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offset-info option
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offset-info
option
-offset-info output-file
This option simplifies access
to C struct’s from assembler. For each member of each structure the compiler
will output a .equ
directive to associate with a symbol with the member’s offset in bytes
into the structure. The symbol itself is the concatenation of the structure’s
tag name and the member’s name, separated by an underscore.
This option will output,
to the specified output-file,
an assembler directive, .equ,
for each member of each structure found in each manipulation.
The .equ
directives for the structures in the header file can be obtained by using
the following input: gcc
-fsyntax-only -offset-info m.s -x c m.h.
m.h
is the header containing the structures, and m.s
holds the directives.
The following is a short
example of output produced by -offset-info.
input file (for example m.h):
struct W {
double d;
int I;
};
struct X {
int a;
int b;
struct Y {
int a;
int b;
};
struct Y y;
struct Y yy[10];
struct Y* p;
}
output file (for example m.s):
.equ W_d,0
9ef
; .equ W_i,8
.equ Y_a,0
.equ Y_b,4
.equ X_a,0
.equ X_b,4
.equ X_y,8
.equ X_yy,16
.equ X_p,96
-offset-info
has the following caveats.
-
No directives are output for
bit-field members.
-
No directives are output for
members whose offsets (as measured in bits) is greater than the word size
of the host.
-
No directives are output for
members whose offsets are not constants. This can happen only in structures
that use some GCC specific extensions allowing for variable sized members.
-
-fargument-alias
-
-fargument-noalias
-
-fargument-noalias-global
Specify the
possible relationships among parameters and between parameters and global
data.
-fargument-alias
specifies that arguments (parameters) may alias each other and may alias
global storage. -fargument-noalias
specifies that arguments do not alias each other, but may alias global
storage. -fargument-noalias-global
specifies that arguments do not alias each other and do not alias global
storage.
Each language will automatically
use whatever option is required by the language standard. You should not
need to use these options yourself.
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