Re: Allow embedded timestamps by C/C++ macros to be set externally (3)

[Eduard Sanou <eduardsanou@openmailbox.org>]

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Hi,

I've worked on applying the changes that have been commented in several
messages from this thread.  Find the patch and changelog attached.

On 16-04-29 09:17:44, Jakub Jelinek wrote:
> First of all, using error instead of fatal_error achieves just that too,
> except that it allows also detecting other errors in the source.
> fatal_error is meant for cases where there is no way to go forward with the
> compilation, while here exists a perfectly reasonable way to go forward (assume
> the env var is not set, use a hardcoded timestamp, ...).

I've changed the use of fatal_error to error_at.  Now the parsing will
return -1 if there's an error, and gcc will be able to output the line
where the __DATE__ or __TIME__ macro was used that caused the error.

> Doing this on the gcc/ side is of course reasonable, but can be done through
> callbacks, libcpp already has lots of other callbacks into the gcc/ code,
> look for e.g. cpp_get_callbacks in gcc/c-family/* and in libcpp/ for
> corresponding code.

I've added a callback that allows parsing the SOURCE_DATE_EPOCH env var
right at the point where the date macros are expanded.  I've removed
some uneeded stuff from my previous patch.

> Also, as a follow-up, guess the driver should set this
> env var for the -fcompare-debug case if not already set, to something that
> matches the current date, so that __TIME__ macros expands the same in
> between both compilations, even when they don't compile both in the same
> second.

I've also patched the driver to set the SOURCE_DATE_EPOCH env var to the
current date when the -fcompare-debug is set.  I've tested this building
llvm with such flag.  
Markus could you verify that the patch indeed fixes the issue?


Martin Sebor wrote:
> I'm sorry I'm a little late but I have a couple of minor comments
> on the patch:

Thanks for the comments :)

> In most texts (e.g. the C and POSIX standards), the name of
> an environment variable doesn't include the dollar sign.  In
> other diagnostic messages GCC doesn't print one.  I suggest
> to follow the established practice and remove the dollar sign
> from this error message as well.

Change applied.

> I would also suggest to issue a single generic error message
> explaining what the valid value of the variable is instead of
> trying to describe what's wrong with it, for example as follows
> (note also the hyphen in "non-negative" which is the prevalent
> style used by other GCC messages and GNU documentation).
> 
>   "environment variable SOURCE_DATE_EPOCH must expand to a non-
>   negative integer less than or equal to %qlli", LLONG_MAX

Applied as well.

> The +%s option to the date command is a non-standard extension
> that's not universally available.  To avoid confusing users on
> systems that don't support it I would suggest to either avoid
> mentioning or to clarify that it's a Linux command.

I've added a comment to clarify this fact in the documentation.

Cheers,
Dhole

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gcc/c-family/ChangeLog:

2016-05-05  Eduard Sanou  <dhole@openmailbox.org>

	* c-common.c (get_source_date_epoch): Renamed to
	cb_get_source_date_epoch.
	* c-common.c (cb_get_source_date_epoch): Use a single generic erorr
	message when the parsing fails.  Use error_at instead of fatal_error.
	* c-common.h (get_source_date_epoch): Renamed to
	cb_get_source_date_epoch.
	* c-common.h (cb_get_source_date_epoch): Prototype.
	* c-common.h (MAX_SOURCE_DATE_EPOCH): Define.
	* c-lex.c (init_c_lex): Set cb->get_source_date_epoch callback.
	* c-lex.c (c_lex_with_flags): Remove initialization of
	source_date_epoch.

gcc/ChangeLog:

2016-05-05  Eduard Sanou  <dhole@openmailbox.org>

	* doc/cppenv.texi: Note that the `%s` in `date` is a non-standard
	extension.
	* gcc.c (driver_handle_option): Call
	setenv_SOURCE_DATE_EPOCH_current_time.
	* gcc.c (setenv_SOURCE_DATE_EPOCH_current_time): New function, sets
	the SOURCE_DATE_EPOCH environment variable to the current time.

libcpp/ChangeLog:

2016-05-05  Eduard Sanou  <dhole@openmailbox.org>

	* include/cpplib.h (cpp_callbacks): Add get_source_date_epoch
	callback.
	* include/cpplib.h (cpp_init_source_date_epoch): Remove.
	* init.c (cpp_init_source_date_epoch): Remove.
	* internal.h (cpp_reader): Remove source_date_epoch.
	* macro.c (_cpp_builtin_macro_text): Use get_source_date_epoch
	callback.

