@ifinfo
This document describes the stabs debugging symbol tables.
-Copyright 1992, 1993 Free Software Foundation, Inc.
+Copyright 1992, 93, 94, 95, 1997 Free Software Foundation, Inc.
Contributed by Cygnus Support. Written by Julia Menapace, Jim Kingdon,
and David MacKenzie.
@end tex
@vskip 0pt plus 1filll
-Copyright @copyright{} 1992, 1993 Free Software Foundation, Inc.
+Copyright @copyright{} 1992, 93, 94, 95, 1997 Free Software Foundation, Inc.
Contributed by Cygnus Support.
Permission is granted to make and distribute verbatim copies of
* Type Descriptors:: Table of type descriptors
* Expanded Reference:: Reference information by stab type
* Questions:: Questions and anomolies
-* Sun Differences:: Differences between GNU stabs and Sun
- native stabs
* Stab Sections:: In some object file formats, stabs are
in sections.
* Symbol Types Index:: Index of symbolic stab symbol type names.
a number follows the @samp{=} then the number is a @var{type-reference}.
For a full description of types, @ref{Types}.
+A @var{type-number} is often a single number. The GNU and Sun tools
+additionally permit a @var{type-number} to be a pair
+(@var{file-number},@var{filetype-number}) (the parentheses appear in the
+string, and serve to distinguish the two cases). The @var{file-number}
+is a number starting with 1 which is incremented for each seperate
+source file in the compilation (e.g., in C, each header file gets a
+different number). The @var{filetype-number} is a number starting with
+1 which is incremented for each new type defined in the file.
+(Separating the file number and the type number permits the
+@code{N_BINCL} optimization to succeed more often; see @ref{Include
+Files}).
+
There is an AIX extension for type attributes. Following the @samp{=}
are any number of type attributes. Each one starts with @samp{@@} and
ends with @samp{;}. Debuggers, including AIX's dbx and GDB 4.10, skip
@findex N_EXCL
The @code{N_BINCL} approach works as follows. An @code{N_BINCL} symbol
specifies the start of an include file. In an object file, only the
-string is significant; the Sun linker puts data into some of the other
+string is significant; the linker puts data into some of the other
fields. The end of the include file is marked by an @code{N_EINCL}
symbol (which has no string field). In an object file, there is no
significant data in the @code{N_EINCL} symbol. @code{N_BINCL} and
an @code{N_BINCL} and @code{N_EINCL} pair (as will generally be the case
for a header file), then it only puts out the stabs once. Each
additional occurance is replaced by an @code{N_EXCL} symbol. I believe
-the Sun (SunOS4, not sure about Solaris) linker is the only one which
-supports this feature.
-
-The SunOS4 linker sets the value of a @code{N_BINCL} symbol to the total
-of all the characters in the stabs strings included in the header file,
-omitting the file number. The value of an @code{N_EXCL} symbol is the
-same as the value of the @code{N_BINCL} symbol it replaces. I do not
-know if this information is used by anything. The @code{N_EINCL} value,
-and the values of the other and description fields for all three, appear
-to always be zero.
+the GNU linker and the Sun (both SunOS4 and Solaris) linker are the only
+ones which supports this feature.
+
+A linker which supports this feature will set the value of a
+@code{N_BINCL} symbol to the total of all the characters in the stabs
+strings included in the header file, omitting any file numbers. The
+value of an @code{N_EXCL} symbol is the same as the value of the
+@code{N_BINCL} symbol it replaces. This information can be used to
+match up @code{N_EXCL} and @code{N_BINCL} symbols which have the same
+filename. The @code{N_EINCL} value, and the values of the other and
+description fields for all three, appear to always be zero.
@findex C_BINCL
@findex C_EINCL
stabs describe the procedure's parameters, its block local variables, and
its block structure.
+If functions can appear in different sections, then the debugger may not
+be able to find the end of a function. Recent versions of GCC will mark
+the end of a function with an @code{N_FUN} symbol with an empty string
+for the name. The value is the address of the end of the current
+function. Without such a symbol, there is no indication of the address
+of the end of a function, and you must assume that it ended at the
+starting address of the next function or at the end of the text section
+for the program.
+
@node Nested Procedures
@section Nested Procedures
@end example
specifies that @code{s_typedef} refers to type number 16. Such stabs
-have symbol type @code{N_LSYM} (or @code{C_DECL} for XCOFF).
+have symbol type @code{N_LSYM} (or @code{C_DECL} for XCOFF). (The Sun
+documentation mentions using @code{N_GSYM} in some cases).
If you are specifying the tag name for a structure, union, or
enumeration, use the @samp{T} symbol descriptor instead. I believe C is
next @code{N_FUN}? (I believe its the first.)
@end itemize
-@node Sun Differences
-@appendix Differences Between GNU Stabs and Sun Native Stabs
-
-@c FIXME: Merge all this stuff into the main body of the document.
-
-@itemize @bullet
-@item
-GNU C stabs define @emph{all} types, file or procedure scope, as
-@code{N_LSYM}. Sun doc talks about using @code{N_GSYM} too.
-
-@item
-Sun C stabs use type number pairs in the format
-(@var{file-number},@var{type-number}) where @var{file-number} is a
-number starting with 1 and incremented for each sub-source file in the
-compilation. @var{type-number} is a number starting with 1 and
-incremented for each new type defined in the compilation. GNU C stabs
-use the type number alone, with no source file number.
-@end itemize
-
@node Stab Sections
@appendix Using Stabs in Their Own Sections
string table. SOM and COFF have no way of linking the sections together
or marking them as string tables.
-For COFF, the @code{.stab} and @code{.stabstr} sections are simply
+For COFF, the @code{.stab} and @code{.stabstr} sections may be simply
concatenated by the linker. GDB then uses the @code{n_desc} fields to
figure out the extent of the original sections. Similarly, the
@code{n_value} fields of the header symbols are added together in order
to get the actual position of the strings in a desired @code{.stabstr}
-section. Although this design obviates any need for the linker to relocate
-or otherwise manipulate @code{.stab} and @code{.stabstr} sections, it also
-requires some care to ensure that the offsets are calculated correctly.
-For instance, if the linker were to pad in between the @code{.stabstr}
-sections before concatenating, then the offsets to strings in the middle
-of the executable's @code{.stabstr} section would be wrong.
+section. Although this design obviates any need for the linker to
+relocate or otherwise manipulate @code{.stab} and @code{.stabstr}
+sections, it also requires some care to ensure that the offsets are
+calculated correctly. For instance, if the linker were to pad in
+between the @code{.stabstr} sections before concatenating, then the
+offsets to strings in the middle of the executable's @code{.stabstr}
+section would be wrong.
+
+The GNU linker is able to optimize stabs information by merging
+duplicate strings and removing duplicate header file information
+(@pxref{Include Files}). When the GNU linker optimizes stabs in
+sections, it removes the leading @code{N_UNDF} symbol, and arranges for
+all the @code{n_strx} fields to be relative to the start of the
+@code{.stabstr} section.
@node ELF Linker Relocation
@appendixsec Having the Linker Relocate Stabs in ELF
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