Hi Matthias and everyone,
During DebConf we talked about a patch for GCC to honour the
SOURCE_DATE_EPOCH env var when using the __DATE__ and __TIME__ macros.
I sent a patch that did this from libcpp/macro.c in the gcc-patches
mailing list. There was a reply from Joseph Myers suggesting that it may be better to put the patch
in some file in the gcc/ directory [0].
I checked the call trace until reaching the macro processing for both
gcc and g++ and found a common function in gcc/c-family/c-lex.c, so I
moved part of the patch there.
Now the patch consists on the following:
- the struct cpp_reader (defined in libcpp/internal.h) now has a new
field: source_date_epoch, with a default value of -1
- the function c_lex_with_flags from gcc/c-family/c-lex.c will check if
SOURCE_DATE_EPOCH is defined in the environment and if so, store the
value in the cpp_reader struct (parse_in), to pass it around the other
functions
- the function _cpp_builtin_macro_text from _cpp_builtin_macro_text will
use the source_date_epoch field from the cpp_reader struct instead of
the value returned by time(NULL) and use gmtime to get a representation
of the timestamp, if source_date_epoch != -1 (that is, it has been defined)
This way, the getenv call happens in the gcc/ directory.
There is one thing that I haven't managed to get nice, as I'm not that
familiar with the gcc source code: the ouptut of the error handling when
parsing SOURCE_DATE_EPOCH in gcc/c-family/c-lex.c doesn't look too good:
"""
$ export SOURCE_DATE_EPOCH="1234a"
$../gcc_build/bin/gcc test_c.c -o test_c
In file included from :0:0:
/usr/include/stdc-predef.h:1:0: error: Environment variable
$SOURCE_DATE_EPOCH: Trailing garbage: a
/* Copyright (C) 1991-2014 Free Software Foundation, Inc.
^
"""
The error function prints the line of the file it was parsing when the
error happened.
What do you think about this patch? I would like you to take a look at
it before sending it to the gcc-patches mailing list. Do you think it's
good to read the SOURCE_DATE_EPOCH env var in gcc/c-family/c-lex.c and
pass it to the macro processing function through the cpp_reader struct?
Or do you think there's a better place?
As a reminder, we now have a spec describing the usage of
SOURCE_DATE_EPOCH as a distribution-agnostic standard for build systems
to exchange a timestamp [1], I'll add the link when sending the patch to
the gcc-patches mailing list.
[0] https://gcc.gnu.org/ml/gcc-patches/2015-06/msg02270.html
[1] https://reproducible-builds.org/specs/source-date-epoch/
Regards,
--
Dhole
diff --git a/gcc/c-family/c-lex.c b/gcc/c-family/c-lex.c
index bb55be8..265195f 100644
--- a/gcc/c-family/c-lex.c
+++ b/gcc/c-family/c-lex.c
@@ -44,6 +44,9 @@ along with GCC; see the file COPYING3. If not see
#include "debug.h"
#include "target.h"
#include "wide-int.h"
+#include "../libcpp/internal.h"
+#include /* For parsing SOURCE_DATE_EPOCH */
+#include /* For parsing SOURCE_DATE_EPOCH */
#include "attribs.h"
@@ -388,6 +391,53 @@ c_common_has_attribute (cpp_reader *pfile)
return result;
}
+
+/* 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)
+{
+ errno = 0;
+ epoch = strtoull (source_date_epoch, &endptr, 10);
+ if ((errno == ERANGE && (epoch == ULLONG_MAX || epoch == 0))
+ || (errno != 0 && epoch == 0))
+ {
+ error ("Environment variable $SOURCE_DATE_EPOCH: strtoull: \
+%s\n", xstrerror(errno));
+ exit (EXIT_FAILURE);
+ }
+ if (endptr == source_date_epoch)
+ {
+ error ("Environment variable $SOURCE_DATE_EPOCH: \
+No digits were found: %s\n", endptr);
+ exit (EXIT_FAILURE);
+ }
+ if (*endptr != '\0')
+ {
+ error ("Environment variable $SOURCE_DATE_EPOCH: \
+Trailing garbage: %s\n", endptr);
+ exit (EXIT_FAILURE);
+}
+ if (epoch > ULONG_MAX)
+ {
+ error ("Environment variable $SOURCE_DATE_EPOCH: \
+value must be smaller than or equal to: %lu but was found to be: \
+%llu \n", ULONG_MAX, epoch);
+ exit (EXIT_FAILURE);
+ }
+ return (long long) epoch;
+}
+ else
+return -1;
+}
/* Read a token and return its type. Fill *VALUE with its value, if
applicable. Fill *CPP_FLAGS with the token's flags, if it is
@@ -403,6 +453,7 @@ c_lex_with_flags (tree *value, location_t *loc, unsigned
char *cpp_flags,
unsigned char add_flags = 0;
enum overflow_type overflow = OT_NONE;
+ parse_in->source_date_epoch = get_source_date_epoch();
timevar_push (TV_CPP);
retry:
tok = cpp_get_token_with_location (parse_in, loc);
diff --git a/libcpp/internal.h b
