skia2/toolchain/ar_trampoline.sh

#!/bin/bash
# Copyright 2021 Google LLC
#
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.

external/clang_linux_amd64/bin/llvm-ar $@
[infra] Add hermetic toolchain for C/C++ using Clang+Musl This can successfully build a C library: bazel build --config=clang //third_party:libpng This can build and run a statically-linked executable: bazel test --config=clang //:bazel_test For more verbose compile and linking output, add the `--features diagnostic` flag to a Bazel command (see _make_diagnostic_flags() in toolchain/clang_toolchain_config.bzl. Similarly, a `--features print_search_dirs` can be used to show where clang is looking for libraries etc to link against. These features are made available for easier debugging. Suggested review order: - Read https://docs.bazel.build/versions/4.2.1/tutorial/cc-toolchain-config.html if unfamiliar with setting up C++ toolchains in Bazel - .bazelrc and WORKSPACE.bazel that configure use and download of the toolchain (Clang 13, musl 1.2.2) - toolchain/build_toolchain.bzl which downloads and assembles the toolchain (w/o installing anything on the host machine) - toolchain/BUILD.bazel and toolchain/trampoline.sh to see the setup of the toolchain rules. - toolchain/clang_toolchain_config.bzl to see the configuration of the toolchain. Pay special attention to the various command line flags that are set. - See that tools/bazel_test.cc has made a new home in experimental/bazel_test/bazel_test.cpp, with a companion BUILD.bazel. Note the addition of some function calls that test use of the C++ standard library. The number being used to test the PNG library is the latest and greatest that verifies we are compiling the one brought in via DEPS (and not a local one). - third_party/ to see how png (and its dependent zlib) have been built. Pay special attention to the musl_compat hack to fix static linking (any idea what the real cause is?) - //BUILD.bazel to see definition of the bazel_test executable. Change-Id: I7b0922d0d45cb9be8df2fd5fa5a1f48492654d5f Bug: skia:12541 Reviewed-on: https://skia-review.googlesource.com/c/skia/+/461178 Reviewed-by: Ben Wagner <bungeman@google.com> Reviewed-by: Leandro Lovisolo <lovisolo@google.com> 2021-10-20 20:20:42 +00:00			`#!/bin/bash`
			`# Copyright 2021 Google LLC`
			`#`
			`# Use of this source code is governed by a BSD-style license that can be`
			`# found in the LICENSE file.`

[bazel] Sketching out HelloWorld sk_app using GL bazel run //example:hello_world --config=clang causes a window to open and draws a circle and a square. Text to follow in a future CL. To make this work, I had to get rid of musl and use glibc. All the shared libraries (.so files) that were pre-built and available for download (e.g. from https://packages.debian.org/bullseye/amd64/libgl1/download) were compiled against glibc. When I tried to run a program statically linked with musl and dynamically linked against things using glibc, I got a segmentation fault on things like calloc(). Initial attempts to use glibc had failed because it was thought that the libc.so.6 file could only be referred to by absolute path (and thus Bazel would not be happy about it). As it turns out, that was simply a misconfiguration of the builtin_sysroot parameter to cc_common.create_cc_toolchain_config_info (see //toolchain/clang_toolchain_config.bzl). By setting that to `external/clang_linux_amd64` and not `external/clang_linux_amd64/usr`, the libc binary which had been extracted to `external/clang_linux_amd64/lib/x86_64-linux-gnu` was perfectly reachable from `external/clang_linux_amd64/usr/usr/lib/x86_64-linux-gnu/libc.so` To bring in the shared libraries to link against (e.g. X11, GL) I made build_toolchain.bzl easier to modify in that we simply need to add a debian download url and sha256 hash to a list (rather than having to plumb this through via arguments). Recommended Review Order: - example/BUILD.bazel (not sure if we always want to set bare link arguments like that or if we want to use "features" to pass those along to the toolchain). - tools/sk_app/BUILD.bazel to see initial cc_library for wrapping sk_app code. - toolchain/build_toolchain.bzl to see removal of musl and new list of debs. - toolchain/clang_toolchain_config.bzl (where use of the no-canonical-prefixes was key to compilation success). Notice also that we statically linked libc++ (I did not have any shared libraries for it locally, so I guessed a typical developer might not either). - Rest of toolchain/ for trivial renames. - bazel/Makefile to see extra docs on those targets and a new target that compiles all the exes so far for a quick way to test the build. - third_party/BUILD.bazel and src/gpu/BUILD.bazel which have non-generated changes. (all other BUILD.bazel files do). - go.mod, which needed to update the infra repo version in order to pick up http://review.skia.org/491736). Change-Id: I8687bd227353040eca2dffa9465798d8bd395027 Bug: skia:12541 Reviewed-on: https://skia-review.googlesource.com/c/skia/+/492117 Reviewed-by: Ben Wagner <bungeman@google.com> Reviewed-by: Leandro Lovisolo <lovisolo@google.com> Commit-Queue: Kevin Lubick <kjlubick@google.com> 2022-01-11 12:35:26 +00:00			`external/clang_linux_amd64/bin/llvm-ar $@`