| a.out.5 (1639) | a.out.5 (5210) |
|---|---|
| 1.\" Copyright (c) 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This man page is derived from documentation contributed to Berkeley by 5.\" Donn Seeley at UUNET Technologies, Inc. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions --- 19 unchanged lines hidden (view full) --- 28.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33.\" SUCH DAMAGE. 34.\" 35.\" @(#)a.out.5 8.1 (Berkeley) 6/5/93 | 1.\" Copyright (c) 1991, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" This man page is derived from documentation contributed to Berkeley by 5.\" Donn Seeley at UUNET Technologies, Inc. 6.\" 7.\" Redistribution and use in source and binary forms, with or without 8.\" modification, are permitted provided that the following conditions --- 19 unchanged lines hidden (view full) --- 28.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 29.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 30.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 31.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 32.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 33.\" SUCH DAMAGE. 34.\" 35.\" @(#)a.out.5 8.1 (Berkeley) 6/5/93 |
| 36.\" $Id$ |
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| 36.\" 37.Dd June 5, 1993 38.Dt A.OUT 5 39.Os 40.Sh NAME 41.Nm a.out 42.Nd format of executable binary files 43.Sh SYNOPSIS --- 37 unchanged lines hidden (view full) --- 81Contains the character strings corresponding to the symbol names. 82.El 83.Pp 84Every binary file begins with an 85.Fa exec 86structure: 87.Bd -literal -offset indent 88struct exec { | 37.\" 38.Dd June 5, 1993 39.Dt A.OUT 5 40.Os 41.Sh NAME 42.Nm a.out 43.Nd format of executable binary files 44.Sh SYNOPSIS --- 37 unchanged lines hidden (view full) --- 82Contains the character strings corresponding to the symbol names. 83.El 84.Pp 85Every binary file begins with an 86.Fa exec 87structure: 88.Bd -literal -offset indent 89struct exec { |
| 89 unsigned short a_mid; 90 unsigned short a_magic; | 90 unsigned long a_midmag; |
| 91 unsigned long a_text; 92 unsigned long a_data; 93 unsigned long a_bss; 94 unsigned long a_syms; 95 unsigned long a_entry; 96 unsigned long a_trsize; 97 unsigned long a_drsize; 98}; 99.Ed 100.Pp 101The fields have the following functions: 102.Bl -tag -width a_trsize | 91 unsigned long a_text; 92 unsigned long a_data; 93 unsigned long a_bss; 94 unsigned long a_syms; 95 unsigned long a_entry; 96 unsigned long a_trsize; 97 unsigned long a_drsize; 98}; 99.Ed 100.Pp 101The fields have the following functions: 102.Bl -tag -width a_trsize |
| 103.It Fa a_mid 104Contains a bit pattern that 105identifies binaries that were built for 106certain sub-classes of an architecture 107.Pq Sq machine IDs 108or variants of the operating system on a given architecture. 109The kernel may not support all machine IDs 110on a given architecture. 111The 112.Fa a_mid 113field is not present on some architectures; 114in this case, the 115.Fa a_magic 116field has type 117.Em unsigned long . 118.It Fa a_magic 119Contains a bit pattern 120.Pq Sq magic number 121that uniquely identifies binary files | 103.It Fa a_midmag 104This field is stored in host byte-order. 105It has a number of sub-components accessed by the macros 106.Dv N_GETFLAG() , 107.Dv N_GETMID() , and 108.Dv N_GETMAGIC() , 109and set by the macro 110.Dv N_SETMAGIC(). 111.Pp 112The macro 113.Dv N_GETFLAG() 114returns a few flags: 115.Bl -tag -width EX_DYNAMIC 116.It Dv EX_DYNAMIC 117indicates that the executable requires the services of the run-time link editor. 118.It Dv EX_PIC 119indicates that the object contains position independent code. This flag is 120set by 121.Xr as 1 122when given the 123.Sq -k 124flag and is preserved by 125.Xr ld 1 126if necessary. 127.El 128.Pp 129If both EX_DYNAMIC and EX_PIC are set, the object file is a position indendent 130executable image (eg. a shared library), which is to be loaded into the 131process address space by the run-time link editor. 132.Pp 133The macro 134.Dv N_GETMID() 135returns the machine-id. 136This indicates which machine(s) the binary is intended to run on. 137.Pp 138.Dv N_GETMAGIC() 139specifies the magic number, which uniquely identifies binary files |
