_phoff = cpu_convert_to_target32(sizeof(Elf32_Ehdr), endian);
> +    elf_header.e_phentsize = cpu_convert_to_target16(sizeof(Elf32_Phdr),
> +                                                     endian);
> +    elf_header.e_phnum = cpu_convert_to_target16(s->phdr_num, endian);
> +    if (s->have_section) {
> +        uint32_t shoff = sizeof(Elf32_Ehdr) + sizeof(Elf32_Phdr) * 
> s->sh_info;
> +
> +        elf_header.e_shoff = cpu_convert_to_target32(shoff, endian);
> +        elf_header.e_shentsize = cpu_convert_to_target16(sizeof(Elf32_Shdr),
> +                                                         endian);
> +        elf_header.e_shnum = cpu_convert_to_target16(1, endian);
> +    }
> +
> +    ret = fd_write_vmcore(&elf_header, sizeof(elf_header), s);
> +    if (ret < 0) {
> +        dump_error(s, "dump: failed to write elf header.\n");
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
> +static int write_elf64_load(DumpState *s, MemoryMapping *memory_mapping,
> +                            int phdr_index, target_phys_addr_t offset)
> +{
> +    Elf64_Phdr phdr;
> +    int ret;
> +    int endian = s->dump_info.d_endian;
> +
> +    memset(&phdr, 0, sizeof(Elf64_Phdr));
> +    phdr.p_type = cpu_convert_to_target32(PT_LOAD, endian);
> +    phdr.p_offset = cpu_convert_to_target64(offset, endian);
> +    phdr.p_paddr = cpu_convert_to_target64(memory_mapping->phys_addr, 
> endian);
> +    if (offset == -1) {
> +        /* When the memory is not stored into vmcore, offset will be -1 */
> +        phdr.p_filesz = 0;
> +    } else {
> +        phdr.p_filesz = cpu_convert_to_target64(memory_mapping->length, 
> endian);
> +    }
> +    phdr.p_memsz = cpu_convert_to_target64(memory_mapping->length, endian);
> +    phdr.p_vaddr = cpu_convert_to_target64(memory_mapping->virt_addr, 
> endian);
> +
> +    ret = fd_write_vmcore(&phdr, sizeof(Elf64_Phdr), s);
> +    if (ret < 0) {
> +        dump_error(s, "dump: failed to write program header table.\n");
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
> +static int write_elf32_load(DumpState *s, MemoryMapping *memory_mapping,
> +                            int phdr_index, target_phys_addr_t offset)
> +{
> +    Elf32_Phdr phdr;
> +    int ret;
> +    int endian = s->dump_info.d_endian;
> +
> +    memset(&phdr, 0, sizeof(Elf32_Phdr));
> +    phdr.p_type = cpu_convert_to_target32(PT_LOAD, endian);
> +    phdr.p_offset = cpu_convert_to_target32(offset, endian);
> +    phdr.p_paddr = cpu_convert_to_target32(memory_mapping->phys_addr, 
> endian);
> +    if (offset == -1) {
> +        /* When the memory is not stored into vmcore, offset will be -1 */
> +        phdr.p_filesz = 0;
> +    } else {
> +        phdr.p_filesz = cpu_convert_to_target32(memory_mapping->length, 
> endian);
> +    }
> +    phdr.p_memsz = cpu_convert_to_target32(memory_mapping->length, endian);
> +    phdr.p_vaddr = cpu_convert_to_target32(memory_mapping->virt_addr, 
> endian);
> +
> +    ret = fd_write_vmcore(&phdr, sizeof(Elf32_Phdr), s);
> +    if (ret < 0) {
> +        dump_error(s, "dump: failed to write program header table.\n");
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
> +static int write_elf64_note(DumpState *s)
> +{
> +    Elf64_Phdr phdr;
> +    int endian = s->dump_info.d_endian;
> +    target_phys_addr_t begin = s->memory_offset - s->note_size;
> +    int ret;
> +
> +    memset(&phdr, 0, sizeof(Elf64_Phdr));
> +    phdr.p_type = cpu_convert_to_target32(PT_NOTE, endian);
> +    phdr.p_offset = cpu_convert_to_target64(begin, endian);
> +    phdr.p_paddr = 0;
> +    phdr.p_filesz = cpu_convert_to_target64(s->note_size, endian);
> +    phdr.p_memsz = cpu_convert_to_target64(s->note_size, endian);
> +    phdr.p_vaddr = 0;
> +
