[PATCH 2/3] Use BUILD_PATH_PREFIX_MAP envvar to transform __FILE__

[Ximin Luo <infinity0@pwned.gg>]

Use the BUILD_PATH_PREFIX_MAP environment variable when expanding the __FILE__
macro, in the same way that debug-prefix-map works for debugging symbol paths.

This patch follows similar lines to the earlier patch for SOURCE_DATE_EPOCH.
Specifically, we read the environment variable not in libcpp but via a hook
which has an implementation defined in gcc/c-family.  However, to achieve this
is more complex than the earlier patch: we need to share the prefix_map data
structure and associated functions between libcpp and c-family.  Therefore, we
need to move these to libiberty.  (For comparison, the SOURCE_DATE_EPOCH patch
did not need this because time_t et. al. are in the standard C library.)

Acknowledgements
----------------

Dhole <dhole@openmailbox.org> who wrote the earlier patch for SOURCE_DATE_EPOCH
which saved me a lot of time on figuring out what to edit.

ChangeLogs
----------

gcc/c-family/ChangeLog:

2017-03-27  Ximin Luo  <infinity0@pwned.gg>

	* c-common.c (cb_get_build_path_prefix_map): Define new call target.
	* c-common.h (cb_get_build_path_prefix_map): Declare call target.
	* c-lex.c (init_c_lex): Set the get_build_path_prefix_map callback.

libcpp/ChangeLog:

2017-03-27  Ximin Luo  <infinity0@pwned.gg>

	* include/cpplib.h (cpp_callbacks): Add get_build_path_prefix_map
	callback.
	* init.c (cpp_create_reader): Initialise build_path_prefix_map field.
	* internal.h (cpp_reader): Add new field build_path_prefix_map.
	* macro.c (_cpp_builtin_macro_text): Set the build_path_prefix_map
	field if unset and apply it when expanding __FILE__ macros.

gcc/testsuite/ChangeLog:

2017-03-27  Ximin Luo  <infinity0@pwned.gg>

	* gcc.dg/cpp/build_path_prefix_map-1.c: New test.
	* gcc.dg/cpp/build_path_prefix_map-2.c: New test.

Index: gcc-7-20170402/gcc/c-family/c-common.c
===================================================================
--- gcc-7-20170402.orig/gcc/c-family/c-common.c
+++ gcc-7-20170402/gcc/c-family/c-common.c
@@ -21,6 +21,7 @@ along with GCC; see the file COPYING3.
 
 #include "config.h"
 #include "system.h"
+#include "prefix-map.h"
 #include "coretypes.h"
 #include "target.h"
 #include "function.h"
@@ -8012,6 +8013,25 @@ cb_get_source_date_epoch (cpp_reader *pf
   return (time_t) epoch;
 }
 
+/* Read BUILD_PATH_PREFIX_MAP from environment to have deterministic relative
+   paths to replace embedded absolute paths to get reproducible results.
+   Returns NULL if BUILD_PATH_PREFIX_MAP is badly formed.  */
+
+prefix_map **
+cb_get_build_path_prefix_map (cpp_reader *pfile ATTRIBUTE_UNUSED)
+{
+  prefix_map **map = XCNEW (prefix_map *);
+
+  const char *arg = getenv ("BUILD_PATH_PREFIX_MAP");
+  if (!arg || prefix_map_parse (map, arg))
+    return map;
+
+  free (map);
+  error_at (input_location, "environment variable BUILD_PATH_PREFIX_MAP is "
+	    "not well formed; see the GCC documentation for more details.");
+  return NULL;
+}
+
 /* Callback for libcpp for offering spelling suggestions for misspelled
    directives.  GOAL is an unrecognized string; CANDIDATES is a
    NULL-terminated array of candidate strings.  Return the closest
Index: gcc-7-20170402/gcc/c-family/c-common.h
===================================================================
--- gcc-7-20170402.orig/gcc/c-family/c-common.h
+++ gcc-7-20170402/gcc/c-family/c-common.h
@@ -1085,6 +1085,11 @@ extern time_t cb_get_source_date_epoch (
    __TIME__ can store.  */
 #define MAX_SOURCE_DATE_EPOCH HOST_WIDE_INT_C (253402300799)
 
+/* Read BUILD_PATH_PREFIX_MAP from environment to have deterministic relative
+   paths to replace embedded absolute paths to get reproducible results.
+   Returns NULL if BUILD_PATH_PREFIX_MAP is badly formed.  */
+extern prefix_map **cb_get_build_path_prefix_map (cpp_reader *pfile);
+
 /* Callback for libcpp for offering spelling suggestions for misspelled
    directives.  */
 extern const char *cb_get_suggestion (cpp_reader *, const char *,
Index: gcc-7-20170402/gcc/c-family/c-lex.c
===================================================================
--- gcc-7-20170402.orig/gcc/c-family/c-lex.c
+++ gcc-7-20170402/gcc/c-family/c-lex.c
@@ -81,6 +81,7 @@ init_c_lex (void)
   cb->read_pch = c_common_read_pch;
   cb->has_attribute = c_common_has_attribute;
   cb->get_source_date_epoch = cb_get_source_date_epoch;
+  cb->get_build_path_prefix_map = cb_get_build_path_prefix_map;
   cb->get_suggestion = cb_get_suggestion;
 
