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POAdd functions in gdb at runtime
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copied!<p>I'm trying to debug some STL based C++ code in gdb. The code has something like </p> <pre><code>int myfunc() { std::map<int,int> m; ... } </code></pre> <p>Now in gdb, inside myfunc using "print m" gives something very ugly. What I've seen recommended is compiling something like</p> <pre><code>void printmap( std::map<int,int> m ) { for( std::map<int,int>::iterator it = ... ) { printf("%d : %d", it->first, it->second ); } } </code></pre> <p>Then in gdb doing</p> <pre><code>(gdb) call printmap( m ) </code></pre> <p>This seems like a good way to handle the issue... but can I put printmap into a seperate object file (or even dynamic library) that I then load into gdb at runtime rather than compiling it into my binary - as recompiling the binary every time I want to look at another STL variable is not fun .. while compiling and loading a single .o file for the print routine may be acceptable.</p> <hr> <p>UPDATE:</p> <p>Prompted by Nikolais suggestion I'm looking at dlopen/dlsym.</p> <p>So I haven't yet got this working but it feels like I'm getting closer.</p> <p>In printit.cpp</p> <pre><code>#include <stdio.h> extern "C" void printit() { printf("OMG Fuzzies"); } </code></pre> <p>Compile to a .so using </p> <pre><code>g++ -Wall -g -fPIC -c printit.cpp g++ -shared -Wl,-undefined,dynamic_lookup -o printit.so printit.o </code></pre> <p>Start my test application and load the .so using dlopen ( 2 = RTLD_NOW ) then try to get the symbol for a debugging function using dlsym.</p> <pre><code>(gdb) break main (gdb) run (gdb) print (void*) dlopen("printit.so", 2 ) $1 = (void *) 0x100270 (gdb) print (void*) dlsym( 0x100270, "_printit" ) $2 = (void *) 0x0 </code></pre> <p>So close but for some reason I cant get that symbol... ( I cant even get it if I put the dlopen/dlsym calls in my executable) I'm guessing I'm either compiling the lib wrong or using dlsym incorrectly.</p> <p>If I can get the symbol I'm assuming I can call the function using something like</p> <pre><code>(gdb) print (( void(*)() )(0x....))() </code></pre> <p>I'm compiling this on OS X 10.4, which might be causing some of my .so woes... any pointers would be appreciated.</p> <hr> <p>Found out how to get all this working. Have posted as a solution below.</p>

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