It looks like it has to do with the gcc typechecking. Since CURLINFO_TLS_SSL_PTR is internally treated categorized as slist type that may be why. But then if this is a problem I'm a little bit puzzled why nobody has ever reported it before.

The type should be struct curl_tlssessioninfo not struct curl_slist, What do you mean you tried to replace and what is segfaulting? Can you show the code?

Below is the code snippet
// struct curl_tlssessioninfo *tls_ssl = NULL; commented out due to compilation issue
struct curl_slist *tls_ssl = NULL;
curl_easy_getinfo(curl_handle, CURLINFO_TLS_SSL_PTR, &tls_ssl);
if (tls_ssl && tls_ssl->data) // NULL checking
{
printf("tls_ssl ->data = %s\n", tls_ssl->data); // --> This is the place where segfault occur
}

Please let me know how to resolve the compilation issue when use "struct curl_tlssessioninfo"

I don't think that tls_ssl->data is a NULL-terminated string. I'd guess that printf simply reads too much because of that and this is the cause of the segfault.

This cannot be the cause of segfault. Even it occur if i just access the first character of tls_ssl->data[0]. It seems the type should be struct curl_tlssessioninfo. How to solve the compilation issue?

See #1525 for my suggested fix.