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diff --git a/man/10/a.out b/man/10/a.out new file mode 100644 index 00000000..6e5841d0 --- /dev/null +++ b/man/10/a.out @@ -0,0 +1,242 @@ +.TH A.OUT 10.6 +.SH NAME +a.out \- native kernel object file format +.SH SYNOPSIS +.B #include <a.out.h> +.SH DESCRIPTION +An executable native binary file has up to six sections: +a header, the program text, the data, +a symbol table, a PC/SP offset table (MC680x0 only), +and finally a PC/line number table. +The header, given by a structure in +.BR <a.out.h> , +contains 4-byte integers in big-endian order: +.PP +.EX +typedef struct Exec { + long magic; /* magic number */ + long text; /* size of text segment */ + long data; /* size of initialized data */ + long bss; /* size of uninitialized data */ + long syms; /* size of symbol table */ + long entry; /* entry point */ + long spsz; /* size of pc/sp offset table */ + long pcsz; /* size of pc/line number table */ +} Exec; +#define _MAGIC(b) ((((4*b)+0)*b)+7) +#define A_MAGIC _MAGIC(8) /* 68020 */ +#define I_MAGIC _MAGIC(11) /* intel 386 */ +#define J_MAGIC _MAGIC(12) /* intel 960 */ +#define K_MAGIC _MAGIC(13) /* sparc */ +#define V_MAGIC _MAGIC(16) /* mips 3000 */ +#define X_MAGIC _MAGIC(17) /* att dsp 3210 */ +#define M_MAGIC _MAGIC(18) /* mips 4000 */ +#define D_MAGIC _MAGIC(19) /* amd 29000 */ +#define E_MAGIC _MAGIC(20) /* arm 7-something */ +#define Q_MAGIC _MAGIC(21) /* powerpc */ +#define N_MAGIC _MAGIC(22) /* mips 4000-le */ +#define L_MAGIC _MAGIC(23) /* dec alpha */ +.EE +.DT +.PP +Sizes are expressed in bytes. +The size of the header is not included in any of the other sizes. +.PP +When a Plan 9 binary file is executed, +a memory image of three segments is +set up: the text segment, the data segment, and the stack. +The text segment begins at a virtual address which is +a multiple of the machine-dependent page size. +The text segment consists of the header and the first +.B text +bytes of the binary file. +The +.B entry +field gives the virtual address of the entry point of the program. +The data segment starts at the first page-rounded virtual address +after the text segment. +It consists of the next +.B data +bytes of the binary file, followed by +.B bss +bytes initialized to zero. +The stack occupies the highest possible locations +in the core image, automatically growing downwards. +.PP +The next +.B syms +(possibly zero) +bytes of the file contain symbol table +entries, each laid out as: +.IP +.EX +uchar value[4]; +char type; +char name[\f2n\fP]; /* NUL-terminated */ +.EE +.PP +The +.B value +is in big-endian order and +the size of the +.B name +field is not pre-defined: it is a zero-terminated array of +variable length. +.PP +The +.B type +field is one of the following characters: +.RS +.TP +.B T +text segment symbol +.PD0 +.TP +.B t +static text segment symbol +.TP +.B L +leaf function text segment symbol +.TP +.B l +static leaf function text segment symbol +.TP +.B D +data segment symbol +.TP +.B d +static data segment symbol +.TP +.B B +bss segment symbol +.TP +.B b +static bss segment symbol +.TP +.B a +automatic (local) variable symbol +.TP +.B p +function parameter symbol +.RE +.PD +.PP +A few others are described below. +The symbols in the symbol table appear in the same order +as the program components they describe. +.PP +The Plan 9 compilers implement a virtual stack frame pointer rather +than dedicating a register; +moreover, on the MC680x0 +there is a variable offset between the stack pointer and the +frame pointer. +Following the symbol table, +MC680x0 executable files contain a +.BR spsz -byte +table encoding the offset +of the stack frame pointer as a function of program location; +this section is not present for other architectures. +The PC/SP table is encoded as a byte stream. +By setting the PC to the base of the text segment +and the offset to zero and interpreting the stream, +the offset can be computed for any PC. +A byte value of 0 is followed by four bytes that hold, in big-endian order, +a constant to be added to the offset. +A byte value of 1 to 64 is multiplied by four and added, without sign +extension, to the offset. +A byte value of 65 to 128 is reduced by 64, multiplied by four, and +subtracted from the offset. +A byte value of 129 to 255 is reduced by 129, multiplied by the quantum +of instruction size +(e.g. two on the MC680x0), +and added to the current PC without changing the offset. +After any of these operations, the instruction quantum is added to the PC. +.PP +A similar table, occupying +.BR pcsz -bytes, +is the next section in an executable; it is present for all architectures. +The same algorithm may be run using this table to +recover the absolute source line number from a given program location. +The absolute line number (starting from zero) counts the newlines +in the C-preprocessed source seen by the compiler. +Three symbol types in the main symbol table facilitate conversion of the absolute +number to source file and line number: +.RS +.TP +.B f +source file name components +.TP +.B z +source file name +.TP +.B Z +source file line offset +.RE +.PP +The +.B f +symbol associates an integer (the +.B value +field of the `symbol') with +a unique file path name component (the +.B name +of the `symbol'). +These path components are used by the +.B z +symbol to represent a file name: the +first byte of the name field is always 0; the remaining +bytes hold a zero-terminated array of 16-bit values (in big-endian order) +that represent file name components from +.B f +symbols. +These components, when separated by slashes, form a file name. +The initial slash of a file name is recorded in the symbol table by an +.B f +symbol; when forming file names from +.B z +symbols an initial slash is not to be assumed. +The +.B z +symbols are clustered, one set for each object file in the program, +before any text symbols from that object file. +The set of +.B z +symbols for an object file form a +.I history stack +of the included source files from which the object file was compiled. +The value associated with each +.B z +symbol is the absolute line number at which that file was included in the source; +if the name associated with the +.B z +symbol is null, the symbol represents the end of an included file, that is, +a pop of the history stack. +If the value of the +.B z +symbol is 1 (one), +it represents the start of a new history stack. +To recover the source file and line number for a program location, +find the text symbol containing the location +and then the first history stack preceding the text symbol in the symbol table. +Next, interpret the PC/line offset table to discover the absolute line number +for the program location. +Using the line number, scan the history stack to find the set of source +files open at that location. +The line number within the file can be found using the line numbers +in the history stack. +The +.B Z +symbols correspond to +.B #line +directives in the source; they specify an adjustment to the line number +to be printed by the above algorithm. The offset is associated with the +first previous +.B z +symbol in the symbol table. +.SH "SEE ALSO" +.IR acid (10.1), +.IR 2a (10.1), +.IR 2l (10.1), +.IR inm (10.1) +.SH BUGS +There is no type information in the symbol table. |