mips-tfile.c

gcc库的原代码,对编程有很大帮助.

/* Update the symbol table (the .T file) in a MIPS object to
   contain debugging information specified by the GNU compiler
   in the form of comments (the mips assembler does not support
   assembly access to debug information).
   Copyright (C) 1991, 1993, 1994. 1995 Free Software Foundation, Inc.
   Contributed by Michael Meissner, [e-mail]
   
This file is part of GNU CC.

GNU CC is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.

GNU CC is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU CC; see the file COPYING.  If not, write to
the Free Software Foundation, 59 Temple Place - Suite 330,
Boston, MA 02111-1307, USA.  */


/* Here is a brief description of the MIPS ECOFF symbol table.  The
   MIPS symbol table has the following pieces:

	Symbolic Header
	    |
	    +--	Auxiliary Symbols
	    |
	    +--	Dense number table
	    |
	    +--	Optimizer Symbols
	    |
	    +--	External Strings
	    |
	    +--	External Symbols
	    |
	    +--	Relative file descriptors
	    |
	    +--	File table
		    |
		    +--	Procedure table
		    |
		    +--	Line number table
		    |
		    +--	Local Strings
		    |
		    +--	Local Symbols

   The symbolic header points to each of the other tables, and also
   contains the number of entries.  It also contains a magic number
   and MIPS compiler version number, such as 2.0.

   The auxiliary table is a series of 32 bit integers, that are
   referenced as needed from the local symbol table.  Unlike standard
   COFF, the aux.  information does not follow the symbol that uses
   it, but rather is a separate table.  In theory, this would allow
   the MIPS compilers to collapse duplicate aux. entries, but I've not
   noticed this happening with the 1.31 compiler suite.  The different
   types of aux. entries are:

    1)	dnLow: Low bound on array dimension.

    2)	dnHigh: High bound on array dimension.

    3)	isym: Index to the local symbol which is the start of the
	function for the end of function first aux. entry.

    4)	width: Width of structures and bitfields.

    5)	count: Count of ranges for variant part.

    6)	rndx: A relative index into the symbol table.  The relative
	index field has two parts: rfd which is a pointer into the
	relative file index table or ST_RFDESCAPE which says the next
	aux. entry is the file number, and index: which is the pointer
	into the local symbol within a given file table.  This is for
	things like references to types defined in another file.

    7)	Type information: This is like the COFF type bits, except it
	is 32 bits instead of 16; they still have room to add new
	basic types; and they can handle more than 6 levels of array,
	pointer, function, etc.  Each type information field contains
	the following structure members:

	    a)	fBitfield: a bit that says this is a bitfield, and the
		size in bits follows as the next aux. entry.

	    b)	continued: a bit that says the next aux. entry is a
		continuation of the current type information (in case
		there are more than 6 levels of array/ptr/function).

	    c)	bt: an integer containing the base type before adding
		array, pointer, function, etc. qualifiers.  The
		current base types that I have documentation for are:

			btNil		-- undefined 
			btAdr		-- address - integer same size as ptr
			btChar		-- character 
			btUChar		-- unsigned character 
			btShort		-- short 
			btUShort	-- unsigned short 
			btInt		-- int 
			btUInt		-- unsigned int 
			btLong		-- long 
			btULong		-- unsigned long 
			btFloat		-- float (real) 
			btDouble	-- Double (real) 
			btStruct	-- Structure (Record) 
			btUnion		-- Union (variant) 
			btEnum		-- Enumerated 
			btTypedef	-- defined via a typedef isymRef 
			btRange		-- subrange of int 
			btSet		-- pascal sets 
			btComplex	-- fortran complex 
			btDComplex	-- fortran double complex 
			btIndirect	-- forward or unnamed typedef 
			btFixedDec	-- Fixed Decimal 
			btFloatDec	-- Float Decimal 
			btString	-- Varying Length Character String 
			btBit		-- Aligned Bit String 
			btPicture	-- Picture
			btVoid		-- Void (MIPS cc revision >= 2.00)

	    d)	tq0 - tq5: type qualifier fields as needed.  The
		current type qualifier fields I have documentation for
		are:

			tqNil		-- no more qualifiers 
			tqPtr		-- pointer 
			tqProc		-- procedure 
			tqArray		-- array 
			tqFar		-- 8086 far pointers 
			tqVol		-- volatile 


   The dense number table is used in the front ends, and disappears by
   the time the .o is created.

   With the 1.31 compiler suite, the optimization symbols don't seem
   to be used as far as I can tell.

