[libc] Tracking progress for adding hermetic testing on baremetal

[saturn691]

Downstream (https://github.com/arm/arm-toolchain/), I have managed to hack together running hermetic testing of unit tests by LLVM.

❯ qemu-system-arm -M mps2-an500 -semihosting -nographic -device loader,file=libc/test/src/stdio/libc.test.src.stdio.printf_test.__hermetic__.__build__ -s -S
[==========] Running 1 test from 1 test suite.
[ RUN      ] LlvmLibcPrintfTest.PrintOut
A simple string with no conversions.
1234567890
1234 and more
[       OK ] LlvmLibcPrintfTest.PrintOut
Ran 1 tests.  PASS: 1  FAIL: 0

In an ideal world, I would like to contribute this upstream, where the embedded build is ran in the post-commit, which in-turn can be used to catch any errors relating to baremetal implementations. In order to do this, I will have to do the following.

However, after a few discussions, it was suggested that that is better done first downstream, with the option to integrate this upstream if it adds enough value.

• Start the mutex implementation ([libc] Mutex implementation for single-threaded baremetal #145358)
• Fix a few bugs with the testing on LLVM-libc
  • Add the -nolibc flag to the baremetal Clang driver ([clang] Add option for -nolibc in Driver/ToolChains/Baremetal.cpp #145700)
  • clock() unimplemented, and therefore LibcTest.cpp doesn't compile ([libc] Fix issue with using clock() in hermetic testing #146069)
  • atexit() currently disabled for baremetal targets.
• Other things that I may have missed when integrating upstream.

[llvmbot]

@llvm/issue-subscribers-libc

Author: William Huynh (saturn691)

Downstream (https://github.com/arm/arm-toolchain/), I have managed to hack together running hermetic testing of unit tests by LLVM.

❯ qemu-system-arm -M mps2-an500 -semihosting -nographic -device loader,file=libc/test/src/stdio/libc.test.src.stdio.printf_test.__hermetic__.__build__ -s -S
[==========] Running 1 test from 1 test suite.
[ RUN      ] LlvmLibcPrintfTest.PrintOut
A simple string with no conversions.
1234567890
1234 and more
[       OK ] LlvmLibcPrintfTest.PrintOut
Ran 1 tests.  PASS: 1  FAIL: 0

In an ideal world, I would like to contribute this upstream, where the embedded build is ran in the post-commit. In order to do this, I will have to do the following.

• Fix a few bugs with the testing on LLVM-libc
• Start the mutex implementation
• Upstream the LLVM-libc support libraries (https://github.com/arm/arm-toolchain/tree/arm-software/arm-software/embedded/llvmlibc-support) into crt1 and semihost.
• Other things that I may have missed when integrating upstream.