From: Paul Walmsley <pjw@kernel.org>
To: Marco Elver <elver@google.com>
Cc: Paul Walmsley <pjw@kernel.org>,
Palmer Dabbelt <palmer@dabbelt.com>,
Albert Ou <aou@eecs.berkeley.edu>,
Alexandre Ghiti <alex@ghiti.fr>,
linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] riscv: Implement _THIS_IP_ using inline asm
Date: Thu, 21 May 2026 15:57:59 -0600 (MDT) [thread overview]
Message-ID: <c860d9bf-2e02-ca67-ca8e-c120dc72cb54@kernel.org> (raw)
In-Reply-To: <20260521000436.3931067-1-elver@google.com>
On Thu, 21 May 2026, Marco Elver wrote:
> Both GCC [1] and Clang [2] consider the generic version of _THIS_IP_ to
> be broken:
>
> #define _THIS_IP_ ({ __label__ __here; __here: (unsigned long)&&__here; })
>
> In particular, the address of a label is only expected to be used with a
> computed goto.
>
> While the generic version more or less works today, it is known to be
> brittle and may break with current and future optimizations. For
> example, Clang -O2 always returns 1 when this function is inlined:
>
> static inline unsigned long get_ip(void)
> { return ({ __label__ __here; __here: (unsigned long)&&__here; }); }
>
> Fix it by overriding _THIS_IP_ in <asm/linkage.h> (which is included by
> <linux/instruction_pointer.h>) using an architecture-specific inline asm
> version. Additionally, avoiding taking the address of a label prevents
> compilers from emitting spurious indirect branch targets (e.g. ENDBR or
> BTI) under control-flow integrity schemes.
>
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120071 [1]
> Link: https://github.com/llvm/llvm-project/issues/138272 [2]
> Signed-off-by: Marco Elver <elver@google.com>
Thanks, queued for v7.2.
- Paul
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prev parent reply other threads:[~2026-05-21 21:58 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-21 0:04 [PATCH] riscv: Implement _THIS_IP_ using inline asm Marco Elver
2026-05-21 10:30 ` David Laight
2026-05-21 21:57 ` Paul Walmsley [this message]
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