libc-related gn variables

[selfisekai]

there are some gn changes needed to compile for musl. currently, dart detects musl by dart_sysroot == "alpine", but that doesn't work when simply compiling for musl on a musl host.

I've submitted this PR into flutter: flutter/buildroot#707 - any comments? I'm hoping for a universal approach for this in dart and flutter

[a-siva]

//cc @athomas @rmacnak-google

[rmacnak-google]

It is possible to select the sysroot using existing flags:

tools/build.py --no-goma --no-clang --arch=x64 --target-sysroot=x64=/ --gn-args "dart_use_tcmalloc=false" create_sdk

[selfisekai]

@rmacnak-google this does not indicate the libc we're compiling for by itself. I still need a few quickfixes like this in gn to compile on/for alpine host:

--- ./build/config/compiler/BUILD.gn.orig
+++ ./build/config/compiler/BUILD.gn
@@ -258,7 +258,7 @@
   # ------------------------------------
   if (is_linux) {
     if (is_clang) {
-      if (dart_sysroot == "alpine") {
+      if (true) {
         # alpine linux target names can be found at:
         # https://pkgs.alpinelinux.org/contents?file=stdc%2B%2B.h&name=libstdc%2B%2B-dev
         if (current_cpu == "arm") {
@@ -672,10 +672,6 @@
       "-Wextra",
     ]
 
-    if (dart_sysroot != "alpine") {
-      cflags += [ "-Werror" ]
-    }
-
     defines = []
     if (!using_sanitizer && !is_clang) {
       # _FORTIFY_SOURCE isn't really supported by Clang now, see

[rmacnak-google]

It works for me with the bootlin toolchains (on a Debian host).

$ build() { ./tools/build.py --no-goma --no-clang --gn-args=dart_use_tcmalloc=false --gn-args=dart_sysroot=\"\" --mode=release $@ create_sdk runtime ; }
$ build --arch=x64 --toolchain=x64=$HOME/toolchains/x86-64--musl--stable-2022.08-1/bin/x86_64-buildroot-linux-musl-
$ build --arch=arm64 --toolchain=arm64=$HOME/toolchains/aarch64--musl--stable-2022.08-2/bin/aarch64-buildroot-linux-musl-
$ build --arch=riscv64 --toolchain=riscv64=$HOME/toolchains/riscv64-lp64d--musl--stable-2022.08-1/bin/riscv64-buildroot-linux-musl-
$ docker run --mount type=bind,source=$PWD/out/ReleaseX64/dart-sdk,target=/dart-sdk alpine /dart-sdk/bin/dart --version
Dart SDK version: 3.1.0-edge.d8b53d97ffedfa33775e401ea0eb69d9cdded3eb (be) (Thu Apr 13 16:45:14 2023 +0000) on "linux_x64"

[selfisekai]

@rmacnak-google here's on my machine: alpine x64 host, gclient-provided clang/gn/ninja replaced with symlinks to system ones

./tools/build.py --no-goma --no-clang --gn-args=dart_use_tcmalloc=false --gn-args=dart_sysroot=\"\" --mode=release --arch=x64 create_sdk runtime - working (well, fails later for bootstrap reasons)

not working because of invalid target provided:

1. clang - valid targets only set if dart_sysroot == "alpine":

   sdk/build/config/compiler/BUILD.gn

   Line 297 in 90d84c8

   cflags += [ "--target=x86_64-linux-gnu" ]