> +    ret = fd_write_vmcore(&phdr, sizeof(Elf64_Phdr), s);
> +    if (ret < 0) {
> +        dump_error(s, "dump: failed to write program header table.\n");
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
> +static int write_elf64_notes(DumpState *s)
> +{
> +    CPUArchState *env;
> +    int ret;
> +    int id;
> +
> +    for (env = first_cpu; env != NULL; env = env->next_cpu) {
> +        id = cpu_index(env);
> +        ret = cpu_write_elf64_note(fd_write_vmcore, env, id, s);
> +        if (ret < 0) {
> +            dump_error(s, "dump: failed to write elf notes.\n");
> +            return -1;
> +        }
> +    }
> +
> +    for (env = first_cpu; env != NULL; env = env->next_cpu) {
> +        ret = cpu_write_elf64_qemunote(fd_write_vmcore, env, s);
> +        if (ret < 0) {
> +            dump_error(s, "dump: failed to write CPU status.\n");
> +            return -1;
> +        }
> +    }
> +
> +    return 0;
> +}
> +
> +static int write_elf32_note(DumpState *s)
> +{
> +    target_phys_addr_t begin = s->memory_offset - s->note_size;
> +    Elf32_Phdr phdr;
> +    int endian = s->dump_info.d_endian;
> +    int ret;
> +
> +    memset(&phdr, 0, sizeof(Elf32_Phdr));
> +    phdr.p_type = cpu_convert_to_target32(PT_NOTE, endian);
> +    phdr.p_offset = cpu_convert_to_target32(begin, endian);
> +    phdr.p_paddr = 0;
> +    phdr.p_filesz = cpu_convert_to_target32(s->note_size, endian);
> +    phdr.p_memsz = cpu_convert_to_target32(s->note_size, endian);
> +    phdr.p_vaddr = 0;
> +
> +    ret = fd_write_vmcore(&phdr, sizeof(Elf32_Phdr), s);
> +    if (ret < 0) {
> +        dump_error(s, "dump: failed to write program header table.\n");
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
> +static int write_elf32_notes(DumpState *s)
> +{
> +    CPUArchState *env;
> +    int ret;
> +    int id;
> +
> +    for (env = first_cpu; env != NULL; env = env->next_cpu) {
> +        id = cpu_index(env);
> +        ret = cpu_write_elf32_note(fd_write_vmcore, env, id, s);
> +        if (ret < 0) {
> +            dump_error(s, "dump: failed to write elf notes.\n");
> +            return -1;
> +        }
> +    }
> +
> +    for (env = first_cpu; env != NULL; env = env->next_cpu) {
> +        ret = cpu_write_elf32_qemunote(fd_write_vmcore, env, s);
> +        if (ret < 0) {
> +            dump_error(s, "dump: failed to write CPU status.\n");
> +            return -1;
> +        }
> +    }
> +
> +    return 0;
> +}
> +
> +static int write_elf_section(DumpState *s, int type)
> +{
> +    Elf32_Shdr shdr32;
> +    Elf64_Shdr shdr64;
> +    int endian = s->dump_info.d_endian;
> +    int shdr_size;
> +    void *shdr;
> +    int ret;
> +
> +    if (type == 0) {
> +        shdr_size = sizeof(Elf32_Shdr);
> +        memset(&shdr32, 0, shdr_size);
> +        shdr32.sh_info = cpu_convert_to_target32(s->sh_info, endian);
> +        shdr = &shdr32;
> +    } else {
> +        shdr_size = sizeof(Elf64_Shdr);
> +        memset(&shdr64, 0, shdr_size);
> +        shdr64.sh_info = cpu_convert_to_target32(s->sh_info, endian);
> +        shdr = &shdr64;
> +    }
> +
> +    ret = fd_write_vmcore(&shdr, shdr_size, s);
> +    if (ret < 0) {
> +        dump_error(s, "dump: failed to write section header table.\n");
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
> +static int write_data(DumpState *s, void *buf, int length)
> +{
> +    int ret;
> +
> +    ret = fd_write_vmcore(buf, length, s);
> +    if (ret < 0) {
> +        dump_error(s, "dump: failed to save memory.\n");
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
> +/* write the memroy to vmcore. 1 page per I/O. */
> +static int write_memory(DumpState *s, RAMBlock *block, ram_addr_t start,
> +                        int64_t size)
> +{
> +    int64_t i;
> +    int ret;
