[PATCH] tools/perf: Fix powerpc gap between kernel end and module start

[Athira Rajeev]

> On 12-Jan-2021, at 3:08 PM, Jiri Olsa <jolsa at redhat.com> wrote:
> 
> On Mon, Dec 28, 2020 at 09:14:14PM -0500, Athira Rajeev wrote:
> 
> SNIP
> 
>> 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 at linux.vnet.ibm.com>
> 
> I can't test, but since the same approach works for arm and s390,
> this also looks ok
> 
> Acked-by: Jiri Olsa <jolsa at redhat.com>
> 
> thanks,
> jirka

Thanks Jiri for reviewing the patch,

Athira
> 
>> ---
>> tools/perf/arch/powerpc/util/Build     |  1 +
>> tools/perf/arch/powerpc/util/machine.c | 24 ++++++++++++++++++++++++
>> 2 files changed, 25 insertions(+)
>> create mode 100644 tools/perf/arch/powerpc/util/machine.c
>> 
>> diff --git a/tools/perf/arch/powerpc/util/Build b/tools/perf/arch/powerpc/util/Build
>> index e86e210bf514..b7945e5a543b 100644
>> --- a/tools/perf/arch/powerpc/util/Build
>> +++ b/tools/perf/arch/powerpc/util/Build
>> @@ -1,4 +1,5 @@
>> perf-y += header.o
>> +perf-y += machine.o
>> perf-y += kvm-stat.o
>> perf-y += perf_regs.o
>> perf-y += mem-events.o
>> diff --git a/tools/perf/arch/powerpc/util/machine.c b/tools/perf/arch/powerpc/util/machine.c
>> new file mode 100644
>> index 000000000000..c30e5cc88c16
>> --- /dev/null
>> +++ b/tools/perf/arch/powerpc/util/machine.c
>> @@ -0,0 +1,24 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +
>> +#include <stdio.h>
>> +#include <string.h>
>> +#include <internal/lib.h> // page_size
>> +#include "debug.h"
>> +#include "symbol.h"
>> +
>> +/* On powerpc kernel text segment start at memory addresses, 0xc000000000000000
>> + * whereas the modules are located at very high memory addresses,
>> + * for example 0xc00800000xxxxxxx. The gap between end of kernel text segment
>> + * and beginning of first module's text segment is very high.
>> + * Therefore do not fill this gap and do not assign it to the kernel dso map.
>> + */
>> +
>> +void arch__symbols__fixup_end(struct symbol *p, struct symbol *c)
>> +{
>> +	if (strchr(p->name, '[') == NULL && strchr(c->name, '['))
>> +		/* Limit the range of last kernel symbol */
>> +		p->end += page_size;
>> +	else
>> +		p->end = c->start;
>> +	pr_debug4("%s sym:%s end:%#lx\n", __func__, p->name, p->end);
>> +}
>> -- 
>> 1.8.3.1