Build failures on MSVC

[reid-p]

With the pattern change from
#if WITH_USB_BACKEND
..
#endif
to
if (WITH_USB_BACKEND) {
....
}

I'm getting linker errors related to usb_context_scan() etc.

MSVC compiler is not smart enough to do dead code removal, or I haven't found the right switches.
Been some other reports in for different libraries of the same issue with MSVC.

Thoughts?

[rgetz]

my thought is don’t modify the source so that it breaks. Sorry - we aren’t general purpose MSVC support - it has issues , but is popular enough we work around them.

The code as is - works. On purpose. We do it that way - not because it is pretty, but because it’s functional.

• Robin

[reid-p]

G'day rgetz,

Sorry let me be more clear. I haven't modified the source.
With commit c10d6e3
treewide: Avoid conditional compilation

msvc 2019 fails to compile libiio. The is due to the pattern change.
#if WITH_USB_BACKEND
..
#endif
to
if (WITH_USB_BACKEND) {
....
}

Prior to this commit it builds and links ok for me.

[rgetz]

Recent builds on Azure don't have problems.

MSVC 2019 64-bit:
https://dev.azure.com/AnalogDevices/OpenSource/_build/results?buildId=8122&view=logs&jobId=3bf45259-f282-5ab9-6af8-d5171104ab20&j=3bf45259-f282-5ab9-6af8-d5171104ab20&t=8bcefb13-031a-5d6c-f5c0-32b1d654e425

and 32-bit:
https://dev.azure.com/AnalogDevices/OpenSource/_build/results?buildId=8122&view=logs&jobId=ad766681-fedf-5bb6-6d2e-1115be53eaad&j=ad766681-fedf-5bb6-6d2e-1115be53eaad&t=d62301a8-0134-58d5-d20d-2758cb22f19d

Are you compiling with any weird flags that turn off optimization?

[pcercuei]

Hi @reid-p,
I can reproduce it, this happens when building the library when the cmake build variant is set to Debug. It will succeed to compile if you set it to Release mode, or RelWithDebInfo (if you need the debug symbols).

[reid-p]

Thanks @pcercuei

Yeap debug builds are the problem with msvc builds failing.

I was trying to create a vcpkg port for libiio for use with msvc.
Which builds the debug libraries first, and that's what I also used for for independent testing.

Having debug builds has been nice occasionally.

[pcercuei]

@reid-p The problem is that MSVC in debug mode is just very stupid. If it sees this code:

if (0)
   call_function();

It will try to link against the call_function symbol even though it's clearly dead code.

I believe for your vcpkg, you should build in RelWithDebInfo mode. The "solution" in our case would be to disable the Debug mode completely.

[rgetz]

@pcercuei Can we disable Debug mode in MSVC?

[pcercuei]

@rgetz I tried but failed, MSVC has a "Debug" mode even when CMake doesn't have one.

[rgetz]

so, do we just document (in the README_BUILD.md) and close?

[pcercuei]

Yes, but maybe leave this bug report open until the README_BUILD.md is updated.

[rgetz]

Added #798