kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 195 insertions, 0 deletions

diff --git a/tools/perf/util/cs-etm-base.c b/tools/perf/util/cs-etm-base.c
new file mode 100644
index 000000000..aebef71d3
--- /dev/null
+++ b/tools/perf/util/cs-etm-base.c
@@ -0,0 +1,195 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * File for any parts of the Coresight decoding that don't require
+ * OpenCSD.
+ */
+
+#include <errno.h>
+#include <inttypes.h>
+
+#include "cs-etm.h"
+
+static const char * const cs_etm_global_header_fmts[] = {
+	[CS_HEADER_VERSION]	= "	Header version		       %llx\n",
+	[CS_PMU_TYPE_CPUS]	= "	PMU type/num cpus	       %llx\n",
+	[CS_ETM_SNAPSHOT]	= "	Snapshot		       %llx\n",
+};
+
+static const char * const cs_etm_priv_fmts[] = {
+	[CS_ETM_MAGIC]		= "	Magic number		       %llx\n",
+	[CS_ETM_CPU]		= "	CPU			       %lld\n",
+	[CS_ETM_NR_TRC_PARAMS]	= "	NR_TRC_PARAMS		       %llx\n",
+	[CS_ETM_ETMCR]		= "	ETMCR			       %llx\n",
+	[CS_ETM_ETMTRACEIDR]	= "	ETMTRACEIDR		       %llx\n",
+	[CS_ETM_ETMCCER]	= "	ETMCCER			       %llx\n",
+	[CS_ETM_ETMIDR]		= "	ETMIDR			       %llx\n",
+};
+
+static const char * const cs_etmv4_priv_fmts[] = {
+	[CS_ETM_MAGIC]		= "	Magic number		       %llx\n",
+	[CS_ETM_CPU]		= "	CPU			       %lld\n",
+	[CS_ETM_NR_TRC_PARAMS]	= "	NR_TRC_PARAMS		       %llx\n",
+	[CS_ETMV4_TRCCONFIGR]	= "	TRCCONFIGR		       %llx\n",
+	[CS_ETMV4_TRCTRACEIDR]	= "	TRCTRACEIDR		       %llx\n",
+	[CS_ETMV4_TRCIDR0]	= "	TRCIDR0			       %llx\n",
+	[CS_ETMV4_TRCIDR1]	= "	TRCIDR1			       %llx\n",
+	[CS_ETMV4_TRCIDR2]	= "	TRCIDR2			       %llx\n",
+	[CS_ETMV4_TRCIDR8]	= "	TRCIDR8			       %llx\n",
+	[CS_ETMV4_TRCAUTHSTATUS] = "	TRCAUTHSTATUS		       %llx\n",
+	[CS_ETMV4_TS_SOURCE]	= "	TS_SOURCE		       %lld\n",
+};
+
+static const char * const cs_ete_priv_fmts[] = {
+	[CS_ETM_MAGIC]		= "	Magic number		       %llx\n",
+	[CS_ETM_CPU]		= "	CPU			       %lld\n",
+	[CS_ETM_NR_TRC_PARAMS]	= "	NR_TRC_PARAMS		       %llx\n",
+	[CS_ETE_TRCCONFIGR]	= "	TRCCONFIGR		       %llx\n",
+	[CS_ETE_TRCTRACEIDR]	= "	TRCTRACEIDR		       %llx\n",
+	[CS_ETE_TRCIDR0]	= "	TRCIDR0			       %llx\n",
+	[CS_ETE_TRCIDR1]	= "	TRCIDR1			       %llx\n",
+	[CS_ETE_TRCIDR2]	= "	TRCIDR2			       %llx\n",
+	[CS_ETE_TRCIDR8]	= "	TRCIDR8			       %llx\n",
+	[CS_ETE_TRCAUTHSTATUS]	= "	TRCAUTHSTATUS		       %llx\n",
+	[CS_ETE_TRCDEVARCH]	= "	TRCDEVARCH                     %llx\n",
+	[CS_ETE_TS_SOURCE]	= "	TS_SOURCE                      %lld\n",
+};
+
+static const char * const param_unk_fmt =
+	"	Unknown parameter [%d]	       %"PRIx64"\n";
+static const char * const magic_unk_fmt =
+	"	Magic number Unknown	       %"PRIx64"\n";
+
+static int cs_etm__print_cpu_metadata_v0(u64 *val, int *offset)
+{
+	int i = *offset, j, nr_params = 0, fmt_offset;
+	u64 magic;
+
+	/* check magic value */
+	magic = val[i + CS_ETM_MAGIC];
+	if ((magic != __perf_cs_etmv3_magic) &&
+	    (magic != __perf_cs_etmv4_magic)) {
+		/* failure - note bad magic value */
+		fprintf(stdout, magic_unk_fmt, magic);
+		return -EINVAL;
+	}
+
+	/* print common header block */
+	fprintf(stdout, cs_etm_priv_fmts[CS_ETM_MAGIC], val[i++]);
+	fprintf(stdout, cs_etm_priv_fmts[CS_ETM_CPU], val[i++]);
+
+	if (magic == __perf_cs_etmv3_magic) {
+		nr_params = CS_ETM_NR_TRC_PARAMS_V0;
+		fmt_offset = CS_ETM_ETMCR;
+		/* after common block, offset format index past NR_PARAMS */
+		for (j = fmt_offset; j < nr_params + fmt_offset; j++, i++)
+			fprintf(stdout, cs_etm_priv_fmts[j], val[i]);
