Re: [PATCH 08/13] hw/xtensa/xtfpga: Replace memcpy()+tswap32() by stl_endian_p()

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

On 10/3/24 23:44, Thomas Huth wrote:
> On 03/10/2024 23.40, Philippe Mathieu-Daudé wrote:
>> OK I guess I'm seeing Thomas point now; this series cover was not clear
>> enough. The goal is to remove TARGET_BIG_ENDIAN so we can build half
>> objects and do a little step toward the single binary.
> 
> Ok, that piece of information was missing in the patch description, indeed.
> But the tswap function should already work with common code, see the target_needs_bswap() 
> stuff in include/exec/tswap.h, so maybe this change here even is not needed at all?

The current practice of target_needs_bswap() merely restricts the scope of 
TARGET_BIG_ENDIAN, allowing devices to be built once.  It still requires TARGET_BIG_ENDIAN 
to exist.

For the goal of single-binary, target_needs_bswap() cannot exist, since there may be no 
one correct answer across the system.  We will need the sort of infrastructure that Phil 
is adding: endianness being chosen by the machine model and/or the instantiated devices.

What is left is deciding on the exact API to use.  The ld/st_endian_p interface with a 
boolean seems reasonable.  It interacts well with TARGET_BIG_ENDIAN as an intermediate 
step, as well as with the virtio legacy cpu mode dependent callback.


r~