[PATCH v2] module: make it clearer when we're handling kallsyms symbols vs exported symbols

Jessica Yu
2018-11-23T16:41:25Z

The module loader internally works with both exported symbols
represented as struct kernel_symbol, as well as Elf symbols from a
module's symbol table. It's hard to distinguish sometimes which type of
symbol we're handling given that some helper function names are not
consistent or helpful. Take get_ksymbol() for instance - are we
looking for an exported symbol or a kallsyms symbol here? Or symname()
and kernel_symbol_name() - which function handles an exported symbol and
which one an Elf symbol?

Clean up and unify the function naming scheme a bit to make it clear
which kind of symbol we're handling. This change only affects static
functions internal to the module loader.

Signed-off-by: Jessica Yu <jeyu@kernel.org>
---

v2: renamed kallsyms_find_* funcs to find_kallsyms_* to follow the
already existing <verb>_<noun> naming convention in module.c

kernel/module.c | 78 ++++++++++++++++++++++++++++++++-------------------------
1 file changed, 44 insertions(+), 34 deletions(-)

diff --git a/kernel/module.c b/kernel/module.c
index 49a405891587..1b5edf78694c 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -495,9 +495,9 @@ struct find_symbol_arg {
const struct kernel_symbol *sym;
};

-static bool check_symbol(const struct symsearch *syms,
- struct module *owner,
- unsigned int symnum, void *data)
+static bool check_exported_symbol(const struct symsearch *syms,
+ struct module *owner,
+ unsigned int symnum, void *data)
{
struct find_symbol_arg *fsa = data;

@@ -555,9 +555,9 @@ static int cmp_name(const void *va, const void *vb)
return strcmp(a, kernel_symbol_name(b));
}

-static bool find_symbol_in_section(const struct symsearch *syms,
- struct module *owner,
- void *data)
+static bool find_exported_symbol_in_section(const struct symsearch *syms,
+ struct module *owner,
+ void *data)
{
struct find_symbol_arg *fsa = data;
struct kernel_symbol *sym;
@@ -565,13 +565,14 @@ static bool find_symbol_in_section(const struct symsearch *syms,
sym = bsearch(fsa->name, syms->start, syms->stop - syms->start,
sizeof(struct kernel_symbol), cmp_name);

- if (sym != NULL && check_symbol(syms, owner, sym - syms->start, data))
+ if (sym != NULL && check_exported_symbol(syms, owner,
+ sym - syms->start, data))
return true;

return false;
}

-/* Find a symbol and return it, along with, (optional) crc and
+/* Find an exported symbol and return it, along with, (optional) crc and
* (optional) module which owns it. Needs preempt disabled or module_mutex. */
const struct kernel_symbol *find_symbol(const char *name,
struct module **owner,
@@ -585,7 +586,7 @@ const struct kernel_symbol *find_symbol(const char *name,
fsa.gplok = gplok;
fsa.warn = warn;

- if (each_symbol_section(find_symbol_in_section, &fsa)) {
+ if (each_symbol_section(find_exported_symbol_in_section, &fsa)) {
if (owner)
*owner = fsa.owner;
if (crc)
@@ -2198,7 +2199,7 @@ EXPORT_SYMBOL_GPL(__symbol_get);
*
* You must hold the module_mutex.
*/
-static int verify_export_symbols(struct module *mod)
+static int verify_exported_symbols(struct module *mod)
{
unsigned int i;
struct module *owner;
@@ -2519,10 +2520,10 @@ static void free_modinfo(struct module *mod)

#ifdef CONFIG_KALLSYMS

-/* lookup symbol in given range of kernel_symbols */
-static const struct kernel_symbol *lookup_symbol(const char *name,
- const struct kernel_symbol *start,
- const struct kernel_symbol *stop)
+/* Lookup exported symbol in given range of kernel_symbols */
+static const struct kernel_symbol *lookup_exported_symbol(const char *name,
+ const struct kernel_symbol *start,
+ const struct kernel_symbol *stop)
{
return bsearch(name, start, stop - start,
sizeof(struct kernel_symbol), cmp_name);
@@ -2533,9 +2534,10 @@ static int is_exported(const char *name, unsigned long value,
{
const struct kernel_symbol *ks;
if (!mod)
- ks = lookup_symbol(name, __start___ksymtab, __stop___ksymtab);
+ ks = lookup_exported_symbol(name, __start___ksymtab, __stop___ksymtab);
else
- ks = lookup_symbol(name, mod->syms, mod->syms + mod->num_syms);
+ ks = lookup_exported_symbol(name, mod->syms, mod->syms + mod->num_syms);
+
return ks != NULL && kernel_symbol_value(ks) == value;
}

@@ -3592,7 +3594,7 @@ static int complete_formation(struct module *mod, struct load_info *info)
mutex_lock(&module_mutex);

/* Find duplicate symbols (must be called under lock). */
- err = verify_export_symbols(mod);
+ err = verify_exported_symbols(mod);
if (err < 0)
goto out;

@@ -3911,15 +3913,19 @@ static inline int is_arm_mapping_symbol(const char *str)
&& (str[2] == '\0' || str[2] == '.');
}

