Currently instruction_pointer() returns pt_regs->ret and so return value
is of type "long", which implicitly stands for "signed long".
While that's perfectly fine when dealing with 32-bit values if return
value of instruction_pointer() gets assigned to 64-bit variable sign
extension may happen.
And at least in one real use-case it happens already.
In perf_prepare_sample() return value of perf_instruction_pointer()
(which is an alias to instruction_pointer() in case of ARC) is assigned
to (struct perf_sample_data)->ip (which type is "u64").
And what we see if instuction pointer points to user-space application
that in case of ARC lays below 0x8000_0000 "ip" gets set properly with
leading 32 zeros. But if instruction pointer points to kernel address
space that starts from 0x8000_0000 then "ip" is set with 32 leadig
"f"-s. I.e. id instruction_pointer() returns 0x8100_0000, "ip" will be
assigned with 0xffff_ffff__8100_0000. Which is obviously wrong.
In particular that issuse broke output of perf, because perf was unable
to associate addresses like 0xffff_ffff__8100_0000 with anything from
/proc/kallsyms.
That's what we used to see:
----------->8----------
6.27% ls [unknown] [k] 0xffffffff8046c5cc
2.96% ls libuClibc-0.9.34-git.so [.] memcpy
2.25% ls libuClibc-0.9.34-git.so [.] memset
1.66% ls [unknown] [k] 0xffffffff80666536
1.54% ls libuClibc-0.9.34-git.so [.] 0x000224d6
1.18% ls libuClibc-0.9.34-git.so [.] 0x00022472
----------->8----------
With that change perf output looks much better now:
----------->8----------
8.21% ls [kernel.kallsyms] [k] memset
3.52% ls libuClibc-0.9.34-git.so [.] memcpy
2.11% ls libuClibc-0.9.34-git.so [.] malloc
1.88% ls libuClibc-0.9.34-git.so [.] memset
1.64% ls [kernel.kallsyms] [k] _raw_spin_unlock_irqrestore
1.41% ls [kernel.kallsyms] [k] __d_lookup_rcu
----------->8----------
Signed-off-by: Alexey Brodkin <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
---
arch/arc/include/asm/ptrace.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/arc/include/asm/ptrace.h b/arch/arc/include/asm/ptrace.h
index 9175597..91694ec 100644
--- a/arch/arc/include/asm/ptrace.h
+++ b/arch/arc/include/asm/ptrace.h
@@ -106,7 +106,7 @@ struct callee_regs {
long r25, r24, r23, r22, r21, r20, r19, r18, r17, r16, r15, r14, r13;
};
-#define instruction_pointer(regs) ((regs)->ret)
+#define instruction_pointer(regs) (unsigned long)((regs)->ret)
#define profile_pc(regs) instruction_pointer(regs)
/* return 1 if user mode or 0 if kernel mode */
--
2.4.3
On Monday 13 July 2015 12:55 PM, Alexey Brodkin wrote:
> Currently instruction_pointer() returns pt_regs->ret and so return value
> is of type "long", which implicitly stands for "signed long".
>
> While that's perfectly fine when dealing with 32-bit values if return
> value of instruction_pointer() gets assigned to 64-bit variable sign
> extension may happen.
>
> And at least in one real use-case it happens already.
> In perf_prepare_sample() return value of perf_instruction_pointer()
> (which is an alias to instruction_pointer() in case of ARC) is assigned
> to (struct perf_sample_data)->ip (which type is "u64").
>
> And what we see if instuction pointer points to user-space application
> that in case of ARC lays below 0x8000_0000 "ip" gets set properly with
> leading 32 zeros. But if instruction pointer points to kernel address
> space that starts from 0x8000_0000 then "ip" is set with 32 leadig
> "f"-s. I.e. id instruction_pointer() returns 0x8100_0000, "ip" will be
> assigned with 0xffff_ffff__8100_0000. Which is obviously wrong.
>
> In particular that issuse broke output of perf, because perf was unable
> to associate addresses like 0xffff_ffff__8100_0000 with anything from
> /proc/kallsyms.
>
> That's what we used to see:
> ----------->8----------
> 6.27% ls [unknown] [k] 0xffffffff8046c5cc
> 2.96% ls libuClibc-0.9.34-git.so [.] memcpy
> 2.25% ls libuClibc-0.9.34-git.so [.] memset
> 1.66% ls [unknown] [k] 0xffffffff80666536
> 1.54% ls libuClibc-0.9.34-git.so [.] 0x000224d6
> 1.18% ls libuClibc-0.9.34-git.so [.] 0x00022472
> ----------->8----------
>
> With that change perf output looks much better now:
> ----------->8----------
> 8.21% ls [kernel.kallsyms] [k] memset
> 3.52% ls libuClibc-0.9.34-git.so [.] memcpy
> 2.11% ls libuClibc-0.9.34-git.so [.] malloc
> 1.88% ls libuClibc-0.9.34-git.so [.] memset
> 1.64% ls [kernel.kallsyms] [k] _raw_spin_unlock_irqrestore
> 1.41% ls [kernel.kallsyms] [k] __d_lookup_rcu
> ----------->8----------
>
> Signed-off-by: Alexey Brodkin <[email protected]>
Thx Alexey - this solves a long standing mystery with some weird perf profiles.
Applied !
Thx,
-Vineet