> +
> +    for (i = 0; i < size / TARGET_PAGE_SIZE; i++) {
> +        ret = write_data(s, block->host + start + i * TARGET_PAGE_SIZE,
> +                         TARGET_PAGE_SIZE);
> +        if (ret < 0) {
> +            return ret;
> +        }
> +    }
> +
> +    if ((size % TARGET_PAGE_SIZE) != 0) {
> +        ret = write_data(s, block->host + start + i * TARGET_PAGE_SIZE,
> +                         size % TARGET_PAGE_SIZE);
> +        if (ret < 0) {
> +            return ret;
> +        }
> +    }
> +
> +    return 0;
> +}
> +
> +/* get the memory's offset in the vmcore */
> +static target_phys_addr_t get_offset(target_phys_addr_t phys_addr,
> +                                     DumpState *s)
> +{
> +    RAMBlock *block;
> +    target_phys_addr_t offset = s->memory_offset;
> +    int64_t size_in_block, start;
> +
> +    if (s->has_filter) {
> +        if (phys_addr < s->begin || phys_addr >= s->begin + s->length) {
> +            return -1;
> +        }
> +    }
> +
> +    QLIST_FOREACH(block, &ram_list.blocks, next) {
> +        if (s->has_filter) {
> +            if (block->offset >= s->begin + s->length ||
> +                block->offset + block->length <= s->begin) {
> +                /* This block is out of the range */
> +                continue;
> +            }
> +
> +            if (s->begin <= block->offset) {
> +                start = block->offset;
> +            } else {
> +                start = s->begin;
> +            }
> +
> +            size_in_block = block->length - (start - block->offset);
> +            if (s->begin + s->length < block->offset + block->length) {
> +                size_in_block -= block->offset + block->length -
> +                                 (s->begin + s->length);
> +            }
> +        } else {
> +            start = block->offset;
> +            size_in_block = block->length;
> +        }
> +
> +        if (phys_addr >= start && phys_addr < start + size_in_block) {
> +            return phys_addr - start + offset;
> +        }
> +
> +        offset += size_in_block;
> +    }
> +
> +    return -1;
> +}
> +
> +static int write_elf_loads(DumpState *s)
> +{
> +    target_phys_addr_t offset;
> +    MemoryMapping *memory_mapping;
> +    uint32_t phdr_index = 1;
> +    int ret;
> +    uint32_t max_index;
> +
> +    if (s->have_section) {
> +        max_index = s->sh_info;
> +    } else {
> +        max_index = s->phdr_num;
> +    }
> +
> +    QTAILQ_FOREACH(memory_mapping, &s->list.head, next) {
> +        offset = get_offset(memory_mapping->phys_addr, s);
> +        if (s->dump_info.d_class == ELFCLASS64) {
> +            ret = write_elf64_load(s, memory_mapping, phdr_index++, offset);
> +        } else {
> +            ret = write_elf32_load(s, memory_mapping, phdr_index++, offset);
> +        }
> +
> +        if (ret < 0) {
> +            return -1;
> +        }
> +
> +        if (phdr_index >= max_index) {
> +            break;
> +        }
> +    }
> +
> +    return 0;
> +}
> +
> +/* write elf header, PT_NOTE and elf note to vmcore. */
> +static int dump_begin(DumpState *s)
> +{
> +    int ret;
> +
> +    /*
> +     * the vmcore's format is:
> +     *   --------------
> +     *   |  elf header |
> +     *   --------------
> +     *   |  PT_NOTE    |
> +     *   --------------
> +     *   |  PT_LOAD    |
> +     *   --------------
> +     *   |  ......     |
> +     *   --------------
> +     *   |  PT_LOAD    |
> +     *   --------------
> +     *   |  sec_hdr    |
> +     *   --------------
> +     *   |  elf note   |
> +     *   --------------
> +     *   |  memory     |
> +     *   --------------
> +     *
> +     * we only know where the memory is saved after we write elf note into
> +     * vmcore.
