[llvm-dev] wrap with symver and LTO

[Gilles Vollant via llvm-dev]

Hello,

 

I've a c++ program  which use log function

 

 

When I compile under Ubuntu 20.04 (or Debian 11 frezze version), the binary
is linked to function log of GLIBC 2.29

I need distribute the binary to Ubuntu 18.04 (and 16.04) computer.

 

My first solution is 

 

which I compile with clang 12 on Ubuntu 20.04 (or Debian 11 frezze version).

 

(Somes peoples had same problem with memcpy)

https://stackoverflow.com/questions/8823267/linking-against-older-symbol-ver
sion-in-a-so-file

https://stackoverflow.com/questions/36461555/is-it-possible-to-statically-li
nk-libstdc-and-wrap-memcpy

https://gist.github.com/nicky-zs/7541169

 

So I add this switch on link command line: -Wl,--wrap=log

 

And I compile in a .C file:

 

 

double __log_glibc_2_2_5(double x);

asm(".symver __log_glibc_2_2_5, log at GLIBC_2.2.5 <mailto:log at GLIBC_2.2.5> ");

 

double __wrap_log(double x)

{

    return __log_glibc_2_2_5(x);

}

 

 

This is perfect Clang WITHOUT Link Time Optimisation. The solution is also
fine with GCC (with and without LTO)

With Clang+LTO, the first call of log do an infinite loop and program never
stop

.

My workaround with clang LTO is using a more complex dlopen/dlsym stuff in
my __wrap_log function.

 

 

Do you think there is a possible solution?

 

Regards

Gilles Vollant

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