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authorVincent Whitchurch <vincent.whitchurch@axis.com>2018-12-14 17:05:55 +0100
committerJessica Yu <jeyu@kernel.org>2018-12-14 20:27:29 +0100
commit93d77e7f1410c366050d6035dcba1a5167c7cf0b (patch)
tree947734dfb461513991c3d8262c0ed6242c1c8178 /kernel/module.c
parent5439c985c5a83a8419f762115afdf560ab72a452 (diff)
ARM: module: Fix function kallsyms on Thumb-2
Thumb-2 functions have the lowest bit set in the symbol value in the symtab. When kallsyms are generated for the vmlinux, the kallsyms are generated from the output of nm, and nm clears the lowest bit. $ arm-linux-gnueabihf-readelf -a vmlinux | grep show_interrupts 95947: 8015dc89 686 FUNC GLOBAL DEFAULT 2 show_interrupts $ arm-linux-gnueabihf-nm vmlinux | grep show_interrupts 8015dc88 T show_interrupts $ cat /proc/kallsyms | grep show_interrupts 8015dc88 T show_interrupts However, for modules, the kallsyms uses the values in the symbol table without modification, so for functions in modules, the lowest bit is set in kallsyms. $ arm-linux-gnueabihf-readelf -a drivers/net/tun.ko | grep tun_get_socket 333: 00002d4d 36 FUNC GLOBAL DEFAULT 1 tun_get_socket $ arm-linux-gnueabihf-nm drivers/net/tun.ko | grep tun_get_socket 00002d4c T tun_get_socket $ cat /proc/kallsyms | grep tun_get_socket 7f802d4d t tun_get_socket [tun] Because of this, the symbol+offset of the crashing instruction shown in oopses is incorrect when the crash is in a module. For example, given a tun_get_socket which starts like this, 00002d4c <tun_get_socket>: 2d4c: 6943 ldr r3, [r0, #20] 2d4e: 4a07 ldr r2, [pc, #28] 2d50: 4293 cmp r3, r2 a crash when tun_get_socket is called with NULL results in: PC is at tun_xdp+0xa3/0xa4 [tun] pc : [<7f802d4c>] As can be seen, the "PC is at" line reports the wrong symbol name, and the symbol+offset will point to the wrong source line if it is passed to gdb. To solve this, add a way for archs to fixup the reading of these module kallsyms values, and use that to clear the lowest bit for function symbols on Thumb-2. After the fix: # cat /proc/kallsyms | grep tun_get_socket 7f802d4c t tun_get_socket [tun] PC is at tun_get_socket+0x0/0x24 [tun] pc : [<7f802d4c>] Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com> Signed-off-by: Jessica Yu <jeyu@kernel.org>
Diffstat (limited to 'kernel/module.c')
-rw-r--r--kernel/module.c43
1 files changed, 27 insertions, 16 deletions
diff --git a/kernel/module.c b/kernel/module.c
index b36ff8a3d562..164bf201eae4 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -3928,7 +3928,7 @@ static const char *find_kallsyms_symbol(struct module *mod,
unsigned long *offset)
{
unsigned int i, best = 0;
- unsigned long nextval;
+ unsigned long nextval, bestval;
struct mod_kallsyms *kallsyms = rcu_dereference_sched(mod->kallsyms);
/* At worse, next value is at end of module */
@@ -3937,10 +3937,15 @@ static const char *find_kallsyms_symbol(struct module *mod,
else
nextval = (unsigned long)mod->core_layout.base+mod->core_layout.text_size;
+ bestval = kallsyms_symbol_value(&kallsyms->symtab[best]);
+
/* Scan for closest preceding symbol, and next symbol. (ELF
starts real symbols at 1). */
for (i = 1; i < kallsyms->num_symtab; i++) {
- if (kallsyms->symtab[i].st_shndx == SHN_UNDEF)
+ const Elf_Sym *sym = &kallsyms->symtab[i];
+ unsigned long thisval = kallsyms_symbol_value(sym);
+
+ if (sym->st_shndx == SHN_UNDEF)
continue;
/* We ignore unnamed symbols: they're uninformative
@@ -3949,21 +3954,21 @@ static const char *find_kallsyms_symbol(struct module *mod,
|| is_arm_mapping_symbol(kallsyms_symbol_name(kallsyms, i)))
continue;
- if (kallsyms->symtab[i].st_value <= addr
- && kallsyms->symtab[i].st_value > kallsyms->symtab[best].st_value)
+ if (thisval <= addr && thisval > bestval) {
best = i;
- if (kallsyms->symtab[i].st_value > addr
- && kallsyms->symtab[i].st_value < nextval)
- nextval = kallsyms->symtab[i].st_value;
+ bestval = thisval;
+ }
+ if (thisval > addr && thisval < nextval)
+ nextval = thisval;
}
if (!best)
return NULL;
if (size)
- *size = nextval - kallsyms->symtab[best].st_value;
+ *size = nextval - bestval;
if (offset)
- *offset = addr - kallsyms->symtab[best].st_value;
+ *offset = addr - bestval;
return kallsyms_symbol_name(kallsyms, best);
}
@@ -4069,8 +4074,10 @@ int module_get_kallsym(unsigned int symnum, unsigned long *value, char *type,
continue;
kallsyms = rcu_dereference_sched(mod->kallsyms);
if (symnum < kallsyms->num_symtab) {
- *value = kallsyms->symtab[symnum].st_value;
- *type = kallsyms->symtab[symnum].st_size;
+ const Elf_Sym *sym = &kallsyms->symtab[symnum];
+
+ *value = kallsyms_symbol_value(sym);
+ *type = sym->st_size;
strlcpy(name, kallsyms_symbol_name(kallsyms, symnum), KSYM_NAME_LEN);
strlcpy(module_name, mod->name, MODULE_NAME_LEN);
*exported = is_exported(name, *value, mod);
@@ -4089,10 +4096,13 @@ static unsigned long find_kallsyms_symbol_value(struct module *mod, const char *
unsigned int i;
struct mod_kallsyms *kallsyms = rcu_dereference_sched(mod->kallsyms);
- for (i = 0; i < kallsyms->num_symtab; i++)
+ for (i = 0; i < kallsyms->num_symtab; i++) {
+ const Elf_Sym *sym = &kallsyms->symtab[i];
+
if (strcmp(name, kallsyms_symbol_name(kallsyms, i)) == 0 &&
- kallsyms->symtab[i].st_shndx != SHN_UNDEF)
- return kallsyms->symtab[i].st_value;
+ sym->st_shndx != SHN_UNDEF)
+ return kallsyms_symbol_value(sym);
+ }
return 0;
}
@@ -4137,12 +4147,13 @@ int module_kallsyms_on_each_symbol(int (*fn)(void *, const char *,
if (mod->state == MODULE_STATE_UNFORMED)
continue;
for (i = 0; i < kallsyms->num_symtab; i++) {
+ const Elf_Sym *sym = &kallsyms->symtab[i];
- if (kallsyms->symtab[i].st_shndx == SHN_UNDEF)
+ if (sym->st_shndx == SHN_UNDEF)
continue;
ret = fn(data, kallsyms_symbol_name(kallsyms, i),
- mod, kallsyms->symtab[i].st_value);
+ mod, kallsyms_symbol_value(sym));
if (ret != 0)
return ret;
}