Hi,
I have a DLL library which declares an "extern __thread int iTlsExtern"
variable, which I can access from the library and from a program.
However, modifications made from the library to iTlsExtern are not
seen from the program.
This seems to come from the fact that the address of the variable
from the library is different from the address from the program.
I'm using gcc 4.8.2, binutils 2.24, mingw-w64-v3.0.0,
pthreads-w32-2-9-1-release. The program is compiled in 64-bit mode.
My test program is given below (files lib.h, lib.c, prog.c and Makefile).
Running prog displays two different values for &iTlsExtern depending
on the address being taken from main or the library. After doing
iTlsExtern=2 in the library, the output from the library is correct but
the output from main is not.
Is there something wrong with the code, the feature macros (from lib.h)
or the compilation flags in the Makefile)?
Is there something else I can provide to investigate the problem?
--
Daniel Villeneuve
----- lib.h
#ifndef LIB_H
#define LIB_H
#ifndef _POSIX_C_SOURCE
#define _POSIX_C_SOURCE 200809L
#endif
#ifndef _MT
#define _MT 1
#endif
#include <stdio.h>
#define EXPORT __declspec(dllexport)
#define IMPORT __declspec(dllimport)
#define thread_local __thread
extern thread_local LIB_DLLPORT int iTlsExtern;
extern LIB_DLLPORT void LibDebug(void);
extern LIB_DLLPORT void LibInit(int);
#endif
----- lib.c
#include "lib.h"
thread_local int iTlsExtern;
void LibDebug(void)
{
fprintf(stderr, "&iTlsExtern (from LibDebug) = %p\n", (void
*)&iTlsExtern);
fprintf(stderr, " iTlsExtern (from LibDebug) = %d\n", iTlsExtern);
}
void LibInit(int i)
{
fprintf(stderr, " setting iTlsExtern to %d (from LibDebug)\n", i);
iTlsExtern = i;
}
----- prog.c
#include <stdio.h>
#include "lib.h"
static void MainDebug(void)
{
fprintf(stderr, "&iTlsExtern (from MainDebug) = %p\n", (void
*)&iTlsExtern);
fprintf(stderr, " iTlsExtern (from MainDebug) = %d\n", iTlsExtern);
}
int main(void)
{
MainDebug();
LibDebug();
LibInit(2);
MainDebug();
LibDebug();
return 0;
}
----- Makefile
CROSS=x86_64-w64-mingw32-
.PHONY: all clean
all: prog.exe
clean:
rm -f prog.exe prog.o liblib.dll.a lib.dll lib.o
prog.exe: prog.o lib.dll
$(CROSS)gcc -std=gnu11 -o prog.exe prog.o \
-Wl,--add-stdcall-alias -Wl,--export-all-symbols -L. -llib -lpthread
prog.o: prog.c lib.h
$(CROSS)gcc -std=gnu11 -DLIB_DLLPORT=IMPORT -o prog.o -c prog.c
lib.dll: lib.o
$(CROSS)gcc -Wl,--out-implib=liblib.dll.a -o lib.dll lib.o \
-shared -Wl,-hliblib.dll.a -Wl,--add-stdcall-alias
-Wl,--export-all-symbols -lpthread
lib.o: lib.c lib.h
$(CROSS)gcc -std=gnu11 -DLIB_DLLPORT=EXPORT -o lib.o -c lib.c
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