diff options
Diffstat (limited to 'share/man/man5/a.out.5')
| -rw-r--r-- | share/man/man5/a.out.5 | 120 |
1 files changed, 94 insertions, 26 deletions
diff --git a/share/man/man5/a.out.5 b/share/man/man5/a.out.5 index 9ad2876572db..f1869995895a 100644 --- a/share/man/man5/a.out.5 +++ b/share/man/man5/a.out.5 @@ -33,6 +33,7 @@ .\" SUCH DAMAGE. .\" .\" @(#)a.out.5 8.1 (Berkeley) 6/5/93 +.\" $Id$ .\" .Dd June 5, 1993 .Dt A.OUT 5 @@ -86,8 +87,7 @@ Every binary file begins with an structure: .Bd -literal -offset indent struct exec { - unsigned short a_mid; - unsigned short a_magic; + unsigned long a_midmag; unsigned long a_text; unsigned long a_data; unsigned long a_bss; @@ -100,25 +100,43 @@ struct exec { .Pp The fields have the following functions: .Bl -tag -width a_trsize -.It Fa a_mid -Contains a bit pattern that -identifies binaries that were built for -certain sub-classes of an architecture -.Pq Sq machine IDs -or variants of the operating system on a given architecture. -The kernel may not support all machine IDs -on a given architecture. -The -.Fa a_mid -field is not present on some architectures; -in this case, the -.Fa a_magic -field has type -.Em unsigned long . -.It Fa a_magic -Contains a bit pattern -.Pq Sq magic number -that uniquely identifies binary files +.It Fa a_midmag +This field is stored in host byte-order. +It has a number of sub-components accessed by the macros +.Dv N_GETFLAG() , +.Dv N_GETMID() , and +.Dv N_GETMAGIC() , +and set by the macro +.Dv N_SETMAGIC(). +.Pp +The macro +.Dv N_GETFLAG() +returns a few flags: +.Bl -tag -width EX_DYNAMIC +.It Dv EX_DYNAMIC +indicates that the executable requires the services of the run-time link editor. +.It Dv EX_PIC +indicates that the object contains position independent code. This flag is +set by +.Xr as 1 +when given the +.Sq -k +flag and is preserved by +.Xr ld 1 +if necessary. +.El +.Pp +If both EX_DYNAMIC and EX_PIC are set, the object file is a position indendent +executable image (eg. a shared library), which is to be loaded into the +process address space by the run-time link editor. +.Pp +The macro +.Dv N_GETMID() +returns the machine-id. +This indicates which machine(s) the binary is intended to run on. +.Pp +.Dv N_GETMAGIC() +specifies the magic number, which uniquely identifies binary files and distinguishes different loading conventions. The field must contain one of the following values: .Bl -tag -width ZMAGIC @@ -194,7 +212,10 @@ struct relocation_info { r_pcrel : 1, r_length : 2, r_extern : 1, - : 4; + r_baserel : 1, + r_jmptable : 1, + r_relative : 1, + r_copy : 1; }; .Ed .Pp @@ -237,7 +258,9 @@ bit is clear, the relocation is .Sq local ; the link editor updates the pointer to reflect changes in the load addresses of the various segments, -rather than changes in the value of a symbol. +rather than changes in the value of a symbol (except when +.Fa r_baserel +is also set (see below). In this case, the content of the .Fa r_symbolnum field is an @@ -245,6 +268,26 @@ field is an value (see below); this type field tells the link editor what segment the relocated pointer points into. +.It Fa r_baserel +If set, the symbol, as identified by the +.Fa r_symbolnum +field, is to be relocated to an offset into the Global Offset Table. +At run-time, the entry in the Global Offset Table at this offset is set to +be the address of the symbol. +.It Fa r_jmptable +If set, the symbol, as identified by the +.Fa r_symbolnum +field, is to be relocated to an offset into the Procedure Linkage Table. +.It Fa r_relative +If set, this relocation is relative to the (run-time) load address of the +image this object file is going to be a part of. This type of relocation +only occurs in shared objects. +.It Fa r_copy +If set, this relocation record identifies a symbol whose contents should +be copied to the location given in +.Fa r_address. +The copying is done by the run-time link-editor from a suitable data +item in a shared object. .El .Pp Symbols map names to addresses (or more generally, strings to values). @@ -346,7 +389,28 @@ such as the values are described in .Xr stab 5 . .It Fa n_other -This field is currently unused. +This field provides information on the nature of the symbol independent of +the symbol's location in terms of segments as determined by the +.Fa n_type +field. Currently, the lower 4 bits of the +.Fa n_other +field hold one of two values: +.Dv AUX_FUNC +and +.Dv AUX_OBJECT +.Po +see +.Aq Pa link.h +for their definitions +.Pc . +.Dv AUX_FUNC +associates the symbol with a callable function, while +.Dv AUX_OBJECT +associates the symbol with data, irrespective of their locations in +either the text or the data segment. +This field is intended to be used by +.Xr ld 1 +for the construction of dynamic executables. .It Fa n_desc Reserved for use by debuggers; passed untouched by the link editor. Different debuggers use this field for different purposes. @@ -364,12 +428,16 @@ The length represents the size of the entire table in bytes, so its minimum value (or the offset of the first string) is always 4 on 32-bit machines. .Sh SEE ALSO +.Xr as 1 , +.Xr gdb 1 , .Xr ld 1 , +.Xr brk 2 , .Xr execve 2 , .Xr nlist 3 , .Xr core 5 , .Xr dbx 5 , -.Xr stab 5 +.Xr stab 5 , +.Xr link 5 .Sh HISTORY The .Pa a.out.h @@ -377,7 +445,7 @@ include file appeared in .At v7 . .Sh BUGS Since not all of the supported architectures use the -.Fa a_mid +.Fa a_midmag field, it can be difficult to determine what architecture a binary will execute on |