> +     */
> +
> +    /* write elf header to vmcore */
> +    if (s->dump_info.d_class == ELFCLASS64) {
> +        ret = write_elf64_header(s);
> +    } else {
> +        ret = write_elf32_header(s);
> +    }
> +    if (ret < 0) {
> +        return -1;
> +    }
> +
> +    if (s->dump_info.d_class == ELFCLASS64) {
> +        /* write PT_NOTE to vmcore */
> +        if (write_elf64_note(s) < 0) {
> +            return -1;
> +        }
> +
> +        /* write all PT_LOAD to vmcore */
> +        if (write_elf_loads(s) < 0) {
> +            return -1;
> +        }
> +
> +        /* write section to vmcore */
> +        if (s->have_section) {
> +            if (write_elf_section(s, 1) < 0) {
> +                return -1;
> +            }
> +        }
> +
> +        /* write notes to vmcore */
> +        if (write_elf64_notes(s) < 0) {
> +            return -1;
> +        }
> +
> +    } else {
> +        /* write PT_NOTE to vmcore */
> +        if (write_elf32_note(s) < 0) {
> +            return -1;
> +        }
> +
> +        /* write all PT_LOAD to vmcore */
> +        if (write_elf_loads(s) < 0) {
> +            return -1;
> +        }
> +
> +        /* write section to vmcore */
> +        if (s->have_section) {
> +            if (write_elf_section(s, 0) < 0) {
> +                return -1;
> +            }
> +        }
> +
> +        /* write notes to vmcore */
> +        if (write_elf32_notes(s) < 0) {
> +            return -1;
> +        }
> +    }
> +
> +    return 0;
> +}
> +
> +/* write PT_LOAD to vmcore */
> +static int dump_completed(DumpState *s)
> +{
> +    dump_cleanup(s);
> +    return 0;
> +}
> +
> +static int get_next_block(DumpState *s, RAMBlock *block)
> +{
> +    while (1) {
> +        block = QLIST_NEXT(block, next);
> +        if (!block) {
> +            /* no more block */
> +            return 1;
> +        }
> +
> +        s->start = 0;
> +        s->block = block;
> +        if (s->has_filter) {
> +            if (block->offset >= s->begin + s->length ||
> +                block->offset + block->length <= s->begin) {
> +                /* This block is out of the range */
> +                continue;
> +            }
> +
> +            if (s->begin > block->offset) {
> +                s->start = s->begin - block->offset;
> +            }
> +        }
> +
> +        return 0;
> +    }
> +}
> +
> +/* write all memory to vmcore */
> +static int dump_iterate(DumpState *s)
> +{
> +    RAMBlock *block;
> +    int64_t size;
> +    int ret;
> +
> +    while (1) {
> +        block = s->block;
> +
> +        size = block->length;
> +        if (s->has_filter) {
> +            size -= s->start;
> +            if (s->begin + s->length < block->offset + block->length) {
> +                size -= block->offset + block->length - (s->begin + 
> s->length);
> +            }
> +        }
> +        ret = write_memory(s, block, s->start, size);
> +        if (ret == -1) {
> +            return ret;
> +        }
> +
> +        ret = get_next_block(s, block);
> +        if (ret == 1) {
> +            dump_completed(s);
> +            return 0;
> +        }
> +    }
> +}
> +
> +static int create_vmcore(DumpState *s)
> +{
> +    int ret;
> +
> +    ret = dump_begin(s);
> +    if (ret < 0) {
> +        return -1;
> +    }
> +
> +    ret = dump_iterate(s);
> +    if (ret < 0) {
> +        return -1;
> +    }
> +
> +    return 0;
> +}
> +
> +static ram_addr_t get_start_block(DumpState *s)
> +{
> +    RAMBlock *block;
> +
> +    if (!s->has_filter) {
> +        s->block = QLIST_FIRST(&ram_list.blocks);
> +        return 0;
> +    }
> +
> +    QLIST_FOREACH(block, &ram_list.blocks, next) {
