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, 372 insertions, 0 deletions

diff --git a/tools/perf/util/parse-events.l b/tools/perf/util/parse-events.l
new file mode 100644
index 000000000..251ce4321
--- /dev/null
+++ b/tools/perf/util/parse-events.l
@@ -0,0 +1,372 @@
+
+%option reentrant
+%option bison-bridge
+%option prefix="parse_events_"
+%option stack
+%option bison-locations
+%option yylineno
+%option noyywrap
+
+%{
+#include <errno.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include "parse-events.h"
+#include "parse-events-bison.h"
+
+char *parse_events_get_text(yyscan_t yyscanner);
+YYSTYPE *parse_events_get_lval(yyscan_t yyscanner);
+int parse_events_get_column(yyscan_t yyscanner);
+int parse_events_get_leng(yyscan_t yyscanner);
+
+static int get_column(yyscan_t scanner)
+{
+	return parse_events_get_column(scanner) - parse_events_get_leng(scanner);
+}
+
+static int value(struct parse_events_state *parse_state, yyscan_t scanner, int base)
+{
+	YYSTYPE *yylval = parse_events_get_lval(scanner);
+	char *text = parse_events_get_text(scanner);
+	u64 num;
+
+	errno = 0;
+	num = strtoull(text, NULL, base);
+	if (errno) {
+		struct parse_events_error *error = parse_state->error;
+		char *help = NULL;
+
+		if (asprintf(&help, "Bad base %d number \"%s\"", base, text) > 0)
+			parse_events_error__handle(error, get_column(scanner), help , NULL);
+
+		return PE_ERROR;
+	}
+
+	yylval->num = num;
+	return PE_VALUE;
+}
+
+static int str(yyscan_t scanner, int token)
+{
+	YYSTYPE *yylval = parse_events_get_lval(scanner);
+	char *text = parse_events_get_text(scanner);
+
+	yylval->str = strdup(text);
+	return token;
+}
+
+static int quoted_str(yyscan_t scanner, int token)
+{
+	YYSTYPE *yylval = parse_events_get_lval(scanner);
+	char *text = parse_events_get_text(scanner);
+
+	/*
+	 * If a text tag specified on the command line
+	 * contains opening single quite ' then it is
+	 * expected that the tag ends with single quote
+	 * as well, like this:
+	 *     name=\'CPU_CLK_UNHALTED.THREAD:cmask=1\'
+	 * quotes need to be escaped to bypass shell
+	 * processing.
+	 */
+	yylval->str = strndup(&text[1], strlen(text) - 2);
+	return token;
+}
+
+/*
+ * This function is called when the parser gets two kind of input:
+ *
+ * 	@cfg1 or @cfg2=config
+ *
+ * The leading '@' is stripped off before 'cfg1' and 'cfg2=config' are given to
+ * bison.  In the latter case it is necessary to keep the string intact so that
+ * the PMU kernel driver can determine what configurable is associated to
+ * 'config'.
+ */
+static int drv_str(yyscan_t scanner, int token)
+{
+	YYSTYPE *yylval = parse_events_get_lval(scanner);
+	char *text = parse_events_get_text(scanner);
+
+	/* Strip off the '@' */
+	yylval->str = strdup(text + 1);
+	return token;
+}
+
+/*
+ * Use yyless to return all the characaters to the input. Update the column for
+ * location debugging. If __alloc is non-zero set yylval to the text for the
+ * returned token's value.
