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Add RISC-V Profiles format #36

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Add RISC-V Profiles format #36

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ec70e4c
Add RISC-V Profiles format
pz9115 May 2, 2023
47389da
Update profiles format descriptions
pz9115 Jun 29, 2023
11a65d4
Update Profile name defination with BNF.
pz9115 Jun 30, 2023
378d5eb
Update the syntax.
pz9115 Jul 18, 2023
f6bd873
Remove incorrect spaces using.
pz9115 Jul 19, 2023
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42 changes: 42 additions & 0 deletions README.mkd
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Expand Up @@ -64,6 +64,48 @@ specification (input is case sensitive, ...).
If the 'C' (compressed) instruction set extension is targeted, the compiler
will generate compressed instructions where possible.

### Profile-based format

Profiles should be recognized and used in the `-march=` option. The benefit of using
the `-march` option is easy for toolchain parsing the profiles string and expanding
it into normal extensions combinations.

Profiles format has the following BNF form `"-march="<profile-name>"+"[option-ext]*`.

`profile-name ::= "RV"<profile-family-name><profile-ratified-year><privilege-mode><ISA-XLEN>`

`profile-family-name ::= "I" | "M" | "A"`

`profile-ratified-year ::= "20" | "22" | "23"`

`privilege-mode ::= "U" | "S" | "M"`

`ISA-XLEN ::= "64" | "32"`

`option-ext ::= 'a legal RISC-V extension name'`

As the spec defines, to use the profiles it should follow profile naming convention
(See [3.4 form spec doc](https://github.com/riscv/riscv-profiles)), the toolchain
will check whether an input profile name is correct at first, then do the parse
work.

To distinguish between ordinary extension input and input with profiles,
profiles are assumed to be entered `at the beginning of the -march option`, and
then input other extensions. Profiles `should use uppercase letters` in the `-march`
option.
Comment on lines +92 to +95
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Incorrect placement of code (backtick) markup?

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I'm trying to emphasize here the rules for using, do you have any good solutions?

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Suggested change
To distinguish between ordinary extension input and input with profiles,
profiles are assumed to be entered `at the beginning of the -march option`, and
then input other extensions. Profiles `should use uppercase letters` in the `-march`
option.
To distinguish between ordinary extension input and input with profiles,
profiles are assumed to be entered `at the beginning of the -march option`, and
then input other extensions. Profiles *should use uppercase letters* in the `-march`
option.


e.g. `-march=RVA20U64` is a legal profile input, it will be expanded into:

`-march=rv64imafdc_zicsr_ziccif_ziccrse_ziccamoa_zicclsm_za128rs`,
which include all the mandatory extensions required by this profile.

`-march=RVA20U64+zba_zbb_zbc_zbs` is also a legal profile input, it will add
four new extensions after expanded profile strings:

`-march=rv64imafdc_zicsr_ziccif_ziccrse_ziccamoa_zicclsm_za128rs_zba_zbb_zbc_zbs`

and `-march=rva20u64` is an illegal profile input, it does not use uppercase letters.

### Issues for consideration
* Whether `riscv32` and `riscv64` should be accepted as synonyms for `rv32`
and `rv64`.
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