Re: [RFC PATCH] target/mips: Allow building without Inter-Thread Communication hardware

[Richard Henderson <richard.henderson@linaro.org>]

On 4/27/21 12:11 PM, Philippe Mathieu-Daudé wrote:
> The Inter-Thread Communication unit (TYPE_MIPS_ITU) is an optional
> device that is only selected by a few machines. However it goes
> deep into the translation code, as the MTC0/MTHC0 SAAR helpers
> call itc_reconfigure().
> 
> When building with no machine selecting the ITU component (which
> is implemented in hw/misc/mips_itu.c), we get the following link
> failure:
> 
>    /usr/bin/ld: target_mips_cp0_helper.c.o: in function `helper_mtc0_saar':
>    target/mips/cp0_helper.c:1118: undefined reference to `itc_reconfigure'
>    /usr/bin/ld: target_mips_cp0_helper.c.o: in function `helper_mthc0_saar':
>    target/mips/cp0_helper.c:1135: undefined reference to `itc_reconfigure'
> 
> Fix by adding a stub, built when the ITU isn't selected.
> 
> Signed-off-by: Philippe Mathieu-Daudé<f4bug@amsat.org>
> ---
> RFC because too much Meson machinery to my taste.
> But how to deal with such architectural devices else?
> 
> To reproduce:
> 
> $ echo CONFIG_JAZZ=y > default-configs/devices/mips64el-softmmu.mak
> $ echo CONFIG_SEMIHOSTING=y >> default-configs/devices/mips64el-softmmu.mak
> $ configure --without-default-devices
> $ ninja qemu-system-mips64el
> $ ./qemu-system-mips64el -M magnum -S
> ---
>   target/mips/cp0_itu-stub.c | 15 +++++++++++++++
>   target/mips/meson.build    |  3 +++
>   2 files changed, 18 insertions(+)
>   create mode 100644 target/mips/cp0_itu-stub.c

Perhaps use __attribute__((weak)) on itc_reconfigure?  Then you don't need the 
stub at all.  You're already protecting the actual call, so there should be no 
change needed there.

We're not using weak so far, but as far as I can tell this is supported by gcc 
on windows as well.


r~