[Qemu-devel] [Bug 597362] Re: qemu-system-sparc singlestep not work in gdbstub

[Thomas Huth]

Triaging old bug reports ... Can you still reproduce this problem with
the latest version of QEMU?

** Changed in: qemu
       Status: New => Incomplete

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https://bugs.launchpad.net/bugs/597362

Title:
  qemu-system-sparc singlestep not work in gdbstub

Status in QEMU:
  Incomplete

Bug description:
  Debugging with gdb-stub does not work with qemu-system-sparc target

  Qemu compiled from current git tree.

  execution string: qemu-system-sparc.exe -s -S -m 256 -L Bios -hda
  sparc.img -boot c
  connect with telnet localhost 1234
  enter '$s#73' (without quotes, this is single step command to gdb stub)
  gdb stub reply '+' (without quotes, as it accept command)
  After this qemu continuously execute instructions in single step mode
  and does not exit to gdb stub after each executed instruction with
  interrupt signal
  ("T%02xthread:%02x;" /gdb_vm_state_change in gdbstub.c/ );

  If we look at target-sparc/translate.c, we can see that
  gen_helper_debug() is not called in single step mode:

  ========================
      if ((pc & TARGET_PAGE_MASK) == (tb->pc & TARGET_PAGE_MASK) &&
          (npc & TARGET_PAGE_MASK) == (tb->pc & TARGET_PAGE_MASK) &&
          !s->singlestep)  {
          /* jump to same page: we can use a direct jump */
          tcg_gen_goto_tb(tb_num);
          tcg_gen_movi_tl(cpu_pc, pc);
          tcg_gen_movi_tl(cpu_npc, npc);
          tcg_gen_exit_tb((long)tb + tb_num);
      } else {
          /* jump to another page: currently not optimized */
          tcg_gen_movi_tl(cpu_pc, pc);
          tcg_gen_movi_tl(cpu_npc, npc);
          tcg_gen_exit_tb(0);
      }
  =========================

  ========================
          /* if single step mode, we generate only one instruction and
             generate an exception */
          if (dc->singlestep) {
              break;
          }
  ========================

  If we look similar code at target-sh4/translate.c we can see that is
  called in this cases:

  ========================
      if ((tb->pc & TARGET_PAGE_MASK) == (dest & TARGET_PAGE_MASK) &&
        !ctx->singlestep_enabled) {
        /* Use a direct jump if in same page and singlestep not enabled */
          tcg_gen_goto_tb(n);
          tcg_gen_movi_i32(cpu_pc, dest);
          tcg_gen_exit_tb((long) tb + n);
      } else {
          tcg_gen_movi_i32(cpu_pc, dest);
          if (ctx->singlestep_enabled)
              gen_helper_debug();
          tcg_gen_exit_tb(0);
      }
  ========================

  ========================
      if (tb->cflags & CF_LAST_IO)
          gen_io_end();
      if (env->singlestep_enabled) {
          tcg_gen_movi_i32(cpu_pc, ctx.pc);
          gen_helper_debug();
      } else {
  ==========================

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