Re: [PATCH v2 40/43] contrib/plugins: extend execlog to track register changes

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Hello Alex,

  just reporting below what might be a riscv only oddity (also applies to
  patch 41 but easier to report here).

Le 03/01/2024 à 18:33, Alex Bennée a écrit :
With the new plugin register API we can now track changes to register
values. Currently the implementation is fairly dumb which will slow
down if a large number of register values are being tracked. This
could be improved by only instrumenting instructions which mention
registers we are interested in tracking.

Example usage:

   ./qemu-aarch64 -D plugin.log -d plugin \
      -cpu max,sve256=on \
      -plugin contrib/plugins/libexeclog.so,reg=sp,reg=z\* \
      ./tests/tcg/aarch64-linux-user/sha512-sve

will display in the execlog any changes to the stack pointer (sp) and
the SVE Z registers.

Signed-off-by: Alex Bennée <alex.bennee@xxxxxxxxxx>
Cc: Akihiko Odaki <akihiko.odaki@xxxxxxxxxx>
Based-On: <20231025093128.33116-19-akihiko.odaki@xxxxxxxxxx>

+static registers_init(int vcpu_index)
+{
+    GPtrArray *registers = g_ptr_array_new();
+    g_autoptr(GArray) reg_list = qemu_plugin_get_registers(vcpu_index);
+
+    if (reg_list && reg_list->len) {
+        /*
+         * Go through each register in the complete list and
+         * see if we want to track it.
+         */
+        for (int r = 0; r < reg_list->len; r++) {
+            qemu_plugin_reg_descriptor *rd = &g_array_index(
+                reg_list, qemu_plugin_reg_descriptor, r);

riscv csrs are not continously numbered and the dynamically generated gdb xml
seems to follow that scheme.
So the calls to Glib string functions output quite a few assertion
warnings because for the non existing csrs rd->name is NULL (and there
are a bit less than 4000 such cases for rv64g).
Checking for NULL and then continue is a simple way to solve the issue, but
I am not sure this is the proper way to proceed, as it might stand in the
generation of the riscv xml description for gdb.

Cheers,
Frédéric

+            for (int p = 0; p < rmatches->len; p++) {
+                g_autoptr(GPatternSpec) pat = g_pattern_spec_new(rmatches->pdata[p]);
+                if (g_pattern_match_string(pat, rd->name)) {
+                    Register *reg = init_vcpu_register(vcpu_index, rd);
+                    g_ptr_array_add(registers, reg);
+                }
+            }
+        }
+    }
+    cpus[num_cpus].registers = registers;
+}





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