HPUX a.out_700[4]
a.out_800(4) Series 700/800 Implementation a.out_800(4)
NAME
a.out - assembler and link editor output
SYNOPSIS
#include <a.out.h>
Remarks:
This manual entry describes the a.out file format for Series 700 and
Series 800 computers. Refer to other a.out(4) manual entries for
descriptions of other valid implementations.
DESCRIPTION
The file name a.out is the output file from the assembler (see as(1)),
compilers, and the linker (see ld(1)). The assembler and compilers
create relocatable object files ready for input to the linker; the
linker creates executable object files and shared library files.
An object file consists of a file header, auxiliary headers, space
dictionary, subspace dictionary, symbol table, relocation information,
compiler records, space string table, symbol string table, and the
data for initialized code and data. Not all of these sections are
required for all object files. The file must begin with the file
header, but the remaining sections do not have to be in any particular
order; the file header contains pointers to each of the other sections
of the file.
A relocatable object file, created by the assembler or compiler, must
contain at least the following sections: file header, space
dictionary, subspace dictionary, symbol table, relocation information,
space string table, symbol string table, and code and data. It may
also contain auxiliary headers and compiler records. Relocatable
files generally contain unresolved symbols; the linker combines
relocatable files and searches libraries to produce an executable
file. The linker can also be used to combine relocatable files and
produce a new relocatable file as output, suitable for input to a
subsequent linker run.
An executable file, created by the linker, typically contains the
following sections: file header, an HP-UX auxiliary header, space
dictionary, subspace dictionary, symbol table, space string table,
symbol string table, and code and data. The linker also copies any
auxiliary headers and compiler records from the input files to the
output file. If the file has been stripped (see strip(1)), it will
not contain a symbol table, symbol string table, or compiler records.
An executable file must not contain any unresolved symbols.
A shared library file, created by the linker, contains the same
sections found in an executable file, with additional information
added to the code section of the file. This additional information
contains a header, export table, import table, and dynamic relocation
records to be used by the dynamic loader.
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Programs for the Series 700/800 architecture consist of two loadable
spaces: a shared, non-writable, code space named $TEXT$; and a
private, writable, data space named $PRIVATE$. A program may contain
other non-loadable spaces that contain data needed by development
tools; for example, symbolic debugging information is contained in a
space named $DEBUG$. The linker treats loadable and unloadable spaces
exactly the same, so the full generality of symbol resolution and
relocation is available for the symbolic debugging information.
Spaces have an addressing range of 4,294,967,296 (2^32) bytes; each
loadable space is divided into four 1,073,741,824 (2^30) byte
quadrants. The HP-UX operating system places all code in the first
quadrant of the $TEXT$ space, all data in the second quadrant of the
$PRIVATE$ space, and all shared library code into the third quadrant
of shared memory space.
Each space is also divided into logical units called subspaces. When
the linker combines relocatable object files, it groups all subspaces
from the input files by name, then arranges the groups within the
space by a sort key associated with each subspace. Subspaces are not
architecturally significant; they merely provide a mechanism for
combining individual parts of spaces independently from many input
files. Some typical subspaces in a program are shown in the following
table:
tab(:); lf4p+1 l. $SHLIB_INFO$:Information needed for dynamic
loading. $MILLICODE$:Code for millicode routines $LIT$:Sharable
literals $CODE$:Code $UNWIND$:Stack unwind information
$GLOBAL$:Outer block declarations for Pascal $DATA$:Static
initialized data $COMMON$:FORTRAN common $SHLIB_DATA$: Imported
data from referenced shared libraries. $BSS$:Uninitialized data
Subspaces can be initialized or uninitialized (although typically,
only $BSS$ is uninitialized). The subspace dictionary entry for an
initialized subspace contains a file pointer to the initialization
data, while the entry for an uninitialized subspace contains only a
32-bit pattern used to initialize the entire area at load time.
In a relocatable file, initialized code and data often contains
references to locations elsewhere in the file, and to unresolved
symbols defined in other files. These references are patched at link
time using the relocation information. Each entry in the relocation
information (a ``fixup'') specifies a location within the initialized
data for a subspace, and an expression that defines the actual value
that should be placed at that location, relative to one or two
symbols.
The linker summarizes the subspace dictionary in the HP-UX auxiliary
header when creating an executable file. HP-UX programs contain only
three separate sections: one for the code, one for initialized data,
and one for uninitialized data. By convention, this auxiliary header
is placed immediately following the file header.
