On Fri, 6 Dec 2024 15:04:42 GMT, Magnus Ihse Bursie <i...@openjdk.org> wrote:
> For various reasons, we have added some extra flags to the compiler command
> line when compiling C/C++ for static libraries. This is a blocker for the
> goal of compiling once, linking twice for static and dynamic library.
> Fortunately, these extra flags are not needed.
>
> Note that `-DSTATIC_BUILD=1` is still kept, but set in
> `SetupNativeCompilation`. Going forward, this flag should only be sent to the
> very small set of files that actually need to know if we're creating a static
> or dynamic library. (But that is a future follow-up.)
>
> The flags I removed, with rationales for removing them:
> * (gcc/clang) `ffunction-sections -fdata-sections`: This forces the compiler
> to create a separate section for each and every function and data entry. The
> idea is that the linker can use this to get rid of dead code when creating
> the static library, and hence saving space. The idea is perhaps good, but it
> does not work. libjvm.so gets about 10% **larger** with these flags than
> without them, so they are not only useless, but actually harmful.
> * (gcc/clang) `-DJNIEXPORT='__attribute__((visibility("default")))'`: This is
> default now anyway so it does not contribute anything.
> * (microsoft)`-DJNIEXPORT=`: The static launcher still does not work fully
> on Windows. (It is an ongoing project to get it to work) However, removing
> this flag is an essential first step, since it otherwise removes the
> `__declspec(dllexport)` annotation, and we are hence renders us unable to
> lookup symbols in the static libraries. (I don't understand why this was
> introduced in the first place.)
> * (gcc) `-Xassembler -mrelax-relocations=no`: This was apparently added for
> compatibility with "older" linkers. Unfortunately, no version was given, and
> the original author of the code does not remember. I can build with no ill
> effects without this flag, so I assume that in the years that has passed, our
> toolchain version increments has made this unnecessary.
>
> There is a small risk of breakage for some old/odd gcc toolchain out there.
> But I can see of no other realistic way of solving this than to remove the
> flag, and if it breaks somewhere, we can re-introduce the flag, but with a
> valid GCC version number attached to it.
This pull request has now been integrated.
Changeset: cbab40bc
Author: Magnus Ihse Bursie <i...@openjdk.org>
URL:
https://git.openjdk.org/jdk/commit/cbab40bce45a2f58906be49c841178fa1dfd457e
Stats: 20 lines in 3 files changed: 0 ins; 19 del; 1 mod
8345683: Remove special flags for files compiled for static libraries
Reviewed-by: erikj
-------------
PR: https://git.openjdk.org/jdk/pull/22606
