Re: What is the correct way to add linker dependency to QEMU build system?

[Alex Bennée]

Paz Offer <poffer@nvidia.com> writes:

> ...after some testing...
> [Trying to add 'libdl' to be linked with QEMU]
>
> I did try to use 'g_module_open/close/symbol', but what I noticed is that 
> 'g_module_close' did not really unload my library.
> So if I would do:
>
> 1 g_module_open(my-lib)
> 2 Load symbols, use my library...
> 3 g_module_close(my-lib)
> 4 Make modifications to my library and reload it:
> 5 g_module_open(my-lib)
>
> Then the library was not really reloaded, and the old instance would
> still be used.

Glib does do reference counting so it won't unload the module until all
references have been dropped. Did you check the return value from the
g_module_close()?


> This did not happen when I used dlopen/dlclose.
> Do we have a way to force 'g_module_close' to unload the library?

On POSIX the underlying mechanism is dlclose() anyway. You can also
check g_module_error() to see if there was an error unloading.

>
> Thanks, Paz
>
> -------------------------------------------------------------------------------------------------------------------------
> From: Peter Maydell <peter.maydell@linaro.org>
> Sent: Thursday, February 29, 2024 7:34 PM
> To: Paz Offer <poffer@nvidia.com>
> Cc: qemu-devel@nongnu.org <qemu-devel@nongnu.org>
> Subject: Re: What is the correct way to add linker dependency to QEMU build 
> system? 
>  
> External email: Use caution opening links or attachments
>
> On Thu, 29 Feb 2024 at 16:10, Paz Offer <poffer@nvidia.com> wrote:
>> I want to add library 'libdl' to be linked with QEMU build for a particular 
>> target (e.g. - qemu-system-arm).
>> Using meson I would typically do 'compiler.find_library(...)', and later add 
>> the returned dependency to the binary
> dependencies list.
>> However, in QEMU I understand that these configurations are done in the 
>> './configure' file?
>>
>> What would be the correct way to do this?
>
> If you can do the job using the glib g_module_open()/
> g_module_symbol() functions (which is how QEMU itself does
> loading of plugin and module DLLs, and which on Unix hosts
> are pretty much wrappers around dlopen/dlsym) then you
> don't need to link against libdl at all.
>
> If this is for something you're planning to upstream
> then it might be worth talking at a higher level about
> what you're aiming to do. (If it's for something downstream
> that you don't plan to ever upstream then you can do
> whatever's easiest for you, of course.)
>
> -- PMM

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro