linux-kernel - [PATCH 2/2] tools: perf: tests: Fix code reading for riscv

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Message-Id: <20241216-perf_fix_riscv_obj_reading-v1-2-b75962660a9b@rivosinc.com>
Date: Mon, 16 Dec 2024 15:12:52 -0800
From: Charlie Jenkins <charlie@...osinc.com>
To: Masahiro Yamada <masahiroy@...nel.org>, 
 Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
 Nathan Chancellor <nathan@...nel.org>, 
 Nick Desaulniers <ndesaulniers@...gle.com>, 
 Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>, 
 Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
 Arnaldo Carvalho de Melo <acme@...nel.org>, 
 Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>, 
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
 Jiri Olsa <jolsa@...nel.org>, Ian Rogers <irogers@...gle.com>, 
 Adrian Hunter <adrian.hunter@...el.com>, 
 Mickaël Salaün <mic@...ikod.net>, 
 Günther Noack <gnoack@...gle.com>, 
 Nelson Chu <nelson@...osinc.com>
Cc: linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org, 
 linux-riscv@...ts.infradead.org, llvm@...ts.linux.dev, 
 linux-perf-users@...r.kernel.org, linux-security-module@...r.kernel.org, 
 Charlie Jenkins <charlie@...osinc.com>
Subject: [PATCH 2/2] tools: perf: tests: Fix code reading for riscv

After binutils commit e43d876 which was first included in binutils 2.41,
riscv no longer supports dumping in the middle of instructions. Increase
the objdump window by 2-bytes to ensure that any instruction that sits
on the boundary of the specified stop-address is not cut in half.

Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
---
 arch/riscv/Kconfig              |  5 +++++
 tools/perf/tests/code-reading.c | 17 ++++++++++++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index d4a7ca0388c071b536df59c0eb11d55f9080c7cd..f164047471267936bc62389b7d7d9a7cbdca8f97 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -229,6 +229,11 @@ config GCC_SUPPORTS_DYNAMIC_FTRACE
 	def_bool CC_IS_GCC
 	depends on $(cc-option,-fpatchable-function-entry=8)
 
+config RISCV_OBJDUMP_SUPPORTS_SPLIT_INSTRUCTION
+	# Some versions of objdump do not support dumping partial instructions
+	def_bool y
+	depends on !(OBJDUMP_IS_GNU && OBJDUMP_VERSION > 24100)
+
 config HAVE_SHADOW_CALL_STACK
 	def_bool $(cc-option,-fsanitize=shadow-call-stack)
 	# https://github.com/riscv-non-isa/riscv-elf-psabi-doc/commit/a484e843e6eeb51f0cb7b8819e50da6d2444d769
diff --git a/tools/perf/tests/code-reading.c b/tools/perf/tests/code-reading.c
index 27c82cfb7e7de42284bf5af9cf7594a3a963052e..605f4a8e1dbc00d8a572503f45053c2f30ad19e3 100644
--- a/tools/perf/tests/code-reading.c
+++ b/tools/perf/tests/code-reading.c
@@ -1,5 +1,6 @@
 // SPDX-License-Identifier: GPL-2.0
 #include <errno.h>
+#include <linux/kconfig.h>
 #include <linux/kernel.h>
 #include <linux/types.h>
 #include <inttypes.h>
@@ -183,9 +184,23 @@ static int read_via_objdump(const char *filename, u64 addr, void *buf,
 	const char *fmt;
 	FILE *f;
 	int ret;
+	u64 stop_address = addr + len;
+
+	if (IS_ENABLED(__riscv) && !IS_ENABLED(CONFIG_RISCV_OBJDUMP_SUPPORTS_SPLIT_INSTRUCTION)) {
+		/*
+		 * On some versions of riscv objdump, dumping in the middle of
+		 * instructions is not supported. riscv instructions are aligned along
+		 * 2-byte intervals and can be either 2-bytes or 4-bytes. This makes it
+		 * possible that the stop-address lands in the middle of a 4-byte
+		 * instruction. Increase the stop_address by two to ensure an
+		 * instruction is not cut in half, but leave the len as-is so only the
+		 * expected number of bytes are collected.
+		 */
+		stop_address += 2;
+	}
 
 	fmt = "%s -z -d --start-address=0x%"PRIx64" --stop-address=0x%"PRIx64" %s";
-	ret = snprintf(cmd, sizeof(cmd), fmt, test_objdump_path, addr, addr + len,
+	ret = snprintf(cmd, sizeof(cmd), fmt, test_objdump_path, addr, stop_address,
 		       filename);
 	if (ret <= 0 || (size_t)ret >= sizeof(cmd))
 		return -1;

-- 
2.34.1