> +        if (block->offset >= s->begin + s->length ||
> +            block->offset + block->length <= s->begin) {
> +            /* This block is out of the range */
> +            continue;
> +        }
> +
> +        s->block = block;
> +        if (s->begin > block->offset) {
> +            s->start = s->begin - block->offset;
> +        } else {
> +            s->start = 0;
> +        }
> +        return s->start;
> +    }
> +
> +    return -1;
> +}
> +
> +static int dump_init(DumpState *s, int fd, bool paging, bool has_filter,
> +                     int64_t begin, int64_t length, Error **errp)
> +{
> +    CPUArchState *env;
> +    int nr_cpus;
> +    int ret;
> +
> +    if (runstate_is_running()) {
> +        vm_stop(RUN_STATE_SAVE_VM);
> +        s->resume = true;
> +    } else {
> +        s->resume = false;
> +    }
> +
> +    s->errp = errp;
> +    s->fd = fd;
> +    s->has_filter = has_filter;
> +    s->begin = begin;
> +    s->length = length;
> +    s->start = get_start_block(s);
> +    if (s->start == -1) {
> +        error_set(errp, QERR_INVALID_PARAMETER, "begin");
> +        goto cleanup;
> +    }
> +
> +    /*
> +     * get dump info: endian, class and architecture.
> +     * If the target architecture is not supported, cpu_get_dump_info() will
> +     * return -1.
> +     *
> +     * if we use kvm, we should synchronize the register before we get dump
> +     * info.
> +     */
> +    nr_cpus = 0;
> +    for (env = first_cpu; env != NULL; env = env->next_cpu) {
> +        cpu_synchronize_state(env);
> +        nr_cpus++;
> +    }
> +
> +    ret = cpu_get_dump_info(&s->dump_info);
> +    if (ret < 0) {
> +        error_set(errp, QERR_UNSUPPORTED);
> +        goto cleanup;
> +    }
> +
> +    /* get memory mapping */
> +    memory_mapping_list_init(&s->list);
> +    if (paging) {
> +        qemu_get_guest_memory_mapping(&s->list);
> +    } else {
> +        qemu_get_guest_simple_memory_mapping(&s->list);
> +    }
> +
> +    if (s->has_filter) {
> +        memory_mapping_filter(&s->list, s->begin, s->length);
> +    }
> +
> +    /*
> +     * calculate phdr_num
> +     *
> +     * the type of ehdr->e_phnum is uint16_t, so we should avoid overflow
> +     */
> +    s->phdr_num = 1; /* PT_NOTE */
> +    if (s->list.num < UINT16_MAX - 2) {
> +        s->phdr_num += s->list.num;
> +        s->have_section = false;
> +    } else {
> +        s->have_section = true;
> +        s->phdr_num = PN_XNUM;
> +        s->sh_info = 1; /* PT_NOTE */
> +
> +        /* the type of shdr->sh_info is uint32_t, so we should avoid 
> overflow */
> +        if (s->list.num <= UINT32_MAX - 1) {
> +            s->sh_info += s->list.num;
> +        } else {
> +            s->sh_info = UINT32_MAX;
> +        }
> +    }
> +
> +    s->note_size = cpu_get_note_size(s->dump_info.d_class,
> +                                     s->dump_info.d_machine, nr_cpus);
> +    if (s->dump_info.d_class == ELFCLASS64) {
> +        if (s->have_section) {
> +            s->memory_offset = sizeof(Elf64_Ehdr) +
> +                               sizeof(Elf64_Phdr) * s->sh_info +
> +                               sizeof(Elf64_Shdr) + s->note_size;
> +        } else {
> +            s->memory_offset = sizeof(Elf64_Ehdr) +
> +                               sizeof(Elf64_Phdr) * s->phdr_num + 
> s->note_size;
> +        }
> +    } else {
> +        if (s->have_section) {
> +            s->memory_offset = sizeof(Elf32_Ehdr) +
> +                               sizeof(Elf32_Phdr) * s->sh_info +
> +                               sizeof(Elf32_Shdr) + s->note_size;
> +        } else {
> +            s->memory_offset = sizeof(Elf32_Ehdr) +