+ */
+#define REWIND(__alloc)				\
+do {								\
+	YYSTYPE *__yylval = parse_events_get_lval(yyscanner);	\
+	char *text = parse_events_get_text(yyscanner);		\
+								\
+	if (__alloc)						\
+		__yylval->str = strdup(text);			\
+								\
+	yycolumn -= strlen(text);				\
+	yyless(0);						\
+} while (0)
+
+static int term(yyscan_t scanner, enum parse_events__term_type type)
+{
+	YYSTYPE *yylval = parse_events_get_lval(scanner);
+
+	yylval->term_type = type;
+	return PE_TERM;
+}
+
+static void modifiers_error(struct parse_events_state *parse_state, yyscan_t scanner,
+			    int pos, char mod_char, const char *mod_name)
+{
+	struct parse_events_error *error = parse_state->error;
+	char *help = NULL;
+
+	if (asprintf(&help, "Duplicate modifier '%c' (%s)", mod_char, mod_name) > 0)
+		parse_events_error__handle(error, get_column(scanner) + pos, help , NULL);
+}
+
+static int modifiers(struct parse_events_state *parse_state, yyscan_t scanner)
+{
+	YYSTYPE *yylval = parse_events_get_lval(scanner);
+	char *text = parse_events_get_text(scanner);
+	struct parse_events_modifier mod = { .precise = 0, };
+
+	for (size_t i = 0, n = strlen(text); i < n; i++) {
+#define CASE(c, field)							\
+		case c:							\
+			if (mod.field) {				\
+				modifiers_error(parse_state, scanner, i, c, #field); \
+				return PE_ERROR;			\
+			}						\
+			mod.field = true;				\
+			break
+
+		switch (text[i]) {
+		CASE('u', user);
+		CASE('k', kernel);
+		CASE('h', hypervisor);
+		CASE('I', non_idle);
+		CASE('G', guest);
+		CASE('H', host);
+		case 'p':
+			mod.precise++;
+			/*
+			 * precise ip:
+			 *
+			 *  0 - SAMPLE_IP can have arbitrary skid
+			 *  1 - SAMPLE_IP must have constant skid
+			 *  2 - SAMPLE_IP requested to have 0 skid
+			 *  3 - SAMPLE_IP must have 0 skid
+			 *
+			 *  See also PERF_RECORD_MISC_EXACT_IP
+			 */
+			if (mod.precise > 3) {
+				struct parse_events_error *error = parse_state->error;
+				char *help = strdup("Maximum precise value is 3");
+
+				if (help) {
+					parse_events_error__handle(error, get_column(scanner) + i,
+								   help , NULL);
+				}
+				return PE_ERROR;
+			}
+			break;
+		CASE('P', precise_max);
+		CASE('S', sample_read);
+		CASE('D', pinned);
+		CASE('W', weak);
+		CASE('e', exclusive);
+		CASE('b', bpf);
+		CASE('R', retire_lat);
+		CASE('X', dont_regroup);
+		default:
+			return PE_ERROR;
+		}
+#undef CASE
+	}
+	yylval->mod = mod;
+	return PE_MODIFIER_EVENT;
+}
+
+#define YY_USER_ACTION					\
+do {							\
+	yylloc->last_column  = yylloc->first_column;	\
+	yylloc->first_column = yycolumn;		\
+	yycolumn += yyleng;				\
+} while (0);
+
+%}
+
+%x mem
+%s config
+%x event
+
+group		[^,{}/]*[{][^}]*[}][^,{}/]*
+event_pmu	[^,{}/]+[/][^/]*[/][^,{}/]*
+event		[^,{}/]+
+
+num_dec		[0-9]+
+num_hex		0x[a-fA-F0-9]{1,16}
+num_raw_hex	[a-fA-F0-9]{1,16}
+/* Regular pattern to match the token PE_NAME. */
+name_start      [a-zA-Z0-9_*?\[\]]
+name		{name_start}[a-zA-Z0-9_*?.\[\]!\-]*
+/* PE_NAME token when inside a config term list, allows ':'. */
+term_name	{name_start}[a-zA-Z0-9_*?.\[\]!\-:]*
+/*
+ * PE_NAME token when quoted, allows ':,.='.
+ * Matches the RHS of terms like: name='COMPLEX_CYCLES_NAME:orig=cycles,desc=chip-clock-ticks'.
+ */
+quoted_name	[\']{name_start}[a-zA-Z0-9_*?.\[\]!\-:,\.=]*[\']
+drv_cfg_term	[a-zA-Z0-9_\.]+(=[a-zA-Z0-9_*?\.:]+)?
+/*
+ * If you add a modifier you need to update modifiers().
+ * Also, the letters in modifier_event must not be in modifier_bp.
+ */
+modifier_event	[ukhpPGHSDIWebRX]{1,17}
+modifier_bp	[rwx]{1,3}
+digit		[0-9]
+non_digit	[^0-9]
+
+%%
+
+%{
+	struct parse_events_state *_parse_state = parse_events_get_extra(yyscanner);
+	{
+		int start_token = _parse_state->stoken;
+
+		if (start_token == PE_START_TERMS)
+			BEGIN(config);
+		else if (start_token == PE_START_EVENTS)
+			BEGIN(event);
+
+		if (start_token) {
+			_parse_state->stoken = 0;
+			/*
+			 * The flex parser does not init locations variable
+			 * via the scan_string interface, so we need do the
+			 * init in here.
+			 */
+			yycolumn = 0;
+			return start_token;
+		}
+         }
+%}
+
+<event>{
+
+{group}		{
+			BEGIN(INITIAL);
+			REWIND(0);
+		}
+
+{event_pmu}	|
+{event}		{
+			BEGIN(INITIAL);
+			REWIND(1);
+			return PE_EVENT_NAME;
+		}
+
+<<EOF>>		{
+			BEGIN(INITIAL);
+			REWIND(0);
+		}
+,		{
+			return ',';
+		}
+}
+
+<config>{
+	/*
+	 * Please update config_term_names when new static term is added.
