Fix debug output in the dynamic linker.

This provides a mini-printf implementation that reduces the
size of the dynamic linker by 25 KB, by preventing the drag of
formatting-related routines from the C library.

Also allow traces to be sent to the log, instead of stdout.

NOTE: You now need to modify Android.mk to enable/disable debug
      output.

linker/Android.mk

@@ -4,6 +4,7 @@ include $(CLEAR_VARS)
 LOCAL_SRC_FILES:= \
 	arch/$(TARGET_ARCH)/begin.S \
 	linker.c \
+	linker_format.c \
 	rt.c \
 	dlfcn.c \
 	debugger.c \
@@ -31,6 +32,10 @@ LOCAL_CFLAGS += -DPRELINK
 LOCAL_CFLAGS += -DLINKER_TEXT_BASE=$(LINKER_TEXT_BASE)
 LOCAL_CFLAGS += -DLINKER_AREA_SIZE=$(LINKER_AREA_SIZE)
 
+# Set LINKER_DEBUG to either 1 or 0
+#
+LOCAL_CFLAGS += -DLINKER_DEBUG=0
+
 # we need to access the Bionic private header <bionic_tls.h>
 # in the linker; duplicate the HAVE_ARM_TLS_REGISTER definition
 # from the libc build

linker/README.TXT

@@ -112,3 +112,32 @@ On x86, the lists of constructors and destructors are placed in special
 sections named ".ctors" and ".dtors", and the DT_INIT / DT_FINI functions
 are in charge of calling them explicitely.
 
+
+Debugging:
+----------
+
+It is possible to enable debug output in the dynamic linker. To do so,
+follow these steps:
+
+1/ Modify the line in Android.mk that says:
+
+    LOCAL_CFLAGS += -DLINKER_DEBUG=0
+
+  Into the following:
+
+    LOCAL_CFLAGS += -DLINKER_DEBUG=1
+
+2/ Force-rebuild the dynamic linker:
+
+    cd bionic/linker
+    mm -B
+
+3/ Rebuild a new system image.
+
+You can increase the verbosity of debug traces by defining the DEBUG
+environment variable to a numeric value from 0 to 2. This will only
+affect new processes being launched.
+
+By default, traces are sent to logcat, with the "linker" tag. You can
+change this to go to stdout instead by setting the definition of
+LINKER_DEBUG_TO_LOG to 0 in "linker_debug.h"

linker/dlfcn.c

@@ -17,6 +17,7 @@
 #include <pthread.h>
 #include <stdio.h>
 #include "linker.h"
+#include "linker_format.h"
 
 /* This file hijacks the symbols stubbed out in libdl.so. */
 
@@ -45,7 +46,7 @@ static pthread_mutex_t dl_lock = PTHREAD_MUTEX_INITIALIZER;
 
 static void set_dlerror(int err)
 {
-    snprintf(dl_err_buf, sizeof(dl_err_buf), "%s: %s", dl_errors[err],
+    format_buffer(dl_err_buf, sizeof(dl_err_buf), "%s: %s", dl_errors[err],
              linker_get_error());
     dl_err_str = (const char *)&dl_err_buf[0];
 };

linker/linker.c

@@ -48,6 +48,7 @@
 
 #include "linker.h"
 #include "linker_debug.h"
+#include "linker_format.h"
 
 #include "ba.h"
 
@@ -142,7 +143,7 @@ static char tmp_err_buf[768];
 static char __linker_dl_err_buf[768];
 #define DL_ERR(fmt, x...)                                                     \
     do {                                                                      \
-        snprintf(__linker_dl_err_buf, sizeof(__linker_dl_err_buf),            \
+        format_buffer(__linker_dl_err_buf, sizeof(__linker_dl_err_buf),            \
                  "%s[%d]: " fmt, __func__, __LINE__, ##x);                    \
         ERROR(fmt "\n", ##x);                                                      \
     } while(0)
@@ -584,7 +585,7 @@ static int open_library(const char *name)
         return fd;
 
     for (path = ldpaths; *path; path++) {
-        n = snprintf(buf, sizeof(buf), "%s/%s", *path, name);
+        n = format_buffer(buf, sizeof(buf), "%s/%s", *path, name);
         if (n < 0 || n >= (int)sizeof(buf)) {
             WARN("Ignoring very long library path: %s/%s\n", *path, name);
             continue;
@@ -593,7 +594,7 @@ static int open_library(const char *name)
             return fd;
     }
     for (path = sopaths; *path; path++) {
-        n = snprintf(buf, sizeof(buf), "%s/%s", *path, name);
+        n = format_buffer(buf, sizeof(buf), "%s/%s", *path, name);
         if (n < 0 || n >= (int)sizeof(buf)) {
             WARN("Ignoring very long library path: %s/%s\n", *path, name);
             continue;

linker/linker_debug.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2008 The Android Open Source Project
+ * Copyright (C) 2008-2010 The Android Open Source Project
  * All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
@@ -31,12 +31,17 @@
 
 #include <stdio.h>
 
-/* WARNING: For linker debugging only.. Be careful not to leave  any of
- * this on when submitting back to repository */
-#define LINKER_DEBUG         0
-#define TRACE_DEBUG          0
-#define DO_TRACE_LOOKUP      0
-#define DO_TRACE_RELO        0
+#ifndef LINKER_DEBUG
+#error LINKER_DEBUG should be defined to either 1 or 0 in Android.mk
+#endif
+
+/* set LINKER_DEBUG_TO_LOG to 1 to send the logs to logcat,
+ * or 0 to use stdout instead.
+ */
+#define LINKER_DEBUG_TO_LOG  1
+#define TRACE_DEBUG          1
+#define DO_TRACE_LOOKUP      1
+#define DO_TRACE_RELO        1
 #define TIMING               0
 #define STATS                0
 #define COUNT_PAGES          0
@@ -59,12 +64,21 @@
  * corruption when the linker uses printf().
  */
 #if LINKER_DEBUG
+#include "linker_format.h"
 extern int debug_verbosity;
-#warning "*** LINKER IS USING printf(); DO NOT CHECK THIS IN ***"
-#define _PRINTVF(v,f,x...)                                                \
-    do {                                                                  \
-        (debug_verbosity > (v)) && (printf(x), ((f) && fflush(stdout)));  \
+#if LINKER_DEBUG_TO_LOG
+extern int format_log(int, const char *, const char *, ...);
+#define _PRINTVF(v,f,x...)                                        \
+    do {                                                          \
+        if (debug_verbosity > (v)) format_log(5-(v),"linker",x);  \
+    } while (0)
+#else /* !LINKER_DEBUG_TO_LOG */
+extern int format_fd(int, const char *, ...);
+#define _PRINTVF(v,f,x...)                           \
+    do {                                             \
+        if (debug_verbosity > (v)) format_fd(1, x);  \
     } while (0)
+#endif /* !LINKER_DEBUG_TO_LOG */
 #else /* !LINKER_DEBUG */
 #define _PRINTVF(v,f,x...)   do {} while(0)
 #endif /* LINKER_DEBUG */