Re: [DynInst_API:] Binary Rewriting using wrapFunction

[Sergej Proskurin <prosig@xxxxxxx>]

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Hello,

> On 15.12.2014 19:38, Josh Stone wrote:

> Note that GCC may use builtin versions of some libc functions, and
> make transformations for efficiency.  For instance, if you didn't
> compile with -fno-builtin-printf, a call like printf("%s\n", str)
> might be translated to puts(str).

I know about this but this should not present any troubles, thanks :)

> How about: 3) Use an LD_PRELOAD approach to insert your custom
> function, and dlsym RTLD_NEXT if that still needs to call the
> original.  You'd have to write your code in its own library, of
> course.  Then you can either use LD_PRELOAD directly, or use
> dyninst loadLibrary -- although I'm not sure if that lets you
> ensure the order of loading.  And this approach will only work with
> dynamic functions, not statically linked.

The LD_PRELOAD approach should work quite well for dynamically linked
library functions. And if it is possible to determine whether a
function in question is statically or dynamically linked, the program
could be designed in such a way that it wraps statically linked
library functions with help of the mentioned BPatch_wrapFunction(...).

Regarding the function "BPatch::loadLibrary(...)":
I have been using it to load my own library filled with predefined
wrappers for shared libraries into the address space of the mutatee.
However, that led to the behaviour, described above: Wrappers to
dynamic function calls are not preserved, when the binary is
statically rewritten (however it works when the process is
instrumented at runtime). Or did I miss something?

I thought (hoped) that Dyninst BPatch::loadLibrary(...) internally
modifies the dynamic symbol tables of the ELF file so that the wrapped
calls will be preserved after binary rewriting :)

Thank you for your help.

Best regards,
Sergej

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