+	} else if (magic == __perf_cs_etmv4_magic) {
+		nr_params = CS_ETMV4_NR_TRC_PARAMS_V0;
+		fmt_offset = CS_ETMV4_TRCCONFIGR;
+		/* after common block, offset format index past NR_PARAMS */
+		for (j = fmt_offset; j < nr_params + fmt_offset; j++, i++)
+			fprintf(stdout, cs_etmv4_priv_fmts[j], val[i]);
+	}
+	*offset = i;
+	return 0;
+}
+
+static int cs_etm__print_cpu_metadata_v1(u64 *val, int *offset)
+{
+	int i = *offset, j, total_params = 0;
+	u64 magic;
+
+	magic = val[i + CS_ETM_MAGIC];
+	/* total params to print is NR_PARAMS + common block size for v1 */
+	total_params = val[i + CS_ETM_NR_TRC_PARAMS] + CS_ETM_COMMON_BLK_MAX_V1;
+
+	if (magic == __perf_cs_etmv3_magic) {
+		for (j = 0; j < total_params; j++, i++) {
+			/* if newer record - could be excess params */
+			if (j >= CS_ETM_PRIV_MAX)
+				fprintf(stdout, param_unk_fmt, j, val[i]);
+			else
+				fprintf(stdout, cs_etm_priv_fmts[j], val[i]);
+		}
+	} else if (magic == __perf_cs_etmv4_magic) {
+		for (j = 0; j < total_params; j++, i++) {
+			/* if newer record - could be excess params */
+			if (j >= CS_ETMV4_PRIV_MAX)
+				fprintf(stdout, param_unk_fmt, j, val[i]);
+			else
+				fprintf(stdout, cs_etmv4_priv_fmts[j], val[i]);
+		}
+	} else if (magic == __perf_cs_ete_magic) {
+		for (j = 0; j < total_params; j++, i++) {
+			/* if newer record - could be excess params */
+			if (j >= CS_ETE_PRIV_MAX)
+				fprintf(stdout, param_unk_fmt, j, val[i]);
+			else
+				fprintf(stdout, cs_ete_priv_fmts[j], val[i]);
+		}
+	} else {
+		/* failure - note bad magic value and error out */
+		fprintf(stdout, magic_unk_fmt, magic);
+		return -EINVAL;
+	}
+	*offset = i;
+	return 0;
+}
+
+static void cs_etm__print_auxtrace_info(u64 *val, int num)
+{
+	int i, cpu = 0, version, err;
+
+	version = val[0];
+
+	for (i = 0; i < CS_HEADER_VERSION_MAX; i++)
+		fprintf(stdout, cs_etm_global_header_fmts[i], val[i]);
+
+	for (i = CS_HEADER_VERSION_MAX; cpu < num; cpu++) {
+		if (version == 0)
+			err = cs_etm__print_cpu_metadata_v0(val, &i);
+		/* printing same for both, but value bit flags added on v2 */
+		else if ((version == 1) || (version == 2))
+			err = cs_etm__print_cpu_metadata_v1(val, &i);
+		if (err)
+			return;
+	}
+}
+
+/*
+ * Do some basic checks and print the auxtrace info header before calling
+ * into cs_etm__process_auxtrace_info_full() which requires OpenCSD to be
+ * linked in. This allows some basic debugging if OpenCSD is missing.
+ */
+int cs_etm__process_auxtrace_info(union perf_event *event,
+				  struct perf_session *session)
+{
+	struct perf_record_auxtrace_info *auxtrace_info = &event->auxtrace_info;
+	int event_header_size = sizeof(struct perf_event_header);
+	int num_cpu;
+	u64 *ptr = NULL;
+	u64 hdr_version;
+
+	/* Ensure priv[] is large enough for the global header entries */
+	if (auxtrace_info->header.size < (event_header_size + INFO_HEADER_SIZE +
+					  CS_ETM_HEADER_SIZE))
+		return -EINVAL;
+
+	/* First the global part */
+	ptr = (u64 *) auxtrace_info->priv;
+
+	/* Look for version of the header */
+	hdr_version = ptr[0];
+	if (hdr_version > CS_HEADER_CURRENT_VERSION) {
+		pr_err("\nCS ETM Trace: Unknown Header Version = %#" PRIx64, hdr_version);
+		pr_err(", version supported <= %x\n", CS_HEADER_CURRENT_VERSION);
+		return -EINVAL;
+	}
+
+	if (dump_trace) {
+		num_cpu = ptr[CS_PMU_TYPE_CPUS] & 0xffffffff;
+		cs_etm__print_auxtrace_info(ptr, num_cpu);
+	}
+
+	return cs_etm__process_auxtrace_info_full(event, session);
+}