On 5/28/23 21:46, Jin Ma wrote:
When testing a extension, it is often necessary for a certain program not to
need some kind of extension, such as the bitmanip extension, to evaluate the
performance or codesize of the extension. However, the current multilib rules
will report an error when it is not a superset of the MULTILIB_REQUIRED list,
which will cause the program to be unable to link normally, thus failing to
achieve the expected purpose.
Hmm, I have troubles understanding what is going on here. What do you
refer to by saying: "it is not a superset of the MULTILIB_REQUIRED list"?
This is a new matching rule added by kito for the multilib of riscv:
https://github.com/gcc-mirror/gcc/commit/d72ca12b846a9f5c01674b280b1817876c77888f
There should be no problem with linking compiled modules together that
make use of different extensions, with the static linker figuring out the
combined set of extensions actually required at run time for the program
loader to consider, as long as the modules do not have contradicting
requirements, e.g. big vs little endianness or RV32 vs RV64.
Can you give me a specific example (compilation options and multilibs
available) of a failure you refer to?
A simple example:
1. Use "--disable-multilib --with-abi =lp64d --with-arch
=rv64imafdc_zba_zbb_zbc_zbs"
to build the toolchain".
2. Use the toolchain to test the impact of zba_zbb_zbc_zbs extensions on the
performance and codesize of some functions or files in the program.
In this case, I may need to use the command "-mabi=lp64d -march=rv64imafdc" for
the compilation of a specific .c file in the program, which will cause the link
to
fail and throw the following error: "FATAL ERROR: Can't find suitable multilib
set for
'-march=rv64imafdc'/'-mabi=lp64d'". This does not satisfy the purpose of the
test.
I feel this case should be build with --with-arch =rv64imafdc and test
with -march=rv64imafdc and -march=rv64imafdc_zba_zbb_zbc_zbs,
but anyway I am OK with option :P
Yes, but with "--with-arch=rv64imafdc" building toolchains, the library will
not contain
zba_zbb_zbc_zbs extensions, so how can we quickly and easily eliminate the
impact of not
using zba_zbb_zbc_zbs extensions in a certain program on program performance
and codesize?
Although-mno-multilib-check is unsafe, it is useful during the development and
testing phases.
But I'm not sure that's a good reason to include an unsafe option like
this in the official GCC sources.
This is the kind of thing that I'd tend to think belongs as a local change.
jeff
