zircon/kernel/BUILD.gn

# Copyright 2019 The Fuchsia Authors
#
# Use of this source code is governed by a MIT-style
# license that can be found in the LICENSE file or at
# https://opensource.org/licenses/MIT

# TODO(54160): Keep this in sync with BUILD.zircon.gn
import("//build/unification/global_variables.gni")
if (is_kernel) {
  config("headers") {
    include_dirs = [
      "include",
      "lib/libc/include",
    ]
    configs = [ "lib/libc:limits-dummy" ]
  }

  # For any standalone static binary.
  config("standalone") {
    ldflags = [
      "-nostdlib",
      "-static",
    ]

    cflags = [
      "-ffreestanding",
      "-include",
      rebase_path("include/hidden.h", root_build_dir),

      # We want `.debug_frame` for the kernel (ZX-62).  And we still want
      # asynchronous unwind tables.  Alas there's (currently) no way to
      # achieve this with our GCC.  At the moment we compile with
      # `-fno-omit-frame-pointer`, which is good because we link with
      # `--gc-sections`, which means `.eh_frame` gets discarded so GCC-built
      # kernels don't have any unwind info (except for assembly)!  Assembler
      # code has its own way of requesting `.debug_frame` vs `.eh_frame` with
      # the `.cfi_sections` directive.
      "-fno-unwind-tables",
    ]

    cflags_cc = [
      # Underlying kernel heap only has default alignment of 8 bytes, so pass
      # this to the compiler as the default new alignment.
      "-faligned-new=8",
    ]

    if (current_cpu == "x64") {
      # This only matters in an environment where interrupt handlers might
      # push trap frames in the same privilege level, like the kernel.
      # e.g. Multiboot probably doesn't actually need it, but it doesn't hurt.
      cflags += [ "-mno-red-zone" ]
    } else if (current_cpu == "arm64") {
      # This matters if vector registers are not available, e.g. in the kernel
      # since the they hold unsaved user state, or in the physmem environment
      # because they might not be enabled in hardware yet.
      if (!is_gcc) {
        cflags += [ "-mgeneral-regs-only" ]
      } else {
        # TODO(mcgrathr): To work around a GCC bug we have to sneak
        # -mgeneral-regs-only in through an arcane mechanism.  See
        # //zircon/kernel/lib/arch/arm64/include/lib/arch/intrin.h for details.
        cflags += [
          "-include",
          rebase_path("arch/arm64/general-regs-only.h", root_build_dir),
        ]
      }
    }

    if (is_gcc && current_os == "fuchsia") {
      cflags += [ "-fpie" ]
    }

    if (!is_gcc && current_os == "fuchsia") {
      # In the Fuchsia-target toolchains there's no way to prevent the
      # compiler driver from passing -pie, so negate it.  BFD ld doesn't
      # have --no-pie, but arm64-elf-gcc doesn't pass -pie either.
      ldflags += [ "-Wl,--no-pie" ]
    }

    if (!is_gcc) {
      # Disable the implicit addition of toolchain-provided libraries to
      # the link by the compiler driver.  No toolchain-provided library is
      # compatible with the kernel's internal ABI.
      #
      # TODO(27356): Clang doesn't have a single straightforward switch to
      # disable all such libraries, though it certainly should.  It
      # provides separate switches to disable the profiling/coverage
      # runtime and to disable all the flavors of runtime implied by
      # -fsanitize=... switches (including any such defaults).  It will
      # still provide other incompatible libraries to the link, but they
      # won't have any effect since they don't define any symbols the link
      # needs.  However, this is a fragile situation that could easily
      # break.
      ldflags += [
        "-noprofilelib",
        "-fno-sanitize-link-runtime",
      ]
    }

    configs = [ "$zx_build_config:no_exceptions" ]
  }

  config("warnings") {
    cflags = [
      "-Wformat=2",
      "-Wvla",
    ]

    # GCC supports `-Wformat-signedness` but Clang currently does not.
    if (is_gcc) {
      cflags += [ "-Wformat-signedness" ]
    }

    cflags_c = [ "-Wmissing-prototypes" ]
  }
}  # is_kernel