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

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Message-ID: <aIO4aLLFrMVp_Yht@debug.ba.rivosinc.com>
Date: Fri, 25 Jul 2025 10:01:28 -0700
From: Deepak Gupta <debug@...osinc.com>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>, Alexandre Ghiti <alex@...ti.fr>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Nathan Chancellor <nathan@...nel.org>,
	Nicolas Schier <nicolas.schier@...ux.dev>,
	Andrew Morton <akpm@...ux-foundation.org>,
	David Hildenbrand <david@...hat.com>,
	Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
	"Liam R. Howlett" <Liam.Howlett@...cle.com>,
	Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>,
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	Michal Hocko <mhocko@...e.com>,
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	Monk Chiang <monk.chiang@...ive.com>,
	Kito Cheng <kito.cheng@...ive.com>,
	Justin Stitt <justinstitt@...gle.com>,
	linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
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	ved@...osinc.com
Subject: Re: [PATCH 01/11] riscv: add landing pad for asm routines.

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