linux-kernel - [patch 09/38] objtool: Add .sym

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Date:   Sun, 17 Jul 2022 01:17:24 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     x86@...nel.org, Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Andrew Cooper <Andrew.Cooper3@...rix.com>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Johannes Wikner <kwikner@...z.ch>,
        Alyssa Milburn <alyssa.milburn@...ux.intel.com>,
        Jann Horn <jannh@...gle.com>, "H.J. Lu" <hjl.tools@...il.com>,
        Joao Moreira <joao.moreira@...el.com>,
        Joseph Nuzman <joseph.nuzman@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: [patch 09/38] objtool: Add .sym_sites section

From: Peter Zijlstra <peterz@...radead.org>

In preparation for call depth tracking provide a section which collects all
all !init symbols to generate thunks for.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
 arch/x86/kernel/vmlinux.lds.S |    7 +++++
 tools/objtool/check.c         |   55 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 62 insertions(+)

--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -297,6 +297,13 @@ SECTIONS
 		*(.call_sites)
 		__call_sites_end = .;
 	}
+
+	. = ALIGN(8);
+	.sym_sites : AT(ADDR(.sym_sites) - LOAD_OFFSET) {
+		__sym_sites = .;
+		*(.sym_sites)
+		__sym_sites_end = .;
+	}
 #endif
 
 #ifdef CONFIG_X86_KERNEL_IBT
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -941,6 +941,56 @@ static int create_direct_call_sections(s
 	return 0;
 }
 
+static int create_sym_thunk_sections(struct objtool_file *file)
+{
+	struct section *sec, *s;
+	struct symbol *sym;
+	unsigned int *loc;
+	int idx;
+
+	sec = find_section_by_name(file->elf, ".sym_sites");
+	if (sec) {
+		INIT_LIST_HEAD(&file->call_list);
+		WARN("file already has .sym_sites section, skipping");
+		return 0;
+	}
+
+	idx = 0;
+	for_each_sec(file, s) {
+		if (!s->text || s->init)
+			continue;
+
+		list_for_each_entry(sym, &s->symbol_list, list)
+			idx++;
+	}
+
+	sec = elf_create_section(file->elf, ".sym_sites", 0, sizeof(unsigned int), idx);
+	if (!sec)
+		return -1;
+
+	idx = 0;
+	for_each_sec(file, s) {
+		if (!s->text || s->init)
+			continue;
+
+		list_for_each_entry(sym, &s->symbol_list, list) {
+
+			loc = (unsigned int *)sec->data->d_buf + idx;
+			memset(loc, 0, sizeof(unsigned int));
+
+			if (elf_add_reloc_to_insn(file->elf, sec,
+						idx * sizeof(unsigned int),
+						R_X86_64_PC32,
+						s, sym->offset))
+				return -1;
+
+			idx++;
+		}
+	}
+
+	return 0;
+}
+
 /*
  * Warnings shouldn't be reported for ignored functions.
  */
@@ -4326,6 +4376,11 @@ int check(struct objtool_file *file)
 		if (ret < 0)
 			goto out;
 		warnings += ret;
+
+		ret = create_sym_thunk_sections(file);
+		if (ret < 0)
+			goto out;
+		warnings += ret;
 	}
 
 	if (opts.mcount) {