Replace the arch_skip_callchain_idx() stub in Powerpc with code that
checks the DWARF debug information and identifies the callchain entry
to skip.
Callgraph before the patch:
14.67% 2234 sprintft libc-2.18.so [.] __random
|
--- __random
|
|--61.12%-- __random
| |
| |--97.15%-- rand
| | do_my_sprintf
| | main
| | generic_start_main.isra.0
| | __libc_start_main
| | 0x0
| |
| --2.85%-- do_my_sprintf
| main
| generic_start_main.isra.0
| __libc_start_main
| 0x0
|
--38.88%-- rand
|
|--94.01%-- rand
| do_my_sprintf
| main
| generic_start_main.isra.0
| __libc_start_main
| 0x0
|
--5.99%-- do_my_sprintf
main
generic_start_main.isra.0
__libc_start_main
0x0
Callgraph after the patch:
14.67% 2234 sprintft libc-2.18.so [.] __random
|
--- __random
|
|--95.93%-- rand
| do_my_sprintf
| main
| generic_start_main.isra.0
| __libc_start_main
| 0x0
|
--4.07%-- do_my_sprintf
main
generic_start_main.isra.0
__libc_start_main
0x0
TODO: For split-debug info objects like glibc, we can only determine
the call-frame-address only when both .eh_frame and .debug_info
sections are available. We should be able to determin the CFA
even without the .eh_frame section.
Fix suggested by Anton Blanchard.
Thanks to valuable input on DWARF debug information from Ulrich Weigand.
Reported-by: Maynard Johnson <mayn...@us.ibm.com>
Tested-by: Maynard Johnson <mayn...@us.ibm.com>
Signed-off-by: Sukadev Bhattiprolu <suka...@linux.vnet.ibm.com>
---
Changelog[v4]
Move Powerpc-specific code into a separate patch
Changelog[v3]
[Jiri Olsa] Rename function to arch_skip_callchain_idx() to be
consistent with behavior.
[Jiri Olsa] Add '__maybe_unused' tags for unused parameters.
Changelog[v2]:
Add missing dwfl_end()
Fix merge conflicts due to some unwind code
tools/perf/arch/powerpc/util/skip-callchain-idx.c | 251 ++++++++++++++++++++-
1 file changed, 246 insertions(+), 5 deletions(-)
diff --git a/tools/perf/arch/powerpc/util/skip-callchain-idx.c
b/tools/perf/arch/powerpc/util/skip-callchain-idx.c
index 7350c36..a7c23a4 100644
--- a/tools/perf/arch/powerpc/util/skip-callchain-idx.c
+++ b/tools/perf/arch/powerpc/util/skip-callchain-idx.c
@@ -16,10 +16,251 @@
#include "util/thread.h"
#include "util/callchain.h"
-/* Stub for now */
-int arch_skip_callchain_idx(struct machine *machine __maybe_unused,
- struct thread *thread __maybe_unused,
- struct ip_callchain *chain __maybe_unused)
+/*
+ * When saving the callchain on Power, the kernel conservatively saves
+ * excess entries in the callchain. A few of these entries are needed
+ * in some cases but not others. If the unnecessary entries are not
+ * ignored, we end up with duplicate arcs in the call-graphs. Use
+ * DWARF debug information to skip over any unnecessary callchain
+ * entries.
+ *
+ * See function header for arch_adjust_callchain() below for more details.
+ *
+ * The libdwfl code in this file is based on code from elfutils
+ * (libdwfl/argp-std.c, libdwfl/tests/addrcfi.c, etc).
+ */
+static char *debuginfo_path;
+
+static const Dwfl_Callbacks offline_callbacks = {
+ .debuginfo_path = &debuginfo_path,
+ .find_debuginfo = dwfl_standard_find_debuginfo,
+ .section_address = dwfl_offline_section_address,
+};
+
+
+/*
+ * Use the DWARF expression for the Call-frame-address and determine
+ * if return address is in LR and if a new frame was allocated.
+ */
+static int check_return_reg(int ra_regno, Dwarf_Frame *frame)
+{
+ Dwarf_Op ops_mem[2];
+ Dwarf_Op dummy;
+ Dwarf_Op *ops = &dummy;
+ size_t nops;
+ int result;
+
+ result = dwarf_frame_register(frame, ra_regno, ops_mem, &ops, &nops);
+ if (result < 0) {
+ pr_debug("dwarf_frame_register() %s\n", dwarf_errmsg(-1));
+ return -1;
+ }
+
+ /*
+ * Check if return address is on the stack.
+ */
+ if (nops != 0 || ops != NULL)
+ return 0;
+
+ /*
+ * Return address is in LR. Check if a frame was allocated
+ * but not-yet used.
+ */
+ result = dwarf_frame_cfa(frame, &ops, &nops);
+ if (result < 0) {
+ pr_debug("dwarf_frame_cfa() returns %d, %s\n", result,
+ dwarf_errmsg(-1));
+ return -1;
+ }
+
+ /*
+ * If call frame address is in r1, no new frame was allocated.
+ */
+ if (nops == 1 && ops[0].atom == DW_OP_bregx && ops[0].number == 1 &&
+ ops[0].number2 == 0)
+ return 1;
+
+ /*
+ * A new frame was allocated but has not yet been used.
+ */
+ return 2;
+}
+
+/*
+ * Get the DWARF frame from the .eh_frame section.
