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libkmod: store common section off/size and use them
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Currently, we repeatedly loop over the elf headers looking for five well
known sections. Just do it once in kmod_elf_new() and reuse the data as
needed.

Note, that not all sections are guaranteed to be available, so check and
ELFDBG print the ones which are missing.

v2: quit looping when found, ELFDBG print missing sections

Signed-off-by: Emil Velikov <[email protected]>
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@evelikov
evelikov committed Nov 11, 2024
1 parent 417d273 commit 56cd05d
Showing 1 changed file with 106 additions and 28 deletions.
134 changes: 106 additions & 28 deletions libkmod/libkmod-elf.c
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,23 @@ struct kmod_modversion64 {
char name[64 - sizeof(uint64_t)];
};

enum kmod_elf_section {
KMOD_ELF_SECTION_KSYMTAB,
KMOD_ELF_SECTION_MODINFO,
KMOD_ELF_SECTION_STRTAB,
KMOD_ELF_SECTION_SYMTAB,
KMOD_ELF_SECTION_VERSIONS,
KMOD_ELF_SECTION_MAX,
};

static const char *const section_name_map[] = {
[KMOD_ELF_SECTION_KSYMTAB] = "__ksymtab_strings",
[KMOD_ELF_SECTION_MODINFO] = ".modinfo",
[KMOD_ELF_SECTION_STRTAB] = ".strtab",
[KMOD_ELF_SECTION_SYMTAB] = ".symtab",
[KMOD_ELF_SECTION_VERSIONS] = "__versions",
};

struct kmod_elf {
const uint8_t *memory;
uint64_t size;
Expand All @@ -45,6 +62,10 @@ struct kmod_elf {
} strings;
uint16_t machine;
} header;
struct {
uint64_t offset;
uint64_t size;
} sections[KMOD_ELF_SECTION_MAX];
};

//#undef ENABLE_ELFDBG
Expand Down Expand Up @@ -248,6 +269,56 @@ static inline int elf_get_section_info(const struct kmod_elf *elf, uint16_t idx,
return -EINVAL;
}

static void kmod_elf_save_sections(struct kmod_elf *elf)
{
const uint16_t all_sec = (1 << KMOD_ELF_SECTION_MAX) - 1;
uint16_t found_sec = 0;

for (uint16_t i = 1; i < elf->header.section.count && found_sec != all_sec; i++) {
uint64_t off, size;
const char *n;
int err = elf_get_section_info(elf, i, &off, &size, &n);
if (err < 0)
continue;
if (streq("__ksymtab_strings", n)) {
elf->sections[KMOD_ELF_SECTION_KSYMTAB].offset = off;
elf->sections[KMOD_ELF_SECTION_KSYMTAB].size = size;
found_sec |= 1 << KMOD_ELF_SECTION_KSYMTAB;
continue;
}
if (streq(".modinfo", n)) {
elf->sections[KMOD_ELF_SECTION_MODINFO].offset = off;
elf->sections[KMOD_ELF_SECTION_MODINFO].size = size;
found_sec |= 1 << KMOD_ELF_SECTION_MODINFO;
continue;
}
if (streq(".strtab", n)) {
elf->sections[KMOD_ELF_SECTION_STRTAB].offset = off;
elf->sections[KMOD_ELF_SECTION_STRTAB].size = size;
found_sec |= 1 << KMOD_ELF_SECTION_STRTAB;
continue;
}
if (streq(".symtab", n)) {
elf->sections[KMOD_ELF_SECTION_SYMTAB].offset = off;
elf->sections[KMOD_ELF_SECTION_SYMTAB].size = size;
found_sec |= 1 << KMOD_ELF_SECTION_SYMTAB;
continue;
}
if (streq("__versions", n)) {
elf->sections[KMOD_ELF_SECTION_VERSIONS].offset = off;
elf->sections[KMOD_ELF_SECTION_VERSIONS].size = size;
found_sec |= 1 << KMOD_ELF_SECTION_VERSIONS;
continue;
}
}

for (uint16_t i = 0; !((1 << i) & found_sec) && i < KMOD_ELF_SECTION_MAX; i++) {
ELFDBG(elf, "section %s not found\n", section_name_map[i]);
elf->sections[i].offset = 0;
elf->sections[i].size = 0;
}
}

struct kmod_elf *kmod_elf_new(const void *memory, off_t size)
{
struct kmod_elf *elf;
Expand Down Expand Up @@ -335,6 +406,7 @@ struct kmod_elf *kmod_elf_new(const void *memory, off_t size)
}
}

kmod_elf_save_sections(elf);
return elf;

invalid:
Expand Down Expand Up @@ -390,13 +462,13 @@ int kmod_elf_get_modinfo_strings(const struct kmod_elf *elf, char ***array)
uint64_t off, size;
const char *strings;
char *s, **a;
int err;

*array = NULL;

err = kmod_elf_get_section(elf, ".modinfo", &off, &size);
if (err < 0)
return err;
off = elf->sections[KMOD_ELF_SECTION_MODINFO].offset;
size = elf->sections[KMOD_ELF_SECTION_MODINFO].size;
if (off == 0)
return -ENODATA;

strings = elf_get_mem(elf, off);

Expand Down Expand Up @@ -486,15 +558,16 @@ int kmod_elf_get_modversions(const struct kmod_elf *elf, struct kmod_modversion
size_t off, crclen, namlen, verlen;

