[libcxx] Require qemu-system-arm for armv7m builder

[DavidSpickett]

And add a check in the python script that the binary given to --qemu actually exists. Otherwise you get a generic Python error:

 # .---command stderr------------
 # | Traceback (most recent call last):
 # |   File "/home/david.spickett/modules-llvm-project/libcxx/utils/qemu_baremetal.py", line 70, in <module>
 # |     exit(main())
 # |   File "/home/david.spickett/modules-llvm-project/libcxx/utils/qemu_baremetal.py", line 66, in main
 # |     os.execvp(qemu_commandline[0], qemu_commandline)
 # |   File "/usr/lib/python3.8/os.py", line 568, in execvp
 # |     _execvpe(file, args)
 # |   File "/usr/lib/python3.8/os.py", line 610, in _execvpe
 # |     raise last_exc
 # |   File "/usr/lib/python3.8/os.py", line 601, in _execvpe
 # |     exec_func(fullname, *argrest)
 # | FileNotFoundError: [Errno 2] No such file or directory
 # `-----------------------------
 # error: command failed with exit status: 1

When it tries to run the entire command later.

For the builder, it's only ever going to use qemu-system-arm so error at config time if it's not there.

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: David Spickett (DavidSpickett)

Changes

And add a check in the python script that the binary given to --qemu actually exists. Otherwise you get a generic Python error:

 # .---command stderr------------
 # | Traceback (most recent call last):
 # |   File "/home/david.spickett/modules-llvm-project/libcxx/utils/qemu_baremetal.py", line 70, in <module>
 # |     exit(main())
 # |   File "/home/david.spickett/modules-llvm-project/libcxx/utils/qemu_baremetal.py", line 66, in main
 # |     os.execvp(qemu_commandline[0], qemu_commandline)
 # |   File "/usr/lib/python3.8/os.py", line 568, in execvp
 # |     _execvpe(file, args)
 # |   File "/usr/lib/python3.8/os.py", line 610, in _execvpe
 # |     raise last_exc
 # |   File "/usr/lib/python3.8/os.py", line 601, in _execvpe
 # |     exec_func(fullname, *argrest)
 # | FileNotFoundError: [Errno 2] No such file or directory
 # `-----------------------------
 # error: command failed with exit status: 1

When it tries to run the entire command later.

For the builder, it's only ever going to use qemu-system-arm so error at config time if it's not there.

---

Full diff: https://github.com/llvm/llvm-project/pull/77067.diff

2 Files Affected:

• (modified) libcxx/cmake/caches/Armv7M-picolibc.cmake (+1-1)
• (modified) libcxx/utils/qemu_baremetal.py (+6)

diff --git a/libcxx/cmake/caches/Armv7M-picolibc.cmake b/libcxx/cmake/caches/Armv7M-picolibc.cmake
index 91cc32fd376e30..3ab80b960ed44a 100644
--- a/libcxx/cmake/caches/Armv7M-picolibc.cmake
+++ b/libcxx/cmake/caches/Armv7M-picolibc.cmake
@@ -39,4 +39,4 @@ set(LIBUNWIND_ENABLE_THREADS OFF CACHE BOOL "")
 set(LIBUNWIND_IS_BAREMETAL ON CACHE BOOL "")
 set(LIBUNWIND_REMEMBER_HEAP_ALLOC ON CACHE BOOL "")
 set(LIBUNWIND_USE_COMPILER_RT ON CACHE BOOL "")
-find_program(QEMU_SYSTEM_ARM qemu-system-arm)
+find_program(QEMU_SYSTEM_ARM qemu-system-arm REQUIRED)
diff --git a/libcxx/utils/qemu_baremetal.py b/libcxx/utils/qemu_baremetal.py
index aaf5b84489066d..126031bbb19c49 100755
--- a/libcxx/utils/qemu_baremetal.py
+++ b/libcxx/utils/qemu_baremetal.py
@@ -16,6 +16,7 @@
 import argparse
 import os
 import sys
+import shutil
 
 
 def main():
@@ -32,8 +33,13 @@ def main():
     parser.add_argument("test_binary")
     parser.add_argument("test_args", nargs=argparse.ZERO_OR_MORE, default=[])
     args = parser.parse_args()
+
+    if not shutil.which(args.qemu):
+        sys.exit(f"Failed to find QEMU binary from --qemu value: '{args.qemu}'")
+
     if not os.path.exists(args.test_binary):
         sys.exit(f"Expected argument to be a test executable: '{args.test_binary}'")
+
     qemu_commandline = [
         args.qemu,
         "-chardev",

[domin144]

LGTM
good error messages are helpful

[mordante]

Thanks! LGTM!