[PATCH v4 0/5] Fully support standalone Clang/LLVM toolchains

[Jessica Clarke]

On 9 Jul 2021, at 20:34, Jessica Clarke <jrtc27 at jrtc27.com> wrote:
> 
> This patch series is comprised of five parts.
> 
> The first patch fixes a warning seen when building with LLVM due to a
> bogus combination of assembly directives.
> 
> The second patch fixes errors seen when trying to build OpenSBI as a
> position-independent binary using LLD that may or may not be an LLD bug
> (the exact meaning of -N/--omagic isn't clear) but can easily be worked
> around without any issue either way.
> 
> The third patch bypasses the Clang driver's helpful nature of not
> honouring -pie for bare-metal binaries as it's normally not something
> you want (arguably that should be an error though, or passed on, since
> just giving a -Wunused-command-line-argument warning can get lost, and
> may be disabled).
> 
> The fourth patch adds build system support for using Clang and LLVM
> binutils, provided your Clang is able to locate a libgcc.a in its search
> path.
> 
> However, pure LLVM toolchains do not use libgcc, they use compiler-rt
> (libclang_rt.builtins.<arch>.a). We could change the Makefile to not
> hard-code -lgcc and instead use -print-libgcc-file-name, but that still
> requires a bare metal compiler-rt built for the right -march/-mabi to be
> present, which is often not the case. Moreover, we need very little from
> libgcc/compiler-rt; RV64 needs nothing, and RV32 only needs 64-bit
> division. Thus, the fifth patch vendors part of FreeBSD's libquad and
> stops linking against libgcc entirely, allowing OpenSBI to be built with
> just a cross-compiler. This means that building with any distro-provided
> LLVM just works, as does compiling with the system Clang compiler and
> LLD linker on FreeBSD without any external packages needed (beyond GNU
> make).
> 
> Changes in v4:
>  * Avoid read-only dynamic relocation error with LLD
>  * Support FW_PIC with LLD when using a bare-metal triple
> 
> Changes in v3:
>  * Fixed the binding warning seen when building with LLVM
>  * Provide a default -target when CROSS_COMPILE isn't set so the
>    variable isn't normally required to be set when cross-compiling with
>    LLVM (but is still honoured if set).
>  * Pass -fuse=bfd when not using LLD to ensure an ld.bfd gets correctly
>    picked up over a plain ld when ld is LLD. Now we always explicitly
>    request Clang and GCC use the linker type corresponding to LD. This
>    allows BFD to be used on FreeBSD for testing purposes despite LLD
>    being the system linker.
> 
> Changes in v2:
>  * Add documentation to README.md
>  * Pass -fuse-ld=lld to Clang when using LLD
>  * Modify commit message of first commit to explain -N -> -Wl,-N change
>  * Bring back the old ?= uses for the non-CROSS_COMPILE (and, now,
>    non-LLVM) case; whilst I still think that's how it should be, it's
>    not required for this patch, just related cleanup I did to reduce
>    the complexity of adding the LLVM case.
> 
> Jessica Clarke (5):
>  fw_base: Don't mark fw_platform_init as both global and weak
>  fw_base: Put data in .data rather than .text
>  firmware: Explicitly pass -pie to the linker, not just the driver
>  Makefile: Support building with Clang and LLVM binutils
>  Drop dependency on libgcc by importing part of FreeBSD's libquad
> 
> Makefile                              |  65 +++++-
> README.md                             |  43 +++-
> firmware/fw_base.S                    |   2 +-
> firmware/objects.mk                   |   2 +-
> lib/utils/libquad/divdi3.c            |  64 ++++++
> lib/utils/libquad/include/limits.h    |  12 ++
> lib/utils/libquad/include/sys/cdefs.h |  12 ++
> lib/utils/libquad/include/sys/types.h |  25 +++
> lib/utils/libquad/moddi3.c            |  66 ++++++
> lib/utils/libquad/objects.mk          |  14 ++
> lib/utils/libquad/qdivrem.c           | 278 ++++++++++++++++++++++++++
> lib/utils/libquad/quad.h              | 105 ++++++++++
> lib/utils/libquad/udivdi3.c           |  52 +++++
> lib/utils/libquad/umoddi3.c           |  54 +++++
> 14 files changed, 784 insertions(+), 10 deletions(-)
> create mode 100644 lib/utils/libquad/divdi3.c
> create mode 100644 lib/utils/libquad/include/limits.h
> create mode 100644 lib/utils/libquad/include/sys/cdefs.h
> create mode 100644 lib/utils/libquad/include/sys/types.h
> create mode 100644 lib/utils/libquad/moddi3.c
> create mode 100644 lib/utils/libquad/objects.mk
> create mode 100644 lib/utils/libquad/qdivrem.c
> create mode 100644 lib/utils/libquad/quad.h
> create mode 100644 lib/utils/libquad/udivdi3.c
> create mode 100644 lib/utils/libquad/umoddi3.c

... all Signed-off-by: Jessica Clarke <jrtc27 at jrtc27.com>, managed to
forget that yet again :(

Jess