ref: 8a788aea84aad3bfbd5b39d78c1925654f3b9e14
dir: /man/6/sbl/
.TH SBL 6 .SH NAME sbl \- symbol table file .SH DESCRIPTION A Limbo symbol table file provides type information for the module in an associated Dis executable file, for use by debuggers and similar applications. They are written by the Limbo compiler when given the .B -g option. The files conventionally have a .B .sbl suffix; they need not be stored in the same directory as the corresponding Dis file. .PP The file consists of a header followed by five tables: .IP .I "header file-table pc-table type-table fn-table data-table" .PP Each table starts with a line containing a decimal count of the items in that table. The count can be zero. The following sections describe the format of table items in each table. In the description, the following terminals are used. .PP A .I "string" is a sequence of letters, digits, and the characters _, ., -, and >. Letters are the Unicode characters a through z and A through Z, and all Unicode characters with encoded values greater than A0 hexadecimal. .PP An .I int is an optional minus sign followed by a sequence of digits, 0 to 9. .PP In the following description, the presence of a space is represented by .B • and a newline by .BR \en . There are no other spaces between syntactic elements in the file format. Other special characters represent themselves. .SS Header .PP The header consists of two items. .ds Os "\v'0.2m'\s-3\|opt\s+3\^\v'-0.2m' .IP .EX .ft I .nf header: magic\f5\en\fP module\f5\en\fP magic: \f5limbo .sbl 2.0\fP module: string .ft R .EE .PP There have been two previous versions of symbol table format, distinguished by the number in .IR magic . Version .B 1. was the original; version .B 1.1 added more references back to the source; and version .B 2.0 replaced the original adt table by a type table and added support for Limbo's .B pick construction. Only version 2.0 is described here; the others are obsolete. .PP .I Module is the name of the module implemented in the Dis file. Symbol file references to identifiers declared by the implementation module are unqualified. A name referenced that is imported from any other module is preceded by .IB m -> where .I m is that module's identifier. .SS File table The file table is a list of file names referenced by the rest of the tables. Each file name is terminated by a newline character; within the name, any character other than a newline is valid. .SS PC table The PC table relates every instruction in the Dis file to the source from which it was compiled. The table is indexed by Dis PC to obtain a reference to the corresponding source. Each item consists of a source description and a statement reference: .IP .EX .ft I pc-item: src stmt \f5\en\fP src: pos\f5,\fPpos• pos: file\f5:\fP\*(Os line\f5.\fP\*(Os char file, line, char, stmt: int .ft R .EE .PP A source description .I src selects source text as a range of characters within lines of a source file. .I File is an index into the file table (origin 0); .I "line" and .I "char" are positions within that source file, with line numbers starting at 1 and character positions at 0. If .I "file" or .I "line" is omitted, it is assumed to have the previous value, or 0 if there is no previous value. .PP .I Stmt is the `statement number' of the instruction. Despite its name, the scope of a statement number is smaller than a Limbo statement: it identifies a region marked by the compiler for treatment as a unit when debugging. For instance, in a .B for statement, the initial expression, increment, test, and body all have unique statement numbers. All instructions compiled from the same region in a Limbo program have the same statement number. The number is that of the innermost region that contains the instruction. .SS Type table The type table describes the Limbo adts used in the Dis file, both locally declared and imported. Each entry describes a .IR type : .IP .EX .I "type:" .ft 5 @ \fItype-index\fP \en a \fIadt-item\fP p \fIadt-item\fP \fItag-table\fP t \fIsize\fP . \fIid-table\fP m \fImodule\fP \en \fIsrc\fP A \fItype\fP C \fItype\fP F \fIfn-name\fP \fItype\fP L \fItype\fP R \fItype\fP n N B b i f s .ft I type-index: int .EE .PP Each leading character specifies a different Limbo type: .IP .RS .TF N .TP 5n .B @ existing type referenced by type table index (not self-referential) .TP .B A .B array of .I type .TP .B a .B adt without .B pick .TP .B B .B big .TP .B b .B byte .TP .B C .B chan of .I type .TP .B F .B fn returning .I type .TP .B f .B real .TP .B i .B int .TP .B L .B list of .I type .TP .B m .B module .TP .B N .BR nil 's type .TP .B n no type (eg, function with no return type) .TP .B p .B adt with .B pick .TP .B R .B ref .I type .TP .B s .B string .TP .B t tuple .PD .RE .PP A .I type-index is an offset in the type table, representing the corresponding type. .I Size is the size in bytes of a value of the given type. The size of basic types is known and does not appear explicitly: .B big and .B real are 64 bits; all others including strings and reference types are 4 bytes. (Strings are represented internally by a pointer.) .PP Each .I "id-table" is preceded by a count of the number of entries, followed by an .I id-item for each entry in the table: .IP .EX .ft I id-table: count \f5\en\fP id-items id-item: id-offset \f5:\fP id-name \f5:\fP src type \f5\en\fP id-offset: int id-name: string count: int .ft R .EE .PP .I Id-offset is the number of bytes from the start of the enclosing object to the value of the object identified by .IR "id-name" . .PP An adt without a .B pick clause is described using an .IR adt-item : .IP .EX .ft I adt-item: adt-name • src size \f5\en\fP id-table adt-name: string size: int .ft R .EE .PP The .I id-table has an entry for every data element of .IR "adt-name" . .PP If an adt has a .B pick clause, the adt's type table entry uses the .B p type character. The invariant part of the adt is described by an .I adt-item (with zero .IR size ) and the variant clause is described by a .I tag-table of the following form: .IP .EX .ft I tag-table: count \f5\en\fP tag-items tag-item: name \f5:\fP src size \f5\en\fP id-table \f1|\fP name \f5:\fP src \f5\en\fP .ft R .EE .PP The .I tag-table describes the variants of a Limbo adt that includes a .B pick clause. The .I name is the .B pick tag for the associated alternative. If the .I size and .I id-table are missing, the given variant has the same description as the previous one. .PP A tuple's .I id-table contains .I id-names of the form .BI t n, where .I n is the 0-origin index of the item in the tuple. .PP .I Src is as previously defined above in the PC table section. .SS Fn table The function table describes each function implemented by the Dis file. .IP .EX .ft I fn-item: fn-pc \f5:\fP fn-name \f5\en\fP args locals return fn-pc: int fn-name: string args, locals: id-table return: type .ft R .EE .PP .I Fn-pc is the starting pc for the Dis instructions for .IR "fn-name" . If the function is a member of an adt, the member name is qualified by the adt name, so that .I fn-name has the form .IB `adt-name . member-name'. Within the .I id-tables for .I args and .IR locals , the .I "id-offset" fields give offsets relative to the function's activation frame. Furthermore, no table entries are made for .I args that are declared .B nil (unused). .SS Data table The data table describes the global variables in the Dis file. It is an .IR "id-table" , with one entry for each global variable. .SH SEE ALSO .IR limbo (1), .IR wm-deb (1), .IR debug (2), .IR dis (6)