On Tue, Feb 06, 2024 at 01:02:26PM +0100, Sebastian Andrzej Siewior wrote:
> with linux kernel v6.8-rc2-RT and the following file as testcase
>
> ----->8--------
>
> #include <linux/spinlock.h>
> #include <linux/local_lock.h>
>
> struct per_cpu_struct {
> local_lock_t lock;
> unsigned int something;
> };
>
> static DEFINE_PER_CPU(struct per_cpu_struct, per_cpu_struct) = {
> .lock = INIT_LOCAL_LOCK(lock),
> };
>
> DEFINE_GUARD(ll_lock, local_lock_t __percpu*,
> local_lock(_T),
> local_unlock(_T))
>
> void function(void);
> void function(void)
> {
> struct per_cpu_struct *pcs = this_cpu_ptr(&per_cpu_struct);
>
> guard(ll_lock)(&per_cpu_struct.lock);
> pcs->something++;
> }
>
> -----8<--------
>
> compiling and running pahole afterwards:
> | make kernel/pahole-tc.o && pahole -J --btf_gen_floats -j --lang_exclude=rust kernel/pahole-tc.o
> | CC kernel/pahole-tc.o
> | error: found variable 'per_cpu_struct' in CU 'kernel/pahole-tc.c' that has void type
>
> This doesn't look good. If I swap the order of "lock" and "something"
> within per_cpu_struct then it goes away.
> The dwarf/die object it complains about has only DW_AT_abstract_origin
> and DW_AT_location set.
> At this point I am not sure if gcc wrongly created the dwarf information
> or of pahole accidentally matches the internal local_lock_t member as
> per_cpu_struct because it starts the same address.
>
> >From dumpwarf the problematic entry is:
> | 0x0000085b: DW_TAG_variable
> | DW_AT_abstract_origin (0x0000099e "t")
> | DW_AT_location (DW_OP_addr 0x0, DW_OP_stack_value)
>
> which looks slightly different in the good case:
> | 0x00000852: DW_TAG_variable
> | DW_AT_abstract_origin (0x00000980 "t")
> | DW_AT_location (0x00000040:
> | [0x0000000000000046, 0x000000000000005b): DW_OP_reg3 RBX
> | [0x000000000000005b, 0x0000000000000061): DW_OP_addr 0x0, DW_OP_stack_value)
> | DW_AT_GNU_locviews (0x0000003c)
>
> I made an archive with c file, the compiled version in bad and good case
> (swapped the first two members), the dumpwarf output and uploaded to
> https://breakpoint.cc/pahole-tc.tar.xz
Lots of great info, I'm on it.
- Arnaldo