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When an a.out file is loaded into memory for execution, three areas of
memory are set up: the a.out code is loaded into the first quadrant
of a new, sharable space; the data (initialized followed by
uninitialized) is loaded into the second quadrant of a new, private
space; and a stack is created beginning at a fixed address near the
middle of the second quadrant of the data space.
If the a.out file uses shared libraries then the dynamic loader
/lib/dld.sl is loaded into memory, and called to map all shared
libraries, requested by the program, into memory. The shared library
text is loaded into the third quadrant of the shared memory space, and
the shared library data is allocated in the second quadrant of the
data space.
The file format described here is a common format for all operating
systems designed for HP's Precision Architecture. Therefore, there
are some fields and structures that are not used on HP-UX or have been
reserved for future use.
File Header
The format of the file header is described by the following structure
declaration from <filehdr.h>.
struct header {
short int system_id; /* system id */
short int a_magic; /* magic number */
unsigned int version_id; /* a.out format version */
struct sys_clock file_time; /* timestamp */
unsigned int entry_space; /* reserved */
unsigned int entry_subspace; /* reserved */
unsigned int entry_offset; /* reserved */
unsigned int aux_header_location; /* file ptr to aux hdrs */
unsigned int aux_header_size; /* sizeof aux hdrs */
unsigned int som_length; /* length of object module */
unsigned int presumed_dp; /* reserved */
unsigned int space_location; /* file ptr to space dict */
unsigned int space_total; /* # of spaces */
unsigned int subspace_location; /* file ptr to subsp dict */
unsigned int subspace_total; /* # of subspaces */
unsigned int loader_fixup_location; /* reserved */
unsigned int loader_fixup_total; /* reserved */
unsigned int space_strings_location; /* file ptr to sp. strings */
unsigned int space_strings_size; /* sizeof sp. strings */
unsigned int init_array_location; /* reserved */
unsigned int init_array_total; /* reserved */
unsigned int compiler_location; /* file ptr to comp recs */
unsigned int compiler_total; /* # of compiler recs */
unsigned int symbol_location; /* file ptr to sym table */
unsigned int symbol_total; /* # of symbols */
unsigned int fixup_request_location; /* file ptr to fixups */
unsigned int fixup_request_total; /* # of fixups */
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unsigned int symbol_strings_location; /* file ptr to sym strings */
unsigned int symbol_strings_size; /* sizeof sym strings */
unsigned int unloadable_sp_location; /* file ptr to debug info */
unsigned int unloadable_sp_size; /* size of debug info */
unsigned int checksum; /* header checksum */
};
The timestamp is a two-word structure as shown below. If unused, both
fields are zero.
struct sys_clock {
unsigned int secs;
unsigned int nanosecs;
};
Auxiliary Headers
The auxiliary headers are contained in a single contiguous area in the
file, and are located by a pointer in the file header. Auxiliary
headers are used for two purposes: users can attach version and
copyright strings to an object file, and an auxiliary header contains
the information needed to load an executable program. In an
executable program, the HP-UX auxiliary header must precede all other
auxiliary headers. The following declarations are found in
<aouthdr.h>.
struct aux_id {
unsigned int mandatory : 1; /* reserved */
unsigned int copy : 1; /* reserved */
unsigned int append : 1; /* reserved */
unsigned int ignore : 1; /* reserved */
unsigned int reserved : 12; /* reserved */
unsigned int type : 16; /* aux hdr type */
unsigned int length; /* sizeof rest of aux hdr */
};
/* Values for the aux_id.type field */
#define HPUX_AUX_ID 4
#define VERSION_AUX_ID 6
#define COPYRIGHT_AUX_ID 9
#define SHLIB_VERSION_AUX_ID 10
struct som_exec_auxhdr { /* HP-UX auxiliary header */
struct aux_id som_auxhdr; /* aux header id */
long exec_tsize; /* text size */
long exec_tmem; /* start address of text */
long exec_tfile; /* file ptr to text */
long exec_dsize; /* data size */
long exec_dmem; /* start address of data */
long exec_dfile; /* file ptr to data */
long exec_bsize; /* bss size */
long exec_entry; /* address of entry point */
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long exec_flags; /* loader flags */
long exec_bfill; /* bss initialization value */
};
/* Values for exec_flags */
#define TRAP_NIL_PTRS 01
struct user_string_aux_hdr { /* Version string auxiliary header */
struct aux_id header_id; /* aux header id */
unsigned int string_length; /* strlen(user_string) */
char user_string[1]; /* user-defined string */
};
struct copyright_aux_hdr { /* Copyright string auxiliary header */
struct aux_id header_id; /* aux header id */
unsigned int string_length; /* strlen(user_string) */
char copyright[1]; /* user-defined string */
};
struct shlib_version_aux_hdr {
struct aux_id header_id; /* aux header id */
short version; /* version number */
};
Space Dictionary
The space dictionary consists of a sequence of space records as
defined in <spacehdr.h>.
