Re: [Qemu-devel] [PATCH v1 15/17] loader: add API to load elf header

[Peter Maydell <peter.maydell@linaro.org>]

On 18 January 2016 at 07:12, Peter Crosthwaite
<crosthwaitepeter@gmail.com> wrote:
> Add an API to load an elf header header from a file. Populates a
> buffer with the header contents, as well as a boolean for whether the
> elf is 64b or not. Both arguments are optional.
>
> Signed-off-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>
> ---
>
>  hw/core/loader.c    | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
>  include/hw/loader.h |  1 +
>  2 files changed, 49 insertions(+)
>
> diff --git a/hw/core/loader.c b/hw/core/loader.c
> index 6b69852..28da8e2 100644
> --- a/hw/core/loader.c
> +++ b/hw/core/loader.c
> @@ -331,6 +331,54 @@ const char *load_elf_strerror(int error)
>      }
>  }
>
> +void load_elf_hdr(const char *filename, void *hdr, bool *is64, Error **errp)
> +{
> +    int fd;
> +    uint8_t e_ident[EI_NIDENT];
> +    size_t hdr_size, off = 0;
> +    bool is64l;
> +
> +    fd = open(filename, O_RDONLY | O_BINARY);
> +    if (fd < 0) {
> +        error_setg_errno(errp, errno, "Fail to open file");

"Failed" (also below).

I don't think we end up with the filename anywhere in the
error message; it would be helpful if we could include it.

> +        return;
> +    }
> +    if (read(fd, e_ident, sizeof(e_ident)) != sizeof(e_ident)) {
> +        error_setg_errno(errp, errno, "Fail to read file");
> +        goto fail;
> +    }
> +    if (e_ident[0] != ELFMAG0 ||
> +        e_ident[1] != ELFMAG1 ||
> +        e_ident[2] != ELFMAG2 ||
> +        e_ident[3] != ELFMAG3) {
> +        error_setg(errp, "Bad ELF magic");
> +        goto fail;
> +    }
> +
> +    is64l = e_ident[EI_CLASS] == ELFCLASS64;
> +    hdr_size = is64l ? sizeof(Elf64_Ehdr) : sizeof(Elf32_Ehdr);
> +    if (is64) {
> +        *is64 = is64l;
> +    }
> +
> +    lseek(fd, 0, SEEK_SET);

You're not checking this lseek for failure (and you don't
need it anyway, because you could just copy the magic bytes
into *hdr and read four fewer bytes).

> +    while (hdr && off < hdr_size) {
> +        size_t br = read(fd, hdr + off, hdr_size - off);
> +        switch (br) {
> +        case 0:
> +            error_setg(errp, "File too short");
> +            goto fail;
> +        case -1:
> +            error_setg_errno(errp, errno, "Failed to read file");
> +            goto fail;
> +        }
> +        off += br;
> +    }
> +
> +fail:
> +    close(fd);
> +}
> +
>  /* return < 0 if error, otherwise the number of bytes loaded in memory */
>  int load_elf(const char *filename, uint64_t (*translate_fn)(void *, uint64_t),
>               void *translate_opaque, uint64_t *pentry, uint64_t *lowaddr,
> diff --git a/include/hw/loader.h b/include/hw/loader.h
> index f7b43ab..33067f8 100644
> --- a/include/hw/loader.h
> +++ b/include/hw/loader.h
> @@ -36,6 +36,7 @@ int load_elf(const char *filename, uint64_t (*translate_fn)(void *, uint64_t),
>               void *translate_opaque, uint64_t *pentry, uint64_t *lowaddr,
>               uint64_t *highaddr, int big_endian, int elf_machine,
>               int clear_lsb);
> +void load_elf_hdr(const char *filename, void *hdr, bool *is64, Error **errp);

Doc comment, please.

>  int load_aout(const char *filename, hwaddr addr, int max_sz,
>                int bswap_needed, hwaddr target_page_size);
>  int load_uimage(const char *filename, hwaddr *ep,
> --
> 1.9.1

thanks
-- PMM