[30/38] Unify read_initial_length implementations

  There are two implementations of read_initial_length in gdb.  This
merges them and moves the resulting function to leb.c.

2020-01-22  Tom Tromey  <tom@tromey.com>

	* dwarf2/read.c (read_initial_length): Move to leb.c.
	* dwarf2/leb.h (read_initial_length): Declare.
	* dwarf2/leb.c (read_initial_length): Move from read.c.  Add
	handle_nonstd parameter.
	* dwarf2/frame.c (read_initial_length): Remove.
	(decode_frame_entry_1): Update.

Change-Id: I34d37bad0f8a584bfa781432cba25e05e1bd5750
---
 gdb/ChangeLog      |  9 +++++++
 gdb/dwarf2/frame.c | 20 +--------------
 gdb/dwarf2/leb.c   | 27 +++++++++++++++++++
 gdb/dwarf2/leb.h   | 41 +++++++++++++++++++++++++++++
 gdb/dwarf2/read.c  | 64 ----------------------------------------------
 5 files changed, 78 insertions(+), 83 deletions(-)
  

On Thu, Jan 23, 2020, 02:00 Tom Tromey <tom@tromey.com> wrote:

> There are two implementations of read_initial_length in gdb.  This
> merges them and moves the resulting function to leb.c.
>
> 2020-01-22  Tom Tromey  <tom@tromey.com>
>
>         * dwarf2/read.c (read_initial_length): Move to leb.c.
>         * dwarf2/leb.h (read_initial_length): Declare.
>         * dwarf2/leb.c (read_initial_length): Move from read.c.  Add
>         handle_nonstd parameter.
>         * dwarf2/frame.c (read_initial_length): Remove.
>         (decode_frame_entry_1): Update.
>
> Change-Id: I34d37bad0f8a584bfa781432cba25e05e1bd5750
> ---
>  gdb/ChangeLog      |  9 +++++++
>  gdb/dwarf2/frame.c | 20 +--------------
>  gdb/dwarf2/leb.c   | 27 +++++++++++++++++++
>  gdb/dwarf2/leb.h   | 41 +++++++++++++++++++++++++++++
>  gdb/dwarf2/read.c  | 64 ----------------------------------------------
>  5 files changed, 78 insertions(+), 83 deletions(-)
>
> diff --git a/gdb/dwarf2/frame.c b/gdb/dwarf2/frame.c
> index 7f57c28be2c..2d928670c6b 100644
> --- a/gdb/dwarf2/frame.c
> +++ b/gdb/dwarf2/frame.c
> @@ -1475,24 +1475,6 @@ const struct objfile_key<dwarf2_fde_table,
>                          gdb::noop_deleter<dwarf2_fde_table>>
>    dwarf2_frame_objfile_data;
>
> -
> -static ULONGEST
> -read_initial_length (bfd *abfd, const gdb_byte *buf,
> -                    unsigned int *bytes_read_ptr)
> -{
> -  ULONGEST result;
> -
> -  result = bfd_get_32 (abfd, buf);
> -  if (result == 0xffffffff)
> -    {
> -      result = bfd_get_64 (abfd, buf + 4);
> -      *bytes_read_ptr = 12;
> -    }
> -  else
> -    *bytes_read_ptr = 4;
> -
> -  return result;
> -}
>
>
>  /* Pointer encoding helper functions.  */
> @@ -1744,7 +1726,7 @@ decode_frame_entry_1 (struct comp_unit *unit, const
> gdb_byte *start,
>    uint64_t uleb128;
>
>    buf = start;
> -  length = read_initial_length (unit->abfd, buf, &bytes_read);
> +  length = read_initial_length (unit->abfd, buf, &bytes_read, false);
>    buf += bytes_read;
>    end = buf + (size_t) length;
>
> diff --git a/gdb/dwarf2/leb.c b/gdb/dwarf2/leb.c
> index d26b48b381c..ef7314ed2b3 100644
> --- a/gdb/dwarf2/leb.c
> +++ b/gdb/dwarf2/leb.c
> @@ -83,3 +83,30 @@ read_signed_leb128 (bfd *abfd, const gdb_byte *buf,
>    *bytes_read_ptr = num_read;
>    return result;
>  }
> +
> +/* See leb.h.  */
> +
> +LONGEST
> +read_initial_length (bfd *abfd, const gdb_byte *buf, unsigned int
> *bytes_read,
> +                    bool handle_nonstd)
> +{
> +  LONGEST length = bfd_get_32 (abfd, buf);
> +
> +  if (length == 0xffffffff)
> +    {
> +      length = bfd_get_64 (abfd, buf + 4);
> +      *bytes_read = 12;
> +    }
> +  else if (handle_nonstd && length == 0)
> +    {
> +      /* Handle the (non-standard) 64-bit DWARF2 format used by IRIX.  */
> +      length = bfd_get_64 (abfd, buf);
> +      *bytes_read = 8;
> +    }
> +  else
> +    {
> +      *bytes_read = 4;
> +    }
> +
> +  return length;
> +}
> diff --git a/gdb/dwarf2/leb.h b/gdb/dwarf2/leb.h
> index b17ab881ba2..29fdffebfec 100644
> --- a/gdb/dwarf2/leb.h
> +++ b/gdb/dwarf2/leb.h
> @@ -89,4 +89,45 @@ extern LONGEST read_signed_leb128 (bfd *, const
> gdb_byte *, unsigned int *);
>
>  extern ULONGEST read_unsigned_leb128 (bfd *, const gdb_byte *, unsigned
> int *);
>
> +/* Read the initial length from a section.  The (draft) DWARF 3


