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objtool: Add support for relocations without addends
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Currently objtool only collects information about relocations with
addends. In recordmcount, which we are about to merge into objtool,
some supported architectures do not use rela relocations.

Signed-off-by: Matt Helsley <mhelsley@vmware.com>
Reviewed-by: Julien Thierry <jthierry@redhat.com>
Reviewed-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
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Matt Helsley authored and Josh Poimboeuf committed Jun 2, 2020
1 parent f197422 commit fb41478
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Showing 3 changed files with 134 additions and 20 deletions.
145 changes: 128 additions & 17 deletions tools/objtool/elf.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -496,6 +496,32 @@ void elf_add_reloc(struct elf *elf, struct reloc *reloc)
elf_hash_add(elf->reloc_hash, &reloc->hash, reloc_hash(reloc));
}

static int read_rel_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
{
if (!gelf_getrel(sec->data, i, &reloc->rel)) {
WARN_ELF("gelf_getrel");
return -1;
}
reloc->type = GELF_R_TYPE(reloc->rel.r_info);
reloc->addend = 0;
reloc->offset = reloc->rel.r_offset;
*symndx = GELF_R_SYM(reloc->rel.r_info);
return 0;
}

static int read_rela_reloc(struct section *sec, int i, struct reloc *reloc, unsigned int *symndx)
{
if (!gelf_getrela(sec->data, i, &reloc->rela)) {
WARN_ELF("gelf_getrela");
return -1;
}
reloc->type = GELF_R_TYPE(reloc->rela.r_info);
reloc->addend = reloc->rela.r_addend;
reloc->offset = reloc->rela.r_offset;
*symndx = GELF_R_SYM(reloc->rela.r_info);
return 0;
}

static int read_relocs(struct elf *elf)
{
struct section *sec;
Expand All @@ -505,7 +531,8 @@ static int read_relocs(struct elf *elf)
unsigned long nr_reloc, max_reloc = 0, tot_reloc = 0;

list_for_each_entry(sec, &elf->sections, list) {
if (sec->sh.sh_type != SHT_RELA)
if ((sec->sh.sh_type != SHT_RELA) &&
(sec->sh.sh_type != SHT_REL))
continue;

sec->base = find_section_by_index(elf, sec->sh.sh_info);
Expand All @@ -525,16 +552,17 @@ static int read_relocs(struct elf *elf)
return -1;
}
memset(reloc, 0, sizeof(*reloc));

if (!gelf_getrela(sec->data, i, &reloc->rela)) {
WARN_ELF("gelf_getrela");
return -1;
switch (sec->sh.sh_type) {
case SHT_REL:
if (read_rel_reloc(sec, i, reloc, &symndx))
return -1;
break;
case SHT_RELA:
if (read_rela_reloc(sec, i, reloc, &symndx))
return -1;
break;
default: return -1;
}

reloc->type = GELF_R_TYPE(reloc->rela.r_info);
reloc->addend = reloc->rela.r_addend;
reloc->offset = reloc->rela.r_offset;
symndx = GELF_R_SYM(reloc->rela.r_info);
reloc->sym = find_symbol_by_index(elf, symndx);
reloc->sec = sec;
if (!reloc->sym) {
Expand Down Expand Up @@ -722,7 +750,37 @@ struct section *elf_create_section(struct elf *elf, const char *name,
return sec;
}

struct section *elf_create_reloc_section(struct elf *elf, struct section *base)
static struct section *elf_create_rel_reloc_section(struct elf *elf, struct section *base)
{
char *relocname;
struct section *sec;

relocname = malloc(strlen(base->name) + strlen(".rel") + 1);
if (!relocname) {
perror("malloc");
return NULL;
}
strcpy(relocname, ".rel");
strcat(relocname, base->name);

sec = elf_create_section(elf, relocname, sizeof(GElf_Rel), 0);
free(relocname);
if (!sec)
return NULL;

base->reloc = sec;
sec->base = base;

