Hi! A few months ago I submited a patch to allow the embedded timestamps by C/C++ macros to be set externally [2], which was already an improvement over [1]. I was told to wait until the GCC 7 stage 1 started to send this patch again.
I'm quoting from the original emails: > As a reminder for the motivation behind this patch, we are working on > the reproducible builds project which aims to provide users with a way > to reproduce bit-for-bit identical binary packages from the source and > build environment. The project involves Debian as well as several other > free software projects. See <https://reproducible-builds.org/> for more > information. > In order to do this, we need to make the build processes > deterministic. As you can imagine, gcc is quite involved in producing > Debian packages. One issue we encounter in many packages that fail to > build reproducibly is the use of the __DATE__, __TIME__ C macros [3], > right now we have 442 affected packages that would need patching > (either removing the macros, or passing a known date externally). > A solution for toolchain packages that embed timestamps during the > build process has been proposed for anyone interested and it consists > of the following: The build environment can export an environment > variable called SOURCE_DATE_EPOCH with a known timestamp in Unix epoch > format (In our case, we use the last date of the package's debian > changelog). The toolchain package running during the build can check > if the exported variable is set and if so, instead of embedding the > local date/time, embed the date/time from SOURCE_DATE_EPOCH. > The proposal to use SOURCE_DATE_EPOCH has now been gathered in a more > formal specification [4], so that any project can adhere to it to > achieve reproducible builds when dealing with timestamps. > It would be very beneficial to our project (and other free software > projects working on reproducible builds) if gcc supported this > feature. I'm attaching a patch for the svn/trunk GCC repository (now GCC 7) that enables this feature: it modifies the behavior of the macros __DATE__ and __TIME__ when the environment variable SOURCE_DATE_EPOCH is exported. Documentation of the environment variable is also provided. Note: I have already gone through the copyright assignment process :) [1] https://gcc.gnu.org/ml/gcc-patches/2015-06/msg02210.html [2] https://gcc.gnu.org/ml/gcc-patches/2015-11/msg01890.html [3] https://wiki.debian.org/ReproducibleBuilds/TimestampsFromCPPMacros [4] https://reproducible-builds.org/specs/source-date-epoch/ Best regards, -- Dhole
diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index f2846bb..3a83673 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -12741,4 +12741,38 @@ valid_array_size_p (location_t loc, tree type, tree
name)
return true;
}
+/* 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. */
+long long
+get_source_date_epoch()
+{
+ char *source_date_epoch;
+ unsigned long long epoch;
+ char *endptr;
+
+ source_date_epoch = getenv ("SOURCE_DATE_EPOCH");
+ if (!source_date_epoch)
+ return -1;
+
+ errno = 0;
+ epoch = strtoull (source_date_epoch, &endptr, 10);
+ if ((errno == ERANGE && (epoch == ULLONG_MAX || epoch == 0))
+ || (errno != 0 && epoch == 0))
+ fatal_error (UNKNOWN_LOCATION, "environment variable $SOURCE_DATE_EPOCH: "
+ "strtoull: %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 > ULONG_MAX)
+ fatal_error (UNKNOWN_LOCATION, "environment variable $SOURCE_DATE_EPOCH: "
+ "value must be smaller than or equal to: %lu but was found to "
+ "be: %llu \n", ULONG_MAX, epoch);
+
+ return (long long) epoch;
+}
+
#include "gt-c-family-c-common.h"
diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index fa3746c..b4d6afc 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -1467,4 +1467,9 @@ extern bool reject_gcc_builtin (const_tree, location_t =
UNKNOWN_LOCATION);
extern void warn_duplicated_cond_add_or_warn (location_t, tree, vec<tree> **);
extern bool valid_array_size_p (location_t, 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 long long get_source_date_epoch();
+
#endif /* ! GCC_C_COMMON_H */
diff --git a/gcc/c-family/c-lex.c b/gcc/c-family/c-lex.c
index 96da4fc..2454c6f 100644
--- a/gcc/c-family/c-lex.c
+++ b/gcc/c-family/c-lex.c
@@ -385,6 +385,10 @@ 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;
+ long long source_date_epoch = -1;
+
+ 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 22c8cb3..e958e93 100644
--- a/gcc/doc/cppenv.texi
+++ b/gcc/doc/cppenv.texi
@@ -79,4 +79,21 @@ main input file is omitted.
