Re: [PATCH 01/11] riscv: add landing pad for asm routines.

From: Deepak Gupta <debug@rivosinc.com>
To: Sami Tolvanen <samitolvanen@google.com>
Cc: Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexandre Ghiti <alex@ghiti.fr>,
	Masahiro Yamada <masahiroy@kernel.org>,
	Nathan Chancellor <nathan@kernel.org>,
	Nicolas Schier <nicolas.schier@linux.dev>,
	Andrew Morton <akpm@linux-foundation.org>,
	David Hildenbrand <david@redhat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@oracle.com>,
	"Liam R. Howlett" <Liam.Howlett@oracle.com>,
	Vlastimil Babka <vbabka@suse.cz>, Mike Rapoport <rppt@kernel.org>,
	Suren Baghdasaryan <surenb@google.com>,
	Michal Hocko <mhocko@suse.com>,
	Nick Desaulniers <nick.desaulniers+lkml@gmail.com>,
	Bill Wendling <morbo@google.com>,
	Monk Chiang <monk.chiang@sifive.com>,
	Kito Cheng <kito.cheng@sifive.com>,
	Justin Stitt <justinstitt@google.com>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	linux-kbuild@vger.kernel.org, linux-mm@kvack.org,
	llvm@lists.linux.dev, rick.p.edgecombe@intel.com,
	broonie@kernel.org, cleger@rivosinc.com, apatel@ventanamicro.com,
	ajones@ventanamicro.com, conor.dooley@microchip.com,
	charlie@rivosinc.com, samuel.holland@sifive.com,
	bjorn@rivosinc.com, fweimer@redhat.com, jeffreyalaw@gmail.com,
	heinrich.schuchardt@canonical.com, andrew@sifive.com,
	ved@rivosinc.com
Subject: Re: [PATCH 01/11] riscv: add landing pad for asm routines.
Date: Fri, 25 Jul 2025 10:01:28 -0700	[thread overview]
Message-ID: <aIO4aLLFrMVp_Yht@debug.ba.rivosinc.com> (raw)
In-Reply-To: <20250725152745.GA1724026@google.com>

On Fri, Jul 25, 2025 at 03:27:45PM +0000, Sami Tolvanen wrote:
>On Thu, Jul 24, 2025 at 04:36:54PM -0700, Deepak Gupta wrote:
>> SYM_* macros are used to define assembly routines. In this patch series,
>> re-define those macros in risc-v arch specific include file to include
>> a landing pad instruction at the beginning. This is done only when the
>> compiler flag for landing pad is enabled (i.e. __riscv_zicfilp).
>>
>> TODO: Update `lpad 0` with `lpad %lpad_hash(name)` after toolchain
>> support.
>
>I glanced through the proposed signature based landing pad labeling
>scheme, but didn't see any mentions of lpad_hash for labeling assembly
>functions. Is there more information somewhere about how this is going
>to be implemented?

Take a look here for generation of type string
https://github.com/sifive/riscv-gcc/blob/f26ae78e21e591f78802a975b68dbde9a224a192/gcc/config/riscv/riscv-func-sig.cc

For hash scheme, take a look here
https://github.com/sifive/riscv-binutils-gdb/commit/1d027fd590c8ad79eba997bcf9b979872ff38eef
`riscv_lpad_hash` function has detail about how 20bit hash is extracted.

>
>Sami