Check warning on line 558 in libkmod/libkmod-elf.c

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libkmod/libkmod-elf.c#L558 

Added line #L558 was not covered by tests
uint64_t sec_off, size;
struct kmod_modversion *a;
int i, count, err;
int i, count;

Check warning on line 561 in libkmod/libkmod-elf.c

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libkmod/libkmod-elf.c#L561 

Added line #L561 was not covered by tests

elf_get_modversion_lengths(elf, &verlen, &crclen, &namlen);

*array = NULL;

err = kmod_elf_get_section(elf, "__versions", &sec_off, &size);
if (err < 0)
return err;
sec_off = elf->sections[KMOD_ELF_SECTION_VERSIONS].offset;
size = elf->sections[KMOD_ELF_SECTION_VERSIONS].size;

Check warning on line 568 in libkmod/libkmod-elf.c

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libkmod/libkmod-elf.c#L567-L568 

Added lines #L567 - L568 were not covered by tests
if (sec_off == 0)
return -ENODATA;

if (size == 0)
return 0;
Expand Down Expand Up @@ -560,11 +633,11 @@ static int elf_strip_vermagic(const struct kmod_elf *elf, uint8_t *changed)
{
uint64_t i, sec_off, size;
const char *strings;
int err;

err = kmod_elf_get_section(elf, ".modinfo", &sec_off, &size);
if (err < 0)
return err == -ENODATA ? 0 : err;
sec_off = elf->sections[KMOD_ELF_SECTION_MODINFO].offset;
size = elf->sections[KMOD_ELF_SECTION_MODINFO].size;
if (sec_off == 0)
return 0;
strings = elf_get_mem(elf, sec_off);

/* skip zero padding */
Expand Down Expand Up @@ -645,14 +718,15 @@ static int kmod_elf_get_symbols_symtab(const struct kmod_elf *elf,
uint64_t i, last, off, size;
const char *strings;
struct kmod_modversion *a;
int count, err;
int count;
size_t total_size;

*array = NULL;

err = kmod_elf_get_section(elf, "__ksymtab_strings", &off, &size);
if (err < 0)
return err;
off = elf->sections[KMOD_ELF_SECTION_KSYMTAB].offset;
size = elf->sections[KMOD_ELF_SECTION_KSYMTAB].size;
if (off == 0)
return -ENODATA;
strings = elf_get_mem(elf, off);

/* skip zero padding */
Expand Down Expand Up @@ -757,16 +831,17 @@ int kmod_elf_get_symbols(const struct kmod_elf *elf, struct kmod_modversion **ar
uint64_t strtablen, symtablen, str_sec_off, sym_sec_off, str_off, sym_off;
struct kmod_modversion *a;
size_t i, count, symcount, symlen;
int err;

err = kmod_elf_get_section(elf, ".strtab", &str_sec_off, &strtablen);
if (err < 0) {
str_sec_off = elf->sections[KMOD_ELF_SECTION_STRTAB].offset;
strtablen = elf->sections[KMOD_ELF_SECTION_STRTAB].size;
if (str_sec_off == 0) {
ELFDBG(elf, "no .strtab found.\n");
goto fallback;
}

err = kmod_elf_get_section(elf, ".symtab", &sym_sec_off, &symtablen);
if (err < 0) {
sym_sec_off = elf->sections[KMOD_ELF_SECTION_SYMTAB].offset;
symtablen = elf->sections[KMOD_ELF_SECTION_SYMTAB].size;
if (sym_sec_off == 0) {
ELFDBG(elf, "no .symtab found.\n");
goto fallback;
}
Expand Down Expand Up @@ -913,13 +988,14 @@ int kmod_elf_get_dependency_symbols(const struct kmod_elf *elf,
uint64_t str_sec_off, sym_sec_off;
struct kmod_modversion *a;
size_t namlen, verlen, symlen, crclen;
int i, count, symcount, vercount, err;
int i, count, symcount, vercount;
bool handle_register_symbols;
uint8_t *visited_versions;
uint64_t *symcrcs;

err = kmod_elf_get_section(elf, "__versions", &ver_off, &versionslen);
if (err < 0) {
ver_off = elf->sections[KMOD_ELF_SECTION_VERSIONS].offset;
versionslen = elf->sections[KMOD_ELF_SECTION_VERSIONS].size;
if (ver_off == 0) {
versionslen = 0;
verlen = 0;
crclen = 0;
Expand All @@ -936,14 +1012,16 @@ int kmod_elf_get_dependency_symbols(const struct kmod_elf *elf,
}
}

err = kmod_elf_get_section(elf, ".strtab", &str_sec_off, &strtablen);
if (err < 0) {
str_sec_off = elf->sections[KMOD_ELF_SECTION_STRTAB].offset;
strtablen = elf->sections[KMOD_ELF_SECTION_STRTAB].size;
if (str_sec_off == 0) {
ELFDBG(elf, "no .strtab found.\n");
return -EINVAL;
}

err = kmod_elf_get_section(elf, ".symtab", &sym_sec_off, &symtablen);
if (err < 0) {
sym_sec_off = elf->sections[KMOD_ELF_SECTION_SYMTAB].offset;
symtablen = elf->sections[KMOD_ELF_SECTION_SYMTAB].size;
if (sym_sec_off == 0) {
ELFDBG(elf, "no .symtab found.\n");
return -EINVAL;
}
Expand Down

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