Re: RFA/mips: Use ".pdr" sections generated by GAS

[Andrew Cagney <ac131313 at cygnus dot com>]

> ECOFF debug information (mdebug) included the concept of a PDR.  MIPS uses
> these for unwinding through functions, among other things.  Right now we can
> get them from mdebug or from code inspection.  But current GNU binutils
> emits ".pdr" sections instead of using the old ".mdebug" style debug info.
>
> This patch lets us read and handle the .pdr sections.  It's only for
> 32-bit, because for 64-bit gas currently emits only half the address.  That
> I'll address later.  It changes a testsuite run from 5591 calls to
> heuristic_proc_desc to 1787 calls.  Most or all of those are because we
> build a heuristic procedure description if we find that we are still in the
> prologue of a function.  The new ".pdr" method finds a PDR successfully for
> nearly all calls to non_heuristic_proc_desc; the others are probably either a
> lingering library on my system built by an older assembler, or signal/solib
> trampolines.  Only 29 misses total.
>
> There's an increase in memory usage per-objfile, but no leaks, and the
> section is generally not large; for all of GDB it is only 78K.
>
> Andrew, does this look OK to you?
Given my knowedge of PDR is limited, I 'll take your word on this.

Some suggested tweeks do follow,

enjoy,
Andrew
> Index: mips-tdep.c
> ===================================================================
> RCS file: /cvs/src/src/gdb/mips-tdep.c,v
> retrieving revision 1.75
> diff -u -p -u -r1.75 mips-tdep.c
> --- mips-tdep.c	9 Jun 2002 19:36:15 -0000	1.75
> +++ mips-tdep.c	11 Jun 2002 16:54:51 -0000
> @@ -425,6 +425,8 @@ static unsigned int heuristic_fence_post
>  #define PROC_REG_OFFSET(proc) ((proc)->pdr.regoffset)
>  #define PROC_FREG_OFFSET(proc) ((proc)->pdr.fregoffset)
>  #define PROC_PC_REG(proc) ((proc)->pdr.pcreg)
> +/* FIXME drow/2002-06-10: If a pointer on the host is bigger than a long,
> +   this will corrupt pdr.iline.  Fortunately we don't use it.  */
>  #define PROC_SYMBOL(proc) (*(struct symbol**)&(proc)->pdr.isym)
Can we simply wack these macros?

>  #define _PROC_MAGIC_ 0x0F0F0F0F
>  #define PROC_DESC_IS_DUMMY(proc) ((proc)->pdr.isym == _PROC_MAGIC_)
> @@ -1932,6 +1934,30 @@ heuristic_proc_desc (CORE_ADDR start_pc,
>    return &temp_proc_desc;
>  }
>  
> +struct mips_objfile_private
> +{
> +  bfd_size_type size;
> +  char *contents;
> +};
> +
> +/* Global used to communicate between non_heuristic_proc_desc and
> +   compare_pdr_entries.  */
.... when doing a qsort.

> +static bfd *the_bfd;
Suggest ``compare_pdr_entries_abfd;''.

> +      /* Search the ".pdr" section generated by GAS.  This includes most of
> +	 the information normally found in ECOFF PDRs.
> +
> +	 Right now GAS only outputs the address as a four-byte sequence.  This
> +	 means that we should not bother with this method on 64-bit targets
> +	 until that is fixed.  */
> +
> +      the_bfd = sec->objfile->obfd;
I suspect the use of ``the_bfd'' global at this point was unintentional vis:

> +      if (priv == NULL
> +	  && (the_bfd->format == bfd_object
> +	      && bfd_get_flavour (the_bfd) == bfd_target_elf_flavour
> +	      && elf_elfheader (the_bfd)->e_ident[EI_CLASS] == ELFCLASS64))
> +	{
Suggest putting the bulk of the comment explaing the ``64 bit problem'' 
here where it is having an effect.


> +	      /* In general, the .pdr section is sorted.  However, in the
> +		 presence of multiple code sections (and other corner cases)
> +		 it can become unsorted.  Sort it so that we can use a faster
> +		 binary search.  */
compare_pdr_entries_abfd = sec->objfile->obfd;

> +	      qsort (priv->contents, priv->size / 32, 32, compare_pdr_entries);
compare_pdr_entries_abfd = NULL;

(I think I'll post a patch adding a gdb_qsort() function that takes a 
context parameter).

Andrew