test(callgrind): add Python regression test for runtime obj-skip

End-to-end test for CALLGRIND_ADD_OBJ_SKIP using the canonical flow:
start with --instr-atstart=no, register the libpython path via the
trapdoor, then turn instrumentation on so the skip applies from the
first instrumented BB.

Author: not-matthias

callgrind/tests/Makefile.am

@@ -10,6 +10,8 @@ EXTRA_DIST = \
 	ann1.post.exp ann1.stderr.exp ann1.vgtest \
 	ann2.post.exp ann2.stderr.exp ann2.vgtest \
 	clreq.vgtest clreq.stderr.exp \
+	runtime_obj_skip_py.vgtest runtime_obj_skip_py.stderr.exp runtime_obj_skip_py.post.exp \
+	runtime_obj_skip_py.py runtime_obj_skip_py_shim.c \
 	bug497723.stderr.exp bug497723.post.exp bug497723.vgtest \
 	simwork1.vgtest simwork1.stdout.exp simwork1.stderr.exp \
 	simwork2.vgtest simwork2.stdout.exp simwork2.stderr.exp \
@@ -38,3 +40,13 @@ inline_samefile_CFLAGS = $(AM_CFLAGS) -O2 -g
 inline_crossfile_CFLAGS = $(AM_CFLAGS) -O2 -g
 
 threads_LDADD = -lpthread
+
+# Shim loaded by runtime_obj_skip_py.py via ctypes. Built unconditionally;
+# the test's prereq skips it if the .so is missing.
+check_DATA = runtime_obj_skip_py_shim.so
+
+runtime_obj_skip_py_shim.so: runtime_obj_skip_py_shim.c
+	$(CC) -shared -fPIC -O2 -I$(top_srcdir) -I$(top_srcdir)/include \
+	    $< -o $@
+
+CLEANFILES = runtime_obj_skip_py_shim.so

callgrind/tests/runtime_obj_skip_py.post.exp

@@ -0,0 +1 @@
+OK

callgrind/tests/runtime_obj_skip_py.py

@@ -0,0 +1,70 @@
+"""Resolve libpython at runtime via sysconfig (mirrors pytest-codspeed's
+approach in instruments/walltime.py), register it for obj-skip via the
+client-request shim, then turn instrumentation on and run a small
+integer workload.
+
+We pass both the sysconfig path AND its os.path.realpath because
+callgrind stores the realpath in obj_node->name (after symlink
+resolution), and the runtime obj-skip check uses exact strcmp."""
+
+import ctypes
+import os
+import sys
+import sysconfig
+
+
+def libpython_candidates() -> list[str]:
+    ldlibrary = sysconfig.get_config_var("LDLIBRARY")
+    libdir = sysconfig.get_config_var("LIBDIR")
+    paths: list[str] = []
+    if ldlibrary and libdir:
+        paths.append(os.path.join(libdir, ldlibrary))
+    if ldlibrary:
+        paths.append(os.path.join(sys.prefix, "lib", ldlibrary))
+    # Add realpath variants so the exact-match obj-skip finds the
+    # file under whichever name the loader actually mapped.
+    resolved: list[str] = []
+    seen: set[str] = set()
+    for p in paths:
+        if not p:
+            continue
+        if p not in seen and os.path.exists(p):
+            resolved.append(p)
+            seen.add(p)
+        try:
+            r = os.path.realpath(p)
+        except OSError:
+            continue
+        if r not in seen and os.path.exists(r):
+            resolved.append(r)
+            seen.add(r)
+    return resolved
+
+
+def main() -> None:
+    here = os.path.dirname(os.path.abspath(__file__))
+    shim = ctypes.CDLL(os.path.join(here, "runtime_obj_skip_py_shim.so"))
+    shim.add_obj_skip.argtypes = [ctypes.c_char_p]
+    shim.add_obj_skip.restype = None
+    shim.start_instr.argtypes = []
+    shim.start_instr.restype = None
+    shim.stop_instr.argtypes = []
+    shim.stop_instr.restype = None
+
+    for path in libpython_candidates():
+        shim.add_obj_skip(path.encode())
+    if sys.executable:
+        shim.add_obj_skip(sys.executable.encode())
+        real = os.path.realpath(sys.executable)
+        if real != sys.executable:
+            shim.add_obj_skip(real.encode())
+
+    shim.start_instr()
+    acc = 0
+    for i in range(10_000):
+        acc = (acc + i * i) ^ (i << 1)
+    shim.stop_instr()
+
+
+if __name__ == "__main__":
+    main()

callgrind/tests/runtime_obj_skip_py.stderr.exp

@@ -0,0 +1,6 @@
+
+
+Events    : Ir
+Collected :
+
+I   refs:

callgrind/tests/runtime_obj_skip_py.vgtest

@@ -0,0 +1,6 @@
+prereq: command -v python3 >/dev/null && test -f runtime_obj_skip_py_shim.so
+prog-asis: python3
+args: runtime_obj_skip_py.py
+vgopts: --instr-atstart=no --compress-strings=no --callgrind-out-file=callgrind.out.runtime_obj_skip_py
+post: sh -c 'c=$(awk "/^ob=/{p=(\$0~/libpython/)} /^fn=/&&p{c++} END{print c+0}" callgrind.out.runtime_obj_skip_py); if [ "$c" -lt 100 ]; then echo OK; else echo "FAIL libpython fns=$c"; fi'
+cleanup: rm -f callgrind.out.runtime_obj_skip_py

callgrind/tests/runtime_obj_skip_py_shim.c

@@ -0,0 +1,20 @@
+/* Shim so Python (via ctypes) can issue callgrind client requests.
+   The requests themselves are inline asm and unreachable from pure
+   Python; this file just wraps them in regular C functions. */
+
+#include "../callgrind.h"
+
+void add_obj_skip(const char* path)
+{
+   CALLGRIND_ADD_OBJ_SKIP(path);
+}
+
+void start_instr(void)
+{
+   CALLGRIND_START_INSTRUMENTATION;
+}
+
+void stop_instr(void)
+{
+   CALLGRIND_STOP_INSTRUMENTATION;
+}