kernel/1338-scripts-sorttable-get-start-stop-mcount-loc-from-elf-file-di.patch

From 0e6fd4e629cfcaf1a4f04e2c9e39e8b5776890a2 Mon Sep 17 00:00:00 2001
From: Jerome Marchand <jmarchan@redhat.com>
Date: Mon, 1 Jun 2026 15:36:32 +0200
Subject: [PATCH] scripts/sorttable: Get start/stop_mcount_loc from ELF file
 directly

JIRA: https://redhat.atlassian.net/browse/RHEL-180193

commit 4acda8edefa1ce66d3de845f1c12745721cd14c3
Author: Steven Rostedt <rostedt@goodmis.org>
Date:   Sun Jan 5 11:22:25 2025 -0500

    scripts/sorttable: Get start/stop_mcount_loc from ELF file directly

    The get_mcount_loc() does a cheesy trick to find the start_mcount_loc and
    stop_mcount_loc values. That trick is:

     file_start = popen(" grep start_mcount System.map | awk '{print $1}' ", "r");

    and

     file_stop = popen(" grep stop_mcount System.map | awk '{print $1}' ", "r");

    Those values are stored in the Elf symbol table. Use that to capture those
    values. Using the symbol table is more efficient and more robust. The
    above could fail if another variable had "start_mcount" or "stop_mcount"
    as part of its name.

    Cc: bpf <bpf@vger.kernel.org>
    Cc: Masami Hiramatsu <mhiramat@kernel.org>
    Cc: Mark Rutland <mark.rutland@arm.com>
    Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Masahiro Yamada <masahiroy@kernel.org>
    Cc: Nathan Chancellor <nathan@kernel.org>
    Cc: Nicolas Schier <nicolas@fjasle.eu>
    Cc: Zheng Yejian <zhengyejian1@huawei.com>
    Cc: Martin  Kelly <martin.kelly@crowdstrike.com>
    Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Link: https://lore.kernel.org/20250105162346.817157047@goodmis.org
    Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Signed-off-by: Jerome Marchand <jmarchan@redhat.com>

diff --git a/scripts/sorttable.c b/scripts/sorttable.c
index ff9b60fc0dd8..656c1e9b5ad9 100644
--- a/scripts/sorttable.c
+++ b/scripts/sorttable.c
@@ -472,42 +472,41 @@ static void *sort_mcount_loc(void *arg)
 }
 
 /* Get the address of __start_mcount_loc and __stop_mcount_loc in System.map */
-static void get_mcount_loc(uint64_t *_start, uint64_t *_stop)
+static void get_mcount_loc(struct elf_mcount_loc *emloc, Elf_Shdr *symtab_sec,
+			   const char *strtab)
 {
-	FILE *file_start, *file_stop;
-	char start_buff[20];
-	char stop_buff[20];
-	int len = 0;
+	Elf_Sym *sym, *end_sym;
+	int symentsize = shdr_entsize(symtab_sec);
+	int found = 0;
+
+	sym = (void *)emloc->ehdr + shdr_offset(symtab_sec);
+	end_sym = (void *)sym + shdr_size(symtab_sec);
+
+	while (sym < end_sym) {
+		if (!strcmp(strtab + sym_name(sym), "__start_mcount_loc")) {
+			emloc->start_mcount_loc = sym_value(sym);
+			if (++found == 2)
+				break;
+		} else if (!strcmp(strtab + sym_name(sym), "__stop_mcount_loc")) {
+			emloc->stop_mcount_loc = sym_value(sym);
+			if (++found == 2)
+				break;
+		}
+		sym = (void *)sym + symentsize;
+	}
 
-	file_start = popen(" grep start_mcount System.map | awk '{print $1}' ", "r");
-	if (!file_start) {
+	if (!emloc->start_mcount_loc) {
 		fprintf(stderr, "get start_mcount_loc error!");
 		return;
 	}
 
