From: Sasha Levin <sashal@kernel.org>
To: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: linux-kernel@vger.kernel.org, Bill Wendling <morbo@google.com>,
Chuck Wolber <chuck@wolber.net>,
Justin Stitt <justinstitt@google.com>,
llvm@lists.linux.dev, Marco Elver <elver@google.com>,
Masami Hiramatsu <mhiramat@kernel.org>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@kernel.org>
Subject: Re: [PATCH v2 11/20] objtool: Detect code coverage instrumentation in noinstr code
Date: Thu, 12 Nov 2026 08:09:06 -0500 [thread overview]
Message-ID: <20261112130906.1316655-1-sashal@kernel.org> (raw)
In-Reply-To: <avVaaxKUA2ArB6RG@jpoimboe>
On Wed, Nov 11, 2026 at 10:23:41PM -0800, Josh Poimboeuf wrote:
>What exactly is the problem with noinstr code incrementing counters
>inline?
The counter is a memory write, and a memory write can trap. In noinstr
code that can happen before we're ready to take another exception.
With GCOV_PROFILE_ALL today, exc_debug_kernel() bumps a counter before
it clears DR7. Set a watchpoint on that counter and the next kernel #DB
never returns, it just keeps re-entering the handler. I tried it on
v7.4-rc1 in a VM and it hangs.
noinstr is already supposed to keep these out, it has had __no_profile
for years. But that doesn't cover what gets inlined into it, and nothing
checks. This patch adds the check.
--
Thanks,
Sasha
next prev parent reply other threads:[~2026-11-12 13:09 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-11-03 1:52 [PATCH v2 00/20] Unify code coverage and add Clang source-based coverage with MC/DC Sasha Levin
2026-11-03 1:52 ` [PATCH v2 01/20] coverage: move gcov and kcov under kernel/coverage/ Sasha Levin
2026-11-05 17:38 ` Peter Oberparleiter
2026-11-03 1:52 ` [PATCH v2 02/20] kbuild: unify static coverage instrumentation as COVERAGE_PROFILE Sasha Levin
2026-11-03 1:52 ` [PATCH v2 03/20] coverage: add a common debugfs interface Sasha Levin
2026-11-05 17:49 ` Peter Oberparleiter
2026-11-06 1:05 ` Sasha Levin
2026-11-03 1:52 ` [PATCH v2 04/20] compiler_types.h: Don't instrument __always_inline functions for coverage Sasha Levin
2026-11-03 1:52 ` [PATCH v2 05/20] context_tracking: Always inline the empty stubs called from noinstr code Sasha Levin
2026-11-03 1:52 ` [PATCH v2 06/20] lockdep: " Sasha Levin
2026-11-03 1:52 ` [PATCH v2 07/20] perf: Always inline the empty perf_lopwr_cb() stub Sasha Levin
2026-11-03 1:52 ` [PATCH v2 08/20] rseq: Always inline the empty stubs called from noinstr code Sasha Levin
2026-11-03 1:52 ` [PATCH v2 09/20] x86: Always inline " Sasha Levin
2026-11-03 1:52 ` [PATCH v2 10/20] x86/sev: Use non-instrumented bitops in the GHCB accessors Sasha Levin
2026-11-04 13:36 ` Sean Christopherson
2026-11-03 1:52 ` [PATCH v2 11/20] objtool: Detect code coverage instrumentation in noinstr code Sasha Levin
2026-11-12 6:23 ` Josh Poimboeuf
2026-11-12 13:09 ` Sasha Levin [this message]
2026-11-03 1:52 ` [PATCH v2 12/20] x86/sev: Stop excluding noinstr.o from code coverage Sasha Levin
2026-11-03 1:52 ` [PATCH v2 13/20] x86/entry: Stop excluding the entry code from KCOV Sasha Levin
2026-11-03 1:52 ` [PATCH v2 14/20] coverage: add Clang's source-based code coverage Sasha Levin
2026-11-03 1:52 ` [PATCH v2 15/20] x86: Enable " Sasha Levin
2026-11-03 1:52 ` [PATCH v2 16/20] coverage: add MC/DC measurement Sasha Levin
2026-11-03 1:52 ` [PATCH v2 17/20] gcov: fix gcov_info_add() merge semantics for IOR counters Sasha Levin
2026-11-05 17:50 ` Peter Oberparleiter
2026-11-03 1:52 ` [PATCH v2 18/20] kconfig: add CC_HAS_CONDITION_COVERAGE for MC/DC support detection Sasha Levin
2026-11-03 1:52 ` [PATCH v2 19/20] gcov: add MC/DC condition coverage support Sasha Levin
2026-11-05 17:56 ` Peter Oberparleiter
2026-11-06 1:05 ` Sasha Levin
2026-11-03 1:52 ` [PATCH v2 20/20] Documentation: dev-tools: document the common code coverage interface Sasha Levin
2026-11-05 17:36 ` [PATCH v2 00/20] Unify code coverage and add Clang source-based coverage with MC/DC Peter Oberparleiter
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