Hi On Tue, Oct 13, 2026 at 12:51 PM Alex Bennée <[email protected]> wrote: > > Marc-André Lureau <[email protected]> writes: > > > Add support for registering coprocessor features that are only visible > > to QEMU's internal APIs (HMP monitor $register expressions, plugins) but > > hidden from GDB's target description XML. > > > > When a feature is registered as internal: > > - It is excluded from the target.xml sent to GDB > > - Its XML is not served via qXfer:features:read > > - 'p'/'P' packets for internal register numbers return E14 > > > > This is useful for exposing system registers to the HMP monitor without > > affecting GDB's register namespace. Exposing aliases or synthetic > > registers through GDB's target description can cause problems: name > > collisions with GDB's pseudo-registers, independent register caching, > > and missing DWARF unwind rules. > > Hmm are they *that* useful for HMP then? > > The front-ends do limit what they export to gdb (see for example > ARM_CP_NO_GDB) generally because reading them causes side-effects. Those > restrictions are also a reason to limit them from the HMP interface.
I am not a user, but I can imagine they are useful for developers. I would like to be able to implement "info registers" purely based on QMP for ex. > > > > > Internal features must be registered after all GDB-visible features to > > keep remote register numbering consistent. This ordering is enforced > > with an assertion. > > > > Signed-off-by: Marc-André Lureau <[email protected]> > > --- > > gdbstub/gdbstub.c | 71 > > ++++++++++++++++++++++++++++++++++++++++++++------ > > include/exec/gdbstub.h | 21 +++++++++++++++ > > 2 files changed, 84 insertions(+), 8 deletions(-) > > > > diff --git a/gdbstub/gdbstub.c b/gdbstub/gdbstub.c > > index 912e31b66744..ac0f76d62333 100644 > > --- a/gdbstub/gdbstub.c > > +++ b/gdbstub/gdbstub.c > > @@ -54,6 +54,7 @@ typedef struct GDBRegisterState { > > gdb_get_reg_cb get_reg; > > gdb_set_reg_cb set_reg; > > const GDBFeature *feature; > > + bool internal; /* hidden from GDB, accessible via API/monitor */ > > } GDBRegisterState; > > > > GDBState gdbserver_state; > > @@ -385,6 +386,11 @@ static const char *get_feature_xml(const char *p, > > const char **newp, > > } > > for (guint i = 0; i < cpu->gdb_regs->len; i++) { > > r = &g_array_index(cpu->gdb_regs, GDBRegisterState, i); > > + /* The core target.xml feature must never be internal. */ > > + g_assert(i > 0 || !r->internal); > > + if (r->internal) { > > + continue; > > + } > > g_ptr_array_add( > > xml, > > g_markup_printf_escaped("<xi:include href=\"%s\"/>", > > @@ -400,6 +406,9 @@ static const char *get_feature_xml(const char *p, const > > char **newp, > > /* Is it one of the features? */ > > for (guint i = 0; i < cpu->gdb_regs->len; i++) { > > r = &g_array_index(cpu->gdb_regs, GDBRegisterState, i); > > + if (r->internal) { > > + continue; > > + } > > if (strncmp(p, r->feature->xmlname, len) == 0) { > > return r->feature->xml; > > } > > @@ -563,13 +572,14 @@ int gdb_write_register(CPUState *cpu, uint8_t > > *mem_buf, int reg) > > > > static void gdb_register_feature(CPUState *cpu, int base_reg, > > gdb_get_reg_cb get_reg, gdb_set_reg_cb > > set_reg, > > - const GDBFeature *feature) > > + const GDBFeature *feature, bool internal) > > { > > GDBRegisterState s = { > > .base_reg = base_reg, > > .get_reg = get_reg, > > .set_reg = set_reg, > > - .feature = feature > > + .feature = feature, > > + .internal = internal > > }; > > > > trace_gdbxml_register_feature(feature->name, feature->xmlname, > > @@ -605,7 +615,7 @@ void gdb_init_cpu(CPUState *cpu) > > assert(feature->base_reg == 0); > > gdb_register_feature(cpu, 0, > > cc->gdb_read_register, cc->gdb_write_register, > > - feature); > > + feature, false); > > cpu->gdb_next_base_reg = cpu->gdb_num_g_regs = feature->num_regs; > > } else { > > cpu->gdb_next_base_reg = cpu->gdb_num_g_regs = > > cc->gdb_num_core_regs; > > @@ -616,20 +626,26 @@ void gdb_init_cpu(CPUState *cpu) > > cc->gdb_num_core_regs); > > } > > > > -void gdb_register_coprocessor(CPUState *cpu, > > - gdb_get_reg_cb get_reg, gdb_set_reg_cb > > set_reg, > > - const GDBFeature *feature) > > +static void do_gdb_register_coprocessor(CPUState *cpu, > > + gdb_get_reg_cb get_reg, > > + gdb_set_reg_cb set_reg, > > + const GDBFeature *feature, > > + bool