+ */
+static Dwarf_Frame *get_eh_frame(Dwfl_Module *mod, Dwarf_Addr pc)
+{
+ int result;
+ Dwarf_Addr bias;
+ Dwarf_CFI *cfi;
+ Dwarf_Frame *frame;
+
+ cfi = dwfl_module_eh_cfi(mod, &bias);
+ if (!cfi) {
+ pr_debug("%s(): no CFI - %s\n", __func__, dwfl_errmsg(-1));
+ return NULL;
+ }
+
+ result = dwarf_cfi_addrframe(cfi, pc, &frame);
+ if (result) {
+ pr_debug("%s(): %s\n", __func__, dwfl_errmsg(-1));
+ return NULL;
+ }
+
+ return frame;
+}
+
+/*
+ * Get the DWARF frame from the .debug_frame section.
+ */
+static Dwarf_Frame *get_dwarf_frame(Dwfl_Module *mod, Dwarf_Addr pc)
+{
+ Dwarf_CFI *cfi;
+ Dwarf_Addr bias;
+ Dwarf_Frame *frame;
+ int result;
+
+ cfi = dwfl_module_dwarf_cfi(mod, &bias);
+ if (!cfi) {
+ pr_debug("%s(): no CFI - %s\n", __func__, dwfl_errmsg(-1));
+ return NULL;
+ }
+
+ result = dwarf_cfi_addrframe(cfi, pc, &frame);
+ if (result) {
+ pr_debug("%s(): %s\n", __func__, dwfl_errmsg(-1));
+ return NULL;
+ }
+
+ return frame;
+}
+
+/*
+ * Return:
+ * 0 if return address for the program counter @pc is on stack
+ * 1 if return address is in LR and no new stack frame was allocated
+ * 2 if return address is in LR and a new frame was allocated (but not
+ * yet used)
+ * -1 in case of errors
+ */
+static int check_return_addr(const char *exec_file, Dwarf_Addr pc)
+{
+ int rc = -1;
+ Dwfl *dwfl;
+ Dwfl_Module *mod;
+ Dwarf_Frame *frame;
+ int ra_regno;
+ Dwarf_Addr start = pc;
+ Dwarf_Addr end = pc;
+ bool signalp;
+
+ dwfl = dwfl_begin(&offline_callbacks);
+ if (!dwfl) {
+ pr_debug("dwfl_begin() failed: %s\n", dwarf_errmsg(-1));
+ return -1;
+ }
+
+ if (dwfl_report_offline(dwfl, "", exec_file, -1) == NULL) {
+ pr_debug("dwfl_report_offline() failed %s\n", dwarf_errmsg(-1));
+ goto out;
+ }
+
+ mod = dwfl_addrmodule(dwfl, pc);
+ if (!mod) {
+ pr_debug("dwfl_addrmodule() failed, %s\n", dwarf_errmsg(-1));
+ goto out;
+ }
+
+ /*
+ * To work with split debug info files (eg: glibc), check both
+ * .eh_frame and .debug_frame sections of the ELF header.
+ */
+ frame = get_eh_frame(mod, pc);
+ if (!frame) {
+ frame = get_dwarf_frame(mod, pc);
+ if (!frame)
+ goto out;
+ }
+
+ ra_regno = dwarf_frame_info(frame, &start, &end, &signalp);
+ if (ra_regno < 0) {
+ pr_debug("Return address register unavailable: %s\n",
+ dwarf_errmsg(-1));
+ goto out;
+ }
+
+ rc = check_return_reg(ra_regno, frame);
+
+out:
+ dwfl_end(dwfl);
+ return rc;
+}
+
+/*
+ * The callchain saved by the kernel always includes the link register (LR).
+ *
+ * 0: PERF_CONTEXT_USER
+ * 1: Program counter (Next instruction pointer)
+ * 2: LR value
+ * 3: Caller's caller
+ * 4: ...
+ *
+ * The value in LR is only needed when it holds a return address. If the
+ * return address is on the stack, we should ignore the LR value.
+ *
+ * Further, when the return address is in the LR, if a new frame was just
+ * allocated but the LR was not saved into it, then the LR contains the
+ * caller, slot 4: contains the caller's caller and the contents of slot 3:
+ * (chain->ips[3]) is undefined and must be ignored.
+ *
+ * Use DWARF debug information to determine if any entries need to be skipped.
+ *
+ * Return:
+ * index: of callchain entry that needs to be ignored (if any)
+ * -1 if no entry needs to be ignored or in case of errors
+ */
+int arch_skip_callchain_idx(struct machine *machine, struct thread *thread,
+ struct ip_callchain *chain)
{
- return -1;
+ struct addr_location al;
+ struct dso *dso = NULL;
+ int rc;
+ u64 ip;
+ u64 skip_slot = -1;
+
+ if (chain->nr < 3)
+ return skip_slot;
+
+ ip = chain->ips[2];
+
+ thread__find_addr_location(thread, machine, PERF_RECORD_MISC_USER,
+ MAP__FUNCTION, ip, &al);
+
+ if (al.map)
+ dso = al.map->dso;
+
+ if (!dso) {
+ pr_debug("%" PRIx64 " dso is NULL\n", ip);
+ return skip_slot;
+ }
+
+ rc = check_return_addr(dso->long_name, ip);
+
+ pr_debug("DSO %s, nr %" PRIx64 ", ip 0x%" PRIx64 "rc %d\n",
+ dso->long_name, chain->nr, ip, rc);
+
+ if (rc == 0) {
+ /*
+ * Return address on stack. Ignore LR value in callchain
+ */
+ skip_slot = 2;
+ } else if (rc == 2) {
+ /*
+ * New frame allocated but return address still in LR.
+ * Ignore the caller's caller entry in callchain.
+ */
+ skip_slot = 3;
+ }
+ return skip_slot;
}
--
1.7.9.5
_______________________________________________
Linuxppc-dev mailing list
Linuxppc-dev@lists.ozlabs.org
https://lists.ozlabs.org/listinfo/linuxppc-dev