struct space_dictionary_record {"
union name_pt name; /* index to space name */
unsigned int is_loadable: 1; /* space is loadable */
unsigned int is_defined: 1; /* space is defined within file */
unsigned int is_private: 1; /* space is not sharable */
unsigned int reserved: 13; /* reserved */
unsigned int sort_key: 8; /* sort key for space */
unsigned int reserved2: 8; /* reserved */
int space_number; /* space index */
int subspace_index; /* index to first subspace */
unsigned int subspace_quantity; /* # of subspaces in space */
int loader_fix_index; /* reserved */
unsigned int loader_fix_quantity; /* reserved */
int init_pointer_index; /* reserved */
unsigned int init_pointer_quantity; /* reserved */
};
The strings for the space names are contained in the space strings
table, which is located by a pointer in the file header. Each entry
in the space strings table is preceded by a 4-byte integer that
defines the length of the string, and is terminated by one to five
null characters to pad the string out to a word boundary. Indices to
this table are relative to the start of the table, and point to the
first byte of the string (not the preceding length word). The union
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defined below is used for all such string pointers; the character
pointer is defined for programs that read the string table into memory
and wish to relocate in-memory copies of space records.
union name_pt {
char *n_name;
unsigned int n_strx;
};
Subspace Dictionary
The subspace dictionary consists of a sequence of subspace records as
defined in <scnhdr.h>. Strings for subspace names are contained in
the space strings table.
struct subspace_dictionary_record {
int space_index;
unsigned int access_control_bits: 7; /* reserved */
unsigned int memory_resident: 1; /* reserved */
unsigned int dup_common: 1; /* COBOL-style common */
unsigned int is_common: 1; /* subspace is a common block */
unsigned int is_loadable: 1; /* subspace is loadable */
unsigned int quadrant: 2; /* reserved */
unsigned int initially_frozen: 1; /* reserved */
unsigned int is_first: 1; /* reserved */
unsigned int code_only: 1; /* subspace contains only code */
unsigned int sort_key: 8; /* subspace sort key */
unsigned int replicate_init: 1; /* reserved */
unsigned int continuation: 1; /* reserved */
unsigned int reserved: 6; /* reserved */
int file_loc_init_value; /* file location or init value */
unsigned int initialization_length; /* length of initialization */
unsigned int subspace_start; /* starting offset */
unsigned int subspace_length; /* total subspace length */
unsigned int reserved2: 16; /* reserved */
unsigned int alignment: 16; /* alignment required */
union name_pt name; /* index of subspace name */
int fixup_request_index; /* index to first fixup */
unsigned int fixup_request_quantity; /* # of fixup requests */
};
Symbol Table
The symbol table consists of a sequence of entries described by the
structure shown below, from <syms.h>. Strings for symbol and
qualifier names are contained in the symbol strings table, whose
structure is identical with the space strings table.
struct symbol_dictionary_record {
unsigned int hidden: 1; /* reserved */
unsigned int symbol_type: 7; /* symbol type */
unsigned int symbol_scope: 4; /* symbol value */
unsigned int check_level: 3; /* type checking level */
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unsigned int must_qualify: 1; /* qualifier required */
unsigned int initially_frozen: 1; /* reserved */
unsigned int memory_resident: 1; /* reserved */
unsigned int is_common: 1; /* common block */
unsigned int dup_common: 1; /* COBOL-style common */
unsigned int xleast: 2; /* reserved */
unsigned int arg_reloc: 10; /* parameter relocation bits */
union name_pt name; /* index to symbol name */
union name_pt qualifier_name; /* index to qual name */
unsigned int symbol_info; /* subspace index */
unsigned int symbol_value; /* symbol value */
};
/* Values for symbol_type */
#define ST_NULL 0 /* unused symbol entry */
#define ST_ABSOLUTE 1 /* non-relocatable symbol */
#define ST_DATA 2 /* data symbol */
#define ST_CODE 3 /* generic code symbol */
#define ST_PRI_PROG 4 /* program entry point */
#define ST_SEC_PROG 5 /* secondary prog entry point*/
#define ST_ENTRY 6 /* procedure entry point */
#define ST_STORAGE 7 /* storage request */
#define ST_STUB 8 /* reserved */
#define ST_MODULE 9 /* Pascal module name */
#define ST_SYM_EXT 10 /* symbol extension record */
#define ST_ARG_EXT 11 /* argument extension record */
#define ST_MILLICODE 12 /* millicode entry point */
#define ST_PLABEL 13 /* reserved */
#define ST_OCT_DIS 14 /* reserved */
#define ST_MILLI_EXT 15 /* reserved */
/* Values for symbol_scope */
#define SS_UNSAT 0 /* unsatisfied reference */
#define SS_EXTERNAL 1 /* reserved */
#define SS_LOCAL 2 /* local symbol */
#define SS_UNIVERSAL 3 /* global symbol */
The meaning of the symbol value depends on the symbol type. For the
code symbols (generic code, program entry points, procedure and
millicode entry points), the low-order two bits of the symbol value
encode the execution privilege level, which is not used on HP-UX, but
is generally set to 3. The symbol value with those bits masked out is
the address of the symbol (which is always a multiple of 4). For data
symbols, the symbol value is simply the address of the symbol. For
storage requests, the symbol value is the number of bytes requested;
the linker allocates space for the largest request for each symbol in
the $BSS$ subspaces, unless a local or universal symbol is found for
that symbol (in which case the storage request is treated like an
unsatisfied reference).
