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 <abrodkin@xxxxxxxxxxxx> Thx Alexey - this solves a long standing mystery with some weird perf profiles. Applied ! Thx, -Vineet -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html