-	file_stop = popen(" grep stop_mcount System.map | awk '{print $1}' ", "r");
-	if (!file_stop) {
+	if (!emloc->stop_mcount_loc) {
 		fprintf(stderr, "get stop_mcount_loc error!");
-		pclose(file_start);
 		return;
 	}
-
-	while (fgets(start_buff, sizeof(start_buff), file_start) != NULL) {
-		len = strlen(start_buff);
-		start_buff[len - 1] = '\0';
-	}
-	*_start = strtoul(start_buff, NULL, 16);
-
-	while (fgets(stop_buff, sizeof(stop_buff), file_stop) != NULL) {
-		len = strlen(stop_buff);
-		stop_buff[len - 1] = '\0';
-	}
-	*_stop = strtoul(stop_buff, NULL, 16);
-
-	pclose(file_start);
-	pclose(file_stop);
 }
 #endif
+
 static int do_sort(Elf_Ehdr *ehdr,
 		   char const *const fname,
 		   table_sort_t custom_sort)
@@ -538,8 +537,6 @@ static int do_sort(Elf_Ehdr *ehdr,
 	unsigned int shstrndx;
 #ifdef MCOUNT_SORT_ENABLED
 	struct elf_mcount_loc mstruct = {0};
-	uint64_t _start_mcount_loc = 0;
-	uint64_t _stop_mcount_loc = 0;
 #endif
 #ifdef UNWINDER_ORC_ENABLED
 	unsigned int orc_ip_size = 0;
@@ -577,13 +574,8 @@ static int do_sort(Elf_Ehdr *ehdr,
 
 #ifdef MCOUNT_SORT_ENABLED
 		/* locate the .init.data section in vmlinux */
-		if (!strcmp(secstrings + idx, ".init.data")) {
-			get_mcount_loc(&_start_mcount_loc, &_stop_mcount_loc);
-			mstruct.ehdr = ehdr;
+		if (!strcmp(secstrings + idx, ".init.data"))
 			mstruct.init_data_sec = shdr;
-			mstruct.start_mcount_loc = _start_mcount_loc;
-			mstruct.stop_mcount_loc = _stop_mcount_loc;
-		}
 #endif
 
 #ifdef UNWINDER_ORC_ENABLED
@@ -627,23 +619,6 @@ static int do_sort(Elf_Ehdr *ehdr,
 		goto out;
 	}
 #endif
-
-#ifdef MCOUNT_SORT_ENABLED
-	if (!mstruct.init_data_sec || !_start_mcount_loc || !_stop_mcount_loc) {
-		fprintf(stderr,
-			"incomplete mcount's sort in file: %s\n",
-			fname);
-		goto out;
-	}
-
-	/* create thread to sort mcount_loc concurrently */
-	if (pthread_create(&mcount_sort_thread, NULL, &sort_mcount_loc, &mstruct)) {
-		fprintf(stderr,
-			"pthread_create mcount_sort_thread failed '%s': %s\n",
-			strerror(errno), fname);
-		goto out;
-	}
-#endif
 	if (!extab_sec) {
 		fprintf(stderr,	"no __ex_table in file: %s\n", fname);
 		goto out;
@@ -663,6 +638,26 @@ static int do_sort(Elf_Ehdr *ehdr,
 	strtab = (const char *)ehdr + shdr_offset(strtab_sec);
 	symtab = (const Elf_Sym *)((const char *)ehdr + shdr_offset(symtab_sec));
 
+#ifdef MCOUNT_SORT_ENABLED
+	mstruct.ehdr = ehdr;
+	get_mcount_loc(&mstruct, symtab_sec, strtab);
+
+	if (!mstruct.init_data_sec || !mstruct.start_mcount_loc || !mstruct.stop_mcount_loc) {
+		fprintf(stderr,
+			"incomplete mcount's sort in file: %s\n",
+			fname);
+		goto out;
+	}
+
+	/* create thread to sort mcount_loc concurrently */
+	if (pthread_create(&mcount_sort_thread, NULL, &sort_mcount_loc, &mstruct)) {
+		fprintf(stderr,
+			"pthread_create mcount_sort_thread failed '%s': %s\n",
+			strerror(errno), fname);
+		goto out;
+	}
+#endif
+
 	if (custom_sort) {
 		custom_sort(extab_image, shdr_size(extab_sec));
 	} else {
-- 
2.50.1 (Apple Git-155)