Maybe it's time to remove the "draft" part about dwarf 3? :)

+   specification allows the initial length to take up either 4 bytes
> +   or 12 bytes.  If the first 4 bytes are 0xffffffff, then the next 8
> +   bytes describe the length and all offsets will be 8 bytes in length
> +   instead of 4.
> +
> +   An older, non-standard 64-bit format is also handled by this
> +   function.  The older format in question stores the initial length
> +   as an 8-byte quantity without an escape value.  Lengths greater
> +   than 2^32 aren't very common which means that the initial 4 bytes
> +   is almost always zero.  Since a length value of zero doesn't make
> +   sense for the 32-bit format, this initial zero can be considered to
> +   be an escape value which indicates the presence of the older 64-bit
> +   format.  As written, the code can't detect (old format) lengths
> +   greater than 4GB.  If it becomes necessary to handle lengths
> +   somewhat larger than 4GB, we could allow other small values (such
> +   as the non-sensical values of 1, 2, and 3) to also be used as
> +   escape values indicating the presence of the old format.
> +
> +   The value returned via bytes_read should be used to increment the
> +   relevant pointer after calling read_initial_length().
> +
> +   [ Note:  read_initial_length() and read_offset() are based on the
> +     document entitled "DWARF Debugging Information Format", revision
> +     3, draft 8, dated November 19, 2001.  This document was obtained
> +     from:
> +
> +       http://reality.sgiweb.org/davea/dwarf3-draft8-011125.pdf
> +
> +     This document is only a draft and is subject to change.  (So beware.)
> +


I wonder if this could be updated to a final version.

