C++ objcopy to make class method weak
-1
I have this header file:
weather.h
#ifndef _WEATHER_H_
#define _WEATHER_H_
#include <string>
using namespace std;
class Weather {
private:
int temp;
public:
Weather();
string announce();
};
#endif
When I compile the related source file, I want to make announce and Weather (the default constructor) weak during compile time.
To do so, the flow looks something like:
g++ -std=c++11 -g -Wall -c weather.cpp
objcopy --weaken-symbol=announce --weaken-symbol=Weather weather.o weather.o
However, when I then compile another version of weather without the weakening? I still get a duplicate symbol error.
I know --weaken exists, but this is just a sample and I do not want to blanket weaken every method in the class.
c++ g++ clang
asked Nov 26 '18 at 0:18
jajabarrjajabarr
8112
add a comment |
-1
I have this header file:
weather.h
#ifndef _WEATHER_H_
#define _WEATHER_H_
#include <string>
using namespace std;
class Weather {
private:
int temp;
public:
Weather();
string announce();
};
#endif
When I compile the related source file, I want to make announce and Weather (the default constructor) weak during compile time.
To do so, the flow looks something like:
g++ -std=c++11 -g -Wall -c weather.cpp
objcopy --weaken-symbol=announce --weaken-symbol=Weather weather.o weather.o
However, when I then compile another version of weather without the weakening? I still get a duplicate symbol error.
I know --weaken exists, but this is just a sample and I do not want to blanket weaken every method in the class.
c++ g++ clang
asked Nov 26 '18 at 0:18
jajabarrjajabarr
8112
Can you post the relevantreadelflines from both weather.o files to confirm one is weak and the other is not? Does using--weaken-symbol announcewithout the equals sign make any difference?
– Paul
Nov 26 '18 at 0:23
Your C++ compiler, like every other C++ compiler in existence, uses name mangling. You need to figure out the mangled names of the constructor and announce. I can guarantee you, with 100% certainty, that it's not "Weather" and "announce".
– Sam Varshavchik
Nov 26 '18 at 0:31
@Paul Objdump isn't showing any weak symbols, and I'm seeing different behavior than when I manually insert weak attributes in the header file (which I don't want to do) SamVarshavchik even when I specify the mangled symbol name it does not work
– jajabarr
Nov 26 '18 at 3:07
@jajabarr Seems to work fine for me. I'll add my solution in an answer
– Paul
Nov 26 '18 at 3:26
This doesn’t address the question, but names that begin with an underscore followed by a capital letter (_WEATHER_H_) and names that contain two consecutive underscores are reserved for use by the implementation. Don’t use them in your code.
– Pete Becker
Nov 26 '18 at 3:48
add a comment |
-1
-1
-1
I have this header file:
weather.h
#ifndef _WEATHER_H_
#define _WEATHER_H_
#include <string>
using namespace std;
class Weather {
private:
int temp;
public:
Weather();
string announce();
};
#endif
When I compile the related source file, I want to make announce and Weather (the default constructor) weak during compile time.
To do so, the flow looks something like:
g++ -std=c++11 -g -Wall -c weather.cpp
objcopy --weaken-symbol=announce --weaken-symbol=Weather weather.o weather.o
However, when I then compile another version of weather without the weakening? I still get a duplicate symbol error.
I know --weaken exists, but this is just a sample and I do not want to blanket weaken every method in the class.
c++ g++ clang
asked Nov 26 '18 at 0:18
jajabarrjajabarr
8112
I have this header file:
weather.h
#ifndef _WEATHER_H_
#define _WEATHER_H_
#include <string>
using namespace std;
class Weather {
private:
int temp;
public:
Weather();
string announce();
};
#endif
When I compile the related source file, I want to make announce and Weather (the default constructor) weak during compile time.
To do so, the flow looks something like:
g++ -std=c++11 -g -Wall -c weather.cpp
objcopy --weaken-symbol=announce --weaken-symbol=Weather weather.o weather.o
However, when I then compile another version of weather without the weakening? I still get a duplicate symbol error.
I know --weaken exists, but this is just a sample and I do not want to blanket weaken every method in the class.
c++ g++ clang
c++ g++ clang
asked Nov 26 '18 at 0:18
jajabarrjajabarr
8112
asked Nov 26 '18 at 0:18
jajabarrjajabarr
8112
asked Nov 26 '18 at 0:18
jajabarrjajabarr
8112
asked Nov 26 '18 at 0:18
jajabarrjajabarr
8112
asked Nov 26 '18 at 0:18
jajabarrjajabarr
8112
8112
Can you post the relevantreadelflines from both weather.o files to confirm one is weak and the other is not? Does using--weaken-symbol announcewithout the equals sign make any difference?