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If a relocatable file is compiled with parameter type checking,
extension records follow symbols that define and reference procedure
entry points and global variables. The first extension record, the
symbol extension record, defines the type of the return value or
global variable, and (if a procedure or function) the number of
parameters and the types of the first three parameters. If more
parameter type descriptors are needed, one or more argument extension
records follow, each containing four more descriptors. A check level
of 0 specifies no type checking; no extension records follow. A check
level of 1 or more specifies checking of the return value or global
variable type. A check level of 2 or more specifies checking of the
number of parameters, and a check level of 3 specifies checking the
types of each individual parameter. The linker performs the requested
level of type checking between unsatisfied symbols and local or
universal symbols as it resolves symbol references.
union arg_descriptor {
struct {
unsigned int reserved: 3; /* not used */
unsigned int packing: 1; /* reserved */
unsigned int alignment: 4; /* byte alignment */
unsigned int reserved2: 1; /* not used */
unsigned int mode: 3; /* use of symbol */
unsigned int structure: 4; /* structure of symbol */
unsigned int hash: 1; /* set if arg_type is hashed */
int arg_type: 15; /* data type */
} arg_desc;
unsigned int word;
};
struct symbol_extension_record {
unsigned int type: 8; /* always ST_SYM_EXT */
unsigned int max_num_args: 8; /* max # of parameters */
unsigned int min_num_args: 8; /* min # of parameters */
unsigned int num_args: 8; /* actual # of parameters */
union arg_descriptor symbol_desc; /* symbol type desc. */
union arg_descriptor argument_desc[3]; /* first 3 parameters */
};
struct argument_desc_array {
unsigned int type: 8; /* always ST_ARG_EXT */
unsigned int reserved: 24; /* not used */
union arg_descriptor argument_desc[4]; /* next 4 parameters */
};
The values for the alignment, mode, structure, and arg_type (when the
data type is not hashed) fields are given in the following table.
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center tab(:) ; cB lB lB lB lB n l l l l .
value:alignment:mode:structure:arg_type _ 0:byte:any:any:any 1:half-
word:value parm:scalar:void 2:word:reference parm:array:signed byte
3:dbl word:value-result:struct:unsigned byte 4::name:pointer:signed
short 5::variable:long ptr:unsigned short 6:64-byte:function return:C
string:signed long 7::procedure:Pascal string:unsigned long 8::long
ref parm:procedure:signed dbl word 9:::function:unsigned dbl word
10:::label:short real 11:page:::real 12::::long real 13::::short
complex 14::::complex 15::::long complex 16::::packed decimal
17::::struct/array
For procedure entry points, the parameter relocation bits define the
locations of the formal parameters and the return value. Normally,
the first four words of the parameter list are passed in general
registers (r26-r23) instead of on the stack, and the return value is
returned in r29. Floating-point parameters in this range are passed
instead in floating-point registers (fr4-fr7) and a floating-point
value is returned in fr4. The parameter relocation bits consist of
five pairs of bits that describe the first four words of the parameter
list and the return value. The leftmost pair of bits describes the
first parameter word, and the rightmost pair of bits describes the
return value. The meanings of these bits are shown in the following
table.
cB | lB n | l. bits meaning _ 00 no parameter or
return value 01 parameter or return value in general register
10 parameter or return value in floating-point register
11 double-precision floating-point value
For double-precision floating-point parameters, the odd-numbered
parameter word should be marked 11 and the even-numbered parameter
word should be marked 10. Double-precision return values are simply
marked 11.
