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Date: Thu, 30 Apr 2015 17:12:31 +0530
From: "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To: acme@...nel.org, masami.hiramatsu.pt@...achi.com
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH] perf probe: Ignore tail calls to probed functions
perf probe currently errors out if there are any tail calls to probed
functions:
[root@...l71be]# perf probe do_fork
Failed to find probe point in any functions.
Error: Failed to add events.
Fix this by teaching perf to ignore tail calls.
Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
---
I'm seeing this with RHEL7 kernels on ppc64. The specific example in this case is do_fork:
<1><82e7e1>: Abbrev Number: 118 (DW_TAG_subprogram)
<82e7e2> DW_AT_external : 1
<82e7e2> DW_AT_name : (indirect string, offset: 0x3dfe0): do_fork
<82e7e6> DW_AT_decl_file : 7
<82e7e7> DW_AT_decl_line : 1583
<82e7e9> DW_AT_prototyped : 1
<82e7e9> DW_AT_type : <0x8110eb>
<82e7ed> DW_AT_inline : 1 (inlined)
<82e7ee> DW_AT_sibling : <0x82e878>
<snip>
<1><830081>: Abbrev Number: 133 (DW_TAG_subprogram)
<830083> DW_AT_external : 1
<830083> DW_AT_name : (indirect string, offset: 0x3cea3): SyS_clone
<830087> DW_AT_decl_file : 7
<830088> DW_AT_decl_line : 1689
<83008a> DW_AT_prototyped : 1
<83008a> DW_AT_type : <0x8110eb>
<83008e> DW_AT_low_pc : 0xc0000000000bc270
<830096> DW_AT_high_pc : 0xc
<83009e> DW_AT_frame_base : 1 byte block: 9c (DW_OP_call_frame_cfa)
<8300a0> DW_AT_GNU_all_call_sites: 1
<8300a0> DW_AT_sibling : <0x830178>
<snip>
<3><830147>: Abbrev Number: 125 (DW_TAG_GNU_call_site)
<830148> DW_AT_low_pc : 0xc0000000000bc27c
<830150> DW_AT_GNU_tail_call: 1
<830150> DW_AT_abstract_origin: <0x82e7e1>
- Naveen
tools/perf/util/dwarf-aux.c | 37 +++++++++++++++++++++++++++++++++++++
tools/perf/util/dwarf-aux.h | 4 ++++
tools/perf/util/probe-finder.c | 12 +++++++++---
3 files changed, 50 insertions(+), 3 deletions(-)
diff --git a/tools/perf/util/dwarf-aux.c b/tools/perf/util/dwarf-aux.c
index c34e024..851a76f 100644
--- a/tools/perf/util/dwarf-aux.c
+++ b/tools/perf/util/dwarf-aux.c
@@ -417,6 +417,43 @@ struct __addr_die_search_param {
Dwarf_Die *die_mem;
};
+static int __die_search_func_tail_cb(Dwarf_Die *fn_die, void *data)
+{
+ struct __addr_die_search_param *ad = data;
+ Dwarf_Addr addr = 0;
+
+ if (dwarf_tag(fn_die) == DW_TAG_subprogram &&
+ !dwarf_highpc(fn_die, &addr) &&
+ addr == ad->addr) {
+ memcpy(ad->die_mem, fn_die, sizeof(Dwarf_Die));
+ return DWARF_CB_ABORT;
+ }
+ return DWARF_CB_OK;
+}
+
+/**
+ * die_find_tailfunc - Search for a non-inlined function with tail call at
+ * given address
+ * @cu_die: a CU DIE which including @addr
+ * @addr: target address
+ * @die_mem: a buffer for result DIE
+ *
+ * Search for a non-inlined function DIE with tail call at @addr. Stores the
+ * DIE to @die_mem and returns it if found. Returns NULL if failed.
+ */
+Dwarf_Die *die_find_tailfunc(Dwarf_Die *cu_die, Dwarf_Addr addr,
+ Dwarf_Die *die_mem)
+{
+ struct __addr_die_search_param ad;
+ ad.addr = addr;
+ ad.die_mem = die_mem;
+ /* dwarf_getscopes can't find subprogram. */
+ if (!dwarf_getfuncs(cu_die, __die_search_func_tail_cb, &ad, 0))
+ return NULL;
+ else
+ return die_mem;
+}
+
/* die_find callback for non-inlined function search */
static int __die_search_func_cb(Dwarf_Die *fn_die, void *data)
{
diff --git a/tools/perf/util/dwarf-aux.h b/tools/perf/util/dwarf-aux.h
index af7dbcd..c9278ed 100644
--- a/tools/perf/util/dwarf-aux.h
+++ b/tools/perf/util/dwarf-aux.h
@@ -82,6 +82,10 @@ extern Dwarf_Die *die_find_child(Dwarf_Die *rt_die,
extern Dwarf_Die *die_find_realfunc(Dwarf_Die *cu_die, Dwarf_Addr addr,
Dwarf_Die *die_mem);
+/* Search a non-inlined function with tail call at given address */
+Dwarf_Die *die_find_tailfunc(Dwarf_Die *cu_die, Dwarf_Addr addr,
+ Dwarf_Die *die_mem);
+
/* Search the top inlined function including given address */
extern Dwarf_Die *die_find_top_inlinefunc(Dwarf_Die *sp_die, Dwarf_Addr addr,
Dwarf_Die *die_mem);
diff --git a/tools/perf/util/probe-finder.c b/tools/perf/util/probe-finder.c
index b5bf9d5..4cb461e 100644
--- a/tools/perf/util/probe-finder.c
+++ b/tools/perf/util/probe-finder.c
@@ -660,9 +660,15 @@ static int call_probe_finder(Dwarf_Die *sc_die, struct probe_finder *pf)
/* If not a real subprogram, find a real one */
if (!die_is_func_def(sc_die)) {
if (!die_find_realfunc(&pf->cu_die, pf->addr, &pf->sp_die)) {
- pr_warning("Failed to find probe point in any "
- "functions.\n");
- return -ENOENT;
+ if (die_find_tailfunc(&pf->cu_die, pf->addr, &pf->sp_die)) {
+ pr_warning("Ignoring tail call from %s\n",
+ dwarf_diename(&pf->sp_die));
+ return 0;
+ } else {
+ pr_warning("Failed to find probe point in any "
+ "functions.\n");
+ return -ENOENT;
+ }
}
} else
memcpy(&pf->sp_die, sc_die, sizeof(Dwarf_Die));
--
2.3.5
--
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