[Bug 264783] graphics/mesa-dri pulls in the entire llvm package

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=264783

--- Comment #4 from Charlie Li <vishwin@freebsd.org> ---
(In reply to Bill Blake from comment #3)
It's not that simple. Especially not without subpackage support in the ports
framework, ie packaging separate portions of the staging section as separate
packages. The work to get there is another story altogether and depends on
everyone's collective cycles availability.

I don't think many folks, myself included, are happy with the situation that
LLVM consumes significant storage, but LLVM is a rather dense software. It is
further complicated by how there is no guarantee of API/ABI stability between
major versions.

For mesa specifically, the part that requires LLVM specifically is the swrast
driver, better known as LLVMpipe, a software graphics renderer. swrast is
dynamically linked to libLLVM (example taken from my
somewhat-off-the-beaten-path copy of mesa):

% readelf -d /usr/local/lib/dri/swrast_dri.so

Dynamic section at offset 0x19242f0 contains 37 entries:
  Tag                Type                  Name/Value
 0x0000000000000001 NEEDED               Shared library: [libglapi.so.0]
 0x0000000000000001 NEEDED               Shared library: [libdrm.so.2]
 0x0000000000000001 NEEDED               Shared library: [libLLVM-14.so]
 0x0000000000000001 NEEDED               Shared library: [libexpat.so.1]
 0x0000000000000001 NEEDED               Shared library: [libz.so.6]
 0x0000000000000001 NEEDED               Shared library: [libm.so.5]
 0x0000000000000001 NEEDED               Shared library: [libdrm_radeon.so.1]
 0x0000000000000001 NEEDED               Shared library: [libelf.so.2]
 0x0000000000000001 NEEDED               Shared library: [libdrm_amdgpu.so.1]
 0x0000000000000001 NEEDED               Shared library: [libc++.so.1]
 0x0000000000000001 NEEDED               Shared library: [libcxxrt.so.1]
 0x0000000000000001 NEEDED               Shared library: [libgcc_s.so.1]
 0x0000000000000001 NEEDED               Shared library: [libthr.so.3]
 0x0000000000000001 NEEDED               Shared library: [libc.so.7]
 0x000000000000000e SONAME               Library soname: [libgallium_dri.so]
 0x0000000000000007 RELA                 0xa480
 0x0000000000000008 RELASZ               500760 (bytes)
 0x0000000000000009 RELAENT              24 (bytes)
 0x000000006ffffff9 RELACOUNT            20420
 0x0000000000000017 JMPREL               0x84898
 0x0000000000000002 PLTRELSZ             16104 (bytes)
 0x0000000000000003 PLTGOT               0x192a6d8
 0x0000000000000014 PLTREL               RELA
 0x0000000000000006 SYMTAB               0x2d0
 0x000000000000000b SYMENT               24 (bytes)
 0x0000000000000005 STRTAB               0x6684
 0x000000000000000a STRSZ                15868 (bytes)
 0x000000006ffffef5 GNU_HASH             0x4f18
 0x0000000000000004 HASH                 0x4f84
 0x0000000000000019 INIT_ARRAY
 0x000000000000001b INIT_ARRAYSZ         112 (bytes)
 0x000000000000000c INIT                 0x6427f4
 0x000000000000000d FINI                 0x642804
 0x000000006ffffff0 VERSYM               0x47b8
 0x000000006ffffffe VERNEED              0x4d78
 0x000000006fffffff VERNEEDNUM           8
 0x0000000000000000 NULL                 0x0

But libLLVM-${LLVM_SUFFIX}.so lives in ${PREFIX}/llvm${LLVM_SUFFIX}/lib, not
${PREFIX}/lib, so as to keep much of the LLVM distribution together in one spot
(because remember, LLVM is dense), which has us invoking ldconfig(8) to add the
LLVM hierarchy into the dynamic linker search path. It is a bad idea to have
multiple copies of the same exact shared object floating around, especially
with the same SONAME, as they have the chance to cause collisions.

Additionally, this and many other programs in and outside the ports tree rely
on other components of LLVM to build or run, often using llvm-config to feed
the build system LLVM configuration information, interfacing with shared or
static objects or a combination of both.

So no, we cannot simply give the library a new name and copy it in.

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