Every procedure call is tagged with a similar set of bits (see
Relocation Information, below), so that the linker can match each call
with the expectations of the procedure entry point. If the call and
entry point mismatch, the linker creates a stub that relocates the
parameters and return value as appropriate.
Relocation Information
Each initialized subspace defines a range of fixups that apply to the
data in that subspace. A fixup request is associated with every word
that requires relocation or that contains a reference to an
unsatisfied symbol. In relocatable object files created prior to HP-
UX Release 3.0 on Series 800 systems each fixup request is a five-word
structure describing a code or data word to be patched at link time.
Object files created on Release 3.0 or later contain variable-length
fixup requests that describe every byte of the subspace. The
version_id field in the file header distinguishes these two formats;
the constant VERSION_ID is found in older object files, and the
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constant NEW_VERSION_ID is found in newer ones.
In older object files, fixups can compute an expression involving
zero, one, or two symbols and a constant, then extract a field of bits
from that result and deposit those bits in any of several different
formats (corresponding to the Precision Architecture instruction set).
The fixup_request_index field in the subspace dictionary entry indexes
into the fixup request area defined by the file header, and the
fixup_request_quantity field refers to the number of fixup requests
used for that subspace. The structure of a fixup request is contained
in <reloc.h>.
struct fixup_request_record {
unsigned int need_data_ref: 1; /* reserved */
unsigned int arg_reloc: 10; /* parameter relocation bits */
unsigned int expression_type: 5; /* how to compute value */
unsigned int exec_level: 2; /* reserved */
unsigned int fixup_format: 6; /* how to deposit bits */
unsigned int fixup_field: 8; /* field to extract */
unsigned int subspace_offset; /* subspace offset of word */
unsigned int symbol_index_one; /* index of first symbol */
unsigned int symbol_index_two; /* index of second symbol */
int fixup_constant; /* constant */
};
/* Values for expression_type */
#define e_one 0 /* symbol1 + constant */
#define e_two 1 /* symbol1 - symbol2 + constant */
#define e_pcrel 2 /* symbol1 - pc + constant */
#define e_con 3 /* constant */
#define e_plabel 7 /* symbol1 + constant */
#define e_abs 18 /* reserved */
/* Values for fixup_field (assembler mnemonics shown) */
#define e_fsel 0 /* F': no change */
#define e_lssel 1 /* LS': inverse of RS' */
#define e_rssel 2 /* RS': rightmost 11 bits, signed */
#define e_lsel 3 /* L': leftmost 21 bits */
#define e_rsel 4 /* R': rightmost 11 bits */
#define e_ldsel 5 /* LD': inverse of RD' */
#define e_rdsel 6 /* RD': rightmost 11 bits, filled left with ones */
#define e_lrsel 7 /* LR': L' with rounded" constant */"
#define e_rrsel 8 /* RR': R' with rounded" constant */"
/* Values for fixup_format (typical instructions shown) */"
#define i_exp14 0 /* 14-bit immediate (LDW, STW) */
#define i_exp21 1 /* 21-bit immediate (LDIL, ADDIL) */
#define i_exp11 2 /* 11-bit immediate (ADDI, SUBI) */
#define i_rel17 3 /* 17-bit pc-relative (BL) */
#define i_rel12 4 /* 12 bit pc-relative (COMBT, COMBF, etc.) */
#define i_data 5 /* whole word */
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#define i_none 6 /* not used */
#define i_abs17 7 /* 17-bit absolute (BE, BLE) */
#define i_milli 8 /* 17-bit millicode call (BLE) */
#define i_break 9 /* reserved (no effect on HP-UX) */
In newer object files, relocation entries consist of a stream of
bytes. The fixup_request_index field in the subspace dictionary entry
is a byte offset into the fixup dictionary defined by the file header,
and the fixup_request_quantity field defines the length of the fixup
request stream, in bytes, for that subspace. The first byte of each
fixup request (the opcode) identifies the request and determines the
length of the request.
In general, the fixup stream is a series of linker instructions that
governs how the linker places data in the a.out file. Certain fixup
requests cause the linker to copy one or more bytes from the input
subspace to the output subspace without change, while others direct
the linker to relocate words or resolve external references. Still
others direct the linker to insert zeroes in the output subspace or to
leave areas uninitialized without copying any data from the input
subspace, and others describe points in the code without contributing
any new data to the output file.
