+.so /usr/lib/tmac/tmac.s
+.MF
+.TL
+Symbol Table Format for Sdb
+.ft R
+.br
+.ps -2
+Case: 39394 File 39394
+.ps +2
+.ft R
+.AU
+H.P. Katseff
+.AI
+.HO
+.NH
+Introduction.
+.PP
+A symbolic debugger, sdb,
+has been implemented for the UNIX/32V operating system.
+This document describes modifications made to
+the C compiler to generate additional
+information about the compiled program and to the
+assembler and loader to process the information.
+It also describes information recognized by the assembler, the loader
+and sdb which are intended for use by compilers for other languages
+such as F77.
+.NH
+The C Compiler
+.PP
+The C compiler was modified to generate additional symbol table
+information describing a compiled program.
+Two new types of symbol table entries are made.
+One describes the variables, giving
+their class (local, register, parameter, global, etc.),
+their declared type in the program
+and their address or offset.
+An additional entry is made for structures giving their size.
+The other type of entry provides a mapping between the source program
+and the object program.
+There is an entry for each source line, procedure and source file
+giving their addresses in the object file.
+All line numbers are relative to the beginning of
+the source file.
+.PP
+All entries are generated with the new assembler pseudo-operation
+`.stab'.
+It always takes 12 arguments of which the first eight usually
+represent the name of the symbol as declared in the C program.
+An underscore is
+.ul
+not
+prepended to the name as in some other symbol table entries.
+A typical entry would be
+.DS C
+\&.stab 'e,'r,'r,'f,'l,'g,0,0,046,0,05,_errflg
+.DE
+For expository convenience,
+names in .stab entries will be listed as one word instead of
+eight separate characters.
+.NH 2
+External symbols defined with .comm
+.PP
+The following entry is made for each external symbol which is
+defined with a .comm pseudo-op.
+.DS C
+\&.stab name,040,0,type,0
+.DE
+The type is a 16-bit value describing the variable's declared type.
+This field is described in section 2.13.
+The debugger determines the variable's address
+from the entry made with the .comm.
+It assumes that the name for this entry is _name.
+.NH 2
+Symbols defined within .data areas
+.PP
+The following entry is made for each symbol which is defined
+as a label in a data area.
+.DS C
+\&.stab name,046,0,type,address
+.DE
+The type is the variable's declared type.
+The address is given symbolically as the label.
+.NH 2
+Symbols defined with .lcomm
+.PP
+The following entry is made for each symbol which is defined with
+a .lcomm pseudo-op.
+.DS C
+\&.stab name,048,0,type,address
+.DE
+The type is the variable's declared type.
+The address is given symbolically as the label.
+The specification of an octal constant with an 8 occurs for historical
+reasons.
+.NH 2
+Register symbols
+.PP
+The following entry is made for each variable whose value
+is in a register.
+.DS C
+\&.stab name,0100,0,type,register
+.DE
+The type is the variable's declared type.
+The register is the register number assigned to the variable.
+.NH 2
+Local non-register symbols
+.PP
+The following entry is made for each local, non-register variable.
+.DS C
+\&.stab name,0200,0,type,offset
+.DE
+The type is the variable's declared type.
+The offset is a positive number indicating its offset in bytes for the
+frame pointer.
+.NH 2
+Parameter symbols
+.PP
+The following entry is made for each procedure parameter.
+.DS C
+\&.stab name,0240,0,type,offset
+.DE
+The type is the variable's declared type.
+The offset is a positive number indicating its offset in bytes from
+the stack pointer.
+.NH 2
+Structure elements
+.PP
+The following entry is made for each structure element.
+.DS C
+\&.stab name,0140,0,type,offset
+.DE
+The type is the element's declared type.
+The offset is its offset within the structure in bytes.
+.NH 2
+Structure symbols
+.PP
+An additional entry is made for structures giving their size in bytes.
+It immediately follows their defining .stab entry.
+It is of the form
+.DS C
+\&.stab name,0376,0,0,length
+.DE
+.NH 2
+Common blocks
+.PP
+The following sequence of entries is used to describe elements of
+Fortran equivalence and common blocks.
+The first is of the form
+.DS C
+\&.stab 0,0342,0,0,0
+.DE
+The entries for each element of the block should then appear
+as if they were structure elements.
+Finally, one of the following
+two entries is used depending on the type of common
+or equivalence block.
+If the block is defined as a .globl symbol, use the entry
+.DS C
+\&.stab name,0344,0,0,0
+.DE
+where name is the name of the block defined in the .globl statement.
+It the block is defined in some other way, use
+.DS C
+\&.stab 0,0348,0,0,address
+.DE
+.NH 2
+Brackets
+.PP
+Since C is a block-structured language,
+it is necessary to know the extent of each block containing symbol definitions.
+An entry is made for each right and left bracket which encloses
+a block with definitions.
+The following entries are for left and right brackets respectively.
+.DS C
+\&.stab 0,0300,0,nesting level,address
+\&.stab 0,0340,0,nesting level,address
+.DE
+The nesting level is the static nesting level of the block.
+It is currently ignored by the debugger.
+The address is the address of the first byte of code for the block
+for the left brackets and the first byte following the block
+for right brackets.
+.NH 2
+Procedures
+.PP
+The following entry is made for each procedure.
+.DS C
+\&.stab name,044,0,linenumber,address
+.DE
+The linenumber is the number of the first line of the procedure in the
+source file.
