Problem compiling many Rosetta Code Nim programs: could not load: libgmp.dylib

[Ryan Carsten Schmidt]

On Dec 31, 2024, at 19:06, Kenneth Wolcott wrote:
> 
> 3. MacPorts port: nim
>   4. nimble is the Nim package manager which comes with the nim port.
>   4. nimble install bignum (seems to successfully install, but I wonder if it is silently installing an x86-64 pre-compiled binary??)
>   5. compile using: nim c ./arithmetic_geometric_mean_calculate_pi
>   6. execute: ./arithmetic_geometric_mean_calculate_pi

I agree, on my Intel Mac with macOS 12 this produces:

could not load: libgmp.dylib
(compile with -d:nimDebugDlOpen for more information)

However it succeeds if I run it this way:

DYLD_FALLBACK_LIBRARY_PATH=/opt/local/lib ./arithmetic_geometric_mean_calculate_pi

Computed 25000 digits in 103 ms
π = 3.141592653589793238...81377399510065895288...

Anytime a program requires you to set DYLD_LIBRARY_PATH or DYLD_FALLBACK_LIBRARY_PATH, the developers are doing it wrong.

The gmp nimble module that the bignum nimble module is using evidently tries to use the gmp library by dlopening it. On macOS, it is necessary to pass the absolute path to the library to be opened, and they are evidently not doing that and are only passing the library name. That may be common on Linux but it is not done that way on macOS. macOS is not Linux. 

Using dlopen at all is not recommended on macOS and has worse performance than doing it the "normal" way, which is to link with the dynamic library.

I'm not sure whether the bug is only in the gmp nimble module or is more pervasive. In searching for this error, I've found reports of it with other libraries as well. It may be a design flaw in nimble or nim that needs a central solution.

I did not find a bug report tracking this problem. I found many reports of problems like this but they all end with the suggestion to set the environment variable, which is just a workaround and not a fix.