+     Details regarding the older, non-standard 64-bit format were
> +     determined empirically by examining 64-bit ELF files produced by
> +     the SGI toolchain on an IRIX 6.5 machine.
> +
> +     - Kevin, July 16, 2002
> +   ] */
> +extern LONGEST read_initial_length (bfd *abfd, const gdb_byte *buf,
> +                                   unsigned int *bytes_read,
> +                                   bool handle_nonstd = true);
> +
>  #endif /* GDB_DWARF2_LEB_H */
> diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
> index f0d39ddb7f8..65e39b22b4f 100644
> --- a/gdb/dwarf2/read.c
> +++ b/gdb/dwarf2/read.c
> @@ -1282,8 +1282,6 @@ static CORE_ADDR read_addr_index (struct dwarf2_cu
> *cu, unsigned int addr_index)
>  static CORE_ADDR read_address (bfd *, const gdb_byte *ptr, struct
> dwarf2_cu *,
>                                unsigned int *);
>
> -static LONGEST read_initial_length (bfd *, const gdb_byte *, unsigned int
> *);
> -
>  static LONGEST read_checked_initial_length_and_offset
>    (bfd *, const gdb_byte *, const struct comp_unit_head *,
>     unsigned int *, unsigned int *);
> @@ -19061,68 +19059,6 @@ read_address (bfd *abfd, const gdb_byte *buf,
> struct dwarf2_cu *cu,
>    return retval;
>  }
>
> -/* Read the initial length from a section.  The (draft) DWARF 3
> -   specification allows the initial length to take up either 4 bytes
> -   or 12 bytes.  If the first 4 bytes are 0xffffffff, then the next 8
> -   bytes describe the length and all offsets will be 8 bytes in length
> -   instead of 4.
> -
> -   An older, non-standard 64-bit format is also handled by this
> -   function.  The older format in question stores the initial length
> -   as an 8-byte quantity without an escape value.  Lengths greater
> -   than 2^32 aren't very common which means that the initial 4 bytes
> -   is almost always zero.  Since a length value of zero doesn't make
> -   sense for the 32-bit format, this initial zero can be considered to
> -   be an escape value which indicates the presence of the older 64-bit
> -   format.  As written, the code can't detect (old format) lengths
> -   greater than 4GB.  If it becomes necessary to handle lengths
> -   somewhat larger than 4GB, we could allow other small values (such
> -   as the non-sensical values of 1, 2, and 3) to also be used as
> -   escape values indicating the presence of the old format.
> -
> -   The value returned via bytes_read should be used to increment the
> -   relevant pointer after calling read_initial_length().
> -
> -   [ Note:  read_initial_length() and read_offset() are based on the
> -     document entitled "DWARF Debugging Information Format", revision
> -     3, draft 8, dated November 19, 2001.  This document was obtained
> -     from:
> -
> -       http://reality.sgiweb.org/davea/dwarf3-draft8-011125.pdf
> -
> -     This document is only a draft and is subject to change.  (So beware.)
> -
> -     Details regarding the older, non-standard 64-bit format were
> -     determined empirically by examining 64-bit ELF files produced by
> -     the SGI toolchain on an IRIX 6.5 machine.
> -
> -     - Kevin, July 16, 2002
> -   ] */
> -
> -static LONGEST
> -read_initial_length (bfd *abfd, const gdb_byte *buf, unsigned int
> *bytes_read)
> -{
> -  LONGEST length = bfd_get_32 (abfd, buf);
> -
> -  if (length == 0xffffffff)
> -    {
> -      length = bfd_get_64 (abfd, buf + 4);
> -      *bytes_read = 12;
> -    }
> -  else if (length == 0)
> -    {
> -      /* Handle the (non-standard) 64-bit DWARF2 format used by IRIX.  */
> -      length = bfd_get_64 (abfd, buf);
> -      *bytes_read = 8;
> -    }
> -  else
> -    {
> -      *bytes_read = 4;
> -    }
> -
> -  return length;
> -}
> -
>  /* Cover function for read_initial_length.
>     Returns the length of the object at BUF, and stores the size of the
>     initial length in *BYTES_READ and stores the size that offsets will be
> in
> --
> 2.17.2
>
>
  

>>>>> "Christian" == Christian Biesinger <cbiesinger@google.com> writes:

Christian>  +/* Read the initial length from a section.  The (draft) DWARF 3

Christian> Maybe it's time to remove the "draft" part about dwarf 3? :)

I'll tack on a separate patch to fix up the comment.
Thanks for pointing this out.

Tom