+The address is the address of the first byte of the procedure.
+.NH 2
+Lines
+.PP
+The following entry is made for each line in the source program.
+.DS C
+\&.stab 0,0104,0,linenumber,address
+.DE
+The linenumber is its number.
+The address is the address of the first byte of code for the line.
+For each block of the program,
+the linenumber entries for that block should follow the entries
+for the variables of that block.
+.NH 2
+Source files
+.PP
+The following entries are made for each source file.
+.DS C
+\&.stab name1,0144,0,0,address
+\&.stab name2,0144,0,0,address
+\&...
+\&.stab namen,0144,0,0,address
+.DE
+Each entry contains 8 successive bytes of the name of the source file.
+The name is terminated by a null byte.
+All bytes following this one should also be null.
+The address is the address of the first byte of code for the first
+procedure of the file.
+.NH 2
+Included source files
+.PP
+The following entry is made for each included source file which
+generates code.
+.DS C
+\&.stab name1,0204,0,0,address
+\&.stab name2,0204,0,0,address
+\&...
+\&.stab namen,0204,0,0,address
+.DE
+This entry should appear each time the file is included.
+A similar entry giving the name of the original file should be
+made at the end of the include.
+The format of the name is identical to that for files.
+This feature is heavily used by programs generated by yacc and lex.
+.NH 2
+Format of types.
+.PP
+This 16 bit quantity type describes the declared type of a variable.
+We use the same scheme as in S.C. Johnson's Portable C Compiler
+[Johnson, 1978].
+The type is divided into the following fields:
+.DS
+ struct {
+ short basic:4;
+ d1:2,
+ d2:2,
+ d3:2,
+ d4:2,
+ d5:2,
+ d6:2,
+ }
+.DE
+There are four derived types:
+.DS
+ 0 none
+ 1 pointer
+ 2 function
+ 3 array
+.DE
+They are indicated in the two bit fields d1, d2, d3, d4, d5 and d6.
+The four bit field basic indicates the basic type as follows:
+.DS
+ 0 undefined
+ 1 function argument
+ 2 character
+ 3 short
+ 4 int
+ 5 long
+ 6 float
+ 7 double
+ 8 structure
+ 9 union
+ 10 enumerated type
+ 11 member of enumerated type
+ 12 unsigned character
+ 13 unsigned short
+ 14 unsigned
+ 15 unsigned long
+.DE
+.NH 1
+The assembler and loader
+.PP
+Each .stab pseudo-operation generates one entry in the symbol table.
+The entry is of the form:
+.DS
+ struct {
+ char name[8];
+ char type;
+ char other;
+ short desc;
+ unsigned value;
+ }
+.DE
+.PP
+The loader uses the four least significant bits of the type field
+to determine how to relocate the .stab entry.
+The following are currently used.
+.DS
+ 0 none
+ 4 text
+ 6 data
+.DE
+.PP
+It is necessary for the assembler and loader to preserve the order
+of symbol table entries produced by .stab pseudo-ops.
+.SH
+Reference
+.LP
+Johnson, S.C., "A Portable Compiler: Theory and Practice",
+.I
+Proc. 5th ACM Symp. on Principles of Programming Languages,
+.R
+January 1978.
+.bp
+.SH
+Appendix
+.PP
+The following definitions are extracted from the file /usr/include/a.out.h.
+.sp 1
+.nf
+.na
+struct nlist { /* symbol table entry */
+ char n_name[8]; /* symbol name */
+ char n_type; /* type flag */
+ char n_other;
+ short n_desc;
+ unsigned n_value; /* value */
+};
+
+ /* values for type flag */
+#define N_UNDF 0 /* undefined */
+#define N_ABS 02 /* absolute */
+#define N_TEXT 04 /* text */
+#define N_DATA 06 /* data */
+#define N_BSS 08
+#define N_TYPE 037
+#define N_FN 037 /* file name symbol */
+
+#define N_GSYM 0040 /* global sym: name,,type,0 */
+#define N_FUN 0044 /* function: name,,linenumber,address */
+#define N_STSYM 0046 /* static symbol: name,,type,address */
+#define N_LCSYM 0048 /* .lcomm symbol: name,,type,address */
+#define N_RSYM 0100 /* register sym: name,,register,offset */
+#define N_SLINE 0104 /* src line: ,,linenumber,address */
+#define N_SSYM 0140 /* structure elt: name,,type,struct_offset */
+#define N_SO 0144 /* source file name: name,,,address */
+#define N_LSYM 0200 /* local sym: name,,type,offset */
+#define N_SOL 0204 /* #line source filename: name,,,address */
+#define N_PSYM 0240 /* parameter: name,,type,offset */
+#define N_LBRAC 0300 /* left bracket: ,,nesting level,address */
+#define N_RBRAC 0340 /* right bracket: ,,nesting level,address */
+#define N_BCOMM 0342 /* begin common: name,,, */
+#define N_ECOMM 0344 /* end common: name,,, */
+#define N_ECOML 0348 /* end common (local name): ,,,address */
+#define N_LENG 0376 /* second stab entry with length information */
+
+#define N_EXT 01 /* external bit, or'ed in */
+
+#define FORMAT "%08x"
+
+#define STABTYPES 0340
+.fi
+.ad
+.SG HO-1353-HPK-sdb
+.sp 2
+Copy to
+.br
+R.W. Lucky
+.br
+C.S. Roberts
projects / unix-history / commitdiff