[native_sim] `CONFIG_SHELL_GETOPT=y` does not build.

[JaagupAverin]

Describe the bug

On native posix platforms, the whole zephyr/lib/posix/ subdirectory is ignored if building natively:

if(NOT CONFIG_NATIVE_LIBC)
add_subdirectory(posix)
endif()

This includes the zephyr/lib/posix/options/getopt subdirectory which implements a non-standard (?) getopt interface, including the structure struct getopt_state, which is referenced when CONFIG_SHELL_GETOPT=y is enabled, generating errors like:

/home/jaagup/projects/forest/zephyr/include/zephyr/shell/shell.h:867:22: error: field has incomplete type 'struct getopt_state'
  867 |         struct getopt_state getopt;
      |                             ^
/home/jaagup/projects/forest/zephyr/include/zephyr/shell/shell.h:867:9: note: forward declaration of 'struct getopt_state'
  867 |         struct getopt_state getopt;
      |

On native posix, the system <getopt.h> is included, which does not define this structure.

I am open to making a PR with some direction of how best work around this conflict.

Regression

• This is a regression.

Steps to reproduce

No response

Relevant log output

Impact

Annoyance – Minor irritation; no significant impact on usability or functionality.

Environment

No response

Additional Context

No response

[ljd42]

Hello @JaagupAverin,

Thanks for your report. It's great that you have already investigated where the problem might be. Would you mind to describe the steps to reproduce the issues?

Thanks!

[aescolar]

The issue is about kconfig dependencies not being properly set when only CONFIG_SHELL_GETOPT is set.
To work around it you can set CONFIG_POSIX_API=y, or CONFIG_PICOLIBC=y ,
otherwise the linked PR will fix the dependency issue.

[JaagupAverin]

Hey! Thanks for taking a look at this. CONFIG_PICOLIBC=y is not an option since we need full libcpp support, and CONFIG_POSIX_API=y doesn't appear to resolve the issue.
Made a small reproducible hello world sample here:
main...JaagupAverin:fox-zephyr:native-sim-sample

[aescolar]

since we need full libcpp support

Oh.. Unfortunately that cannot be fixed with just toggling a Kconfig then..
The issue here is that:

• As you mentioned, this getopt is far from just the standard getopt. And SHELL_GETOPT needs lib/posix/options/getopt/ and not just a standard getopt(). Today this is bundled with other POSIX API components.
• In general CONFIG_POSIX_API is incompatible with the host C library.
• So when one sets POSIX_API we default to build with an embedded C library (PICO). And we can do that only because we build the C library from the source for the host. But for the C++ library we do not (yet) have a source version.
• So the combination of POSIX_API + CPP in native_sim is not supported.

As an immediate workaround, that should get things working for you, you could apply a hack like this in your app cmake file:

diff --git a/samples/cpp/hello_world/CMakeLists.txt b/samples/cpp/hello_world/CMakeLists.txt
index da4e1f7da41..f36af1e54e6 100644
--- a/samples/cpp/hello_world/CMakeLists.txt
+++ b/samples/cpp/hello_world/CMakeLists.txt
@@ -6,3 +6,8 @@ find_package(Zephyr REQUIRED HINTS $ENV{ZEPHYR_BASE})
 project(hello_cpp_world)
 
 target_sources(app PRIVATE src/main.cpp)
+target_sources(app PRIVATE
+       ${ZEPHYR_BASE}/lib/posix/options/getopt/getopt.c
+       ${ZEPHYR_BASE}/lib/posix/options/getopt/getopt_common.c)
+
+zephyr_include_directories(${ZEPHYR_BASE}/lib/posix/options/getopt/)

As a long term fix, it would be a bit more elaborate:

• @keith-packard had started looking into having the C++ library also as a source module we could build. Initially we discussed about being able to build it for the host, but this I think got a bit stranded and it is not specially easy. If we got this working, this combination would become possible.
• Independently of this (@cfriedt), we could get this getopt component to be something we could select independently of anything else from the POSIX_API. Its current bundling if and only if CONFIG_POSIX_C_LIB_EXT is set, is a bit off due to this being a non standard getopt, and therefore no C library could provide this getopt interface (and therefore set CONFIG_TC_PROVIDES_POSIX_C_LIB_EXT). Having getopt be a separate component which CONFIG_POSIX_C_LIB_EXT would enable and which could also be selected for C libraries which otherwise could provide CONFIG_TC_PROVIDES_POSIX_C_LIB_EXT would also solve this.

[cfriedt]

• Independently of this (@cfriedt), we could get this getopt component to be something we could select independently of anything else from the POSIX_API.

See #88547

Eventually, it would be nice to just use standard getopt(), or perhaps a semi-custom but reentrant getopt_r().

IIRC, the main reason for the additional state is because there may be multiple simultaneous shells open. But a reentrant version of getopt() should fix that.

[cfriedt]

• Independently of this (@cfriedt), we could get this getopt component to be something we could select independently of anything else from the POSIX_API.

See #88547

Eventually, it would be nice to just use standard getopt(), or perhaps a semi-custom / reentrant getopt_r().

IIRC, the main reason for the nonstandard getopt_state is because there may be multiple simultaneous threads that use it. However, getopt() uses global variables to keep track of state. A reentrant version of getopt() should fix that.

[keith-packard]

I was unable to get libstdc++ to build on the native host while using a nonstandard C library -- the gcc build system just doesn't understand that at all. Other than that limitation, the libstdc++ module seems to work fine.