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libdrgn: find kernel module name in kernels < v4.13

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If we can't find the module name in .modinfo, fall back to
.gnu.linkonce.this_module.
This commit is contained in:
Omar Sandoval 2019-05-14 15:39:16 -07:00
parent e4b8af7807
commit 0026eeae66
1 changed files with 51 additions and 19 deletions
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70
libdrgn/program.c
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@ -961,22 +961,30 @@ out_fd:
return err;
}
static struct drgn_error *get_module_name(Elf_Scn *modinfo_scn,
static struct drgn_error *get_module_name(struct drgn_program *prog,
Elf_Scn *this_module_scn,
Elf_Scn *modinfo_scn,
const char **ret)
{
struct drgn_error *err;
Elf_Data *data;
const char *p, *end;
const char *p, *end, *nul;
struct drgn_qualified_type module_type;
struct drgn_member_info name_member;
size_t name_offset;
/*
* Since Linux kernel commit 3e2e857f9c3a ("module: Add module name to
* modinfo") (in v4.13), we can get the module name from .modinfo.
* Before that, we need to get it from .gnu.linkonce.this_module, which
* contains a struct module.
*/
err = read_elf_section(modinfo_scn, &data);
if (err)
return err;
p = data->d_buf;
end = p + data->d_size;
while (p < end) {
const char *nul;
nul = memchr(p, 0, end - p);
if (!nul)
break;
@ -986,8 +994,29 @@ static struct drgn_error *get_module_name(Elf_Scn *modinfo_scn,
}
p = nul + 1;
}
err = read_elf_section(this_module_scn, &data);
if (err)
return err;
err = drgn_program_find_type(prog, "struct module", NULL,
&module_type);
if (err)
return err;
err = drgn_program_member_info(prog, module_type.type, "name",
&name_member);
if (err)
return err;
name_offset = name_member.bit_offset / 8;
if (name_offset < data->d_size) {
p = data->d_buf + name_offset;
nul = memchr(p, 0, data->d_size - name_offset);
if (nul && nul != p) {
*ret = p;
return NULL;
}
}
return drgn_error_create(DRGN_ERROR_LOOKUP,
"could not find name in .modinfo section");
"could not find module name in .modinfo or .gnu.linkonce.this_module");
}
static struct drgn_error *get_symbol_section_name(Elf *elf, size_t shstrndx,
@ -1031,7 +1060,7 @@ kernel_relocation_hook(struct drgn_program *prog, const char *name,
Elf *elf;
GElf_Ehdr ehdr_mem, *ehdr;
size_t shstrndx;
Elf_Scn *scn, *modinfo_scn = NULL, *symtab_scn = NULL;
Elf_Scn *scn, *this_module_scn, *modinfo_scn, *symtab_scn;
const char *section_name, *module_name;
uint64_t section_address;
@ -1049,8 +1078,8 @@ kernel_relocation_hook(struct drgn_program *prog, const char *name,
if (elf_getshdrstrndx(elf, &shstrndx))
return drgn_error_libelf();
/* Find .modinfo and .symtab. */
scn = NULL;
/* Find .gnu.linkonce.this_module, .modinfo, and .symtab. */
scn = modinfo_scn = this_module_scn = symtab_scn = NULL;
while ((scn = elf_nextscn(elf, scn))) {
GElf_Shdr *shdr, shdr_mem;
const char *scnname;
@ -1062,24 +1091,27 @@ kernel_relocation_hook(struct drgn_program *prog, const char *name,
scnname = elf_strptr(elf, shstrndx, shdr->sh_name);
if (!scnname)
continue;
if (strcmp(scnname, ".modinfo") == 0)
if (strcmp(scnname, ".gnu.linkonce.this_module") == 0)
this_module_scn = scn;
else if (strcmp(scnname, ".modinfo") == 0)
modinfo_scn = scn;
else if (strcmp(scnname, ".symtab") == 0)
symtab_scn = scn;
}
if (!modinfo_scn) {
return drgn_error_create(DRGN_ERROR_LOOKUP,
"could not find .modinfo section");
}
if (!symtab_scn) {
return drgn_error_create(DRGN_ERROR_LOOKUP,
"could not find .symtab section");
}
err = get_module_name(modinfo_scn, &module_name);
if (!this_module_scn || !modinfo_scn) {
return drgn_error_create(DRGN_ERROR_LOOKUP,
"'%s' is not from vmlinux or a kernel module");
}
err = get_module_name(prog, this_module_scn, modinfo_scn, &module_name);
if (err)
return err;
if (!symtab_scn) {
return drgn_error_format(DRGN_ERROR_LOOKUP,
"could not find .symtab section in %s",
module_name);
}
err = get_symbol_section_name(elf, shstrndx, symtab_scn, name,
sym->address, &section_name);
if (err)