> +                               sizeof(Elf32_Phdr) * s->phdr_num + 
> s->note_size;
> +        }
> +    }
> +
> +    return 0;
> +
> +cleanup:
> +    if (s->resume) {
> +        vm_start();
> +    }
> +
> +    return -1;
> +}
> +
> +void qmp_dump_guest_memory(bool paging, const char *file, bool has_begin,
> +                           int64_t begin, bool has_length, int64_t length,
> +                           Error **errp)
> +{
> +    const char *p;
> +    int fd = -1;
> +    DumpState *s;
> +    int ret;
> +
> +    if (has_begin && !has_length) {
> +        error_set(errp, QERR_MISSING_PARAMETER, "length");
> +        return;
> +    }
> +    if (!has_begin && has_length) {
> +        error_set(errp, QERR_MISSING_PARAMETER, "begin");
> +        return;
> +    }
> +
> +#if !defined(WIN32)
> +    if (strstart(file, "fd:", &p)) {
> +        fd = monitor_get_fd(cur_mon, p);
> +        if (fd == -1) {
> +            error_set(errp, QERR_FD_NOT_FOUND, p);
> +            return;
> +        }
> +    }
> +#endif
> +
> +    if  (strstart(file, "file:", &p)) {
> +        fd = qemu_open(p, O_WRONLY | O_CREAT | O_TRUNC | O_BINARY, S_IRUSR);
> +        if (fd < 0) {
> +            error_set(errp, QERR_OPEN_FILE_FAILED, p);
> +            return;
> +        }
> +    }
> +
> +    if (fd == -1) {
> +        error_set(errp, QERR_INVALID_PARAMETER, "protocol");
> +        return;
> +    }
> +
> +    s = g_malloc(sizeof(DumpState));
> +
> +    ret = dump_init(s, fd, paging, has_begin, begin, length, errp);
> +    if (ret < 0) {
> +        g_free(s);
> +        return;
> +    }
> +
> +    if (create_vmcore(s) < 0 && !error_is_set(s->errp)) {
> +        error_set(errp, QERR_IO_ERROR);
> +    }
> +
> +    g_free(s);
> +}
> +
> +#else
> +/* we need this function in hmp.c */
> +void qmp_dump_guest_memory(bool paging, const char *file, bool has_begin,
> +                           int64_t begin, bool has_length, int64_t length,
> +                           Error **errp)
> +{
> +    error_set(errp, QERR_UNSUPPORTED);
> +}
> +#endif
> diff --git a/elf.h b/elf.h
> index e1422b8..9c9acfa 100644
> --- a/elf.h
> +++ b/elf.h
> @@ -1037,6 +1037,11 @@ typedef struct elf64_sym {
>  
>  #define EI_NIDENT    16
>  
> +/* Special value for e_phnum.  This indicates that the real number of
> +   program headers is too large to fit into e_phnum.  Instead the real
> +   value is in the field sh_info of section 0.  */
> +#define PN_XNUM         0xffff
> +
>  typedef struct elf32_hdr{
>    unsigned char      e_ident[EI_NIDENT];
>    Elf32_Half e_type;
> diff --git a/hmp-commands.hx b/hmp-commands.hx
> index 461fa59..89e96eb 100644
> --- a/hmp-commands.hx
> +++ b/hmp-commands.hx
> @@ -878,6 +878,34 @@ server will ask the spice/vnc client to automatically 
> reconnect using the
>  new parameters (if specified) once the vm migration finished successfully.
>  ETEXI
>  
> +#if defined(CONFIG_HAVE_CORE_DUMP)
> +    {
> +        .name       = "dump-guest-memory",
> +        .args_type  = "paging:-p,protocol:s,begin:i?,length:i?",
> +        .params     = "[-p] protocol [begin] [length]",
> +        .help       = "dump guest memory to file"
> +                      "\n\t\t\t begin(optional): the starting physical 
> address"
> +                      "\n\t\t\t length(optional): the memory size, in bytes",
> +        .user_print = monitor_user_noop,
> +        .mhandler.cmd = hmp_dump_guest_memory,
> +    },
> +
> +
> +STEXI
> address@hidden dump-guest-memory [-p] @var{protocol} @var{begin} @var{length}
> address@hidden dump-guest-memory
> +Dump guest memory to @var{protocol}. The file can be processed with crash or
> +gdb.