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diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index d45bf1b..22974c5 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -12788,7 +12788,7 @@ valid_array_size_p (location_t loc, tree type, tree name)
    timestamp to replace embedded current dates to get reproducible
    results.  Returns -1 if SOURCE_DATE_EPOCH is not defined.  */
 time_t
-get_source_date_epoch ()
+cb_get_source_date_epoch (cpp_reader *pfile ATTRIBUTE_UNUSED)
 {
   char *source_date_epoch;
   long long epoch;
@@ -12800,19 +12800,14 @@ get_source_date_epoch ()
 
   errno = 0;
   epoch = strtoll (source_date_epoch, &endptr, 10);
-  if ((errno == ERANGE && (epoch == LLONG_MAX || epoch == LLONG_MIN))
-      || (errno != 0 && epoch == 0))
-    fatal_error (UNKNOWN_LOCATION, "environment variable $SOURCE_DATE_EPOCH: "
-		 "strtoll: %s\n", xstrerror(errno));
-  if (endptr == source_date_epoch)
-    fatal_error (UNKNOWN_LOCATION, "environment variable $SOURCE_DATE_EPOCH: "
-		 "no digits were found: %s\n", endptr);
-  if (*endptr != '\0')
-    fatal_error (UNKNOWN_LOCATION, "environment variable $SOURCE_DATE_EPOCH: "
-		 "trailing garbage: %s\n", endptr);
-  if (epoch < 0)
-    fatal_error (UNKNOWN_LOCATION, "environment variable $SOURCE_DATE_EPOCH: "
-		 "value must be nonnegative: %lld \n", epoch);
+  if (errno != 0 || endptr == source_date_epoch || *endptr != '\0'
+      || epoch < 0 || epoch > MAX_SOURCE_DATE_EPOCH)
+    {
+      error_at (input_location, "environment variable SOURCE_DATE_EPOCH must "
+	        "expand to a non-negative integer less than or equal to %ld",
+		MAX_SOURCE_DATE_EPOCH);
+      return (time_t) -1;
+    }
 
   return (time_t) epoch;
 }
diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index 1714284..dea2900 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -1086,6 +1086,16 @@ extern vec<tree, va_gc> *make_tree_vector_copy (const vec<tree, va_gc> *);
    c_register_builtin_type.  */
 extern GTY(()) tree registered_builtin_types;
 
+/* Read SOURCE_DATE_EPOCH from environment to have a deterministic
+   timestamp to replace embedded current dates to get reproducible
+   results.  Returns -1 if SOURCE_DATE_EPOCH is not defined.  */
+extern time_t cb_get_source_date_epoch (cpp_reader *pfile);
+
+/* The value (as a unix timestamp) corresponds to date 
+   "Dec 31 9999 23:59:59 UTC", which is the latest date that __DATE__ and 
+   __TIME__ can store.  */
+#define MAX_SOURCE_DATE_EPOCH 253402300799
+
 /* In c-gimplify.c  */
 extern void c_genericize (tree);
 extern int c_gimplify_expr (tree *, gimple_seq *, gimple_seq *);
@@ -1480,9 +1490,4 @@ extern bool valid_array_size_p (location_t, tree, tree);
 extern bool cilk_ignorable_spawn_rhs_op (tree);
 extern bool cilk_recognize_spawn (tree, tree *);
 
