How can user find out what extensions supported when use riscv-gnu-toolchain without a source code sight?

[pz9115]

When user use riscv-gnu-toolchain, a common problem is that they don't know what extensions was supported for their toolchain.

Should we add some features for toolchain that make user use more convenient.

[cmuellner]

For me the output of gcc -v is enough to find the corresponding sources.
However, I agree that this is not a user-friendly way.

What helps with ABIs and code models is gcc --target-help, but this does not list all acceptable march substrings.

BTW, AArch64 supports this:

echo | aarch64-linux-gnu-gcc -march=armv8.42-a -dM -E -
cc1: error: unknown value ‘armv8.42-a’ for ‘-march’
cc1: note: valid arguments are: armv8-a armv8.1-a armv8.2-a armv8.3-a armv8.4-a armv8.5-a armv8.6-a armv8-r; did you mean ‘armv8.2-a’?

And on x86 it is possible to get a list of supported march strings using gcc -v --help.

However, given the fact, that users can compose the march string on RISC-V, someone would have to write a patch, that collects all supported extensions and prints them (preferably as part of --target-help).

[kito-cheng]

A potential proposal is adding -mtune=?, -mcpu=? and -march=? to list all supported option for those options, clang already supported first 2 option, so I think it would be great create some issue on https://github.com/riscv-non-isa/riscv-toolchain-conventions

[kito-cheng]

Issue created riscv-non-isa/riscv-toolchain-conventions#24

[TommyMurphyTM1234]

Maybe I'm looking at this too simplistically, but doesn't the following provide the required info?

riscv64-unknown-elf-gcc -dumpspecs | grep arch
--traditional-format %(subtarget_asm_debugging_spec) %{fpie|fPIE|fpic|fPIC:-fpic} %{march=*} %{mabi=*} %{mno-relax} %{mbig-endian} %{mlittle-endian} %(subtarget_asm_spec)%{misa-spec=*}
-melf%{march=rv32*:32}%{march=rv64*:64}lriscv %{mno-relax:--no-relax} %{mbig-endian:-EB} %{mlittle-endian:-EL} %{shared}
march=rv64imafdv_zve32f_zve32x_zve64d_zve64f_zve64x_zvl128b_zvl32b_zvl64b mabi=lp64d

riscv64-unknown-elf-gcc -print-multi-lib
...

That provides the default arch/abi for the toolchain (last line of the grepped -dumpspecs ouput) and the set of other arch/abi pairs supported by the available multilibs.

Edit: I just noticed that the output from -v does not correctly correspond to the output from -dumpspecs (rv64gc versus rv64imafdv_zve32f_zve32x_zve64d_zve64f_zve64x_zvl128b_zvl32b_zvl64b respectively):

riscv64-unknown-elf-gcc -v
Using built-in specs.
COLLECT_GCC=./riscv64-unknown-elf-gcc
COLLECT_LTO_WRAPPER=/home/tommy/Downloads/riscv-tools/rvv64/installed-tools/libexec/gcc/riscv64-unknown-elf/12.0.1/lto-wrapper
Target: riscv64-unknown-elf
Configured with: /home/tommy/Downloads/riscv-tools/rvv64/riscv-gcc/configure --target=riscv64-unknown-elf --prefix=/home/tommy/Downloads/riscv-tools/rvv64/installed-tools --disable-shared --disable-threads --enable-languages=c,c++ --with-pkgversion= --with-system-zlib --enable-tls --with-newlib --with-sysroot=/home/tommy/Downloads/riscv-tools/rvv64/installed-tools/riscv64-unknown-elf --with-native-system-header-dir=/include --disable-libmudflap --disable-libssp --disable-libquadmath --disable-libgomp --disable-nls --disable-tm-clone-registry --src=.././riscv-gcc --disable-multilib --with-abi=lp64d --with-arch=rv64gv --with-tune=rocket --with-isa-spec=2.2 'CFLAGS_FOR_TARGET=-Os   -mcmodel=medlow' 'CXXFLAGS_FOR_TARGET=-Os   -mcmodel=medlow'
Thread model: single
Supported LTO compression algorithms: zlib
gcc version 12.0.1 20220505 (prerelease) () 

This may be a separate issue relating to the inference of some extensions over and above those specific in the --with-arch= configuration option?

[TommyMurphyTM1234]

No update in over a year and it seems to me that earlier posts explain how to obtain the relevant info so I am closing this issue.