linux-kernel - [PATCH v4 10/16] objtool: Use target file class size instead of a compiled constant

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Date:   Sun,  2 Oct 2022 16:12:34 +0530
From:   Sathvika Vasireddy <sv@...ux.ibm.com>
To:     linuxppc-dev@...ts.ozlabs.org
Cc:     jpoimboe@...hat.com, peterz@...radead.org,
        linux-kernel@...r.kernel.org, aik@...abs.ru, mpe@...erman.id.au,
        mingo@...hat.com, christophe.leroy@...roup.eu, rostedt@...dmis.org,
        mbenes@...e.cz, npiggin@...il.com, chenzhongjin@...wei.com,
        naveen.n.rao@...ux.vnet.ibm.com, sv@...ux.ibm.com
Subject: [PATCH v4 10/16] objtool: Use target file class size instead of a compiled constant

From: Christophe Leroy <christophe.leroy@...roup.eu>

In order to allow using objtool on cross-built kernels,
determine size of long from elf data instead of using
sizeof(long) at build time.

For the time being this covers only mcount.

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
[Sathvika Vasireddy: Rename variable "size" to "addrsize" and function
"elf_class_size()" to "elf_class_addrsize()", and modify
create_mcount_loc_sections() function to follow reverse christmas tree
format to order local variable declarations.]
Signed-off-by: Sathvika Vasireddy <sv@...ux.ibm.com>
---
 tools/objtool/check.c               | 18 ++++++++++--------
 tools/objtool/elf.c                 |  8 ++++++--
 tools/objtool/include/objtool/elf.h |  8 ++++++++
 3 files changed, 24 insertions(+), 10 deletions(-)

diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index c36e7a020d80..738de23cb9e8 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -852,9 +852,9 @@ static int create_ibt_endbr_seal_sections(struct objtool_file *file)
 
 static int create_mcount_loc_sections(struct objtool_file *file)
 {
-	struct section *sec;
-	unsigned long *loc;
+	int addrsize = elf_class_addrsize(file->elf);
 	struct instruction *insn;
+	struct section *sec;
 	int idx;
 
 	sec = find_section_by_name(file->elf, "__mcount_loc");
@@ -871,23 +871,25 @@ static int create_mcount_loc_sections(struct objtool_file *file)
 	list_for_each_entry(insn, &file->mcount_loc_list, call_node)
 		idx++;
 
-	sec = elf_create_section(file->elf, "__mcount_loc", 0, sizeof(unsigned long), idx);
+	sec = elf_create_section(file->elf, "__mcount_loc", 0, addrsize, idx);
 	if (!sec)
 		return -1;
 
+	sec->sh.sh_addralign = addrsize;
+
 	idx = 0;
 	list_for_each_entry(insn, &file->mcount_loc_list, call_node) {
+		void *loc;
 
-		loc = (unsigned long *)sec->data->d_buf + idx;
-		memset(loc, 0, sizeof(unsigned long));
+		loc = sec->data->d_buf + idx;
+		memset(loc, 0, addrsize);
 
-		if (elf_add_reloc_to_insn(file->elf, sec,
-					  idx * sizeof(unsigned long),
+		if (elf_add_reloc_to_insn(file->elf, sec, idx,
 					  R_X86_64_64,
 					  insn->sec, insn->offset))
 			return -1;
 
-		idx++;
+		idx += addrsize;
 	}
 
 	return 0;
diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index c25e957c1e52..40c6d53b081f 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -1124,6 +1124,7 @@ static struct section *elf_create_rela_reloc_section(struct elf *elf, struct sec
 {
 	char *relocname;
 	struct section *sec;
+	int addrsize = elf_class_addrsize(elf);
 
 	relocname = malloc(strlen(base->name) + strlen(".rela") + 1);
 	if (!relocname) {
@@ -1133,7 +1134,10 @@ static struct section *elf_create_rela_reloc_section(struct elf *elf, struct sec
 	strcpy(relocname, ".rela");
 	strcat(relocname, base->name);
 
-	sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rela), 0);
+	if (addrsize == sizeof(u32))
+		sec = elf_create_section(elf, relocname, 0, sizeof(Elf32_Rela), 0);
+	else
+		sec = elf_create_section(elf, relocname, 0, sizeof(GElf_Rela), 0);
 	free(relocname);
 	if (!sec)
 		return NULL;
@@ -1142,7 +1146,7 @@ static struct section *elf_create_rela_reloc_section(struct elf *elf, struct sec
 	sec->base = base;
 
 	sec->sh.sh_type = SHT_RELA;
-	sec->sh.sh_addralign = 8;
+	sec->sh.sh_addralign = addrsize;
 	sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
 	sec->sh.sh_info = base->idx;
 	sec->sh.sh_flags = SHF_INFO_LINK;
diff --git a/tools/objtool/include/objtool/elf.h b/tools/objtool/include/objtool/elf.h
index 16f4067b82ae..78b3aa2e546d 100644
--- a/tools/objtool/include/objtool/elf.h
+++ b/tools/objtool/include/objtool/elf.h
@@ -142,6 +142,14 @@ static inline bool has_multiple_files(struct elf *elf)
 	return elf->num_files > 1;
 }
 
+static inline int elf_class_addrsize(struct elf *elf)
+{
+	if (elf->ehdr.e_ident[EI_CLASS] == ELFCLASS32)
+		return sizeof(u32);
+	else
+		return sizeof(u64);
+}
+
 struct elf *elf_open_read(const char *name, int flags);
 struct section *elf_create_section(struct elf *elf, const char *name, unsigned int sh_flags, size_t entsize, int nr);
 
-- 
2.31.1