The include file <reloc.h> defines constants for each major opcode.
Many fixup requests use a range of opcodes; only a constant for the
beginning of the range is defined. The meaning of each fixup request
is described below. The opcode ranges and parameters for each fixup
are described in the table further below.
R_NO_RELOCATION
Copy L bytes with no relocation.
R_ZEROES Insert L zero bytes into the output subspace.
R_UNINIT Skip L bytes in the output subspace.
R_RELOCATION Copy one data word with relocation. The word is
assumed to contain a 32-bit pointer relative to its own
subspace.
R_DATA_ONE_SYMBOL
Copy one data word with relocation relative to an
external symbol whose symbol index is S.
R_DATA_PLABEL Copy one data word as a 32-bit procedure label,
referring to the symbol S. The original contents of
the word should be 0 (no static link) or 2 (static link
required).
R_SPACE_REF Copy one data word as a space reference. This fixup
request is not currently supported.
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R_REPEATED_INIT
Copy L bytes from the input subspace, replicating the
data to fill M bytes in the output subspace.
R_PCREL_CALL Copy one instruction word with relocation. The word is
assumed to be a pc-relative procedure call instruction
(for example, BL). The target procedure is identified
by symbol S, and the parameter relocation bits are R.
R_ABS_CALL Copy one instruction word with relocation. The word is
assumed to be an absolute procedure call instruction
(for example, BLE). The target procedure is identified
by symbol S, and the parameter relocation bits are R.
R_DP_RELATIVE Copy one instruction word with relocation. The word is
assumed to be a dp-relative load or store instruction
(for example, ADDIL, LDW, STW). The target symbol is
identified by symbol S. The linker forms the
difference between the value of the symbol S and the
value of the symbol $global$. By convention, the value
of $global$ is always contained in register 27.
Instructions other than LDIL and ADDIL may have a small
constant in the displacement field of the instruction.
R_DLT_REL Copy one instruction word with relocation. The word is
assumed to be a register-r18-relative load or store
instruction (for example, LDW, LDO, STW). The target
symbol is identified by symbol S. The linker computes
a linkage table offset relative to register 18
(reserved for a linkage table pointer in position-
independent code) for the symbol S.
R_CODE_ONE_SYMBOL
Copy one instruction word with relocation. The word is
assumed to be an instruction referring to symbol S (for
example, LDIL, LDW, BE). Instructions other than LDIL
and ADDIL may have a small constant in the displacement
field of the instruction.
R_MILLI_REL Copy one instruction word with relocation. The word is
assumed to be a short millicode call instruction (for
example, BLE). The linker forms the difference between
the value of the target symbol S and the value of
symbol 1 in the module's symbol table. By convention,
the value of symbol 1 should have been previously
loaded into the base register used in the BLE
instruction. The instruction may have a small constant
in the displacement field of the instruction.
R_CODE_PLABEL Copy one instruction word with relocation. The word is
assumed to be part of a code sequence forming a
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procedure label (for example, LDIL, LDO), referring to
symbol S. The LDO instruction should contain the value
0 (no static link) or 2 (static link required) in its
displacement field.
R_BREAKPOINT Copy one instruction word conditionally. On HP-UX, the
linker always replaces the word with a NOP instruction.
R_ENTRY Define a procedure entry point. The stack unwind bits,
U, and the frame size, F, are recorded in a stack
unwind descriptor.
R_ALT_ENTRY Define an alternate procedure entry point.
R_EXIT Define a procedure exit point.
R_BEGIN_TRY Define the beginning of a try/recover region.
R_END_TRY Define the end of a try/recover region. The offset R
defines the distance in bytes from the end of the
region to the beginning of the recover block.
R_BEGIN_BRTAB Define the beginning of a branch table.
R_END_BRTAB Define the end of a branch table.
R_AUX_UNWIND Define an auxiliary unwind table. CN is a symbol index
of the symbol that labels the beginning of the
compilation unit string table. SN is the offset,
relative to the CN symbol, of the scope name string.
SK is an integer specifying the scope kind.
R_STATEMENT Define the beginning of statement number N.
R_SEC_STATEMENT
Define the beginning of a secondary statement number N.
R_DATA_EXPR Pop one word from the expression stack and copy one
data word from the input subspace to the output
subspace, adding the popped value to it.
R_CODE_EXPR Pop one word from the expression stack, and copy one
instruction word from the input subspace to the output
subspace, adding the popped value to the displacement
field of the instruction.