> +  protocol: destination file(started with "file:") or destination file
> +            descriptor (started with "fd:")
> +    paging: do paging to get guest's memory mapping
> +     begin: the starting physical address. It's optional, and should be
> +            specified with length together.
> +    length: the memory size, in bytes. It's optional, and should be specified
> +            with begin together.
> +ETEXI
> +#endif
> +
>      {
>          .name       = "snapshot_blkdev",
>          .args_type  = "reuse:-n,device:B,snapshot-file:s?,format:s?",
> diff --git a/hmp.c b/hmp.c
> index f3e5163..eba1a2f 100644
> --- a/hmp.c
> +++ b/hmp.c
> @@ -943,3 +943,25 @@ void hmp_device_del(Monitor *mon, const QDict *qdict)
>      qmp_device_del(id, &err);
>      hmp_handle_error(mon, &err);
>  }
> +
> +void hmp_dump_guest_memory(Monitor *mon, const QDict *qdict)
> +{
> +    Error *errp = NULL;
> +    int paging = qdict_get_try_bool(qdict, "paging", 0);
> +    const char *file = qdict_get_str(qdict, "protocol");
> +    bool has_begin = qdict_haskey(qdict, "begin");
> +    bool has_length = qdict_haskey(qdict, "length");
> +    int64_t begin = 0;
> +    int64_t length = 0;
> +
> +    if (has_begin) {
> +        begin = qdict_get_int(qdict, "begin");
> +    }
> +    if (has_length) {
> +        length = qdict_get_int(qdict, "length");
> +    }
> +
> +    qmp_dump_guest_memory(paging, file, has_begin, begin, has_length, length,
> +                          &errp);
> +    hmp_handle_error(mon, &errp);
> +}
> diff --git a/hmp.h b/hmp.h
> index 443b812..5cf3241 100644
> --- a/hmp.h
> +++ b/hmp.h
> @@ -61,5 +61,6 @@ void hmp_block_job_set_speed(Monitor *mon, const QDict 
> *qdict);
>  void hmp_block_job_cancel(Monitor *mon, const QDict *qdict);
>  void hmp_migrate(Monitor *mon, const QDict *qdict);
>  void hmp_device_del(Monitor *mon, const QDict *qdict);
> +void hmp_dump_guest_memory(Monitor *mon, const QDict *qdict);
>  
>  #endif
> diff --git a/memory_mapping.c b/memory_mapping.c
> index adb1595..8810bb0 100644
> --- a/memory_mapping.c
> +++ b/memory_mapping.c
> @@ -220,3 +220,30 @@ void 
> qemu_get_guest_simple_memory_mapping(MemoryMappingList *list)
>          create_new_memory_mapping(list, block->offset, 0, block->length);
>      }
>  }
> +
> +void memory_mapping_filter(MemoryMappingList *list, int64_t begin,
> +                           int64_t length)
> +{
> +    MemoryMapping *cur, *next;
> +
> +    QTAILQ_FOREACH_SAFE(cur, &list->head, next, next) {
> +        if (cur->phys_addr >= begin + length ||
> +            cur->phys_addr + cur->length <= begin) {
> +            QTAILQ_REMOVE(&list->head, cur, next);
> +            list->num--;
> +            continue;
> +        }
> +
> +        if (cur->phys_addr < begin) {
> +            cur->length -= begin - cur->phys_addr;
> +            if (cur->virt_addr) {
> +                cur->virt_addr += begin - cur->phys_addr;
> +            }
> +            cur->phys_addr = begin;
> +        }
> +
> +        if (cur->phys_addr + cur->length > begin + length) {
> +            cur->length -= cur->phys_addr + cur->length - begin - length;
> +        }
> +    }
> +}
> diff --git a/memory_mapping.h b/memory_mapping.h
> index 190de12..a1aa64f 100644
> --- a/memory_mapping.h
> +++ b/memory_mapping.h
> @@ -63,6 +63,9 @@ static inline int 
> qemu_get_guest_memory_mapping(MemoryMappingList *list)
>  /* get guest's memory mapping without do paging(virtual address is 0). */
>  void qemu_get_guest_simple_memory_mapping(MemoryMappingList *list);
>  
> +void memory_mapping_filter(MemoryMappingList *list, int64_t begin,
> +                           int64_t length);
> +
>  #else
>  
>  /* We use MemoryMappingList* in cpu-all.h */
> diff --git a/qapi-schema.json b/qapi-schema.json
> index 6499895..5b4d121 100644
> --- a/qapi-schema.json
> +++ b/qapi-schema.json
> @@ -1722,3 +1722,36 @@
>  # Since: 0.14.0
>  ##
>  { 'command': 'device_del', 'data': {'id': 'str'} }
> +
> +##
> +# @dump-guest-memory
> +#
> +# Dump guest's memory to vmcore.

