From: Alexander Sverdlin <[email protected]>
"unwind: Index not found eef26358" warnings keep popping up on
CONFIG_ARM_MODULE_PLTS-enabled systems if the PC points to a PLT veneer.
Teach the unwinder how to deal with them, taking into account they don't
change state of the stack or register file except loading PC.
Tested-by: Kursad Oney <[email protected]>
Link: https://lore.kernel.org/linux-arm-kernel/[email protected]/
Signed-off-by: Alexander Sverdlin <[email protected]>
---
arch/arm/include/asm/module.h | 5 +++++
arch/arm/kernel/module-plts.c | 14 ++++++++++++++
arch/arm/kernel/unwind.c | 13 ++++++++++++-
3 files changed, 31 insertions(+), 1 deletion(-)
diff --git a/arch/arm/include/asm/module.h b/arch/arm/include/asm/module.h
index 5546c9751478c..07c51a34f77d5 100644
--- a/arch/arm/include/asm/module.h
+++ b/arch/arm/include/asm/module.h
@@ -37,6 +37,11 @@ struct mod_arch_specific {
struct module;
u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val);
+#ifdef CONFIG_ARM_MODULE_PLTS
+bool in_module_plt(unsigned long loc);
+#else
+static inline bool in_module_plt(unsigned long loc) { return false; }
+#endif
#ifdef CONFIG_THUMB2_KERNEL
#define HAVE_ARCH_KALLSYMS_SYMBOL_VALUE
diff --git a/arch/arm/kernel/module-plts.c b/arch/arm/kernel/module-plts.c
index 1fc309b41f944..af7c322ebed68 100644
--- a/arch/arm/kernel/module-plts.c
+++ b/arch/arm/kernel/module-plts.c
@@ -284,3 +284,17 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
mod->arch.core.plt->sh_size, mod->arch.init.plt->sh_size);
return 0;
}
+
+bool in_module_plt(unsigned long loc)
+{
+ struct module *mod;
+ bool ret;
+
+ preempt_disable();
+ mod = __module_text_address(loc);
+ ret = mod && (loc - (u32)mod->arch.core.plt_ent < mod->arch.core.plt_count * PLT_ENT_SIZE ||
+ loc - (u32)mod->arch.init.plt_ent < mod->arch.init.plt_count * PLT_ENT_SIZE);
+ preempt_enable();
+
+ return ret;
+}
diff --git a/arch/arm/kernel/unwind.c b/arch/arm/kernel/unwind.c
index a37ea6c772cd5..53be7ea6181b3 100644
--- a/arch/arm/kernel/unwind.c
+++ b/arch/arm/kernel/unwind.c
@@ -28,6 +28,7 @@
#include <linux/slab.h>
#include <linux/spinlock.h>
#include <linux/list.h>
+#include <linux/module.h>
#include <asm/stacktrace.h>
#include <asm/traps.h>
@@ -395,8 +396,18 @@ int unwind_frame(struct stackframe *frame)
idx = unwind_find_idx(frame->pc);
if (!idx) {
- if (frame->pc && kernel_text_address(frame->pc))
+ if (frame->pc && kernel_text_address(frame->pc)) {
+ if (in_module_plt(frame->pc) && frame->pc != frame->lr) {
+ /*
+ * Quoting Ard: Veneers only set PC using a
+ * PC+immediate LDR, and so they don't affect
+ * the state of the stack or the register file
+ */
+ frame->pc = frame->lr;
+ return URC_OK;
+ }
pr_warn("unwind: Index not found %08lx\n", frame->pc);
+ }
return -URC_FAILURE;
}
--
2.35.1
On 7/6/22 09:31, Alexander A Sverdlin wrote:
> From: Alexander Sverdlin <[email protected]>
>
> "unwind: Index not found eef26358" warnings keep popping up on
> CONFIG_ARM_MODULE_PLTS-enabled systems if the PC points to a PLT veneer.
> Teach the unwinder how to deal with them, taking into account they don't
> change state of the stack or register file except loading PC.
>
> Tested-by: Kursad Oney <[email protected]>
> Link: https://lore.kernel.org/linux-arm-kernel/[email protected]/
> Signed-off-by: Alexander Sverdlin <[email protected]>
I would be inclined to slap a Fixes tag to this patch so we get it back
ported where appropriate, however it is not clear to me which specific
commit(s) we should be listing here.
Thanks Alexander!
--
Florian
Hello Florian,
On 06/07/2022 20:09, Florian Fainelli wrote:
>>
>> "unwind: Index not found eef26358" warnings keep popping up on
>> CONFIG_ARM_MODULE_PLTS-enabled systems if the PC points to a PLT veneer.
>> Teach the unwinder how to deal with them, taking into account they don't
>> change state of the stack or register file except loading PC.
>>
>> Tested-by: Kursad Oney <[email protected]>
>> Link: https://lore.kernel.org/linux-arm-kernel/[email protected]/
>> Signed-off-by: Alexander Sverdlin <[email protected]>
>
> I would be inclined to slap a Fixes tag to this patch so we get it back ported where appropriate, however it is not clear to me which specific
> commit(s) we should be listing here.
usually I don't hesitate to add "Fixes:" tag and this patch definitely could be ported to some
stable versions, but it's hard to say what it fixes. It's actually a combination of rarely
(if at all) used ARM_MODULE_PLTS functionality and other *debug* features, where unwinder is
used. In very similar case of commit 79f32b221b18c15a98507b101ef4beb52444cc6f
("ARM: 9079/1: ftrace: Add MODULE_PLTS support") I wasn't able to figure out which commit
I'm fixing.
