Re: [PATCH v3 04/14] dump: Allocate header

[Marc-André Lureau]

On Thu, Jul 21, 2022 at 5:23 PM Janosch Frank <frankja@linux.ibm.com> wrote:
>
> Allocating the header lets us write it at a later time and hence also
> allows us to change section and segment table offsets until we
> finally write it.
>
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>

you could have added from v2

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>

> ---
>  dump/dump.c           | 127 +++++++++++++++++++++---------------------
>  include/sysemu/dump.h |   1 +
>  2 files changed, 64 insertions(+), 64 deletions(-)
>
> diff --git a/dump/dump.c b/dump/dump.c
> index 5c9ed25c5a..2d04e06815 100644
> --- a/dump/dump.c
> +++ b/dump/dump.c
> @@ -98,6 +98,7 @@ static int dump_cleanup(DumpState *s)
>      memory_mapping_list_free(&s->list);
>      close(s->fd);
>      g_free(s->guest_note);
> +    g_free(s->elf_header);
>      s->guest_note = NULL;
>      if (s->resume) {
>          if (s->detached) {
> @@ -126,73 +127,49 @@ static int fd_write_vmcore(const void *buf, size_t 
> size, void *opaque)
>      return 0;
>  }
>
> -static void write_elf64_header(DumpState *s, Error **errp)
> +static void prepare_elf64_header(DumpState *s)
>  {
> -    /*
> -     * phnum in the elf header is 16 bit, if we have more segments we
> -     * set phnum to PN_XNUM and write the real number of segments to a
> -     * special section.
> -     */
> -    uint16_t phnum = MIN(s->phdr_num, PN_XNUM);
> -    Elf64_Ehdr elf_header;
> -    int ret;
> +    uint16_t phnum = s->phdr_num >= PN_XNUM ? PN_XNUM : s->phdr_num;
> +    Elf64_Ehdr *elf_header = s->elf_header;
>
> -    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_to_dump16(s, ET_CORE);
> -    elf_header.e_machine = cpu_to_dump16(s, s->dump_info.d_machine);
> -    elf_header.e_version = cpu_to_dump32(s, EV_CURRENT);
> -    elf_header.e_ehsize = cpu_to_dump16(s, sizeof(elf_header));
> -    elf_header.e_phoff = cpu_to_dump64(s, s->phdr_offset);
> -    elf_header.e_phentsize = cpu_to_dump16(s, sizeof(Elf64_Phdr));
> -    elf_header.e_phnum = cpu_to_dump16(s, phnum);
> +    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_to_dump16(s, ET_CORE);
> +    elf_header->e_machine = cpu_to_dump16(s, s->dump_info.d_machine);
> +    elf_header->e_version = cpu_to_dump32(s, EV_CURRENT);
> +    elf_header->e_ehsize = cpu_to_dump16(s, sizeof(*elf_header));
> +    elf_header->e_phoff = cpu_to_dump64(s, s->phdr_offset);
> +    elf_header->e_phentsize = cpu_to_dump16(s, sizeof(Elf64_Phdr));
> +    elf_header->e_phnum = cpu_to_dump16(s, phnum);
>      if (s->shdr_num) {
> -        elf_header.e_shoff = cpu_to_dump64(s, s->shdr_offset);
> -        elf_header.e_shentsize = cpu_to_dump16(s, sizeof(Elf64_Shdr));
> -        elf_header.e_shnum = cpu_to_dump16(s, s->shdr_num);
> -    }
> -
> -    ret = fd_write_vmcore(&elf_header, sizeof(elf_header), s);
> -    if (ret < 0) {
> -        error_setg_errno(errp, -ret, "dump: failed to write elf header");
> +        elf_header->e_shoff = cpu_to_dump64(s, s->shdr_offset);
> +        elf_header->e_shentsize = cpu_to_dump16(s, sizeof(Elf64_Shdr));
> +        elf_header->e_shnum = cpu_to_dump16(s, s->shdr_num);
>      }
>  }
>
> -static void write_elf32_header(DumpState *s, Error **errp)
> +static void prepare_elf32_header(DumpState *s)
>  {
> -    /*
> -     * phnum in the elf header is 16 bit, if we have more segments we
> -     * set phnum to PN_XNUM and write the real number of segments to a
> -     * special section.
> -     */
> -    uint16_t phnum = MIN(s->phdr_num, PN_XNUM);
> -    Elf32_Ehdr elf_header;
> -    int ret;
> +    uint16_t phnum = s->phdr_num >= PN_XNUM ? PN_XNUM : s->phdr_num;
> +    Elf32_Ehdr *elf_header = s->elf_header;
>
> -    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] = s->dump_info.d_endian;
> -    elf_header.e_ident[EI_VERSION] = EV_CURRENT;
> -    elf_header.e_type = cpu_to_dump16(s, ET_CORE);
