linux-kernel - [PATCH v1 0/2] Use BTF to trim return values

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Message-Id: <20251207142742.229924-1-dolinux.peng@gmail.com>
Date: Sun,  7 Dec 2025 22:27:40 +0800
From: Donglin Peng <dolinux.peng@...il.com>
To: rostedt@...dmis.org
Cc: linux-trace-kernel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	pengdonglin <pengdonglin@...omi.com>
Subject: [PATCH v1 0/2] Use BTF to trim return values

From: pengdonglin <pengdonglin@...omi.com>

The current funcgraph-retval implementation has two limitations:

1. It prints a return value even when the traced function returns void.
2. When the return type is narrower than a register, the printed value may
   be incorrect because high bits can contain undefined data.

Both issues are addressed by using BTF to obtain the precise return type
of each traced function:

- Return values are now printed only for functions whose return type is
  not void.
- The value is truncated to the actual width of the return type, ensuring
  correct representation.

These changes make the funcgraph-retval output more accurate and remove
noise from void functions.

pengdonglin (2):
  fgraph: use BTF to trim and filter return values
  tracing: Update funcgraph-retval documentation

 Documentation/trace/ftrace.rst       | 74 +++++++++++++++-------------
 kernel/trace/trace_functions_graph.c | 64 ++++++++++++++++++++----
 2 files changed, 94 insertions(+), 44 deletions(-)

-- 
2.34.1