Add suffix to mbedtls_log to avoid link name conflict error

[Taowyoo]

Summary of Changes in this PR

This PR addresses the link name conflict error that occurs when using different versions of the mbedtls crate in a single project, by adopting the approach used in PR #234.

Rationale Behind the Approach

During testing, it was discovered that simply renaming mbedtls_log resolves the linking error. Therefore, the export_name attribute is employed here, as done in PR #243.

Upon further investigation, it was found that the linker error stems from multiple definitions of mbedtls_log in the Rust code. The C compiler attempts to locate and link the mbedtls_log function implemented in Rust to the C library, but it encounters duplicate instances of the function with the same name.

It's important to note that the linking search direction is from C to Rust, so naming on the C side is not a concern. Functions named mbedtls_printf in multiple rust_printf.c files are similar to other functions in the C mbedtls code and do not cause link name conflict errors.

[jethrogb]

I'm not convinced this actually works, or at least you fail to explain how this works. There are certainly multiple global symbols named mbedtls_printf in the compiled objects, so this should result in symbol conflicts. Even if it "works", this basically means one mbedtls_printf implementation is picked at random, which would result in surprising behavior at best.

Functions named mbedtls_printf in multiple rust_printf.c files are similar to other functions in the C mbedtls code

This doesn't make sense to me

[Taowyoo]

I got your point. You're correct

I had wrong understanding here

Functions named mbedtls_printf in multiple rust_printf.c files are similar to other functions in the C mbedtls code.

Let me rephrase what happened here:

First, compiler will compile rust_printf.c to rust_printf.o where: mbedtls_log is Undefined symbol and mbedtls_printf is local defined symbol

# part output of `nm rust_printf.o`
                 U mbedtls_log
0000000000000000 T mbedtls_printf

So compiler try to find mbedtls_log in rust compiled objects and here is where original error occurs.
And by changing name of mbedtls_log , this error is resolved by this PR.

But there indeed are multiple mbedtls_printf in multiple rust_printf.o. By inspecting to the compiled libmbedtls-abc.rlib files, the the content of rust_printf.o is being placed to the rlib file correspondingly because mbedtls rlib file is compiled separately by the build.rs script.

So I guess the reason why compiler do not throw conflict error here is: it does not detect the usage/re-export on mbedtls_printf, but this is not guaranteed in runtime and the behavior on runtime will become undefined.

In short, the approach in this PR does not solve the problem correctly.

I will close this PR, and could you please review the approve the #244 if it's ok?