-/* Read SOURCE_DATE_EPOCH from environment to have a deterministic
-   timestamp to replace embedded current dates to get reproducible
-   results.  Returns -1 if SOURCE_DATE_EPOCH is not defined.  */
-extern time_t get_source_date_epoch (void);
-
 #endif /* ! GCC_C_COMMON_H */
diff --git a/gcc/c-family/c-lex.c b/gcc/c-family/c-lex.c
index 38a428d..8f33d86 100644
--- a/gcc/c-family/c-lex.c
+++ b/gcc/c-family/c-lex.c
@@ -80,6 +80,7 @@ init_c_lex (void)
   cb->valid_pch = c_common_valid_pch;
   cb->read_pch = c_common_read_pch;
   cb->has_attribute = c_common_has_attribute;
+  cb->get_source_date_epoch = cb_get_source_date_epoch;
 
   /* Set the debug callbacks if we can use them.  */
   if ((debug_info_level == DINFO_LEVEL_VERBOSE
@@ -389,9 +390,6 @@ c_lex_with_flags (tree *value, location_t *loc, unsigned char *cpp_flags,
   enum cpp_ttype type;
   unsigned char add_flags = 0;
   enum overflow_type overflow = OT_NONE;
-  time_t source_date_epoch = get_source_date_epoch ();
-
-  cpp_init_source_date_epoch (parse_in, source_date_epoch);
 
   timevar_push (TV_CPP);
  retry:
diff --git a/gcc/doc/cppenv.texi b/gcc/doc/cppenv.texi
index e958e93..8cefd52 100644
--- a/gcc/doc/cppenv.texi
+++ b/gcc/doc/cppenv.texi
@@ -81,7 +81,6 @@ main input file is omitted.
 @end ifclear
 
 @item SOURCE_DATE_EPOCH
-
 If this variable is set, its value specifies a UNIX timestamp to be
 used in replacement of the current date and time in the @code{__DATE__}
 and @code{__TIME__} macros, so that the embedded timestamps become
@@ -89,8 +88,9 @@ reproducible.
 
 The value of @env{SOURCE_DATE_EPOCH} must be a UNIX timestamp,
 defined as the number of seconds (excluding leap seconds) since
-01 Jan 1970 00:00:00 represented in ASCII, identical to the output of
-@samp{@command{date +%s}}.
+01 Jan 1970 00:00:00 represented in ASCII; identical to the output of
+@samp{@command{date +%s}} on GNU/Linux and other systems that support the
+@code{%s} extension in the @code{date} command.
 
 The value should be a known timestamp such as the last modification
 time of the source or package and it should be set by the build
diff --git a/gcc/gcc.c b/gcc/gcc.c
index 1af5920..0b11cb5 100644
--- a/gcc/gcc.c
+++ b/gcc/gcc.c
@@ -403,6 +403,7 @@ static const char *pass_through_libs_spec_func (int, const char **);
 static const char *replace_extension_spec_func (int, const char **);
 static const char *greater_than_spec_func (int, const char **);
 static char *convert_white_space (char *);
+static void setenv_SOURCE_DATE_EPOCH_current_time (void);
 \f
 /* The Specs Language
 
@@ -3837,6 +3838,7 @@ driver_handle_option (struct gcc_options *opts,
       else
 	compare_debug_opt = arg;
       save_switch (compare_debug_replacement_opt, 0, NULL, validated, true);
+      setenv_SOURCE_DATE_EPOCH_current_time ();
       return true;
 
     case OPT_fdiagnostics_color_:
@@ -9853,6 +9855,30 @@ path_prefix_reset (path_prefix *prefix)
   prefix->max_len = 0;
 }
 
