| Message ID | 20181029082555.32626-1-vincent.whitchurch@axis.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | ARM: module: Fix function kallsyms on Thumb-2 | expand |
Hi Vincent,
Thank you for the patch! Perhaps something to improve:
[auto build test WARNING on arm/for-next]
[also build test WARNING on v4.19 next-20181019]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Vincent-Whitchurch/ARM-module-Fix-function-kallsyms-on-Thumb-2/20181029-162842
base: git://git.armlinux.org.uk/~rmk/linux-arm.git for-next
config: i386-randconfig-x000-201843 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
# save the attached .config to linux build tree
make ARCH=i386
All warnings (new ones prefixed by >>):
In file included from kernel/bpf/core.c:28:0:
>> include/linux/moduleloader.h:89:35: warning: 'struct mod_kallsyms' declared inside parameter list will not be visible outside of this definition or declaration
void module_fixup_kallsyms(struct mod_kallsyms *kallsyms);
^~~~~~~~~~~~
vim +89 include/linux/moduleloader.h
88
> 89 void module_fixup_kallsyms(struct mod_kallsyms *kallsyms);
90
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
Hi Vincent,
Thank you for the patch! Perhaps something to improve:
[auto build test WARNING on arm/for-next]
[also build test WARNING on v4.19 next-20181029]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]
url: https://github.com/0day-ci/linux/commits/Vincent-Whitchurch/ARM-module-Fix-function-kallsyms-on-Thumb-2/20181029-162842
base: git://git.armlinux.org.uk/~rmk/linux-arm.git for-next
config: x86_64-randconfig-j1-10290909 (attached as .config)
compiler: gcc-4.9 (Debian 4.9.4-2) 4.9.4
reproduce:
# save the attached .config to linux build tree
make ARCH=x86_64
All warnings (new ones prefixed by >>):
In file included from kernel/bpf/core.c:28:0:
>> include/linux/moduleloader.h:89:35: warning: 'struct mod_kallsyms' declared inside parameter list
void module_fixup_kallsyms(struct mod_kallsyms *kallsyms);
^
>> include/linux/moduleloader.h:89:35: warning: its scope is only this definition or declaration, which is probably not what you want
vim +89 include/linux/moduleloader.h
88
> 89 void module_fixup_kallsyms(struct mod_kallsyms *kallsyms);
90
---
0-DAY kernel test infrastructure Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all Intel Corporation
diff --git a/arch/arm/kernel/module.c b/arch/arm/kernel/module.c index 3ff571c2c71c..771f86318d84 100644 --- a/arch/arm/kernel/module.c +++ b/arch/arm/kernel/module.c @@ -399,6 +399,20 @@ int module_finalize(const Elf32_Ehdr *hdr, const Elf_Shdr *sechdrs, return 0; } +#if defined(CONFIG_THUMB2_KERNEL) && defined(CONFIG_KALLSYMS) +void module_fixup_kallsyms(struct mod_kallsyms *kallsyms) +{ + int i; + + for (i = 0; i < kallsyms->num_symtab; i++) { + Elf_Sym *sym = &kallsyms->symtab[i]; + + if (ELF_ST_TYPE(sym->st_info) == STT_FUNC) + sym->st_value &= ~1; + } +} +#endif + void module_arch_cleanup(struct module *mod) { diff --git a/include/linux/moduleloader.h b/include/linux/moduleloader.h index 31013c2effd3..92387dd49b82 100644 --- a/include/linux/moduleloader.h +++ b/include/linux/moduleloader.h @@ -86,6 +86,8 @@ void module_arch_cleanup(struct module *mod); /* Any cleanup before freeing mod->module_init */ void module_arch_freeing_init(struct module *mod); +void module_fixup_kallsyms(struct mod_kallsyms *kallsyms); + #ifdef CONFIG_KASAN #include <linux/kasan.h> #define MODULE_ALIGN (PAGE_SIZE << KASAN_SHADOW_SCALE_SHIFT) diff --git a/kernel/module.c b/kernel/module.c index 49a405891587..ded4f4b49824 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -2659,6 +2659,10 @@ static void layout_symtab(struct module *mod, struct load_info *info) mod->init_layout.size = debug_align(mod->init_layout.size); } +void __weak module_fixup_kallsyms(struct mod_kallsyms *kallsyms) +{ +} + /* * We use the full symtab and strtab which layout_symtab arranged to * be appended to the init section. Later we switch to the cut-down @@ -2680,6 +2684,8 @@ static void add_kallsyms(struct module *mod, const struct load_info *info) /* Make sure we get permanent strtab: don't use info->strtab. */ mod->kallsyms->strtab = (void *)info->sechdrs[info->index.str].sh_addr; + module_fixup_kallsyms(mod->kallsyms); + /* Set types up while we still have access to sections. */ for (i = 0; i < mod->kallsyms->num_symtab; i++) mod->kallsyms->symtab[i].st_info
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 268: 000000e1 44 FUNC GLOBAL DEFAULT 2 tun_get_socket $ arm-linux-gnueabihf-nm drivers/net/tun.ko | grep tun_get_socket 000000e0 T tun_get_socket $ cat /proc/kallsyms | grep tun_get_socket 7fcd30e1 t tun_get_socket [tun] Because of this, the 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, 000000e0 <tun_get_socket>: e0: b500 push {lr} e2: f7ff fffe bl 0 <__gnu_mcount_nc> e6: 4b08 ldr r3, [pc, #32] e8: 6942 ldr r2, [r0, #20] ea: 429a cmp r2, r3 ec: d002 beq.n f4 <tun_get_socket+0x14> a crash when tun_get_socket is called with NULL results in: PC is at tun_get_socket+0x7/0x2c [tun] pc : [<7fcdb0e8>] which can result in the incorrect line being reported by gdb if this symbol+offset is used there. If the crash is on the first instruction of a function, the "PC is at" line would also report the symbol name of the preceding function. To solve this, fix up these symbols like nm does. For this, we need a new hook in the generic module loading code, before the symbols' st_info is overwritten by add_kallsyms(). After the fix: $ cat /proc/kallsyms | grep tun_get_socket 7fcd30e0 t tun_get_socket [tun] PC is at tun_get_socket+0x8/0x2c [tun] pc : [<7fcdb0e8>] Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com> --- arch/arm/kernel/module.c | 14 ++++++++++++++ include/linux/moduleloader.h | 2 ++ kernel/module.c | 6 ++++++ 3 files changed, 22 insertions(+)