> -    elf_header.e_machine = cpu_to_dump16(s, s->dump_info.d_machine);
> -    elf_header.e_version = cpu_to_dump32(s, EV_CURRENT);
> -    elf_header.e_ehsize = cpu_to_dump16(s, sizeof(elf_header));
> -    elf_header.e_phoff = cpu_to_dump32(s, s->phdr_offset);
> -    elf_header.e_phentsize = cpu_to_dump16(s, sizeof(Elf32_Phdr));
> -    elf_header.e_phnum = cpu_to_dump16(s, phnum);
> +    memcpy(elf_header, ELFMAG, SELFMAG);
> +    elf_header->e_ident[EI_CLASS] = ELFCLASS32;
> +    elf_header->e_ident[EI_DATA] = s->dump_info.d_endian;
> +    elf_header->e_ident[EI_VERSION] = EV_CURRENT;
> +    elf_header->e_type = cpu_to_dump16(s, ET_CORE);
> +    elf_header->e_machine = cpu_to_dump16(s, s->dump_info.d_machine);
> +    elf_header->e_version = cpu_to_dump32(s, EV_CURRENT);
> +    elf_header->e_ehsize = cpu_to_dump16(s, sizeof(*elf_header));
> +    elf_header->e_phoff = cpu_to_dump32(s, s->phdr_offset);
> +    elf_header->e_phentsize = cpu_to_dump16(s, sizeof(Elf32_Phdr));
> +    elf_header->e_phnum = cpu_to_dump16(s, phnum);
>      if (s->shdr_num) {
> -        elf_header.e_shoff = cpu_to_dump32(s, s->shdr_offset);
> -        elf_header.e_shentsize = cpu_to_dump16(s, sizeof(Elf32_Shdr));
> -        elf_header.e_shnum = cpu_to_dump16(s, s->shdr_num);
> -    }
> -
> -    ret = fd_write_vmcore(&elf_header, sizeof(elf_header), s);
> -    if (ret < 0) {
> -        error_setg_errno(errp, -ret, "dump: failed to write elf header");
> +        elf_header->e_shoff = cpu_to_dump32(s, s->shdr_offset);
> +        elf_header->e_shentsize = cpu_to_dump16(s, sizeof(Elf32_Shdr));
> +        elf_header->e_shnum = cpu_to_dump16(s, s->shdr_num);
>      }
>  }
>
> @@ -528,6 +505,26 @@ static void write_elf_notes(DumpState *s, Error **errp)
>      }
>  }
>
> +static void prepare_elf_header(DumpState *s)
> +{
> +    if (dump_is_64bit(s)) {
> +        prepare_elf64_header(s);
> +    } else {
> +        prepare_elf32_header(s);
> +    }
> +}
> +
> +static void write_elf_header(DumpState *s, Error **errp)
> +{
> +    size_t size = dump_is_64bit(s) ? sizeof(Elf64_Ehdr) : sizeof(Elf32_Ehdr);
> +    int ret;
> +
> +    ret = fd_write_vmcore(s->elf_header, size, s);
> +    if (ret < 0) {
> +        error_setg_errno(errp, -ret, "dump: failed to write elf header");
> +    }
> +}
> +
>  /* write elf header, PT_NOTE and elf note to vmcore. */
>  static void dump_begin(DumpState *s, Error **errp)
>  {
> @@ -557,12 +554,11 @@ static void dump_begin(DumpState *s, Error **errp)
>       * vmcore.
>       */
>
> -    /* write elf header to vmcore */
> -    if (dump_is_64bit(s)) {
> -        write_elf64_header(s, errp);
> -    } else {
> -        write_elf32_header(s, errp);
> -    }
> +    /* Write elf header to buffer */
> +    prepare_elf_header(s);
> +
> +    /* Start to write stuff into file descriptor */
> +    write_elf_header(s, errp);
>      if (*errp) {
>          return;
>      }
> @@ -1642,6 +1638,9 @@ static void dump_init(DumpState *s, int fd, bool 
> has_format,
>          goto cleanup;
>      }
>
> +    s->elf_header = g_malloc0(dump_is_64bit(s) ?
> +                              sizeof(Elf64_Ehdr) : sizeof(Elf32_Ehdr));
> +
>      /*
>       * The goal of this block is to (a) update the previously guessed
>       * phys_base, (b) copy the guest note out of the guest.
> diff --git a/include/sysemu/dump.h b/include/sysemu/dump.h
> index 7025e50682..58f41bbf45 100644
> --- a/include/sysemu/dump.h
> +++ b/include/sysemu/dump.h
> @@ -171,6 +171,7 @@ typedef struct DumpState {
>      int64_t begin;             /* Start address of the chunk we want to dump 
> */
>      int64_t length;            /* Length of the dump we want to dump */
>
> +    void *elf_header;
>      uint8_t *note_buf;          /* buffer for notes */
>      size_t note_buf_offset;     /* the writing place in note_buf */
>      uint32_t nr_cpus;           /* number of guest's cpu */
> --
> 2.34.1
>