+static void
+setenv_SOURCE_DATE_EPOCH_current_time ()
+{
+  /* Array size is 21 = ceil(log_10(2^64)) + 1 to hold string representations
+     of 64 bit integers.  */
+  char source_date_epoch[21];
+  time_t tt;
+  struct tm *tb = NULL;
+
+  errno = 0;
+  tt = time (NULL);
+  if (tt < (time_t) 0 || errno != 0)
+    tt = (time_t) 0;
+
+  tb = gmtime (&tt);
+
+  if (!strftime (source_date_epoch, 21, "%s", tb))
+    snprintf (source_date_epoch, 21, "0");
+  /* Using setenv instead of xputenv because we want the variable to remain
+     after finalizing so that it's still set in the second run when using
+     -fcompare-debug.  */
+  setenv ("SOURCE_DATE_EPOCH", source_date_epoch, 0);
+}
+
 /* Restore all state within gcc.c to the initial state, so that the driver
    code can be safely re-run in-process.
 
diff --git a/libcpp/include/cpplib.h b/libcpp/include/cpplib.h
index 4998b3a..9d70cc8 100644
--- a/libcpp/include/cpplib.h
+++ b/libcpp/include/cpplib.h
@@ -594,6 +594,9 @@ struct cpp_callbacks
 
   /* Callback that can change a user builtin into normal macro.  */
   bool (*user_builtin_macro) (cpp_reader *, cpp_hashnode *);
+
+  /* Callback to parse SOURCE_DATE_EPOCH from environment.  */
+  time_t (*get_source_date_epoch) (cpp_reader *);
 };
 
 #ifdef VMS
@@ -784,9 +787,6 @@ extern void cpp_init_special_builtins (cpp_reader *);
 /* Set up built-ins like __FILE__.  */
 extern void cpp_init_builtins (cpp_reader *, int);
 
-/* Initialize the source_date_epoch value.  */
-extern void cpp_init_source_date_epoch (cpp_reader *, time_t);
-
 /* This is called after options have been parsed, and partially
    processed.  */
 extern void cpp_post_options (cpp_reader *);
diff --git a/libcpp/init.c b/libcpp/init.c
index f5ff85b..1970bc5 100644
--- a/libcpp/init.c
+++ b/libcpp/init.c
@@ -533,13 +533,6 @@ cpp_init_builtins (cpp_reader *pfile, int hosted)
     _cpp_define_builtin (pfile, "__OBJC__ 1");
 }
 
-/* Initialize the source_date_epoch value.  */
-void
-cpp_init_source_date_epoch (cpp_reader *pfile, time_t source_date_epoch)
-{
-  pfile->source_date_epoch = source_date_epoch; 
-}
-
 /* Sanity-checks are dependent on command-line options, so it is
    called as a subroutine of cpp_read_main_file.  */
 #if CHECKING_P
diff --git a/libcpp/internal.h b/libcpp/internal.h
index e3eb26b..9ce8707 100644
--- a/libcpp/internal.h
+++ b/libcpp/internal.h
@@ -502,10 +502,6 @@ struct cpp_reader
   const unsigned char *date;
   const unsigned char *time;
 
-  /* Externally set timestamp to replace current date and time useful for
-     reproducibility.  */
-  time_t source_date_epoch;
-
   /* EOF token, and a token forcing paste avoidance.  */
   cpp_token avoid_paste;
   cpp_token eof;
diff --git a/libcpp/macro.c b/libcpp/macro.c
index c2a8376..5f7ffbd 100644
--- a/libcpp/macro.c
+++ b/libcpp/macro.c
@@ -359,8 +359,9 @@ _cpp_builtin_macro_text (cpp_reader *pfile, cpp_hashnode *node,
 
 	  /* Set a reproducible timestamp for __DATE__ and __TIME__ macro
 	     usage if SOURCE_DATE_EPOCH is defined.  */
-	  if (pfile->source_date_epoch != (time_t) -1)
-	     tb = gmtime (&pfile->source_date_epoch);
+	  tt = pfile->cb.get_source_date_epoch (pfile);
+	  if (tt != (time_t) -1)
+	    tb = gmtime (&tt);
 	  else
 	    {
 	      /* (time_t) -1 is a legitimate value for "number of seconds

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