– Paul
Nov 26 '18 at 0:23
Your C++ compiler, like every other C++ compiler in existence, uses name mangling. You need to figure out the mangled names of the constructor and announce. I can guarantee you, with 100% certainty, that it's not "Weather" and "announce".
– Sam Varshavchik
Nov 26 '18 at 0:31
@Paul Objdump isn't showing any weak symbols, and I'm seeing different behavior than when I manually insert weak attributes in the header file (which I don't want to do) SamVarshavchik even when I specify the mangled symbol name it does not work
– jajabarr
Nov 26 '18 at 3:07
@jajabarr Seems to work fine for me. I'll add my solution in an answer
– Paul
Nov 26 '18 at 3:26
This doesn’t address the question, but names that begin with an underscore followed by a capital letter (_WEATHER_H_) and names that contain two consecutive underscores are reserved for use by the implementation. Don’t use them in your code.
– Pete Becker
Nov 26 '18 at 3:48
add a comment |
Can you post the relevantreadelflines from both weather.o files to confirm one is weak and the other is not? Does using--weaken-symbol announcewithout the equals sign make any difference?
– Paul
Nov 26 '18 at 0:23
Your C++ compiler, like every other C++ compiler in existence, uses name mangling. You need to figure out the mangled names of the constructor and announce. I can guarantee you, with 100% certainty, that it's not "Weather" and "announce".
– Sam Varshavchik
Nov 26 '18 at 0:31
@Paul Objdump isn't showing any weak symbols, and I'm seeing different behavior than when I manually insert weak attributes in the header file (which I don't want to do) SamVarshavchik even when I specify the mangled symbol name it does not work
– jajabarr
Nov 26 '18 at 3:07
@jajabarr Seems to work fine for me. I'll add my solution in an answer
– Paul
Nov 26 '18 at 3:26
This doesn’t address the question, but names that begin with an underscore followed by a capital letter (_WEATHER_H_) and names that contain two consecutive underscores are reserved for use by the implementation. Don’t use them in your code.
– Pete Becker
Nov 26 '18 at 3:48
Can you post the relevant
readelf lines from both weather.o files to confirm one is weak and the other is not? Does using --weaken-symbol announce without the equals sign make any difference?– Paul
Nov 26 '18 at 0:23
Can you post the relevant
readelf lines from both weather.o files to confirm one is weak and the other is not? Does using --weaken-symbol announce without the equals sign make any difference?– Paul
Nov 26 '18 at 0:23
Your C++ compiler, like every other C++ compiler in existence, uses name mangling. You need to figure out the mangled names of the constructor and announce. I can guarantee you, with 100% certainty, that it's not "Weather" and "announce".
– Sam Varshavchik
Nov 26 '18 at 0:31
Your C++ compiler, like every other C++ compiler in existence, uses name mangling. You need to figure out the mangled names of the constructor and announce. I can guarantee you, with 100% certainty, that it's not "Weather" and "announce".
– Sam Varshavchik
Nov 26 '18 at 0:31
@Paul Objdump isn't showing any weak symbols, and I'm seeing different behavior than when I manually insert weak attributes in the header file (which I don't want to do) SamVarshavchik even when I specify the mangled symbol name it does not work
– jajabarr
Nov 26 '18 at 3:07
@Paul Objdump isn't showing any weak symbols, and I'm seeing different behavior than when I manually insert weak attributes in the header file (which I don't want to do) SamVarshavchik even when I specify the mangled symbol name it does not work
– jajabarr
Nov 26 '18 at 3:07
@jajabarr Seems to work fine for me. I'll add my solution in an answer
– Paul
Nov 26 '18 at 3:26
@jajabarr Seems to work fine for me. I'll add my solution in an answer
– Paul
Nov 26 '18 at 3:26
This doesn’t address the question, but names that begin with an underscore followed by a capital letter (
_WEATHER_H_) and names that contain two consecutive underscores are reserved for use by the implementation. Don’t use them in your code.– Pete Becker
Nov 26 '18 at 3:48
This doesn’t address the question, but names that begin with an underscore followed by a capital letter (
_WEATHER_H_) and names that contain two consecutive underscores are reserved for use by the implementation. Don’t use them in your code.– Pete Becker
Nov 26 '18 at 3:48
add a comment |
1 Answer
1
active
oldest
votes
1
Weakening the symbols in the one file and linking all the objects together works for me. Make sure you are relinking all the objects (including all constructors).
weather1.cpp
Weather::Weather() {}
string Weather::announce()
{
return string("Bad weather");
}
weather2.cpp
Weather::Weather() {}
string Weather::announce()
{
return string("Bad weather 2");
}
build.sh
g++ weather1.cpp -c -o weather1.o
g++ weather2.cpp -c -o weather2.o
g++ test.cpp -c -o test.o
objcopy --weaken-symbol=_ZN7Weather8announceEv --weaken-symbol=_ZN7WeatherC2Ev --weaken-symbol=_ZN7WeatherC1Ev weather2.o weather2.o
g++ *.o -o test.out
Depending on whether I weaken weather1.o or weather2.o, I see different outputs from my test main function:
int main()
{
Weather w;
std::cout << w.announce() << "n";
return 0;
}
answered Nov 26 '18 at 3:31
PaulPaul
3606
Similarly, it also works to weaken only certain symbols and redefine those in the other file.