I expect those who use ARM_MODULE_PLT and any kind of debugging to be able to backport the
patch downstream ;)
--
Best regards,
Alexander Sverdlin.
Hello Russel,
shall I add this one to your patch tracker?
There is little interest to this patch, but also no complaints, as I can tell.
On 06/07/2022 18:31, Alexander A Sverdlin wrote:
> From: Alexander Sverdlin <[email protected]>
>
> "unwind: Index not found eef26358" warnings keep popping up on
> CONFIG_ARM_MODULE_PLTS-enabled systems if the PC points to a PLT veneer.
> Teach the unwinder how to deal with them, taking into account they don't
> change state of the stack or register file except loading PC.
>
> Tested-by: Kursad Oney <[email protected]>
> Link: https://lore.kernel.org/linux-arm-kernel/[email protected]/
> Signed-off-by: Alexander Sverdlin <[email protected]>
> ---
> arch/arm/include/asm/module.h | 5 +++++
> arch/arm/kernel/module-plts.c | 14 ++++++++++++++
> arch/arm/kernel/unwind.c | 13 ++++++++++++-
> 3 files changed, 31 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/include/asm/module.h b/arch/arm/include/asm/module.h
> index 5546c9751478c..07c51a34f77d5 100644
> --- a/arch/arm/include/asm/module.h
> +++ b/arch/arm/include/asm/module.h
> @@ -37,6 +37,11 @@ struct mod_arch_specific {
>
> struct module;
> u32 get_module_plt(struct module *mod, unsigned long loc, Elf32_Addr val);
> +#ifdef CONFIG_ARM_MODULE_PLTS
> +bool in_module_plt(unsigned long loc);
> +#else
> +static inline bool in_module_plt(unsigned long loc) { return false; }
> +#endif
>
> #ifdef CONFIG_THUMB2_KERNEL
> #define HAVE_ARCH_KALLSYMS_SYMBOL_VALUE
> diff --git a/arch/arm/kernel/module-plts.c b/arch/arm/kernel/module-plts.c
> index 1fc309b41f944..af7c322ebed68 100644
> --- a/arch/arm/kernel/module-plts.c
> +++ b/arch/arm/kernel/module-plts.c
> @@ -284,3 +284,17 @@ int module_frob_arch_sections(Elf_Ehdr *ehdr, Elf_Shdr *sechdrs,
> mod->arch.core.plt->sh_size, mod->arch.init.plt->sh_size);
> return 0;
> }
> +
> +bool in_module_plt(unsigned long loc)
> +{
> + struct module *mod;
> + bool ret;
> +
> + preempt_disable();
> + mod = __module_text_address(loc);
> + ret = mod && (loc - (u32)mod->arch.core.plt_ent < mod->arch.core.plt_count * PLT_ENT_SIZE ||
> + loc - (u32)mod->arch.init.plt_ent < mod->arch.init.plt_count * PLT_ENT_SIZE);
> + preempt_enable();
> +
> + return ret;
> +}
> diff --git a/arch/arm/kernel/unwind.c b/arch/arm/kernel/unwind.c
> index a37ea6c772cd5..53be7ea6181b3 100644
> --- a/arch/arm/kernel/unwind.c
> +++ b/arch/arm/kernel/unwind.c
> @@ -28,6 +28,7 @@
> #include <linux/slab.h>
> #include <linux/spinlock.h>
> #include <linux/list.h>
> +#include <linux/module.h>
>
> #include <asm/stacktrace.h>
> #include <asm/traps.h>
> @@ -395,8 +396,18 @@ int unwind_frame(struct stackframe *frame)
>
> idx = unwind_find_idx(frame->pc);
> if (!idx) {
> - if (frame->pc && kernel_text_address(frame->pc))
> + if (frame->pc && kernel_text_address(frame->pc)) {
> + if (in_module_plt(frame->pc) && frame->pc != frame->lr) {
> + /*
> + * Quoting Ard: Veneers only set PC using a
> + * PC+immediate LDR, and so they don't affect
> + * the state of the stack or the register file
> + */
> + frame->pc = frame->lr;
> + return URC_OK;
> + }
> pr_warn("unwind: Index not found %08lx\n", frame->pc);
> + }
> return -URC_FAILURE;
> }
>
--
Best regards,
Alexander Sverdlin.
On Wed, Jul 6, 2022 at 6:33 PM Alexander A Sverdlin
<[email protected]> wrote:
> From: Alexander Sverdlin <[email protected]>
>
> "unwind: Index not found eef26358" warnings keep popping up on
> CONFIG_ARM_MODULE_PLTS-enabled systems if the PC points to a PLT veneer.
> Teach the unwinder how to deal with them, taking into account they don't
> change state of the stack or register file except loading PC.
>
> Tested-by: Kursad Oney <[email protected]>
> Link: https://lore.kernel.org/linux-arm-kernel/[email protected]/
> Signed-off-by: Alexander Sverdlin <[email protected]>
This looks correct to me.
Reviewed-by: Linus Walleij <[email protected]>
Please add this to Russell's patch tracker.
Yours,
Linus Walleij