On 2014/12/10 08:50PM, Michael Ellerman wrote:
> On Tue, 2014-12-09 at 23:04 +0530, Naveen N. Rao wrote:
> > If using the symbol table, symbol addresses are not being fixed up
> > properly, resulting in probes being placed at wrong addresses:
> >
> > # perf probe do_fork
> > Added new event:
> > probe:do_fork (on do_fork)
> >
> > You can now use it in all perf tools, such as:
> >
> > perf record -e probe:do_fork -aR sleep 1
> >
> > # cat /sys/kernel/debug/tracing/kprobe_events
> > p:probe/do_fork _text+635952
> > # printf "%x" 635952
> > 9b430
> > # grep do_fork /boot/System.map
> > c0000000000ab430 T .do_fork
>
> OK, but why is that happening? And why does checking for ET_DYN fix it?
The section header indicates 0x10000 as the offset:
Section Headers:
[Nr] Name Type Address Offset
Size EntSize Flags Link Info Align
[ 0] NULL 0000000000000000 00000000
0000000000000000 0000000000000000 0 0 0
[ 1] .text PROGBITS c000000000000000 00010000
0000000000806678 0000000000000000 AX 0 0 256
This is used during fixup and perf only expects this to be needed for
ET_EXEC, though we use ET_DYN on ppc64.
> > Fix by checking for ELF type ET_DYN used by ppc64 kernels.
>
> We sometimes produce ET_DYN kernels, but only if CONFIG_RELOCATABLE=y.
Ok.
- Naveen
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