build: add gen-imports to create libc.imports

This adds a python script to generate libc.imports as the shell
utilities may not be available on Windows.

Author: compnerd

.azure-pipelines.yml

@@ -48,8 +48,7 @@ jobs:
         rustup update stable --no-self-update
         rustup default stable
         rustup component add llvm-tools-preview
-        echo "##vso[task.setvariable variable=WASM_NM;]$(rustc --print sysroot|sed 's|C:|/c|'|sed 's|\\|/|g')/lib/rustlib/x86_64-pc-windows-msvc/bin/llvm-nm.exe"
-      displayName: Install llvm-nm (Windows)
+      displayName: Install LLVM tools (Windows)
       condition: and(succeeded(), eq( variables['Agent.OS'], 'Windows_NT' ))
     - bash: |
         echo "##vso[task.setvariable variable=LLVM_AR]$(which llvm-ar)"
@@ -59,10 +58,18 @@ jobs:
         echo ##vso[task.setvariable variable=LLVM_AR]%CD%\citools\clang-rust\bin\llvm-ar.exe
       displayName: Find llvm-ar (Windows)
       condition: and(succeeded(), eq(variables['Agent.OS'], 'Windows_NT'))
+    - bash: |
+        echo "##vso[task.setvariable variable=LLVM_NM]$(which llvm-nm)"
+      displayName: Find llvm-nm (!Windows)
+      condition: and(succeeded(), not(eq(variables['Agent.OS'], 'Windows_NT')))
+    - bash: |
+        echo "##vso[task.setvariable variable=LLVM_NM]$(rustc --print sysroot)\\lib\\rustlib\\x86_64-pc-windows-msvc\\bin\\llvm-nm.exe"
+      displayName: Find llvm-nm (Windows)
+      condition: and(succeeded(), eq(variables['Agent.OS'], 'Windows_NT'))
     - task: CMake@1
       inputs:
         workingDirectory: $(Build.BinariesDirectory)
-        cmakeArgs: -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_SYSTEM_NAME=Generic -DCMAKE_AR=$(LLVM_AR) -DCMAKE_C_COMPILER=clang -S $(Build.SourcesDirectory)
+        cmakeArgs: -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=RelWithDebInfo -DCMAKE_SYSTEM_NAME=Generic -DCMAKE_AR=$(LLVM_AR) -DCMAKE_NM=$(LLVM_NM) -DCMAKE_C_COMPILER=clang -S $(Build.SourcesDirectory)
       displayName: Configure
     - task: CMake@1
       inputs:

CMakeLists.txt

@@ -11,6 +11,8 @@ include(CMakeDependentOption)
 
 option(ENABLE_THREADS "enable threads" OFF)
 
+find_package(Python COMPONENTS Interpreter REQUIRED)
+
 add_compile_options(--sysroot=${CMAKE_BINARY_DIR}/sysroot)
 
 # WebAssembly floating point match doesn't trap
@@ -1133,3 +1135,16 @@ foreach(stub m rt pthread crypt util xnet resolve dl)
   add_custom_target(${stub} ALL
     DEPENDS ${CMAKE_BINARY_DIR}/sysroot/lib/lib${stub}.a)
 endforeach()
+
+add_custom_command(OUTPUT ${CMAKE_BINARY_DIR}/sysroot/lib/libc.imports
+  COMMAND
+    ${Python_EXECUTABLE} ${PROJECT_SOURCE_DIR}/tools/gen-imports.py
+    --nm ${CMAKE_NM}
+    --output ${CMAKE_BINARY_DIR}/sysroot/lib/libc.imports
+    $<TARGET_FILE:c>
+    ${CMAKE_BINARY_DIR}/sysroot/lib/crt1.o
+  DEPENDS
+    ${PROJECT_SOURCE_DIR}/tools/gen-imports.py)
+add_custom_target(libc.imports ALL
+  DEPENDS ${CMAKE_BINARY_DIR}/sysroot/lib/libc.imports)
+add_dependencies(libc.imports c crt1.o)

tools/gen-imports.py

@@ -0,0 +1,50 @@
+# -*- encoding: utf-8 -*-
+"""Generate import file for a target
+
+This utility scans a static library to identify the undefined symbols which are
+externally visible which it expects to have provided.  This is used to generate
+the import file definitions for WASI.
+
+Example:
+    $ python gen-imports.py --nm llvm-nm --prefix __wasi_ libc.a
+"""
+
+import argparse
+import os
+import re
+import subprocess
+import sys
+
+from subprocess import Popen
+
+def main(argv):
+    parser = argparse.ArgumentParser('gen-imports')
+    parser.add_argument('--nm', default = 'nm')
+    parser.add_argument('--prefix', default = '_?_wasi_')
+    parser.add_argument('--output', required = True)
+
+    args, unparsed = parser.parse_known_args()
+
+    args.nm = os.path.normpath(args.nm)
+    args.output = os.path.normpath(args.output)
+
+    process = Popen([
+                        args.nm,
+                        '--undefined-only',
+                        '--extern-only',
+                        '--just-symbol-name',
+                     ] + unparsed,
+                    stdout = subprocess.PIPE)
+    output, error = process.communicate()
+
+    prefix = re.compile(args.prefix)
+    lines = output.decode('utf-8').splitlines()
+    symbols = [ line for line in lines if not line.endswith(':') ]
+
+    with open(args.output, 'w') as imports:
+        for symbol in sorted(set(symbols)):
+            if prefix.match(symbol):
+                imports.write('{}\n'.format(symbols))
+
+if __name__ == '__main__':
+    main(sys.argv)