Re: [PATCH 2/2] objtool: Add support for relocations without addends

From: Julien Thierry
Date: Tue Jun 02 2020 - 03:37:29 EST


Hi Matt,

On 5/29/20 10:01 PM, Matt Helsley wrote:
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@xxxxxxxxxx>
---
tools/objtool/elf.c | 146 +++++++++++++++++++++++++++++++++++-----
tools/objtool/elf.h | 7 +-
tools/objtool/orc_gen.c | 2 +-
3 files changed, 135 insertions(+), 20 deletions(-)

diff --git a/tools/objtool/elf.c b/tools/objtool/elf.c
index c21e8417637b..5034918494b6 100644
--- a/tools/objtool/elf.c
+++ b/tools/objtool/elf.c
@@ -490,6 +490,32 @@ 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;
@@ -499,7 +525,8 @@ 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);
@@ -519,16 +546,17 @@ 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) {
@@ -716,7 +744,38 @@ 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;
+}
+
+

Nit: Extra new line.

Otherwise:

Reviewed-by: Julien Thierry <jthierry@xxxxxxxxxx>

--
Julien Thierry