perf powerpc: Fix gap between kernel end and module start

perf powerpc: Fix gap between kernel end and module start

Running "perf mem report" in TUI mode fails with ENOMEM message in
powerpc:

  failed to process sample

Running with debug and verbose options points that issue is while
allocating memory for sample histograms.

The error path is:

  symbol__inc_addr_samples() ->
    __symbol__inc_addr_samples() ->
      annotated_source__histogram()

symbol__inc_addr_samples() calls annotated_source__alloc_histograms ()
to allocate memory for sample histograms using calloc(). Here calloc()
fails since the size of symbol is huge. The size of a symbol is
calculated as difference between its start and end address.

Example histogram allocation that fails is:

  sym->name is _end
  sym->start is 0xc0000000027a0000
  sym->end is 0xc008000003890000
  symbol__size(sym) is 0x80000010f0000

In the above case, the difference between sym->start
(0xc0000000027a0000) and sym->end (0xc008000003890000) is huge.

This is same problem as in s390 and arm64 which are fixed in commits:

  b9c0a64901d5 ("perf annotate: Fix s390 gap between kernel end and module start")
  78886f3ed37e ("perf symbols: Fix arm64 gap between kernel start and module end")

When this symbol was read first, its start and end address was set to
address which matches with data from /proc/kallsyms.

After symbol__new():

  symbol__new: _end 0xc0000000027a0000-0xc0000000027a0000

  From /proc/kallsyms:
  ...
  c000000002799370 b backtrace_flag
  c000000002799378 B radix_tree_node_cachep
  c000000002799380 B __bss_stop
  c0000000027a0000 B _end
  c008000003890000 t icmp_checkentry      [ip_tables]
  c008000003890038 t ipt_alloc_initial_table      [ip_tables]
  c008000003890468 T ipt_do_table [ip_tables]
  c008000003890de8 T ipt_unregister_table_pre_exit        [ip_tables]
  ...

Perf calls function symbols__fixup_end() which sets the end of symbol to
0xc008000003890000, which is the next address and this is the start
address of first module (icmp_checkentry in above) which will make the
huge symbol size of 0x80000010f0000.

After symbols__fixup_end:

  symbols__fixup_end: sym->name: _end
  sym->start: 0xc0000000027a0000
  sym->end: 0xc008000003890000

On powerpc, kernel text segment is located at 0xc000000000000000 whereas
the modules are located at very high memory addresses,
0xc00800000xxxxxxx. Since the gap between end of kernel text segment and
beginning of first module's address is high, histogram allocation using
calloc fails.

Fix this by detecting the kernel's last symbol and limiting the range of
last kernel symbol to pagesize.

Signed-off-by: Athira Rajeev<atrajeev@linux.vnet.ibm.com>
Acked-by: Jiri Olsa <jolsa@redhat.com>
Tested-By: Kajol Jain <kjain@linux.ibm.com>
Cc: Madhavan Srinivasan <maddy@linux.ibm.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1609208054-1566-1-git-send-email-atrajeev@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>