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

[Athira Rajeev]

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 above case, 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:
'commit b9c0a64901d5 ("perf annotate: Fix s390 gap between kernel end
and module start")'
'commit 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 at linux.vnet.ibm.com>
---
 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