GDB remote protocol supports two reverse debugging commands: reverse step and reverse continue. This patch adds support of the first one to the gdbstub. Reverse step is intended to step one instruction in the backwards direction. This is not possible in regular execution. But replayed execution is deterministic, therefore we can load one of the prior snapshots and proceed to the desired step. It is equivalent to stepping one instruction back. There should be at least one snapshot preceding the debugged part of the replay log. Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> -- v4 changes: - inverted condition in cpu_handle_guest_debug (suggested by Alex Bennée) Message-Id: <160174522341.12451.1498758422543765253.stgit@pasha-ThinkPad-X280> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
150 lines
4.7 KiB
C
150 lines
4.7 KiB
C
/*
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* Generic intermediate code generation.
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*
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* Copyright (C) 2016-2017 Lluís Vilanova <vilanova@ac.upc.edu>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or later.
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* See the COPYING file in the top-level directory.
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*/
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#include "qemu/osdep.h"
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#include "qemu/error-report.h"
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#include "cpu.h"
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#include "tcg/tcg.h"
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#include "tcg/tcg-op.h"
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#include "exec/exec-all.h"
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#include "exec/gen-icount.h"
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#include "exec/log.h"
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#include "exec/translator.h"
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#include "exec/plugin-gen.h"
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#include "sysemu/replay.h"
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/* Pairs with tcg_clear_temp_count.
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To be called by #TranslatorOps.{translate_insn,tb_stop} if
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(1) the target is sufficiently clean to support reporting,
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(2) as and when all temporaries are known to be consumed.
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For most targets, (2) is at the end of translate_insn. */
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void translator_loop_temp_check(DisasContextBase *db)
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{
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if (tcg_check_temp_count()) {
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qemu_log("warning: TCG temporary leaks before "
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TARGET_FMT_lx "\n", db->pc_next);
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}
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}
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void translator_loop(const TranslatorOps *ops, DisasContextBase *db,
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CPUState *cpu, TranslationBlock *tb, int max_insns)
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{
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int bp_insn = 0;
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bool plugin_enabled;
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/* Initialize DisasContext */
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db->tb = tb;
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db->pc_first = tb->pc;
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db->pc_next = db->pc_first;
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db->is_jmp = DISAS_NEXT;
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db->num_insns = 0;
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db->max_insns = max_insns;
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db->singlestep_enabled = cpu->singlestep_enabled;
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ops->init_disas_context(db, cpu);
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tcg_debug_assert(db->is_jmp == DISAS_NEXT); /* no early exit */
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/* Reset the temp count so that we can identify leaks */
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tcg_clear_temp_count();
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/* Start translating. */
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gen_tb_start(db->tb);
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ops->tb_start(db, cpu);
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tcg_debug_assert(db->is_jmp == DISAS_NEXT); /* no early exit */
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plugin_enabled = plugin_gen_tb_start(cpu, tb);
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while (true) {
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db->num_insns++;
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ops->insn_start(db, cpu);
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tcg_debug_assert(db->is_jmp == DISAS_NEXT); /* no early exit */
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if (plugin_enabled) {
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plugin_gen_insn_start(cpu, db);
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}
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/* Pass breakpoint hits to target for further processing */
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if (!db->singlestep_enabled
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&& unlikely(!QTAILQ_EMPTY(&cpu->breakpoints))) {
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CPUBreakpoint *bp;
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QTAILQ_FOREACH(bp, &cpu->breakpoints, entry) {
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if (bp->pc == db->pc_next) {
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if (ops->breakpoint_check(db, cpu, bp)) {
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bp_insn = 1;
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break;
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}
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}
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}
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/* The breakpoint_check hook may use DISAS_TOO_MANY to indicate
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that only one more instruction is to be executed. Otherwise
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it should use DISAS_NORETURN when generating an exception,
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but may use a DISAS_TARGET_* value for Something Else. */
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if (db->is_jmp > DISAS_TOO_MANY) {
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break;
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}
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}
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/* Disassemble one instruction. The translate_insn hook should
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update db->pc_next and db->is_jmp to indicate what should be
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done next -- either exiting this loop or locate the start of
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the next instruction. */
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if (db->num_insns == db->max_insns
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&& (tb_cflags(db->tb) & CF_LAST_IO)) {
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/* Accept I/O on the last instruction. */
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gen_io_start();
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ops->translate_insn(db, cpu);
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} else {
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ops->translate_insn(db, cpu);
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}
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/* Stop translation if translate_insn so indicated. */
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if (db->is_jmp != DISAS_NEXT) {
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break;
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}
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/*
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* We can't instrument after instructions that change control
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* flow although this only really affects post-load operations.
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*/
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if (plugin_enabled) {
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plugin_gen_insn_end();
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}
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/* Stop translation if the output buffer is full,
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or we have executed all of the allowed instructions. */
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if (tcg_op_buf_full() || db->num_insns >= db->max_insns) {
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db->is_jmp = DISAS_TOO_MANY;
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break;
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}
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}
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/* Emit code to exit the TB, as indicated by db->is_jmp. */
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ops->tb_stop(db, cpu);
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gen_tb_end(db->tb, db->num_insns - bp_insn);
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if (plugin_enabled) {
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plugin_gen_tb_end(cpu);
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}
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/* The disas_log hook may use these values rather than recompute. */
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db->tb->size = db->pc_next - db->pc_first;
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db->tb->icount = db->num_insns;
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#ifdef DEBUG_DISAS
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if (qemu_loglevel_mask(CPU_LOG_TB_IN_ASM)
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&& qemu_log_in_addr_range(db->pc_first)) {
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FILE *logfile = qemu_log_lock();
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qemu_log("----------------\n");
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ops->disas_log(db, cpu);
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qemu_log("\n");
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qemu_log_unlock(logfile);
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}
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#endif
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}
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