SPRUI03E June 2015 – January 2023
Identify Global Symbols
.global symbol1[, ... ,symboln]
.def symbol1[, ... ,symboln]
.ref symbol1[, ... ,symboln]
Three directives identify global symbols that are defined externally or can be referenced externally:
The .def directive identifies a symbol that is defined in the current module and can be accessed by other files. The assembler places this symbol in the symbol table.
The .ref directive identifies a symbol that is used in the current module but is defined in another module. The linker resolves this symbol's definition at link time.
The .global directive acts as a .ref or a .def, as needed.
A global symbol is defined in the same manner as any other symbol; that is, it appears as a label or is defined by the .set, .equ, .bss or .usect directive. If a global symbol is defined more than once, the linker issues a multiple-definition error. (The assembler can provide a similar multiple-definition error for local symbols.) The .ref directive always creates a symbol table entry for a symbol, whether the module uses the symbol or not; .global, however, creates an entry only if the module actually uses the symbol.
A symbol can be declared global for either of two reasons:
This example shows four files. The file1.lst and file2.lst refer to each other for all symbols used; file3.lst and file4.lst are similarly related.
The file1.lst and file3.lst files are equivalent. Both files define the symbol INIT and make it available to other modules; both files use the external symbols X, Y, and Z. Also, file1.lst uses the .global directive to identify these global symbols; file3.lst uses .ref and .def to identify the symbols.
The file2.lst and file4.lst files are equivalent. Both files define the symbols X, Y, and Z and make them available to other modules; both files use the external symbol INIT. Also, file2.lst uses the .global directive to identify these global symbols; file4.lst uses .ref and .def to identify the symbols.
file1.lst
1 ; Global symbol defined in this file
2 .global INIT
3 ; Global symbols defined in file2.lst
4 .global X, Y, Z
5 00000000 INIT:
6 00000000 00902058 ADD.L1 0x01,A4,A1
7 00000004 00000000! .word X
8 ; .
9 ; .
10 ; .
11 .endfile2.lst
1 ; Global symbols defined in this file
2 .global X, Y, Z
3 ; Global symbol defined in file1.lst
4 .global INIT
5 00000001 X: .set 1
6 00000002 Y: .set 2
7 00000003 Z: .set 3
8 00000000 00000000! .word INIT
9 ; .
10 ; .
11 ; .
12 .end file3.lst
1 ; Global symbol defined in this file
2 .def INIT
3 ; Global symbols defined in file4.lst
4 .ref X, Y, Z
5 00000000 INIT:
6 00000000 00902058 ADD.L1 0x01,A4,A1
7 00000004 00000000! .word X
8 ; .
9 ; .
10 ; .
11 .end file4.lst
1 ; Global symbols defined in this file
2 .def X, Y, Z
3 ; Global symbol defined in file3.lst
4 .ref INIT
5 00000001 X: .set 1
6 00000002 Y: .set 2
7 00000003 Z: .set 3
8 00000000 00000000! .word INIT
9 ; .
10 ; .
11 ; .
12 .end