Add libsymtrap.so

Author: mkozlowski

Makefile

@@ -12,7 +12,7 @@ LDFLAGS =
 
 SRC = $(wildcard *.c)
 ALL = $(SRC:%.c=%)
-ALT = vdso
+ALT = vdso libsymtrap.so
 DEF := $(filter-out $(ALT), $(ALL))
 TXT = cc-version.txt cc-defines.txt
 
@@ -29,7 +29,10 @@ $(RSB): %: %.rs Makefile
 	$(RC) $<
 
 vdso: %: %.c Makefile
-	$(CC) $(CFLAGS) $< -o $@ $(LDFLAGS) -ldl
+	$(CC) $(CFLAGS) $< -o $@ -ldl $(LDFLAGS)
+
+libsymtrap.so: %: %.c Makefile
+	$(CC) $(CFLAGS) -fPIC -shared $< -o $@ -Wl,-z,initfirst -ldl $(LDFLAGS)
 
 cc-version.txt: Makefile
 	echo CC=$(CC) > $@

libsymtrap.so.c

@@ -0,0 +1,174 @@
+#define _GNU_SOURCE
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <stdarg.h>
+#include <dlfcn.h>
+#include <execinfo.h>
+#include <time.h>
+#include <sys/ioctl.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <string.h>
+
+
+/*
+ * This library is intended to be preloaded so that it can abort at a specific
+ * point and generate a core dump for analysis. It needs to be manually altered
+ * to match specific case.
+ *
+ * Notes:
+ *   -funwind-tables might be needed on some architectures (arm, riscv)
+ *    for backtrace() to work
+ *   -rdynamic can help make backtrace() output more readable
+ *
+ * Backtrace output can be further decoded with add2line:
+ * $ addr2line -fp -e ./elf addr
+ *
+ */
+
+
+#define DLSYM_CHECK(handle) do { \
+	if ((handle) != NULL) { \
+		/* fprintf(stdout, "libsymtrap.so: wrapping %s()\n", __func__); */ \
+	} else { \
+		fprintf(stderr, "%s\n", dlerror()); \
+		abort(); \
+	} \
+} while (0)
+
+
+static void do_abort(void)
+{
+	int size;
+	void *buffer[64];
+
+	size = backtrace(buffer, sizeof(buffer));
+	fprintf(stderr, "backtrace() returned %d addresses:\n", size);
+	backtrace_symbols_fd(buffer, size, STDERR_FILENO);
+	abort();
+}
+
+
+#if 1
+/*
+ * extern int clock_gettime (clockid_t __clock_id, struct timespec *__tp) __THROW;
+ */
+int clock_gettime(clockid_t clock_id, struct timespec *tp)
+{
+	static int (*__clock_gettime)(clockid_t, struct timespec *) = NULL;
+	static unsigned long count = 0;
+
+	if (__clock_gettime == NULL) {
+		__clock_gettime = (int (*)(clockid_t, struct timespec *))dlsym(RTLD_NEXT, "clock_gettime");
+		DLSYM_CHECK(__clock_gettime);
+	}
+
+	/*
+	 * app under certain load generated 3~5k calls / second so the idea was
+	 * to abort but only when file flag exists
+	 */
+	if (++count % 4000 == 0) {
+		int ret;
+
+		ret = access("/tmp/symtrap_clock_gettime", F_OK);
+		if (!ret)
+			do_abort();
+	}
+
+	return __clock_gettime(clock_id, tp);
+}
+#endif
+
+#if 1
+/*
+ * extern int ioctl (int __fd, unsigned long int __request, ...) __THROW;
+ */
+int ioctl(int fd, unsigned long int request, ...)
+{
+	int ret;
+	va_list args;
+	static int (*__ioctl)(int, unsigned long int, ...) = NULL;
+	unsigned long int ioc;
+
+	if (__ioctl == NULL) {
+		__ioctl = (int (*)(int, unsigned long int, ...))dlsym(RTLD_NEXT, "ioctl");
+		DLSYM_CHECK(__ioctl);
+	}
+
+	/*
+	 * ioctl from strace:
+	 * ioctl(11, _IOC(0, 0x64, 0x05, 0x65), 0xb60a4bb8);
+	 */
+	ioc = _IOC(0, 0x64, 0x05, 0x65);
+
+	/* abort on matching ioctl */
+	if (request == ioc)
+		do_abort();
+
+	va_start(args, request);
+	ret = __ioctl(fd, request, args);
+	va_end(args);
+
+	return ret;
+}
+#endif
+
+#if 1
+/*
+ * match this file name
+ */
+#define FILE_PATH "/dev/input/event1"
+
+/*
+ * extern int open (const char *__file, int __oflag, ...) __nonnull ((1));
+ */
+int open(const char *pathname, int flags, ...)
+{
+	int ret;
+	va_list args;
+	static int (*__open)(const char *, int, ...) = NULL;
+
+	if (__open == NULL) {
+		__open = (int (*)(const char *, int, ...))dlsym(RTLD_NEXT, "open");
+		DLSYM_CHECK(__open);
+	}
+
+	/* abort on matching file name */
+	if (!strcmp(pathname, FILE_PATH))
+		do_abort();
+
+	va_start(args, flags);
+	ret = __open(pathname, flags, args);
+	va_end(args);
+
+	return ret;
+}
+
+/*
+ * extern int open64 (const char *__file, int __oflag, ...) __nonnull ((1));
+ */
+int open64(const char *pathname, int flags, ...)
+{
+	int ret;
+	va_list args;
+	static int (*__open64)(const char *, int, ...) = NULL;
+
+	if (__open64 == NULL) {
+		__open64 = (int (*)(const char *, int, ...))dlsym(RTLD_NEXT, "open64");
+		DLSYM_CHECK(__open64);
+	}
+
+	/* abort on matching file name */
+	if (!strcmp(pathname, FILE_PATH))
+		do_abort();
+
+	va_start(args, flags);
+	ret = __open64(pathname, flags, args);
+	va_end(args);
+
+	return ret;
+}
+#endif