| 122and distinguishes different loading conventions. 123The field must contain one of the following values: 124.Bl -tag -width ZMAGIC 125.It Dv OMAGIC 126The text and data segments immediately follow the header 127and are contiguous. 128The kernel loads both text and data segments into writable memory. 129.It Dv NMAGIC --- 59 unchanged lines hidden (view full) --- 189structure: 190.Bd -literal -offset indent 191struct relocation_info { 192 int r_address; 193 unsigned int r_symbolnum : 24, 194 r_pcrel : 1, 195 r_length : 2, 196 r_extern : 1, | 140and distinguishes different loading conventions. 141The field must contain one of the following values: 142.Bl -tag -width ZMAGIC 143.It Dv OMAGIC 144The text and data segments immediately follow the header 145and are contiguous. 146The kernel loads both text and data segments into writable memory. 147.It Dv NMAGIC --- 59 unchanged lines hidden (view full) --- 207structure: 208.Bd -literal -offset indent 209struct relocation_info { 210 int r_address; 211 unsigned int r_symbolnum : 24, 212 r_pcrel : 1, 213 r_length : 2, 214 r_extern : 1, |
| 197 : 4; | 215 r_baserel : 1, 216 r_jmptable : 1, 217 r_relative : 1, 218 r_copy : 1; |
| 198}; 199.Ed 200.Pp 201The 202.Fa relocation_info 203fields are used as follows: 204.Bl -tag -width r_symbolnum 205.It Fa r_address --- 26 unchanged lines hidden (view full) --- 232Set if this relocation requires an external reference; 233the link editor must use a symbol address to update the pointer. 234When the 235.Fa r_extern 236bit is clear, the relocation is 237.Sq local ; 238the link editor updates the pointer to reflect 239changes in the load addresses of the various segments, | 219}; 220.Ed 221.Pp 222The 223.Fa relocation_info 224fields are used as follows: 225.Bl -tag -width r_symbolnum 226.It Fa r_address --- 26 unchanged lines hidden (view full) --- 253Set if this relocation requires an external reference; 254the link editor must use a symbol address to update the pointer. 255When the 256.Fa r_extern 257bit is clear, the relocation is 258.Sq local ; 259the link editor updates the pointer to reflect 260changes in the load addresses of the various segments, |
| 240rather than changes in the value of a symbol. | 261rather than changes in the value of a symbol (except when 262.Fa r_baserel 263is also set (see below). |
| 241In this case, the content of the 242.Fa r_symbolnum 243field is an 244.Fa n_type 245value (see below); 246this type field tells the link editor 247what segment the relocated pointer points into. | 264In this case, the content of the 265.Fa r_symbolnum 266field is an 267.Fa n_type 268value (see below); 269this type field tells the link editor 270what segment the relocated pointer points into. |
| 271.It Fa r_baserel 272If set, the symbol, as identified by the 273.Fa r_symbolnum 274field, is to be relocated to an offset into the Global Offset Table. 275At run-time, the entry in the Global Offset Table at this offset is set to 276be the address of the symbol. 277.It Fa r_jmptable 278If set, the symbol, as identified by the 279.Fa r_symbolnum 280field, is to be relocated to an offset into the Procedure Linkage Table. 281.It Fa r_relative 282If set, this relocation is relative to the (run-time) load address of the 283image this object file is going to be a part of. This type of relocation 284only occurs in shared objects. 285.It Fa r_copy 286If set, this relocation record identifies a symbol whose contents should 287be copied to the location given in 288.Fa r_address. 289The copying is done by the run-time link-editor from a suitable data 290item in a shared object. |