$ ./tools/build.py --no-goma --clang --gn-args=dart_use_tcmalloc=false --gn-args=dart_sysroot=\"\" --mode=release --arch=x64 create_sdk runtime

ninja: job failed: ../../buildtools/linux-x64/clang/bin/clang++ -MMD -MF obj/runtime/vm/compiler/libdart_compiler_precompiler_testing.method_recognizer.o.d -DTOOLCHAIN_VERSION=system -DNDEBUG -DTARGET_ARCH_X64 -DDART_TARGET_OS_LINUX -DDART_PRECOMPILER -DTESTING -I../../runtime -I../.. -Igen -I../../runtime/include -m64 -march=x86-64 -msse2 -fPIE --target=x86_64-linux-gnu -fcolor-diagnostics -Wall -Wextra -Werror -Wendif-labels -Wno-missing-field-initializers -Wno-unused-parameter -Wno-tautological-constant-compare -Wno-unused-but-set-variable -Wno-deprecated-non-prototype -fdebug-prefix-map=/home/lauren/dart/sdk=../.. -no-canonical-prefixes -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -Wheader-hygiene -Wstring-conversion -O2 -fno-ident -fdata-sections -ffunction-sections -g3 -ggdb3 -Wno-unused-parameter -Wno-unused-private-field -Wnon-virtual-dtor -Wvla -Woverloaded-virtual -Wno-comments -g3 -ggdb3 -fno-rtti -fno-exceptions -Wimplicit-fallthrough -fno-strict-vtable-pointers -O2 -fno-omit-frame-pointer -fvisibility-inlines-hidden -fno-omit-frame-pointer -std=c++17 -fno-rtti -c ../../runtime/vm/compiler/method_recognizer.cc -o obj/runtime/vm/compiler/libdart_compiler_precompiler_testing.method_recognizer.o
In file included from ../../runtime/vm/compiler/method_recognizer.cc:5:
In file included from ../../runtime/vm/compiler/method_recognizer.h:8:
In file included from ../../runtime/vm/allocation.h:8:
In file included from ../../runtime/platform/allocation.h:8:
In file included from ../../runtime/platform/address_sanitizer.h:8:
../../runtime/platform/globals.h:92:10: fatal error: 'cassert' file not found
#include <cassert>  // For assert() in constant expressions.
         ^~~~~~~~~
1 error generated.

2. anything other than x64 or x86 with gcc (would fail no matter if cross or not) - workaround available by --gn-args='arm64_toolchain_prefix="aarch64-linux-musl-"' and so on for each architecture - defined by prefix here: https://github.com/dart-lang/sdk/blob/90d84c849472b375e0fbb7321f800208180cd14b/build/toolchain/linux/BUILD.gn

$ ./tools/build.py --no-goma --no-clang --gn-args=dart_use_tcmalloc=false --gn-args=dart_sysroot=\"\" --mode=release --arch=arm64 create_sdk runtime

ninja: job failed: aarch64-linux-gnu-g++ -MMD -MF obj/runtime/vm/compiler/libdart_compiler_precompiler.write_barrier_elimination.o.d -D_FORTIFY_SOURCE=2 -DNDEBUG -DTARGET_ARCH_ARM64 -DDART_TARGET_OS_LINUX -DDART_PRECOMPILER -I../../runtime -I../.. -Igen -I../../runtime/include -fPIE -Wall -Wextra -Werror -Wendif-labels -Wno-missing-field-initializers -Wno-unused-parameter -Wno-ignored-qualifiers -fdebug-prefix-map=/home/lauren/dart/sdk=../.. -no-canonical-prefixes -D_FILE_OFFSET_BITS=64 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -O2 -fno-ident -fdata-sections -ffunction-sections -g3 -ggdb3 -Wno-unused-parameter -Wno-unused-private-field -Wnon-virtual-dtor -Wvla -Woverloaded-virtual -Wno-comments -g3 -ggdb3 -fno-rtti -fno-exceptions -Wno-cast-function-type -O2 -fvisibility-inlines-hidden -fno-omit-frame-pointer -std=c++17 -fno-rtti -c ../../runtime/vm/compiler/write_barrier_elimination.cc -o obj/runtime/vm/compiler/libdart_compiler_precompiler.write_barrier_elimination.o
/bin/sh: aarch64-linux-gnu-g++: not found

[selfisekai]

submitted: https://dart-review.googlesource.com/c/sdk/+/295520