R_FSEL Use an F' field selector for the next fixup request
instead of the default appropriate for the instruction.
R_LSEL Use an L-class field selector for the next fixup
request instead of the default appropriate for the
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instruction. Depending on the current rounding mode,
L', LS', LD', or LR' may be used.
R_RSEL Use an R-class field selector for the next fixup
request instead of the default appropriate for the
instruction. Depending on the current rounding mode,
R', RS', RD', or RR' may be used.
R_N_MODE Select round-down mode (L'/R'). This is the default
mode at the beginning of each subspace. This setting
remains in effect until explicitly changed or until the
end of the subspace.
R_S_MODE Select round-to-nearest-page mode (LS'/RS'). This
setting remains in effect until explicitly changed or
until the end of the subspace.
R_D_MODE Select round-up mode (LD'/RD'). This setting remains
in effect until explicitly changed or until the end of
the subspace.
R_R_MODE Select round-down-with-adjusted-constant mode
(LR'/RR'). This setting remains in effect until
explicitly changed or until the end of the subspace.
R_DATA_OVERRIDE
Use the constant V for the next fixup request in place
of the constant from the data word or instruction in
the input subspace.
R_TRANSLATED Toggle ``translated'' mode. This fixup request is
generated only by the linker during a relocatable link
to indicate a subspace that was originally read from an
old-format relocatable object file.
R_COMP1 Stack operations. The second byte of this fixup
request contains a secondary opcode. In the
descriptions below, A refers to the top of the stack
and B refers to the next item on the stack. All items
on the stack are considered signed 32-bit integers.
R_PUSH_PCON1 Push the (positive) constant
V.
R_PUSH_DOT Push the current virtual
address.
R_MAX Pop A and B, then push max(A,
B).
R_MIN Pop A and B, then push min(A,
B).
R_ADD Pop A and B, then push A + B.
R_SUB Pop A and B, then push B - A.
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R_MULT Pop A and B, then push A * B.
R_DIV Pop A and B, then push B / A.
R_MOD Pop A and B, then push B % A.
R_AND Pop A and B, then push A & B.
R_OR Pop A and B, then push A | B.
R_XOR Pop A and B, then push A XOR
B.
R_NOT Replace A with its complement.
R_LSHIFT If C = 0, pop A and B, then
push B << A. Otherwise,
replace A with A << C.
R_ARITH_RSHIFT If C = 0, pop A and B, then
push B >> A. Otherwise,
replace A with A >> C. The
shifting is done with sign
extension.
R_LOGIC_RSHIFT If C = 0, pop A and B, then
push B >> A. Otherwise,
replace A with A >> C. The
shifting is done with zero
fill.
R_PUSH_NCON1 Push the (negative) constant
V.
R_COMP2 More stack operations.
R_PUSH_PCON2 Push the (positive) constant
V.
R_PUSH_SYM Push the value of the symbol
S.
R_PUSH_PLABEL Push the value of a procedure
label for symbol S. The
static link bit is L.
R_PUSH_NCON2 Push the (negative) constant
V.
R_COMP3 More stack operations.
R_PUSH_PROC Push the value of the
procedure entry point S. The
parameter relocation bits are
R.
R_PUSH_CONST Push the constant V.
R_PREV_FIXUP The linker keeps a queue of the last four unique
multi-byte fixup requests; this is an abbreviation for
a fixup request identical to one on the queue. The
queue index X references one of the four; X = 0 refers
to the most recent. As a side effect of this fixup
request, the referenced fixup is moved to the front of
the queue.
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R_RESERVED Fixups in this range are reserved for internal use by
the compilers and linker.
The following table shows the mnemonic fixup request type and length
and parameter information for each range of opcodes. In the
parameters column, the symbol D refers to the difference between the
opcode and the beginning of the range described by that table entry;
the symbols B1, B2, B3, and B4 refer to the value of the next one,
two, three, or four bytes of the fixup request, respectively.
center; lB cB cB lB lf4 c n lf4p+1.
