HACKING.md

MODIFYING OPENSSL SOURCE

This document describes the way to add custom modifications to OpenSSL sources.

If you are adding new C source files

Please update the build.info files in the directories where you placed the C source files, to include a line like this for each new C source file:

• In crypto/ or any of its subdirectories (intended for libcrypto):

  SOURCE[../libcrypto]={name-of-C-source-file}
  

• In ssl/ or any of its subdirectories (intended for libssl):

  SOURCE[../libssl]={name-of-C-source-file}
  

Do note that the path given as the SOURCE attribute must be adapted appropriately for the location of the build.info file, as it's a relative path to where the library itself is built, for example:

• For crypto/build.info, the library path should be ../libcrypto

• For crypto/evp/build.info, the library path should be ../../libcrypto

• For ssl/build.info, the library path should be ../libssl

• For ssl/quic/build.info, the library path should be ../../libssl

To know more about build.info files, please read doc/internal/man7/build.info.pod. For better viewing, consider converting it to HTML or PDF using pod2html or pod2pdf.

Adding new public functions

If you are adding new public functions to the custom library build, you need to either add a prototype in one of the existing OpenSSL header files, or provide a new header file and edit.

Only headers in the include/openssl subdirectory are considered for public functions. If you're creating a new header file, it must be located in that directory.

Functions declared in include/openssl header files are assumed to be part of the libcrypto library unless specified otherwise. If your new functions are meant for the libssl library, you will need to edit Configurations/unix-Makefile.tmpl and add the header file name in the array my @sslheaders_tmpl.

Updating OpenSSL's bookkeeping files

OpenSSL has a few bookkeeping files to keep track of exposed functions, most importantly util/libcrypto.num and util/libssl.num. Any time a new public function - as defined above - is added, these files must be updated.

To make such an update, please do the following:

./Configure -Werror --strict-warnings [your-options]
make update

If you plan to submit the changes you made to OpenSSL (see CONTRIBUTING.md), it's also worth running the following after running make update, to ensure that documentation has correct format.

make doc-nits

Do note that make update also generates files related to OIDs (in the crypto/objects/ folder) and errors messages.

If a git merge error occurs in one of these generated files, then the generated files need to be removed and regenerated using make update. To aid in this process, the generated files can be committed separately so they can be removed easily by reverting that commit.