sec->sh.sh_type = SHT_REL;
sec->sh.sh_addralign = 8;
sec->sh.sh_link = find_section_by_name(elf, ".symtab")->idx;
sec->sh.sh_info = base->idx;
sec->sh.sh_flags = SHF_INFO_LINK;

return sec;
}

static struct section *elf_create_rela_reloc_section(struct elf *elf, struct section *base)
{
char *relocname;
struct section *sec;
Expand Down Expand Up @@ -752,16 +810,53 @@ struct section *elf_create_reloc_section(struct elf *elf, struct section *base)
return sec;
}

int elf_rebuild_reloc_section(struct section *sec)
struct section *elf_create_reloc_section(struct elf *elf,
struct section *base,
int reltype)
{
switch (reltype) {
case SHT_REL: return elf_create_rel_reloc_section(elf, base);
case SHT_RELA: return elf_create_rela_reloc_section(elf, base);
default: return NULL;
}
}

static int elf_rebuild_rel_reloc_section(struct section *sec, int nr)
{
struct reloc *reloc;
int nr, idx = 0, size;
GElf_Rela *relocs;
int idx = 0, size;
GElf_Rel *relocs;

nr = 0;
list_for_each_entry(reloc, &sec->reloc_list, list)
nr++;
/* Allocate a buffer for relocations */
size = nr * sizeof(*relocs);
relocs = malloc(size);
if (!relocs) {
perror("malloc");
return -1;
}

sec->data->d_buf = relocs;
sec->data->d_size = size;

sec->sh.sh_size = size;

idx = 0;
list_for_each_entry(reloc, &sec->reloc_list, list) {
relocs[idx].r_offset = reloc->offset;
relocs[idx].r_info = GELF_R_INFO(reloc->sym->idx, reloc->type);
idx++;
}

return 0;
}

static int elf_rebuild_rela_reloc_section(struct section *sec, int nr)
{
struct reloc *reloc;
int idx = 0, size;
GElf_Rela *relocs;

/* Allocate a buffer for relocations with addends */
size = nr * sizeof(*relocs);
relocs = malloc(size);
if (!relocs) {
Expand All @@ -785,6 +880,22 @@ int elf_rebuild_reloc_section(struct section *sec)
return 0;
}

int elf_rebuild_reloc_section(struct section *sec)
{
struct reloc *reloc;
int nr;

nr = 0;
list_for_each_entry(reloc, &sec->reloc_list, list)
nr++;

switch (sec->sh.sh_type) {
case SHT_REL: return elf_rebuild_rel_reloc_section(sec, nr);
case SHT_RELA: return elf_rebuild_rela_reloc_section(sec, nr);
default: return -1;
}
}

int elf_write(const struct elf *elf)
{
struct section *sec;
Expand Down
7 changes: 5 additions & 2 deletions tools/objtool/elf.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -61,7 +61,10 @@ struct symbol {
struct reloc {
struct list_head list;
struct hlist_node hash;
GElf_Rela rela;
union {
GElf_Rela rela;
GElf_Rel rel;
};
struct section *sec;
struct symbol *sym;
unsigned int type;
Expand Down Expand Up @@ -116,7 +119,7 @@ static inline u32 reloc_hash(struct reloc *reloc)

struct elf *elf_open_read(const char *name, int flags);
struct section *elf_create_section(struct elf *elf, const char *name, size_t entsize, int nr);
struct section *elf_create_reloc_section(struct elf *elf, struct section *base);
struct section *elf_create_reloc_section(struct elf *elf, struct section *base, int reltype);
void elf_add_reloc(struct elf *elf, struct reloc *reloc);
int elf_write(const struct elf *elf);
void elf_close(struct elf *elf);
Expand Down
2 changes: 1 addition & 1 deletion tools/objtool/orc_gen.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -181,7 +181,7 @@ int create_orc_sections(struct objtool_file *file)
if (!sec)
return -1;

ip_relocsec = elf_create_reloc_section(file->elf, sec);
ip_relocsec = elf_create_reloc_section(file->elf, sec, SHT_RELA);
if (!ip_relocsec)
return -1;

Expand Down

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