– Paul
Nov 26 '18 at 3:35
Interesting to note that if both functions are marked weak, the first one in the final link command will be the one used.
– Paul
Nov 26 '18 at 3:52
This is what I ended up finding - Thank you! Funnily enough I had the code for this written but it wasn't working on mac. I found a bug thread saying objcopy had some issues with macOS and x86 architecture - I ended up having to run it in a linux VM to see any progress.
– jajabarr
Nov 27 '18 at 1:19
add a comment |
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1 Answer
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1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
1
Weakening the symbols in the one file and linking all the objects together works for me. Make sure you are relinking all the objects (including all constructors).
weather1.cpp
Weather::Weather() {}
string Weather::announce()
{
return string("Bad weather");
}
weather2.cpp
Weather::Weather() {}
string Weather::announce()
{
return string("Bad weather 2");
}
build.sh
g++ weather1.cpp -c -o weather1.o
g++ weather2.cpp -c -o weather2.o
g++ test.cpp -c -o test.o
objcopy --weaken-symbol=_ZN7Weather8announceEv --weaken-symbol=_ZN7WeatherC2Ev --weaken-symbol=_ZN7WeatherC1Ev weather2.o weather2.o
g++ *.o -o test.out
Depending on whether I weaken weather1.o or weather2.o, I see different outputs from my test main function:
int main()
{
Weather w;
std::cout << w.announce() << "n";
return 0;
}
answered Nov 26 '18 at 3:31
PaulPaul
3606
Similarly, it also works to weaken only certain symbols and redefine those in the other file.
– Paul
Nov 26 '18 at 3:35
Interesting to note that if both functions are marked weak, the first one in the final link command will be the one used.
– Paul
Nov 26 '18 at 3:52
This is what I ended up finding - Thank you! Funnily enough I had the code for this written but it wasn't working on mac. I found a bug thread saying objcopy had some issues with macOS and x86 architecture - I ended up having to run it in a linux VM to see any progress.
– jajabarr
Nov 27 '18 at 1:19
add a comment |
1
Weakening the symbols in the one file and linking all the objects together works for me. Make sure you are relinking all the objects (including all constructors).
weather1.cpp
Weather::Weather() {}
string Weather::announce()
{
return string("Bad weather");
}
weather2.cpp
Weather::Weather() {}
string Weather::announce()
{
return string("Bad weather 2");
}
build.sh
g++ weather1.cpp -c -o weather1.o
g++ weather2.cpp -c -o weather2.o
g++ test.cpp -c -o test.o
objcopy --weaken-symbol=_ZN7Weather8announceEv --weaken-symbol=_ZN7WeatherC2Ev --weaken-symbol=_ZN7WeatherC1Ev weather2.o weather2.o
g++ *.o -o test.out
Depending on whether I weaken weather1.o or weather2.o, I see different outputs from my test main function:
int main()
{
Weather w;
std::cout << w.announce() << "n";
return 0;
}
answered Nov 26 '18 at 3:31
PaulPaul
3606
Similarly, it also works to weaken only certain symbols and redefine those in the other file.
– Paul
Nov 26 '18 at 3:35
Interesting to note that if both functions are marked weak, the first one in the final link command will be the one used.
– Paul
Nov 26 '18 at 3:52
This is what I ended up finding - Thank you! Funnily enough I had the code for this written but it wasn't working on mac. I found a bug thread saying objcopy had some issues with macOS and x86 architecture - I ended up having to run it in a linux VM to see any progress.
– jajabarr
Nov 27 '18 at 1:19
add a comment |
1
1
1
Weakening the symbols in the one file and linking all the objects together works for me. Make sure you are relinking all the objects (including all constructors).
weather1.cpp
Weather::Weather() {}
string Weather::announce()
{
return string("Bad weather");
}
weather2.cpp
Weather::Weather() {}
string Weather::announce()
{
return string("Bad weather 2");
}
build.sh
g++ weather1.cpp -c -o weather1.o
g++ weather2.cpp -c -o weather2.o
g++ test.cpp -c -o test.o
objcopy --weaken-symbol=_ZN7Weather8announceEv --weaken-symbol=_ZN7WeatherC2Ev --weaken-symbol=_ZN7WeatherC1Ev weather2.o weather2.o
g++ *.o -o test.out
Depending on whether I weaken weather1.o or weather2.o, I see different outputs from my test main function:
int main()
{
Weather w;
std::cout << w.announce() << "n";
return 0;
}
answered Nov 26 '18 at 3:31
PaulPaul
3606
Weakening the symbols in the one file and linking all the objects together works for me. Make sure you are relinking all the objects (including all constructors).
