Re: [PATCH v3 08/10] stackdepot: add architecture hooks for compact frame storage

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [High] stackdepot: uninitialized frame in
  arch_stack_depot_frame_decompress()
--

commit 29af5949877efb1954b766cd936a7c6ac5d5fb21
Author: Caleb Kan <ckan@cloudflare.com>

stackdepot: add architecture hooks for compact frame storage

This commit introduces architecture hooks for compressing and decompressing
stack depot frames into 32-bit payloads on arm64 and x86-64, with a generic
no-op fallback for other architectures.

> diff --git a/include/asm-generic/stackdepot.h b/include/asm-generic/stackdepot.h
> new file mode 100644
> index 0000000000000..846975767bdd4
> --- /dev/null
> +++ b/include/asm-generic/stackdepot.h
> @@ -0,0 +1,19 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __ASM_GENERIC_STACKDEPOT_H
> +#define __ASM_GENERIC_STACKDEPOT_H
> +
> +#include <linux/types.h>
> +
> +static inline bool
> +arch_stack_depot_frame_try_compress(unsigned long frame, u32 *low)
> +{
> +	return false;
> +}
> +
> +static inline void
> +arch_stack_depot_frame_decompress(u32 low, unsigned long *frame)
> +{
> +	/* Generic code never compresses frames, so this hook is unreachable. */
> +}

[Severity: High]
Does leaving *frame untouched here cause uninitialized-variable warnings
when callers pass an uninitialized local to
arch_stack_depot_frame_decompress()?

When commit "stackdepot: Store compressed frames in stack records" wires
this into depot_stack_entry(), it declares an uninitialized local frame,
calls arch_stack_depot_frame_decompress(..., &frame) when
stack->flags & STACK_RECORD_COMPRESSED is set, and returns frame.  On
architectures using this generic header, the compiler cannot tell that
STACK_RECORD_COMPRESSED is never set at runtime, so inlining the empty body
leaves frame uninitialized and breaks the build under -Wuninitialized /
-Wmaybe-uninitialized.  Setting *frame = 0 (or calling unreachable()) would
avoid this.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261113185702.1332171-1-matt@readmodwrite.com?part=8