I think it's a good idea to mention that this is a synchronous operation that
can take very long depending on the amount of guest memory.

> +#
> +# @paging: if true, do paging to get guest's memory mapping. The @paging's
> +# default value of @paging is false, If you want to use gdb to process the
> +# core, please set @paging to true. The reason why the @paging's value is
> +# false:

paging is an required argument. If you want to make it optional, you have to
change the args_type field in qmp-commands.hx and change the schema file
accordingly.

> +#   1. guest machine in a catastrophic state can have corrupted memory,
> +#      which we cannot trust.
> +#   2. The guest machine can be in read-mode even if paging is enabled.
> +#      For example: the guest machine uses ACPI to sleep, and ACPI sleep
> +#      state goes in real-mode
> +# @protocol: the filename or file descriptor of the vmcore. The supported
> +# protocol can be file or fd:
> +#   1. file: the protocol starts with "file:", and the following string is
> +#      the file's path.
> +#   2. fd: the protocol starts with "fd:", and the following string is the
> +#      fd's name.
> +# @begin: #optional if specified, the starting physical address.
> +# @length: #optional if specified, the memory size, in bytes. If you don't
> +# want to dump all guest's memory, please specify the start @begin and
> +# @length
> +#
> +# Returns: nothing on success

You have to describe the possible errors. You can look in qapi-schema.json
for examples.

> +#
> +# Since: 1.1
> +##
> +{ 'command': 'dump-guest-memory',
> +  'data': { 'paging': 'bool', 'protocol': 'str', '*begin': 'int',
> +            '*length': 'int' } }
> diff --git a/qmp-commands.hx b/qmp-commands.hx
> index f972332..4c888a9 100644
> --- a/qmp-commands.hx
> +++ b/qmp-commands.hx
> @@ -604,6 +604,42 @@ Example:
>  EQMP
>  
>      {
> +        .name       = "dump-guest-memory",
> +        .args_type  = "paging:b,protocol:s,begin:i?,end:i?",
> +        .params     = "[-p] protocol [begin] [length]",
> +        .help       = "dump guest memory to file",
> +        .user_print = monitor_user_noop,
> +        .mhandler.cmd_new = qmp_marshal_input_dump_guest_memory,
> +    },
> +
> +SQMP
> +dump
> +
> +
> +Dump guest memory to file. The file can be processed with crash or gdb.
> +
> +Arguments:
> +
> +- "paging": do paging to get guest's memory mapping (json-bool)
> +- "protocol": destination file(started with "file:") or destination file
> +              descriptor (started with "fd:") (json-string)
> +- "begin": the starting physical address. It's optional, and should be 
> specified
> +           with length together (json-int)
> +- "length": the memory size, in bytes. It's optional, and should be specified
> +            with begin together (json-int)
> +
> +Example:
> +
> +-> { "execute": "dump-guest-memory", "arguments": { "protocol": "fd:dump" } }
> +<- { "return": {} }
> +
> +Notes:
> +
> +(1) All boolean arguments default to false
> +
> +EQMP
> +
> +    {
>          .name       = "netdev_add",
>          .args_type  = "netdev:O",
>          .params     = "[user|tap|socket],id=str[,prop=value][,...]",