weather1.cpp
Weather::Weather() {}
string Weather::announce()
{
return string("Bad weather");
}
weather2.cpp
Weather::Weather() {}
string Weather::announce()
{
return string("Bad weather 2");
}
build.sh
g++ weather1.cpp -c -o weather1.o
g++ weather2.cpp -c -o weather2.o
g++ test.cpp -c -o test.o
objcopy --weaken-symbol=_ZN7Weather8announceEv --weaken-symbol=_ZN7WeatherC2Ev --weaken-symbol=_ZN7WeatherC1Ev weather2.o weather2.o
g++ *.o -o test.out
Depending on whether I weaken weather1.o or weather2.o, I see different outputs from my test main function:
int main()
{
Weather w;
std::cout << w.announce() << "n";
return 0;
}
answered Nov 26 '18 at 3:31
PaulPaul
3606
answered Nov 26 '18 at 3:31
PaulPaul
3606
answered Nov 26 '18 at 3:31
PaulPaul
3606
answered Nov 26 '18 at 3:31
PaulPaul
3606
3606
Similarly, it also works to weaken only certain symbols and redefine those in the other file.
– Paul
Nov 26 '18 at 3:35
Interesting to note that if both functions are marked weak, the first one in the final link command will be the one used.
– Paul
Nov 26 '18 at 3:52
This is what I ended up finding - Thank you! Funnily enough I had the code for this written but it wasn't working on mac. I found a bug thread saying objcopy had some issues with macOS and x86 architecture - I ended up having to run it in a linux VM to see any progress.
– jajabarr
Nov 27 '18 at 1:19
add a comment |
Similarly, it also works to weaken only certain symbols and redefine those in the other file.
– Paul
Nov 26 '18 at 3:35
Interesting to note that if both functions are marked weak, the first one in the final link command will be the one used.
– Paul
Nov 26 '18 at 3:52
This is what I ended up finding - Thank you! Funnily enough I had the code for this written but it wasn't working on mac. I found a bug thread saying objcopy had some issues with macOS and x86 architecture - I ended up having to run it in a linux VM to see any progress.
– jajabarr
Nov 27 '18 at 1:19
Similarly, it also works to weaken only certain symbols and redefine those in the other file.
– Paul
Nov 26 '18 at 3:35
Similarly, it also works to weaken only certain symbols and redefine those in the other file.
– Paul
Nov 26 '18 at 3:35
Interesting to note that if both functions are marked weak, the first one in the final link command will be the one used.
– Paul
Nov 26 '18 at 3:52
Interesting to note that if both functions are marked weak, the first one in the final link command will be the one used.
– Paul
Nov 26 '18 at 3:52
This is what I ended up finding - Thank you! Funnily enough I had the code for this written but it wasn't working on mac. I found a bug thread saying objcopy had some issues with macOS and x86 architecture - I ended up having to run it in a linux VM to see any progress.
– jajabarr
Nov 27 '18 at 1:19
This is what I ended up finding - Thank you! Funnily enough I had the code for this written but it wasn't working on mac. I found a bug thread saying objcopy had some issues with macOS and x86 architecture - I ended up having to run it in a linux VM to see any progress.
– jajabarr
Nov 27 '18 at 1:19
add a comment |
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Can you post the relevant
readelflines from both weather.o files to confirm one is weak and the other is not? Does using--weaken-symbol announcewithout the equals sign make any difference?– Paul
Nov 26 '18 at 0:23
Your C++ compiler, like every other C++ compiler in existence, uses name mangling. You need to figure out the mangled names of the constructor and announce. I can guarantee you, with 100% certainty, that it's not "Weather" and "announce".
– Sam Varshavchik
Nov 26 '18 at 0:31
@Paul Objdump isn't showing any weak symbols, and I'm seeing different behavior than when I manually insert weak attributes in the header file (which I don't want to do) SamVarshavchik even when I specify the mangled symbol name it does not work
– jajabarr
Nov 26 '18 at 3:07
@jajabarr Seems to work fine for me. I'll add my solution in an answer
– Paul
Nov 26 '18 at 3:26
This doesn’t address the question, but names that begin with an underscore followed by a capital letter (
_WEATHER_H_) and names that contain two consecutive underscores are reserved for use by the implementation. Don’t use them in your code.– Pete Becker
Nov 26 '18 at 3:48