   /* Set the debug callbacks if we can use them.  */
Index: gcc-7-20170402/libcpp/include/cpplib.h
===================================================================
--- gcc-7-20170402.orig/libcpp/include/cpplib.h
+++ gcc-7-20170402/libcpp/include/cpplib.h
@@ -607,6 +607,9 @@ struct cpp_callbacks
   /* Callback to parse SOURCE_DATE_EPOCH from environment.  */
   time_t (*get_source_date_epoch) (cpp_reader *);
 
+  /* Callback to parse BUILD_PATH_PREFIX_MAP from environment.  */
+  struct prefix_map **(*get_build_path_prefix_map) (cpp_reader *);
+
   /* Callback for providing suggestions for misspelled directives.  */
   const char *(*get_suggestion) (cpp_reader *, const char *, const char *const *);
 };
Index: gcc-7-20170402/libcpp/init.c
===================================================================
--- gcc-7-20170402.orig/libcpp/init.c
+++ gcc-7-20170402/libcpp/init.c
@@ -261,6 +261,9 @@ cpp_create_reader (enum c_lang lang, cpp
   /* Initialize source_date_epoch to -2 (not yet set).  */
   pfile->source_date_epoch = (time_t) -2;
 
+  /* Initialize build_path_prefix_map to NULL (not yet set).  */
+  pfile->build_path_prefix_map = NULL;
+
   /* The expression parser stack.  */
   _cpp_expand_op_stack (pfile);
 
Index: gcc-7-20170402/libcpp/internal.h
===================================================================
--- gcc-7-20170402.orig/libcpp/internal.h
+++ gcc-7-20170402/libcpp/internal.h
@@ -507,6 +507,11 @@ struct cpp_reader
      set to -1 to disable it or to a non-negative value to enable it.  */
   time_t source_date_epoch;
 
+  /* Externally set prefix-map to transform absolute paths, useful for
+     reproducibility.  It should be initialized to NULL (not yet set or
+     disabled) or to a `struct prefix_map` double pointer to enable it.  */
+  struct prefix_map **build_path_prefix_map;
+
   /* EOF token, and a token forcing paste avoidance.  */
   cpp_token avoid_paste;
   cpp_token eof;
Index: gcc-7-20170402/libcpp/macro.c
===================================================================
--- gcc-7-20170402.orig/libcpp/macro.c
+++ gcc-7-20170402/libcpp/macro.c
@@ -26,6 +26,7 @@ along with this program; see the file CO
 #include "system.h"
 #include "cpplib.h"
 #include "internal.h"
+#include "prefix-map.h"
 
 typedef struct macro_arg macro_arg;
 /* This structure represents the tokens of a macro argument.  These
@@ -291,7 +292,17 @@ _cpp_builtin_macro_text (cpp_reader *pfi
 	unsigned int len;
 	const char *name;
 	uchar *buf;
+	prefix_map **map = pfile->build_path_prefix_map;
 	
+	/* Set a prefix-map for __FILE__ if BUILD_PATH_PREFIX_MAP is defined.  */
+	if (map == NULL && pfile->cb.get_build_path_prefix_map != NULL)
+	  {
+	    map = pfile->cb.get_build_path_prefix_map (pfile);
+	    if (map == NULL)
+	      abort ();
+	    pfile->build_path_prefix_map = map;
+	  }
+
 	if (node->value.builtin == BT_FILE)
 	  name = linemap_get_expansion_filename (pfile->line_table,
 						 pfile->line_table->highest_line);
@@ -301,6 +312,11 @@ _cpp_builtin_macro_text (cpp_reader *pfi
 	    if (!name)
 	      abort ();
 	  }
+
+	/* Apply the prefix-map for deterministic path output.  */
+	if (map != NULL)
+	  name = prefix_map_remap_alloca (*map, name);
+
 	len = strlen (name);
 	buf = _cpp_unaligned_alloc (pfile, len * 2 + 3);
 	result = buf;
Index: gcc-7-20170402/gcc/testsuite/gcc.dg/cpp/build_path_prefix_map-1.c
===================================================================
--- /dev/null
+++ gcc-7-20170402/gcc/testsuite/gcc.dg/cpp/build_path_prefix_map-1.c
@@ -0,0 +1,11 @@
+/* __FILE__ should strip BUILD_PATH_PREFIX_MAP if the latter is a prefix. */
+/* { dg-do run } */
+/* { dg-set-compiler-env-var BUILD_PATH_PREFIX_MAP "MACROTEST=$srcdir" } */
+
+int
+main ()
+{
+  if (__builtin_strcmp (__FILE__, "MACROTEST/gcc.dg/cpp/build_path_prefix_map-1.c") != 0)
+    __builtin_abort ();
+  return 0;
+}
Index: gcc-7-20170402/gcc/testsuite/gcc.dg/cpp/build_path_prefix_map-2.c
===================================================================
--- /dev/null
+++ gcc-7-20170402/gcc/testsuite/gcc.dg/cpp/build_path_prefix_map-2.c
@@ -0,0 +1,12 @@
+/* __FILE__ should not be relative if BUILD_PATH_PREFIX_MAP is not set, and gcc is
+   asked to compile an absolute filename as is the case with this test.  */
+/* { dg-do run } */
+/* { dg-set-compiler-env-var BUILD_PATH_PREFIX_MAP } */
+
+int
+main ()
+{
+  if (__builtin_strcmp (__FILE__, "./gcc.dg/cpp/build_path_prefix_map-2.c") == 0)
+    __builtin_abort ();
+  return 0;
+}