[PATCH 0/3] RISC-V: Make ISA parser stricter (with code clarity improvement)

[Tsukasa OI <research_trasio@irq.a4lg.com>]

[note: my copyright assignment is already complete on 2022-01-19]

Current GNU Toolchain accepts invalid RISC-V ISA string containing
invalid underscores (double underscores or trailing underscore).  This
patchset will reject those.

It's not sure that prohibiting those invalid patterns helps users from
accident but would be better than nothing.

As a part of this patchset, PATCH 1/3 removes unnecessary loop in the
ISA string parser (riscv_parse_subset function).  It is a requirement to
reject invalid trailing underscore after a multi-letter extension but it
also improves clarity of the code, regardless of whether invalid
underscores are rejected.



Removal of Unnecessary Loop (PATCH 1/3):

riscv_parse_prefixed_ext function (formerly,
riscv_parse_sv_or_non_std_ext function) used to parse multi-letter
extension with SINGLE type of prefix ('Z', 'S', likewise...).  At the
time when this function is created, iterating over prefix type was
absolutely necessary.

However, commit e601909a3287bf541c6a7d82214bb387d2c76d82 ("RISC-V:
Support to parse the multi-letter prefix in the architecture string.")
by Nelson Chu changed the situation.  Updated riscv_parse_prefixed_ext
function now parses all prefix types in a single call and no longer
requires a loop (in fact, this function is called only once and "while"
loop in riscv_parse_subset function does not actually "loop").

I added trailing underscore-checking code (in PATCH 2/3) at the end of
riscv_parse_prefixed_ext function.  That means, my PATCH 2/3 assumes
that riscv_parse_prefixed_ext is called only once.

PATCH 1/3 ensures that riscv_parse_prefixed_ext is called only once and
that improves the clarity, even without other patches.



Invalid Double Underscores (Rejected in PATCH 2/3):

multi-multi extensions (e.g. Zicsr and Zifencei) must be separated by
AN underscore.  Quoting ISA Manual (version 20191213),

27.6 "Additional Standard Extension Names":
> Extensions with the “Z” prefix must be separated from other multi-
> letter extensions by AN underscore, e.g., “RV32IMACZicsr_Zifencei”.

27.7 "Supervisor-level Instruction-Set Extensions":
> Supervisor-level extensions must be separated from other multi-letter
> extensions by AN underscore.

27.10 "Non-Standard Extension Names":
> They must be separated from other multi-letter extensions by AN
> underscore.

Although multiple underscores are not explicitly prohibited to separate
single-multi or single-single extension pairs, it's not natural to
assume that multiple underscores are allowed here as "AN underscore" is
required to avoid “P” extension ambiguity.

27.5 "Underscores":
> Because the “P” extension for Packed SIMD can be confused for the
> decimal point in a version number, it must be preceded by AN
> underscore if it follows a number.



Invalid Trailing Underscore (Rejected in PATCH 2/3):

This is not allowed in any way because all underscores are intended to
be used to separate ISA extensions.



Tests (PATCH 3/3):

New tests contain invalid ISA strings.




Tsukasa OI (3):
  RISC-V: Remove a loop in the ISA parser
  RISC-V: Stricter underscore handling for ISA
  RISC-V: Tests for ISA string handling (underscore)

 bfd/elfxx-riscv.c                             | 36 ++++++++++++++-----
 .../riscv/march-fail-underscore-double-01.d   |  3 ++
 .../riscv/march-fail-underscore-double-02.d   |  3 ++
 .../riscv/march-fail-underscore-double-03.d   |  3 ++
 .../riscv/march-fail-underscore-double-04.d   |  3 ++
 .../riscv/march-fail-underscore-double-05.d   |  3 ++
 .../riscv/march-fail-underscore-double-06.d   |  3 ++
 .../riscv/march-fail-underscore-double-07.d   |  3 ++
 .../riscv/march-fail-underscore-double-08.d   |  3 ++
 .../gas/riscv/march-fail-underscore-double.l  |  2 ++
 .../riscv/march-fail-underscore-trailing-01.d |  3 ++
 .../riscv/march-fail-underscore-trailing-02.d |  3 ++
 .../riscv/march-fail-underscore-trailing-03.d |  3 ++
 .../riscv/march-fail-underscore-trailing-04.d |  3 ++
 .../riscv/march-fail-underscore-trailing.l    |  2 ++
 15 files changed, 68 insertions(+), 8 deletions(-)
 create mode 100644 gas/testsuite/gas/riscv/march-fail-underscore-double-01.d
 create mode 100644 gas/testsuite/gas/riscv/march-fail-underscore-double-02.d
 create mode 100644 gas/testsuite/gas/riscv/march-fail-underscore-double-03.d
 create mode 100644 gas/testsuite/gas/riscv/march-fail-underscore-double-04.d
 create mode 100644 gas/testsuite/gas/riscv/march-fail-underscore-double-05.d
 create mode 100644 gas/testsuite/gas/riscv/march-fail-underscore-double-06.d
 create mode 100644 gas/testsuite/gas/riscv/march-fail-underscore-double-07.d
 create mode 100644 gas/testsuite/gas/riscv/march-fail-underscore-double-08.d
 create mode 100644 gas/testsuite/gas/riscv/march-fail-underscore-double.l
 create mode 100644 gas/testsuite/gas/riscv/march-fail-underscore-trailing-01.d
 create mode 100644 gas/testsuite/gas/riscv/march-fail-underscore-trailing-02.d
 create mode 100644 gas/testsuite/gas/riscv/march-fail-underscore-trailing-03.d
 create mode 100644 gas/testsuite/gas/riscv/march-fail-underscore-trailing-04.d
 create mode 100644 gas/testsuite/gas/riscv/march-fail-underscore-trailing.l


base-commit: 3a3e333f65483b864bf2624392f8aa4a88c7a498
-- 
2.32.0