-static const char *symname(struct mod_kallsyms *kallsyms, unsigned int symnum)
+static const char *kallsyms_symbol_name(struct mod_kallsyms *kallsyms, unsigned int symnum)
{
return kallsyms->strtab + kallsyms->symtab[symnum].st_name;
}

-static const char *get_ksymbol(struct module *mod,
- unsigned long addr,
- unsigned long *size,
- unsigned long *offset)
+/*
+ * Given a module and address, find the corresponding symbol and return its name
+ * while providing its size and offset if needed.
+ */
+static const char *find_kallsyms_symbol(struct module *mod,
+ unsigned long addr,
+ unsigned long *size,
+ unsigned long *offset)
{
unsigned int i, best = 0;
unsigned long nextval;
@@ -3939,8 +3945,8 @@ static const char *get_ksymbol(struct module *mod,

/* We ignore unnamed symbols: they're uninformative
* and inserted at a whim. */
- if (*symname(kallsyms, i) == '\0'
- || is_arm_mapping_symbol(symname(kallsyms, i)))
+ if (*kallsyms_symbol_name(kallsyms, i) == '\0'
+ || is_arm_mapping_symbol(kallsyms_symbol_name(kallsyms, i)))
continue;

if (kallsyms->symtab[i].st_value <= addr
@@ -3958,7 +3964,8 @@ static const char *get_ksymbol(struct module *mod,
*size = nextval - kallsyms->symtab[best].st_value;
if (offset)
*offset = addr - kallsyms->symtab[best].st_value;
- return symname(kallsyms, best);
+
+ return kallsyms_symbol_name(kallsyms, best);
}

void * __weak dereference_module_function_descriptor(struct module *mod,
@@ -3983,7 +3990,8 @@ const char *module_address_lookup(unsigned long addr,
if (mod) {
if (modname)
*modname = mod->name;
- ret = get_ksymbol(mod, addr, size, offset);
+
+ ret = find_kallsyms_symbol(mod, addr, size, offset);
}
/* Make a copy in here where it's safe */
if (ret) {
@@ -4006,9 +4014,10 @@ int lookup_module_symbol_name(unsigned long addr, char *symname)
if (within_module(addr, mod)) {
const char *sym;

- sym = get_ksymbol(mod, addr, NULL, NULL);
+ sym = find_kallsyms_symbol(mod, addr, NULL, NULL);
if (!sym)
goto out;
+
strlcpy(symname, sym, KSYM_NAME_LEN);
preempt_enable();
return 0;
@@ -4031,7 +4040,7 @@ int lookup_module_symbol_attrs(unsigned long addr, unsigned long *size,
if (within_module(addr, mod)) {
const char *sym;

- sym = get_ksymbol(mod, addr, size, offset);
+ sym = find_kallsyms_symbol(mod, addr, size, offset);
if (!sym)
goto out;
if (modname)
@@ -4062,7 +4071,7 @@ int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
if (symnum < kallsyms->num_symtab) {
*value = kallsyms->symtab[symnum].st_value;
*type = kallsyms->symtab[symnum].st_info;
- strlcpy(name, symname(kallsyms, symnum), KSYM_NAME_LEN);
+ strlcpy(name, kallsyms_symbol_name(kallsyms, symnum), KSYM_NAME_LEN);
strlcpy(module_name, mod->name, MODULE_NAME_LEN);
*exported = is_exported(name, *value, mod);
preempt_enable();
@@ -4074,13 +4083,14 @@ int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
return -ERANGE;
}

-static unsigned long mod_find_symname(struct module *mod, const char *name)
+/* Given a module and name of symbol, find and return the symbol's value */
+static unsigned long find_kallsyms_symbol_value(struct module *mod, const char *name)
{
unsigned int i;
struct mod_kallsyms *kallsyms = rcu_dereference_sched(mod->kallsyms);

for (i = 0; i < kallsyms->num_symtab; i++)
- if (strcmp(name, symname(kallsyms, i)) == 0 &&
+ if (strcmp(name, kallsyms_symbol_name(kallsyms, i)) == 0 &&
kallsyms->symtab[i].st_shndx != SHN_UNDEF)
return kallsyms->symtab[i].st_value;
return 0;
@@ -4097,12 +4107,12 @@ unsigned long module_kallsyms_lookup_name(const char *name)
preempt_disable();
if ((colon = strnchr(name, MODULE_NAME_LEN, ':')) != NULL) {
if ((mod = find_module_all(name, colon - name, false)) != NULL)
- ret = mod_find_symname(mod, colon+1);
+ ret = find_kallsyms_symbol_value(mod, colon+1);
} else {
list_for_each_entry_rcu(mod, &modules, list) {
if (mod->state == MODULE_STATE_UNFORMED)
continue;
- if ((ret = mod_find_symname(mod, name)) != 0)
+ if ((ret = find_kallsyms_symbol_value(mod, name)) != 0)
break;
}
}
@@ -4131,7 +4141,7 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *,
if (kallsyms->symtab[i].st_shndx == SHN_UNDEF)
continue;

- ret = fn(data, symname(kallsyms, i),
+ ret = fn(data, kallsyms_symbol_name(kallsyms, i),
mod, kallsyms->symtab[i].st_value);
if (ret != 0)
return ret;
--
2.16.4