perf tools powerpc: Adjust callchain based on DWARF debug info (a60335ba) · Commits · 戴 / test

tools/perf/arch/powerpc/Makefile

+1 −0

Original line number	Diff line number	Diff line
		@@ -3,3 +3,4 @@ PERF_HAVE_DWARF_REGS := 1
		LIB_OBJS += $(OUTPUT)arch/$(ARCH)/util/dwarf-regs.o
		endif
		LIB_OBJS += $(OUTPUT)arch/$(ARCH)/util/header.o
		LIB_OBJS += $(OUTPUT)arch/$(ARCH)/util/skip-callchain-idx.o

tools/perf/arch/powerpc/util/skip-callchain-idx.c

0 → 100644

+266 −0

Original line number	Diff line number	Diff line
		/*
		* Use DWARF Debug information to skip unnecessary callchain entries.
		*
		* Copyright (C) 2014 Sukadev Bhattiprolu, IBM Corporation.
		* Copyright (C) 2014 Ulrich Weigand, IBM Corporation.
		*
		* This program is free software; you can redistribute it and/or
		* modify it under the terms of the GNU General Public License
		* as published by the Free Software Foundation; either version
		* 2 of the License, or (at your option) any later version.
		*/
		#include <inttypes.h>
		#include <dwarf.h>
		#include <elfutils/libdwfl.h>

		#include "util/thread.h"
		#include "util/callchain.h"

		/*
		* 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)
		{
		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;
		}

tools/perf/config/Makefile

+4 −0

Original line number	Diff line number	Diff line
		@@ -48,6 +48,10 @@ ifneq ($(ARCH),$(filter $(ARCH),x86 arm))
		NO_LIBDW_DWARF_UNWIND := 1
		endif

		ifeq ($(ARCH),powerpc)
		CFLAGS += -DHAVE_SKIP_CALLCHAIN_IDX
		endif

		ifeq ($(LIBUNWIND_LIBS),)
		NO_LIBUNWIND := 1
		else

tools/perf/util/callchain.h

+13 −0

Original line number	Diff line number	Diff line
		@@ -176,4 +176,17 @@ static inline void callchain_cursor_snapshot(struct callchain_cursor *dest,
		dest->first = src->curr;
		dest->nr -= src->pos;
		}

		#ifdef HAVE_SKIP_CALLCHAIN_IDX
		extern int arch_skip_callchain_idx(struct machine *machine,
		struct thread thread, struct ip_callchain chain);
		#else
		static inline int arch_skip_callchain_idx(struct machine *machine __maybe_unused,
		struct thread *thread __maybe_unused,
		struct ip_callchain *chain __maybe_unused)
		{
		return -1;
		}
		#endif

		#endif /* __PERF_CALLCHAIN_H */

tools/perf/util/machine.c

+16 −2

Original line number	Diff line number	Diff line
		@@ -1281,7 +1281,9 @@ static int machine__resolve_callchain_sample(struct machine *machine,
		u8 cpumode = PERF_RECORD_MISC_USER;
		int chain_nr = min(max_stack, (int)chain->nr);
		int i;
		int j;
		int err;
		int skip_idx __maybe_unused;

		callchain_cursor_reset(&callchain_cursor);

		@@ -1290,14 +1292,26 @@ static int machine__resolve_callchain_sample(struct machine *machine,
		return 0;
		}

		/*
		* Based on DWARF debug information, some architectures skip
		* a callchain entry saved by the kernel.
		*/
		skip_idx = arch_skip_callchain_idx(machine, thread, chain);

		for (i = 0; i < chain_nr; i++) {
		u64 ip;
		struct addr_location al;

		if (callchain_param.order == ORDER_CALLEE)
		ip = chain->ips[i];
		j = i;
		else
		ip = chain->ips[chain->nr - i - 1];
		j = chain->nr - i - 1;

		#ifdef HAVE_SKIP_CALLCHAIN_IDX
		if (j == skip_idx)
		continue;
		#endif
		ip = chain->ips[j];

		if (ip >= PERF_CONTEXT_MAX) {
		switch (ip) {

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