From: Daniel Kahn Gillmor Date: Sun, 12 Jul 2015 15:50:47 -0400 Subject: Embed _psl_compile_time derived from $SOURCE_DATE_EPOCH if set Making packages build byte-for-byte reproducibly from a given toolchain+source makes it much easier to corroborate builds by testing against other build infrastructure. By default, libpsl currently embeds the current unix timestamp in _psl_compile_time, which makes it bytewise incompatible if it is rebuild even on the same machine one second later. Dropping _psl_compile_time and psl_builtin_compile_time() would fix this, but would cause an API/ABI change for the library. The next time libpsl goes through an API/ABI change anyway, this might be worth consideration, but maybe such a simple change doesn't warrant an SONAME bump, so this changeset proposes to embed the environment variable $SOURCE_DATE_EPOCH if it is set during build, falling back to the current behavior if $SOURCE_DATE_EPOCH is unset. See https://wiki.debian.org/ReproducibleBuilds/TimestampsProposal for more information about $SOURCE_DATE_EPOCH. --- src/psl2c.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/src/psl2c.c b/src/psl2c.c index e634a97..1fc5877 100644 --- a/src/psl2c.c +++ b/src/psl2c.c @@ -157,6 +157,7 @@ int main(int argc, const char **argv) struct stat st; size_t cmdsize = 16 + strlen(argv[1]); char *cmd = alloca(cmdsize), checksum[64] = ""; + char *source_date_epoch = NULL; #if 0 /* include library code did not generate punycode, so let's do it for the builtin data */ @@ -177,7 +178,10 @@ int main(int argc, const char **argv) if (stat(argv[1], &st) != 0) st.st_mtime = 0; fprintf(fpout, "static time_t _psl_file_time = %lu;\n", st.st_mtime); - fprintf(fpout, "static time_t _psl_compile_time = %lu;\n", time(NULL)); + if (source_date_epoch = getenv("SOURCE_DATE_EPOCH")) + fprintf(fpout, "static time_t _psl_compile_time = %lu;\n", atol(source_date_epoch)); + else + fprintf(fpout, "static time_t _psl_compile_time = %lu;\n", time(NULL)); fprintf(fpout, "static const char _psl_sha1_checksum[] = \"%s\";\n", checksum); fprintf(fpout, "static const char _psl_filename[] = \"%s\";\n", argv[1]);