Red Hat ENTERPRISE LINUX 3 - USING ID Using Instructions page 29

Chapter 3. Invocation
This message occurs when some (sub)expression accesses an address ultimately given by the
sum of two constants (Win32 import tables only allow one). Instances where this may occur
include accesses to member fields of struct variables imported from a DLL, as well as using
a constant index into an array variable imported from a DLL. Any multiword variable (arrays,
structs, long long, etc) may trigger this error condition. However, regardless of the exact data
type of the offending exported variable, ld will always detect it, issue the warning, and exit.
There are several ways to address this difficulty, regardless of the data type of the exported
variable:
One way is to use -enable-runtime-pseudo-reloc switch. This leaves the task of adjusting ref-
erences in your client code for runtime environment, so this method works only when runtime
environtment supports this feature.
A second solution is to force one of the 'constants' to be a variable - that is, unknown and un-
optimizable at compile time. For arrays, there are two possibilities: a) make the indexee (the
array's address) a variable, or b) make the 'constant' index a variable. Thus:
extern type extern_array[];
extern_array[1] --
{ volatile type *t=extern_array; t[1] }
or
extern type extern_array[];
extern_array[1] --
{ volatile int t=1; extern_array[t] }
For structs (and most other multiword data types) the only option is to make the struct itself (or
the long long, or the ...) variable:
extern struct s extern_struct;
extern_struct.field --
{ volatile struct s *t=&extern_struct; t-
or
extern long long extern_ll;
extern_ll --
{ volatile long long * local_ll=&extern_ll; *local_ll }
A third method of dealing with this difficulty is to abandon 'auto-import' for the offending
symbol and mark it with
ing compile-time #defines to indicate whether you are building a DLL, building client code that
will link to the DLL, or merely building/linking to a static library. In making the choice between
the various methods of resolving the 'direct address with constant offset' problem, you should
consider typical real-world usage:
Original:
--foo.h
extern int arr[];
--foo.c
#include "foo.h"
void main(int argc, char **argv){
printf("%d\n",arr[1]);
}
Solution 1:
--foo.h
extern int arr[];
--foo.c
#include "foo.h"
void main(int argc, char **argv){
/* This workaround is for win32 and cygwin; do not "optimize" */
volatile int *parr = arr;
printf("%d\n",parr[1]);
}
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__declspec(dllimport)
field }
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. However, in practice that requires us-
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