   The linker is the first entity that creates the relative file
   descriptor table, and I believe it is used so that the individual
   file table pointers don't have to be rewritten when the objects are
   merged together into the program file.

   Unlike COFF, the basic symbol & string tables are split into
   external and local symbols/strings.  The relocation information
   only goes off of the external symbol table, and the debug
   information only goes off of the internal symbol table.  The
   external symbols can have links to an appropriate file index and
   symbol within the file to give it the appropriate type information.
   Because of this, the external symbols are actually larger than the
   internal symbols (to contain the link information), and contain the
   local symbol structure as a member, though this member is not the
   first member of the external symbol structure (!).  I suspect this
   split is to make strip easier to deal with.

   Each file table has offsets for where the line numbers, local
   strings, local symbols, and procedure table starts from within the
   global tables, and the indexs are reset to 0 for each of those
   tables for the file.

   The procedure table contains the binary equivalents of the .ent
   (start of the function address), .frame (what register is the
   virtual frame pointer, constant offset from the register to obtain
   the VFP, and what register holds the return address), .mask/.fmask
   (bitmask of saved registers, and where the first register is stored
   relative to the VFP) assembler directives.  It also contains the
   low and high bounds of the line numbers if debugging is turned on.

   The line number table is a compressed form of the normal COFF line
   table.  Each line number entry is either 1 or 3 bytes long, and
   contains a signed delta from the previous line, and an unsigned
   count of the number of instructions this statement takes.

   The local symbol table contains the following fields:

    1)	iss: index to the local string table giving the name of the
	symbol.

    2)	value: value of the symbol (address, register number, etc.).

    3)	st: symbol type.  The current symbol types are:

	    stNil	  -- Nuthin' special
	    stGlobal	  -- external symbol
	    stStatic	  -- static
	    stParam	  -- procedure argument
	    stLocal	  -- local variable
	    stLabel	  -- label
	    stProc	  -- External Procedure
	    stBlock	  -- beginning of block
	    stEnd	  -- end (of anything)
	    stMember	  -- member (of anything)
	    stTypedef	  -- type definition
	    stFile	  -- file name
	    stRegReloc	  -- register relocation
	    stForward	  -- forwarding address
	    stStaticProc  -- Static procedure
	    stConstant	  -- const

    4)	sc: storage class.  The current storage classes are:

	    scText	  -- text symbol
	    scData	  -- initialized data symbol
	    scBss	  -- un-initialized data symbol
	    scRegister	  -- value of symbol is register number
	    scAbs	  -- value of symbol is absolute
	    scUndefined   -- who knows?
	    scCdbLocal	  -- variable's value is IN se->va.??
	    scBits	  -- this is a bit field
	    scCdbSystem	  -- value is IN debugger's address space
	    scRegImage	  -- register value saved on stack
	    scInfo	  -- symbol contains debugger information
	    scUserStruct  -- addr in struct user for current process
	    scSData	  -- load time only small data
	    scSBss	  -- load time only small common
	    scRData	  -- load time only read only data
	    scVar	  -- Var parameter (fortranpascal)
	    scCommon	  -- common variable
	    scSCommon	  -- small common
	    scVarRegister -- Var parameter in a register
	    scVariant	  -- Variant record
	    scSUndefined  -- small undefined(external) data
	    scInit	  -- .init section symbol

    5)	index: pointer to a local symbol or aux. entry.



   For the following program:

	#include <stdio.h>

	main(){
		printf("Hello World!\n");
		return 0;
	}

   Mips-tdump produces the following information:
   
   Global file header:
       magic number             0x162
       # sections               2
       timestamp                645311799, Wed Jun 13 17:16:39 1990
       symbolic header offset   284
       symbolic header size     96
       optional header          56
       flags                    0x0
   
   Symbolic header, magic number = 0x7009, vstamp = 1.31:
   
       Info                      Offset      Number       Bytes
       ====                      ======      ======      =====
   
       Line numbers                 380           4           4 [13]
       Dense numbers                  0           0           0
       Procedures Tables            384           1          52
       Local Symbols                436          16         192
       Optimization Symbols           0           0           0
       Auxiliary Symbols            628          39         156
       Local Strings                784          80          80
       External Strings             864         144         144
       File Tables                 1008           2         144
       Relative Files                 0           0           0
       External Symbols            1152          20         320
   
   File #0, "hello2.c"
   
       Name index  = 1          Readin      = No
       Merge       = No         Endian      = LITTLE
       Debug level = G2         Language    = C
       Adr         = 0x00000000
   
