gdbstub: Consider GDBFeature::base_reg in gdb_register_coprocessor()

When a feature XML file provides a "regnum=" tag to indicate
the registers base index, respect it, as it might not be the
same as our current number of registered entries, in particular
when there are gaps.

This fixes a bug with the "power-fpu.xml" file [*] which was
loaded at index 70 while the base register is 71. This latent
bug was exposed by commit 1ec0fbe2dda ("target/ppc: Fix
CPUClass::gdb_num_core_regs value").

[*] https://lore.kernel.org/qemu-devel/e44df309-d40d-46f0-88a8-7ac55f9a3634@fhofhammer.de/

Reported-by: Florian Hofhammer <florian.hofhammer@fhofhammer.de>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Tested-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Link: https://lore.kernel.org/qemu-devel/20260310232045.58440-13-philmd@linaro.org
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>

diff --git a/gdbstub/gdbstub.c b/gdbstub/gdbstub.c
index 69038c66f2b35be4e67d1ce4a8464345f31aea7e..c3c944e965b9cc7dac0107ee133817a2bab79896 100644 (file)
--- a/gdbstub/gdbstub.c
+++ b/gdbstub/gdbstub.c
@@ -601,6 +601,7 @@ void gdb_init_cpu(CPUState *cpu)
     if (xmlfile) {
         assert(!cc->gdb_num_core_regs);
         feature = gdb_find_static_feature(xmlfile);
+        assert(feature->base_reg == 0);
         gdb_register_feature(cpu, 0,
                              cc->gdb_read_register, cc->gdb_write_register,
                              feature);
@@ -630,6 +631,11 @@ void gdb_register_coprocessor(CPUState *cpu,
         }
     }
 
+    if (base_reg < feature->base_reg) {
+        trace_gdbxml_register_coprocessor_gap(base_reg,
+                                              feature->base_reg);
+        base_reg = feature->base_reg;
+    }
     gdb_register_feature(cpu, base_reg, get_reg, set_reg, feature);
 
     /* Add to end of list.  */

diff --git a/gdbstub/trace-events b/gdbstub/trace-events
index 8caee36c2424a50b32fda677add8d9a1a2d3e463..5bc8394674361195b5fe1ed2cab56277e9d09b1e 100644 (file)
--- a/gdbstub/trace-events
+++ b/gdbstub/trace-events
@@ -29,6 +29,7 @@ gdbstub_err_checksum_incorrect(uint8_t expected, uint8_t got) "got command packe
 gdbstub_err_unexpected_runpkt(uint8_t ch) "unexpected packet (0x%02x) while target running"
 
 gdbxml_init_cpu(const char *typename, unsigned id, unsigned gdb_num_regs, unsigned gdb_num_g_regs, unsigned gdb_num_core_regs) "%s:%d regs:%u g_regs:%u core_regs:%u"
+gdbxml_register_coprocessor_gap(unsigned gdb_num_regs, unsigned base_reg) "regs %u -> %u"
 gdbxml_register_feature(const char *featname, const char *xmlname, unsigned base_reg, unsigned num_regs) "%s (%s) @%u +%u"
 gdbxml_feature_builder_header(const char *name, const char *xmlname, int num_regs) "%s (%s) regs:%d"
 gdbxml_feature_builder_content(const char *xml) "%s"