Re: [PATCH 3/7] dump: Add more offset variables

[Marc-André Lureau]

On Tue, Mar 1, 2022 at 6:22 PM Janosch Frank <frankja@linux.ibm.com> wrote:
>
> Offset calculations are easy enough to get wrong. Let's add a few
> variables to make moving around elf headers and data sections easier.
>
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>

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

> ---
>  dump/dump.c           | 34 ++++++++++++++--------------------
>  include/sysemu/dump.h |  4 ++++
>  2 files changed, 18 insertions(+), 20 deletions(-)
>
> diff --git a/dump/dump.c b/dump/dump.c
> index ce3a5e7003..242f83db95 100644
> --- a/dump/dump.c
> +++ b/dump/dump.c
> @@ -137,13 +137,11 @@ static void write_elf64_header(DumpState *s, Error 
> **errp)
>      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, sizeof(Elf64_Ehdr));
> +    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) {
> -        uint64_t shoff = sizeof(Elf64_Ehdr) + sizeof(Elf64_Phdr) * 
> s->phdr_num;
> -
> -        elf_header.e_shoff = cpu_to_dump64(s, shoff);
> +        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);
>      }
> @@ -169,13 +167,11 @@ static void write_elf32_header(DumpState *s, Error 
> **errp)
>      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, sizeof(Elf32_Ehdr));
> +    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) {
> -        uint32_t shoff = sizeof(Elf32_Ehdr) + sizeof(Elf32_Phdr) * 
> s->phdr_num;
> -
> -        elf_header.e_shoff = cpu_to_dump32(s, shoff);
> +        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);
>      }
> @@ -238,12 +234,11 @@ static void write_elf32_load(DumpState *s, 
> MemoryMapping *memory_mapping,
>  static void write_elf64_note(DumpState *s, Error **errp)
>  {
>      Elf64_Phdr phdr;
> -    hwaddr begin = s->memory_offset - s->note_size;
>      int ret;
>
>      memset(&phdr, 0, sizeof(Elf64_Phdr));
>      phdr.p_type = cpu_to_dump32(s, PT_NOTE);
> -    phdr.p_offset = cpu_to_dump64(s, begin);
> +    phdr.p_offset = cpu_to_dump64(s, s->note_offset);
>      phdr.p_paddr = 0;
>      phdr.p_filesz = cpu_to_dump64(s, s->note_size);
>      phdr.p_memsz = cpu_to_dump64(s, s->note_size);
> @@ -303,13 +298,12 @@ static void write_elf64_notes(WriteCoreDumpFunction f, 
> DumpState *s,
>
>  static void write_elf32_note(DumpState *s, Error **errp)
>  {
> -    hwaddr begin = s->memory_offset - s->note_size;
>      Elf32_Phdr phdr;
>      int ret;
>
>      memset(&phdr, 0, sizeof(Elf32_Phdr));
>      phdr.p_type = cpu_to_dump32(s, PT_NOTE);
> -    phdr.p_offset = cpu_to_dump32(s, begin);
> +    phdr.p_offset = cpu_to_dump32(s, s->note_offset);
>      phdr.p_paddr = 0;
>      phdr.p_filesz = cpu_to_dump32(s, s->note_size);
>      phdr.p_memsz = cpu_to_dump32(s, s->note_size);
> @@ -1828,15 +1822,15 @@ static void dump_init(DumpState *s, int fd, bool 
> has_format,
>      }
>
>      if (s->dump_info.d_class == ELFCLASS64) {
> -        s->memory_offset = sizeof(Elf64_Ehdr) +
> -                           sizeof(Elf64_Phdr) * s->phdr_num +
> -                           sizeof(Elf64_Shdr) * s->shdr_num +
> -                           s->note_size;
> +        s->phdr_offset = sizeof(Elf64_Ehdr);
> +        s->shdr_offset = s->phdr_offset + sizeof(Elf64_Phdr) * s->phdr_num;
> +        s->note_offset = s->shdr_offset + sizeof(Elf64_Shdr) * s->shdr_num;
> +        s->memory_offset = s->note_offset + s->note_size;
>      } else {
> -        s->memory_offset = sizeof(Elf32_Ehdr) +
> -                           sizeof(Elf32_Phdr) * s->phdr_num +
> -                           sizeof(Elf32_Shdr) * s->shdr_num +
> -                           s->note_size;
> +        s->phdr_offset = sizeof(Elf32_Ehdr);
> +        s->shdr_offset = s->phdr_offset + sizeof(Elf32_Phdr) * s->phdr_num;
> +        s->note_offset = s->shdr_offset + sizeof(Elf32_Shdr) * s->shdr_num;
> +        s->memory_offset = s->note_offset + s->note_size;
>      }
>
>      return;
> diff --git a/include/sysemu/dump.h b/include/sysemu/dump.h
> index 19458bffbd..ffc2ea1072 100644
> --- a/include/sysemu/dump.h
> +++ b/include/sysemu/dump.h
> @@ -159,6 +159,10 @@ typedef struct DumpState {
>      bool resume;
>      bool detached;
>      ssize_t note_size;
> +    hwaddr shdr_offset;
> +    hwaddr phdr_offset;
> +    hwaddr section_offset;
> +    hwaddr note_offset;
>      hwaddr memory_offset;
>      int fd;
>
> --
> 2.32.0
>