+	 */
+config			{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_CONFIG); }
+config1			{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_CONFIG1); }
+config2			{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_CONFIG2); }
+config3			{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_CONFIG3); }
+config4			{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_CONFIG4); }
+name			{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_NAME); }
+period			{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_SAMPLE_PERIOD); }
+freq			{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_SAMPLE_FREQ); }
+branch_type		{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_BRANCH_SAMPLE_TYPE); }
+time			{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_TIME); }
+call-graph		{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_CALLGRAPH); }
+stack-size		{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_STACKSIZE); }
+max-stack		{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_MAX_STACK); }
+nr			{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_MAX_EVENTS); }
+inherit			{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_INHERIT); }
+no-inherit		{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_NOINHERIT); }
+overwrite		{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_OVERWRITE); }
+no-overwrite		{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_NOOVERWRITE); }
+percore			{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_PERCORE); }
+aux-output		{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_AUX_OUTPUT); }
+aux-action		{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_AUX_ACTION); }
+aux-sample-size		{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_AUX_SAMPLE_SIZE); }
+metric-id		{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_METRIC_ID); }
+cpu			{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_CPU); }
+ratio-to-prev		{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_RATIO_TO_PREV); }
+legacy-hardware-config 	{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_LEGACY_HARDWARE_CONFIG); }
+legacy-cache-config	{ return term(yyscanner, PARSE_EVENTS__TERM_TYPE_LEGACY_CACHE_CONFIG); }
+r{num_raw_hex}		{ return str(yyscanner, PE_RAW); }
+r0x{num_raw_hex}	{ return str(yyscanner, PE_RAW); }
+,			{ return ','; }
+"/"			{ BEGIN(INITIAL); return '/'; }
+{num_dec}		{ return value(_parse_state, yyscanner, 10); }
+{num_hex}		{ return value(_parse_state, yyscanner, 16); }
+{term_name}		{ return str(yyscanner, PE_NAME); }
+@{drv_cfg_term}		{ return drv_str(yyscanner, PE_DRV_CFG_TERM); }
+}
+
+<mem>{
+{modifier_bp}		{ return str(yyscanner, PE_MODIFIER_BP); }
+	/*
+	 * The colon before memory access modifiers can get mixed up with the
+	 * colon before event modifiers. Fortunately none of the option letters
+	 * are the same, so trailing context can be used disambiguate the two
+	 * cases.
+	 */
+":"/{modifier_bp}	{ return PE_BP_COLON; }
+	/*
+	 * The slash before memory length can get mixed up with the slash before
+	 * config terms. Fortunately config terms do not start with a numeric
+	 * digit, so trailing context can be used disambiguate the two cases.
+	 */
+"/"/{digit}		{ return PE_BP_SLASH; }
+"/"/{non_digit}		{ BEGIN(config); return '/'; }
+{num_dec}		{ return value(_parse_state, yyscanner, 10); }
+{num_hex}		{ return value(_parse_state, yyscanner, 16); }
+	/*
+	 * We need to separate 'mem:' scanner part, in order to get specific
+	 * modifier bits parsed out. Otherwise we would need to handle PE_NAME
+	 * and we'd need to parse it manually. During the escape from <mem>
+	 * state we need to put the escaping char back, so we dont miss it.
+	 */
+.			{ unput(*yytext); BEGIN(INITIAL); }
+	/*
+	 * We destroy the scanner after reaching EOF,
+	 * but anyway just to be sure get back to INIT state.
+	 */
+<<EOF>>			{ BEGIN(INITIAL); }
+}
+
+mem:			{ BEGIN(mem); return PE_PREFIX_MEM; }
+r{num_raw_hex}		{ return str(yyscanner, PE_RAW); }
+{num_dec}		{ return value(_parse_state, yyscanner, 10); }
+{num_hex}		{ return value(_parse_state, yyscanner, 16); }
+
+{modifier_event}	{ return modifiers(_parse_state, yyscanner); }
+{name}			{ return str(yyscanner, PE_NAME); }
+{quoted_name}		{ return quoted_str(yyscanner, PE_NAME); }
+"/"			{ BEGIN(config); return '/'; }
+,			{ BEGIN(event); return ','; }
+:			{ return ':'; }
+"{"			{ BEGIN(event); return '{'; }
+"}"			{ return '}'; }
+=			{ return '='; }
+\n			{ }
+.			{ }
+
+%%