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

Source file repositories/reference/linux-study-clean/tools/perf/arch/powerpc/util/skip-callchain-idx.c

File Facts

System
Linux kernel
Corpus path
tools/perf/arch/powerpc/util/skip-callchain-idx.c
Extension
.c
Size
6332 bytes
Lines
258
Domain
Support Tooling And Documentation
Bucket
tools
Inferred role
Support Tooling And Documentation: implementation source
Status
source implementation candidate

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Use DWARF Debug information to skip unnecessary callchain entries.
 *
 * Copyright (C) 2014 Sukadev Bhattiprolu, IBM Corporation.
 * Copyright (C) 2014 Ulrich Weigand, IBM Corporation.
 */
#include <inttypes.h>
#include <dwarf.h>
#include <elfutils/libdwfl.h>

#include "util/thread.h"
#include "util/callchain.h"
#include "util/debug.h"
#include "util/dso.h"
#include "util/event.h" // struct ip_callchain
#include "util/map.h"
#include "util/symbol.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).
 */

/*
 * 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[3];
	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 return address
	 * is in a register (typically R0), it is yet to be saved on
	 * the stack.
	 */
	if ((nops != 0 || ops != NULL) &&
		!(nops == 1 && ops[0].atom == DW_OP_regx &&
			ops[0].number2 == 0 && ops[0].offset == 0))
		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)
{

Annotation

Implementation Notes