[Qemu-devel] qemu-system-sparc singlestep not work in gdbstub

[Vitaliy Vorobyov]

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 {
==========================