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

Sathvika Vasireddy
2022-10-02T10:45:50Z

From: Christophe Leroy <christophe.leroy@csgroup.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@infradead.org>
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.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@linux.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