mnemonic opcodes lengthparameters _
R_NO_RELOCATION 0-23 1L = (D+1) * 4 24-
27 2 L = (D<<8 + B1 + 1) * 4 28-
30 3 L = (D<<16 + B2 + 1) * 4
31 4 L = B3 + 1
R_ZEROES 32 2L = (B1 + 1) * 4
33 4 L = B3 + 1
R_UNINIT 34 2L = (B1 + 1) * 4
35 4 L = B3 + 1
R_RELOCATION 36 1none
R_DATA_ONE_SYMBOL 37 2S = B1
38 4 S = B3
R_DATA_PLABEL 39 2S = B1
40 4 S = B3
R_SPACE_REF 41 1none
R_REPEATED_INIT 42 2L = 4; M = (B1 + 1) * 4
43 3 L = B1 * 4; M = (B1 + 1) * L
44 5 L = B1 * 4; M = (B3 + 1) * 4
45 8 L = B3 + 1; M = B4 + 1
R_PCREL_CALL 48-57 2R = rbits1(D); S = B1
58-59 3 R = rbits2(D<<8 + B1); S = B1
60-61 5 R = rbits2(D<<8 + B1); S = B3
R_ABS_CALL 64-73 2R = rbits1(D); S = B1
74-75 3 R = rbits2(D<<8 + B1); S = B1
76-77 5 R = rbits2(D<<8 + B1); S = B3
R_DP_RELATIVE 80-111 1S = D
112 2 S = B1
113 4 S = B3
R_DLT_REL 120 2S = B1
121 4 S = B3
R_CODE_ONE_SYMBOL 128-159 1S = D
160 2 S = B1
161 2 S = B3
R_MILLI_REL 174 2S = B1
175 4 S = B3
R_CODE_PLABEL 176 2S = B1
177 4 S = B3
R_BREAKPOINT 178 1none
R_ENTRY 179 9U,F = B8 (U is 37 bits; F is 27
bits) 180 6 U = B5 >> 3; F = pop A
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R_ALT_ENTRY 181 1none
R_EXIT 182 1none
R_BEGIN_TRY 183 1none
R_END_TRY 184 1R = 0
185 2 R = B1 * 4
186 4 R = B3 * 4
R_BEGIN_BRTAB 187 1none
R_END_BRTAB 188 1none
R_STATEMENT 189 2N = B1
190 3 N = B2
191 4 N = B3
R_DATA_EXPR 192 1none
R_CODE_EXPR 193 1none
R_FSEL 194 1none
R_LSEL 195 1none
R_RSEL 196 1none
R_N_MODE 197 1none
R_S_MODE 198 1none
R_D_MODE 199 1none
R_R_MODE 200 1none
R_DATA_OVERRIDE 201 1V = 0
202 2 V = B1
203 3 V = B2
204 4 V = B3
205 5 V = B4
R_TRANSLATED 206 1none
R_AUX_UNWIND 207 12CU,SN,SK = B11 (CU is 24 bits;
SN is 32 bits; SK is 32
bits) R_COMP1 208 2OP = B1; V = OP & 0x3f; C
= OP & 0x1f R_COMP2 209 5OP = B1; S = B3; L
= OP & 1; V = ((OP & 0x7f) <<
24) | S R_COMP3 210 6OP = B1; V = B4;
R = ((OP & 1) << 8) | (V >> 16);
S = V & 0xffffff
R_PREV_FIXUP 211-214 1X = D
R_SEC_STMT 215 1none
R_RESERVED 224-255 -reserved
Parameter relocation bits are encoded in the fixup requests in two
ways, noted as rbits1 and rbits2 in the above table. The first
encoding recognizes that the most common procedure calls have only
general register arguments with no holes in the parameter list. The
encoding for such calls is simply the number of parameters in general
registers (0 to 4), plus 5 if there is a return value in a general
register.
The second encoding is more complex; the 10 argument relocation bits
are compressed into 9 bits by eliminating some impossible
combinations. The encoding is the combination of three contributions.
The first contribution is the pair of bits for the return value, which
are not modified. The second contribution is 9 if the first two
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parameter words together form a double-precision parameter; otherwise,
it is 3 times the pair of bits for the first word plus the pair of
bits for the second word. Similarly, the third contribution is formed
based on the third and fourth parameter words. The second
contribution is multiplied by 40, the third is multiplied by 4, then
the three are added together.
Compiler Records
Compiler records are placed in relocatable files by each compiler or
assembler to identify the version of the compiler that was used to
produce the file. These records are copied into the executable file
by the linker, but are strippable. The structure of a compiler record
is shown below. All strings are contained in the symbol string table.
struct compilation_unit {
union name_pt name;
union name_pt language_name;
union name_pt product_id;
union name_pt version_id;
int reserved;
struct sys_clock compile_time;
struct sys_clock source_time;
};
SEE ALSO
as_300(1), as_800(1), cc(1), ld(1), nm_300(1), nm_800(1), strip(1),
crt0(3), end(3C), a.out_300(4), magic(4).
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