Details

Reviewers

brooks
emaste
imp
jrtc27

Commits

rG6acae3bbe337: src.conf: Add WITH_LLVM_LINK_STATIC_LIBRARIES build knob
rG908ca4f6af8a: src.conf: Add WITH_LLVM_LINK_STATIC_LIBRARIES build knob
rGded12d66a3eb: src.conf: Add WITH_LLVM_LINK_STATIC_LIBRARIES build knob
rG8d5a11cd0137: src.conf: Add WITH_LLVM_LINK_STATIC_LIBRARIES build knob

Summary

In commit 2e47f35be5dc libllvm, libclang and liblldb were converted into
private shared libraries. This allowed clang, lld, lldb, and other llvm
tools to be linked against these shared libraries, which makes them
smaller and avoids duplication.

However, this also comes at the cost of some performance, since the
dynamic libraries are quite large, and contain lots of long symbols
(mangled C++ identifiers).

Add a WITH_LLVM_STATIC build knob that can be used to go back to the
previous behavior: libllvm, libclang and liblldb are built as internal
static libraries, i.e. only available during buildworld, and fully
linked into the various executables such as clang, lld, etc.

PR: 287447
MFC after: 1 week

Diff Detail

Repository

rG FreeBSD src repository

Lint

Lint Passed

Unit

No Test Coverage

Build Status

Buildable 69430
Build 66313: arc lint + arc unit

Event Timeline

dim created this revision.Jun 20 2025, 5:22 PM

Herald added subscribers: ziaee, bdrewery. · View Herald TranscriptJun 20 2025, 5:22 PM

dim requested review of this revision.Jun 20 2025, 5:22 PM

Harbormaster completed remote builds in B65000: Diff 157391.Jun 20 2025, 5:22 PM

Also include src.opts.mk in libllvm's and liblldb's Makefiles, otherwise
MK_ variables might not be defined.

Harbormaster completed remote builds in B65001: Diff 157392.Jun 20 2025, 5:25 PM

IMO we should expand on the user-facing effect in the option descriptions - i.e., for WITH_LLVM_STATIC the Clang/LLVM toolchain binaries will be much larger but start more quickly. WITHOUT_LLVM_STATIC the Clang/LLVM binaries will be smaller, but will take longer to start.

lib/clang/liblldb/Makefile
4	Makes sense for consistency but I assume we don't actually build liblldb as a cross-tool?

In D50956#1163146, @emaste wrote:

IMO we should expand on the user-facing effect in the option descriptions - i.e., for WITH_LLVM_STATIC the Clang/LLVM toolchain binaries will be much larger but start more quickly. WITHOUT_LLVM_STATIC the Clang/LLVM binaries will be smaller, but will take longer to start.

I looked at a few other WITH/WITHOUT descriptions and they're usually rather terse, but you're probably right. Better to to explicit about the purpose of the knob.

lib/clang/liblldb/Makefile
4	Makes sense for consistency but I assume we don't actually build liblldb as a cross-tool? You're right, this is a copy/pasted pair of lines from the other two Makefiles. TOOLS_PREFIX is only defined when bootstrapping the compiler, and indeed we never build lldb during that phase.

Adjust comment in liblldb Makefile
Expand descriptions in WITH/WITHOUT fragments

Harbormaster completed remote builds in B65004: Diff 157397.Jun 20 2025, 7:42 PM

Btw there is still one rather nasty fly in the ointment for this patch: in tools/build/depend-cleanup.sh we have a hack to delete libllvm.a, libclang.a and liblldb.a from the obj tree. I don't know of a way to get at the MK_LLVM_STATIC option value in that shell script though. Does anybody have any good idea for that? Run ${MAKE} in some form that spits out the value?

Add hack to ensure depend-cleanup.sh does not inadvertently delete static llvm/clang etc libraries.

Harbormaster completed remote builds in B65120: Diff 157709.Jun 27 2025, 4:30 PM

Rebase, and remove depend-cleanup.sh stuff, which was flaky anyway. Any MK_ option change should always be done via a full rebuild.

Harbormaster completed remote builds in B69107: Diff 167656.Dec 7 2025, 2:01 PM

Don't worry about depend-cleanup.sh, D52011 will take care of it.

des added inline comments.Dec 7 2025, 5:30 PM

tools/build/options/WITHOUT_LLVM_STATIC
2 ↗	(On Diff #167656)	This is mandoc code, sentences should start on a new line.
tools/build/options/WITH_LLVM_STATIC
2 ↗	(On Diff #167656)	This is mandoc code, sentences should start on a new line.

des added inline comments.Dec 7 2025, 5:31 PM

tools/build/options/WITHOUT_LLVM_STATIC
2 ↗	(On Diff #167656)	BTW, you don't need to provide both files. Since this option defaults to no, you only need to provide the `WITH_` variant.

emaste added inline comments.Dec 7 2025, 6:18 PM

tools/build/options/WITHOUT_LLVM_STATIC
2 ↗	(On Diff #167656)	I think it's fine to keep both for the benefit of downstream projects who might use a different default.

des added inline comments.Dec 7 2025, 6:45 PM

tools/build/options/WITHOUT_LLVM_STATIC
2 ↗	(On Diff #167656)	I'm not going to insist, it doesn't hurt to have both, as long as they're kept in sync.

I'm not sure about the option name and descriptions; WITH_LLVM_STATIC suggests that these will be statically linked binaries. And, Build LLVM libraries (libllvm, libclang, liblldb) as internal static libraries. isn't a great user-facing description because it's just an artifact of the build process and the user doesn't see the result. Maybe "Link LLVM libraries (libllvm, libclang, liblldb) directly into each of the binaries that use them."? What do you think about calling it WITH_LLVM_LIBRARIES?