The current kernel ifunc implementation creates a PLT entry for each
ifunc definition. ifunc calls therefore consist of a call to the
PLT entry followed by an indirect jump. The jump target is written
during boot when the kernel linker resolves R_[*]_IRELATIVE relocations.
This implementation is defined by requirements for userland code, where
text relocations are avoided. This requirement is not present for the
kernel, so the implementation has avoidable overhead (namely, an extra
indirect jump per call).
Address this for now by adding a special option to the static linker
to inhibit PLT creation for ifuncs. Instead, relocations to ifunc call
sites are passed through to the output file, so the kernel linker can
enumerate such call sites and apply PC-relative relocations directly
to the text section. Thus the overhead of an ifunc call becomes exactly
the same as that of an ordinary function call. This option is only for
use by the kernel and will not work for regular programs.
The final form of this optimization is up for debate; for now, this
change is simple and static enough to be acceptable as an interim
solution.
Reviewed by: emaste
Discussed with: arichardson, dim
MFC after: 1 month
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D16748
LLD_BOOTSTRAP (build) is independent of LLD_IS_LD (installed) so they
should not be based on each other.
This is related to upcoming WITH_SYSTEM_LINKER work.
Reviewed by: emaste
Sponsored by: Dell EMC
Differential Revision: https://reviews.freebsd.org/D15836
Upstream lld has no man page. Introduce a basic one for FreeBSD based on
ld.lld --help, with a brief introduction and additional detail for some
options.
We'll continue refining this in FreeBSD, and then submit it upstream once
the first round of edits are complete.
Submitted by: krion, Arshan Khanifar, emaste, bjk
MFC after: 2 weeks
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D13813
During the upgrade of clang/llvm etc to 3.9.0 in r309124, the PACKAGE
directive in the usr.bin/clang/*.mk files got dropped accidentally.
Restore it, with a few minor changes and additions:
* Correct license in clang.ucl to NCSA
* Add PACKAGE=clang for clang and most of the "ll" tools
* Put lldb in its own package
* Put lld in its own package
Reviewed by: gjb, jmallett
X-MFC-With: 309124
Differential Revision: https://reviews.freebsd.org/D8666
If set it installs LLD as /usr/bin/ld. LLD (as of version 3.9) is not
capable of linking the world and kernel, but can self-host and link many
substantial applications. GNU ld continues to be used for the world and
kernel build, regardless of how this knob is set.
It is on by default for arm64, and off for all other CPU architectures.
Sponsored by: The FreeBSD Foundation