@ifclear cppmanual
@xref{Preprocessor Options}.
@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
+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}}.
+
+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
+process.
+
@end vtable
diff --git a/libcpp/include/cpplib.h b/libcpp/include/cpplib.h
index 35b0375..4cd5170 100644
--- a/libcpp/include/cpplib.h
+++ b/libcpp/include/cpplib.h
@@ -784,6 +784,9 @@ 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 *, long long);
+
/* 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 4343075..514282e 100644
--- a/libcpp/init.c
+++ b/libcpp/init.c
@@ -533,6 +533,13 @@ 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, long long 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 9ce8707..5fc41da 100644
--- a/libcpp/internal.h
+++ b/libcpp/internal.h
@@ -502,6 +502,10 @@ struct cpp_reader
const unsigned char *date;
const unsigned char *time;
+ /* Externally set timestamp to replace current date and time useful for
+ reproducibility. */
+ long long 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 c251553..833f36b 100644
--- a/libcpp/macro.c
+++ b/libcpp/macro.c
@@ -357,13 +357,20 @@ _cpp_builtin_macro_text (cpp_reader *pfile, cpp_hashnode
*node,
time_t tt;
struct tm *tb = NULL;
- /* (time_t) -1 is a legitimate value for "number of seconds
- since the Epoch", so we have to do a little dance to
- distinguish that from a genuine error. */
- errno = 0;
- tt = time(NULL);
- if (tt != (time_t)-1 || errno == 0)
- tb = localtime (&tt);
+ /* Set a reproducible timestamp for __DATE__ and __TIME__ macro
+ usage if SOURCE_DATE_EPOCH is defined. */
+ if (pfile->source_date_epoch != -1)
+ tb = gmtime ((time_t*) &pfile->source_date_epoch);
+ else
+ {
+ /* (time_t) -1 is a legitimate value for "number of seconds
+ since the Epoch", so we have to do a little dance to
+ distinguish that from a genuine error. */
+ errno = 0;
+ tt = time (NULL);
+ if (tt != (time_t)-1 || errno == 0)
+ tb = localtime (&tt);
+ }
if (tb)
{
gcc/c-family/ChangeLog:
2016-04-18 Eduard Sanou <dh...@openmailbox.org>
Matthias Klose <d...@debian.org>
* c-common.c (get_source_date_epoch): New function, gets the environment
variable SOURCE_DATE_EPOCH and parses it as long long with error
handling.
* c-common.h (get_source_date_epoch): Prototype.
* c-lex.c (c_lex_with_flags): set parse_in->source_date_epoch.
gcc/ChangeLog:
2016-04-18 Eduard Sanou <dh...@openmailbox.org>
Matthias Klose <d...@debian.org>
* doc/cppenv.texi: Document SOURCE_DATE_EPOCH environment variable.
libcpp/ChangeLog:
2016-04-18 Eduard Sanou <dh...@openmailbox.org>
Matthias Klose <d...@debian.org>
* include/cpplib.h (cpp_init_source_date_epoch): Prototype.
* init.c (cpp_init_source_date_epoch): New function.
* internal.h: Added source_date_epoch variable to struct
cpp_reader to store a reproducible date.
* macro.c (_cpp_builtin_macro_text): Set pfile->date timestamp from
pfile->source_date_epoch instead of localtime if source_date_epoch is
set, to be used for __DATE__ and __TIME__ macros to help reproducible
builds.
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