       Info                       Start      Number        Size      Offset
       ====                       =====      ======        ====      ======
       Local strings                  0          15          15         784
       Local symbols                  0           6          72         436
       Line numbers                   0          13          13         380
       Optimization symbols           0           0           0           0
       Procedures                     0           1          52         384
       Auxiliary symbols              0          14          56         628
       Relative Files                 0           0           0           0
   
    There are 6 local symbols, starting at 436

	Symbol# 0: "hello2.c"
	    End+1 symbol  = 6
	    String index  = 1
	    Storage class = Text        Index  = 6
	    Symbol type   = File        Value  = 0

	Symbol# 1: "main"
	    End+1 symbol  = 5
	    Type          = int
	    String index  = 10
	    Storage class = Text        Index  = 12
	    Symbol type   = Proc        Value  = 0

	Symbol# 2: ""
	    End+1 symbol  = 4
	    String index  = 0
	    Storage class = Text        Index  = 4
	    Symbol type   = Block       Value  = 8

	Symbol# 3: ""
	    First symbol  = 2
	    String index  = 0
	    Storage class = Text        Index  = 2
	    Symbol type   = End         Value  = 28

	Symbol# 4: "main"
	    First symbol  = 1
	    String index  = 10
	    Storage class = Text        Index  = 1
	    Symbol type   = End         Value  = 52

	Symbol# 5: "hello2.c"
	    First symbol  = 0
	    String index  = 1
	    Storage class = Text        Index  = 0
	    Symbol type   = End         Value  = 0

    There are 14 auxiliary table entries, starting at 628.

	* #0               0, [   0/      0], [ 0 0:0 0:0:0:0:0:0]
	* #1              24, [  24/      0], [ 6 0:0 0:0:0:0:0:0]
	* #2               8, [   8/      0], [ 2 0:0 0:0:0:0:0:0]
	* #3              16, [  16/      0], [ 4 0:0 0:0:0:0:0:0]
	* #4              24, [  24/      0], [ 6 0:0 0:0:0:0:0:0]
	* #5              32, [  32/      0], [ 8 0:0 0:0:0:0:0:0]
	* #6              40, [  40/      0], [10 0:0 0:0:0:0:0:0]
	* #7              44, [  44/      0], [11 0:0 0:0:0:0:0:0]
	* #8              12, [  12/      0], [ 3 0:0 0:0:0:0:0:0]
	* #9              20, [  20/      0], [ 5 0:0 0:0:0:0:0:0]
	* #10             28, [  28/      0], [ 7 0:0 0:0:0:0:0:0]
	* #11             36, [  36/      0], [ 9 0:0 0:0:0:0:0:0]
	  #12              5, [   5/      0], [ 1 1:0 0:0:0:0:0:0]
	  #13             24, [  24/      0], [ 6 0:0 0:0:0:0:0:0]

    There are 1 procedure descriptor entries, starting at 0.

	Procedure descriptor 0:
	    Name index   = 10          Name          = "main"
	    .mask 0x80000000,-4        .fmask 0x00000000,0
	    .frame $29,24,$31
	    Opt. start   = -1          Symbols start = 1
	    First line # = 3           Last line #   = 6
	    Line Offset  = 0           Address       = 0x00000000

	There are 4 bytes holding line numbers, starting at 380.
	    Line           3,   delta     0,   count  2
	    Line           4,   delta     1,   count  3
	    Line           5,   delta     1,   count  2
	    Line           6,   delta     1,   count  6

   File #1, "/usr/include/stdio.h"

    Name index  = 1          Readin      = No
    Merge       = Yes        Endian      = LITTLE
    Debug level = G2         Language    = C
    Adr         = 0x00000000

    Info                       Start      Number        Size      Offset
    ====                       =====      ======        ====      ======
    Local strings                 15          65          65         799
    Local symbols                  6          10         120         508
    Line numbers                   0           0           0         380
    Optimization symbols           0           0           0           0
    Procedures                     1           0           0         436
    Auxiliary symbols             14          25         100         684
    Relative Files                 0           0           0           0

    There are 10 local symbols, starting at 442

	Symbol# 0: "/usr/include/stdio.h"
	    End+1 symbol  = 10
	    String index  = 1
	    Storage class = Text        Index  = 10
	    Symbol type   = File        Value  = 0

	Symbol# 1: "_iobuf"
	    End+1 symbol  = 9
	    String index  = 22
	    Storage class = Info        Index  = 9
	    Symbol type   = Block       Value  = 20

	Symbol# 2: "_cnt"
	    Type          = int
	    String index  = 29
	    Storage class = Info        Index  = 4
	    Symbol type   = Member      Value  = 0

	Symbol# 3: "_ptr"