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SubjectRe: [PATCH v12 0/5] Add kprobe and kretprobe support for LoongArch
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On 02/06/2023 08:48 PM, Jeff Xie wrote:
> On Mon, Feb 6, 2023 at 8:13 PM Huacai Chen <chenhuacai@kernel.org> wrote:
>>
>> Hi, Jeff,
>>
>> Now I add kprobes on ftrace support in
>> https://github.com/loongson/linux/commits/loongarch-next, please test
>> again. Thank you.
>>
>
> When using the kprobe example module kprobe_example.ko, I haven't seen
> any errors.
>
> But when using the ftrace to probe the symbol + offset, the kernel will panic:
> e.g. probe the scheduler_tick+4 is fine, but when probe the
> scheduler_tick+5, the kernel will panic.
>

Thanks for your test.

We can see that the instruction address is 4-byte alignment,
this is because the instruction length is 32-bit on LoongArch.

$ objdump -d vmlinux > dump.txt
$ grep -A 20 scheduler_tick dump.txt | head -21
9000000000279fc8 <scheduler_tick>:
9000000000279fc8: 03400000 andi $zero, $zero, 0x0
9000000000279fcc: 03400000 andi $zero, $zero, 0x0
9000000000279fd0: 02ff4063 addi.d $sp, $sp, -48(0xfd0)
9000000000279fd4: 29c08077 st.d $s0, $sp, 32(0x20)
9000000000279fd8: 29c06078 st.d $s1, $sp, 24(0x18)
9000000000279fdc: 29c04079 st.d $s2, $sp, 16(0x10)
9000000000279fe0: 29c0207a st.d $s3, $sp, 8(0x8)
9000000000279fe4: 29c0a061 st.d $ra, $sp, 40(0x28)
9000000000279fe8: 2700007b stptr.d $s4, $sp, 0
9000000000279fec: 24001844 ldptr.w $a0, $tp, 24(0x18)
9000000000279ff0: 1a02edd9 pcalau12i $s2, 5998(0x176e)
9000000000279ff4: 1a034bac pcalau12i $t0, 6749(0x1a5d)
9000000000279ff8: 02f56339 addi.d $s2, $s2, -680(0xd58)
9000000000279ffc: 00410c9a slli.d $s3, $a0, 0x3
900000000027a000: 28aae18d ld.w $t1, $t0, -1352(0xab8)
900000000027a004: 380c6b2e ldx.d $t2, $s2, $s3
900000000027a008: 1a022fcc pcalau12i $t0, 4478(0x117e)
900000000027a00c: 02f20198 addi.d $s1, $t0, -896(0xc80)
900000000027a010: 00150317 move $s0, $s1
900000000027a014: 004081ac slli.w $t0, $t1, 0x0

So we should check the probe address at the beginning of
arch_prepare_kprobe(), some other archs do the same thing.

$ git diff
diff --git a/arch/loongarch/kernel/kprobes.c
b/arch/loongarch/kernel/kprobes.c
index bdab707b6edf..56c8c4b09a42 100644
--- a/arch/loongarch/kernel/kprobes.c
+++ b/arch/loongarch/kernel/kprobes.c
@@ -79,6 +79,9 @@ NOKPROBE_SYMBOL(arch_prepare_simulate);

int arch_prepare_kprobe(struct kprobe *p)
{
+ if ((unsigned long)p->addr & 0x3)
+ return -EILSEQ;
+
/* copy instruction */
p->opcode = *p->addr;

Thanks,
Tiezhu

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