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| 248.El 249.Pp 250Symbols map names to addresses (or more generally, strings to values). 251Since the link-editor adjusts addresses, 252a symbol's name must be used to stand for its address 253until an absolute value has been assigned. 254Symbols consist of a fixed-length record in the symbol table 255and a variable-length name in the string table. --- 85 unchanged lines hidden (view full) --- 341The 342.Dv N_STAB 343mask selects bits of interest to symbolic debuggers 344such as 345.Xr gdb 1 ; 346the values are described in 347.Xr stab 5 . 348.It Fa n_other | 291.El 292.Pp 293Symbols map names to addresses (or more generally, strings to values). 294Since the link-editor adjusts addresses, 295a symbol's name must be used to stand for its address 296until an absolute value has been assigned. 297Symbols consist of a fixed-length record in the symbol table 298and a variable-length name in the string table. --- 85 unchanged lines hidden (view full) --- 384The 385.Dv N_STAB 386mask selects bits of interest to symbolic debuggers 387such as 388.Xr gdb 1 ; 389the values are described in 390.Xr stab 5 . 391.It Fa n_other |
| 349This field is currently unused. | 392This field provides information on the nature of the symbol independent of 393the symbol's location in terms of segments as determined by the 394.Fa n_type 395field. Currently, the lower 4 bits of the 396.Fa n_other 397field hold one of two values: 398.Dv AUX_FUNC 399and 400.Dv AUX_OBJECT 401.Po 402see 403.Aq Pa link.h 404for their definitions 405.Pc . 406.Dv AUX_FUNC 407associates the symbol with a callable function, while 408.Dv AUX_OBJECT 409associates the symbol with data, irrespective of their locations in 410either the text or the data segment. 411This field is intended to be used by 412.Xr ld 1 413for the construction of dynamic executables. |
| 350.It Fa n_desc 351Reserved for use by debuggers; passed untouched by the link editor. 352Different debuggers use this field for different purposes. 353.It Fa n_value 354Contains the value of the symbol. 355For text, data and bss symbols, this is an address; 356for other symbols (such as debugger symbols), 357the value may be arbitrary. 358.El 359.Pp 360The string table consists of an 361.Em unsigned long 362length followed by null-terminated symbol strings. 363The length represents the size of the entire table in bytes, 364so its minimum value (or the offset of the first string) 365is always 4 on 32-bit machines. 366.Sh SEE ALSO | 414.It Fa n_desc 415Reserved for use by debuggers; passed untouched by the link editor. 416Different debuggers use this field for different purposes. 417.It Fa n_value 418Contains the value of the symbol. 419For text, data and bss symbols, this is an address; 420for other symbols (such as debugger symbols), 421the value may be arbitrary. 422.El 423.Pp 424The string table consists of an 425.Em unsigned long 426length followed by null-terminated symbol strings. 427The length represents the size of the entire table in bytes, 428so its minimum value (or the offset of the first string) 429is always 4 on 32-bit machines. 430.Sh SEE ALSO |
| 431.Xr as 1 , 432.Xr gdb 1 , |
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| 367.Xr ld 1 , | 433.Xr ld 1 , |
| 434.Xr brk 2 , |
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| 368.Xr execve 2 , 369.Xr nlist 3 , 370.Xr core 5 , 371.Xr dbx 5 , | 435.Xr execve 2 , 436.Xr nlist 3 , 437.Xr core 5 , 438.Xr dbx 5 , |
| 372.Xr stab 5 | 439.Xr stab 5 , 440.Xr link 5 |
| 373.Sh HISTORY 374The 375.Pa a.out.h 376include file appeared in 377.At v7 . 378.Sh BUGS 379Since not all of the supported architectures use the | 441.Sh HISTORY 442The 443.Pa a.out.h 444include file appeared in 445.At v7 . 446.Sh BUGS 447Since not all of the supported architectures use the |
| 380.Fa a_mid | 448.Fa a_midmag |
| 381field, 382it can be difficult to determine what 383architecture a binary will execute on 384without examining its actual machine code. 385Even with a machine identifier, 386the byte order of the 387.Fa exec 388header is machine-dependent. 389.Pp 390Nobody seems to agree on what 391.Em bss 392stands for. 393.Pp 394New binary file formats may be supported in the future, 395and they probably will not be compatible at any level 396with this ancient format. | 449field, 450it can be difficult to determine what 451architecture a binary will execute on 452without examining its actual machine code. 453Even with a machine identifier, 454the byte order of the 455.Fa exec 456header is machine-dependent. 457.Pp 458Nobody seems to agree on what 459.Em bss 460stands for. 461.Pp 462New binary file formats may be supported in the future, 463and they probably will not be compatible at any level 464with this ancient format. |