internal) > > { > > GDBRegisterState *s; > > guint i; > > int base_reg = cpu->gdb_next_base_reg; > > > > for (i = 0; i < cpu->gdb_regs->len; i++) { > > - /* Check for duplicates. */ > > s = &g_array_index(cpu->gdb_regs, GDBRegisterState, i); > > + /* Check for duplicates. */ > > if (s->feature == feature) { > > return; > > } > > + /* GDB-visible features must not follow internal ones. */ > > + if (!internal) { > > + g_assert(!s->internal); > > + } > > } > > > > if (base_reg < feature->base_reg) { > > @@ -637,12 +653,27 @@ void gdb_register_coprocessor(CPUState *cpu, > > feature->base_reg); > > base_reg = feature->base_reg; > > } > > - gdb_register_feature(cpu, base_reg, get_reg, set_reg, feature); > > + gdb_register_feature(cpu, base_reg, get_reg, set_reg, feature, > > internal); > > > > /* Add to end of list. */ > > cpu->gdb_next_base_reg = base_reg + feature->num_regs; > > } > > > > +void gdb_register_coprocessor(CPUState *cpu, > > + gdb_get_reg_cb get_reg, gdb_set_reg_cb > > set_reg, > > + const GDBFeature *feature) > > +{ > > + do_gdb_register_coprocessor(cpu, get_reg, set_reg, feature, false); > > +} > > + > > +void gdb_register_internal_coprocessor(CPUState *cpu, > > + gdb_get_reg_cb get_reg, > > + gdb_set_reg_cb set_reg, > > + const GDBFeature *feature) > > +{ > > + do_gdb_register_coprocessor(cpu, get_reg, set_reg, feature, true); > > +} > > + > > void gdb_unregister_coprocessor_all(CPUState *cpu) > > { > > /* > > @@ -1223,6 +1254,18 @@ static void handle_remove_bp(GArray *params, void > > *user_ctx) > > * the remote gdb to fallback to older methods. > > */ > > > > +static bool gdb_register_is_internal(CPUState *cpu, int reg) > > +{ > > + for (guint i = 0; i < cpu->gdb_regs->len; i++) { > > + GDBRegisterState *r = &g_array_index(cpu->gdb_regs, > > GDBRegisterState, i); > > + > > + if (r->base_reg <= reg && reg < r->base_reg + > > r->feature->num_regs) { > > + return r->internal; > > + } > > + } > > + return false; > > +} > > + > > static void handle_set_reg(GArray *params, void *user_ctx) > > { > > int reg_size; > > @@ -1232,6 +1275,12 @@ static void handle_set_reg(GArray *params, void > > *user_ctx) > > return; > > } > > > > + if (gdb_register_is_internal(gdbserver_state.g_cpu, > > + gdb_get_cmd_param(params, 0)->val_ull)) { > > + gdb_put_packet("E14"); > > + return; > > + } > > + > > reg_size = strlen(gdb_get_cmd_param(params, 1)->data) / 2; > > gdb_hextomem(gdbserver_state.mem_buf, gdb_get_cmd_param(params, > > 1)->data, reg_size); > > gdb_write_register(gdbserver_state.g_cpu, > > gdbserver_state.mem_buf->data, > > @@ -1248,6 +1297,12 @@ static void handle_get_reg(GArray *params, void > > *user_ctx) > > return; > > } > > > > + if (gdb_register_is_internal(gdbserver_state.g_cpu, > > + gdb_get_cmd_param(params, 0)->val_ull)) { > > + gdb_put_packet("E14"); > > + return; > > + } > > + > > reg_size = gdb_read_register(gdbserver_state.g_cpu, > > gdbserver_state.mem_buf, > > gdb_get_cmd_param(params, 0)->val_ull); > > diff --git a/include/exec/gdbstub.h b/include/exec/gdbstub.h > > index 75eb4d9c365e..1bc778324758 100644 > > --- a/include/exec/gdbstub.h > > +++ b/include/exec/gdbstub.h > > @@ -40,6 +40,27 @@ void gdb_register_coprocessor(CPUState *cpu, > > gdb_get_reg_cb get_reg, gdb_set_reg_cb > > set_reg, > > const GDBFeature *feature); > > > > +/** > > + * gdb_register_internal_coprocessor() - register internal registers > > + * > > + * Like gdb_register_coprocessor(), but the feature is NOT exposed to > > + * GDB via the target description XML. The registers are only > > + * accessible through QEMU's internal APIs (HMP monitor ``$register`` > > + * expressions via gdb_get_register_list()). > > + * > > + * Internal features must be registered after all GDB-visible features > > + * to avoid register numbering mismatches with GDB. > > + * > > + * @cpu - the CPU associated with registers > > + * @get_reg - get function > > + * @set_reg - set function > > + * @feature - the GDBFeature describing the registers > > + */ > > +void gdb_register_internal_coprocessor(CPUState *cpu, > > + gdb_get_reg_cb get_reg, > > + gdb_set_reg_cb set_reg, > > + const GDBFeature *feature); > > + > > /** > > * gdb_unregister_coprocessor_all() - unregisters supplemental set of > > registers > > * @cpu - the CPU associated with registers > > -- > Alex Bennée > Virtualisation Tech Lead @ Linaro >
