Hey Akira,
> not sure what it should be named but the curly brackets is supposed to
> be started at a new line
Thanks for the quick turnaround. They are, of course, called
"squigglies". ;-)
I've attached an updated patch that addresses all the issues you
mention, as well as fixing a rather embarrassing typo in the first
line of the commit message. :)
Best wishes,
--
,''`.
: :' : Chris Lamb
`. `'` lamby@xxxxxxxxxx / chris-lamb.co.uk
`-
From c31e9092fe499ee6d775ca6180def7b5f826de0f Mon Sep 17 00:00:00 2001
From: Chris Lamb <chris@xxxxxxxxxxxxxxxx>
Date: Sat, 28 Apr 2018 12:21:24 -0700
Subject: [PATCH] Ensure cache checksums are deterministic
Whilst working on the Reproducible Builds[0] effort, we noticed that
fontconfig generates unreproducible cache files.
This is due to fc-cache uses the modification timestamps of each
directory in the "checksum" and "checksum_nano" members of the _FcCache
struct. This is so that it can identify which cache files are valid
and/or require regeneration.
This patch changes the behaviour of the checksum calculations to prefer
the value of the SOURCE_DATE_EPOCH[1] environment variable over the
directory's own mtime. This variable can then be exported by build
systems to ensure reproducible output.
If SOURCE_DATE_EPOCH is not set or is newer than the mtime of the
directory, the existing behaviour is unchanged.
This work was sponsored by Tails[2].
[0] https://reproducible-builds.org/
[1] https://reproducible-builds.org/specs/source-date-epoch/
[2] https://tails.boum.org/
---
src/fccache.c | 58 +++++++++++++++++++++++++++++++++++++++++++++------
1 file changed, 52 insertions(+), 6 deletions(-)
diff --git a/src/fccache.c b/src/fccache.c
index 7abb750..6318135 100644
--- a/src/fccache.c
+++ b/src/fccache.c
@@ -989,6 +989,54 @@ FcDirCacheLoadFile (const FcChar8 *cache_file, struct stat *file_stat)
return cache;
}
+static int
+FcDirChecksum (struct stat *statb)
+{
+ int ret = (int) statb->st_mtime;
+ char *endptr;
+ char *source_date_epoch;
+ unsigned long long epoch;
+
+ source_date_epoch = getenv("SOURCE_DATE_EPOCH");
+ if (source_date_epoch) {
+ epoch = strtoull(source_date_epoch, &endptr, 10);
+
+ if (endptr == source_date_epoch)
+ fprintf (stderr,
+ "Fontconfig: SOURCE_DATE_EPOCH invalid\n");
+ else if ((errno == ERANGE && (epoch == ULLONG_MAX || epoch == 0))
+ || (errno != 0 && epoch == 0))
+ fprintf (stderr,
+ "Fontconfig: SOURCE_DATE_EPOCH: strtoull: %s: %llu\n",
+ strerror(errno), epoch);
+ else if (*endptr != '\0')
+ fprintf (stderr,
+ "Fontconfig: SOURCE_DATE_EPOCHh has trailing garbage\n");
+ else if (epoch > ULONG_MAX)
+ fprintf (stderr,
+ "Fontconfig: SOURCE_DATE_EPOCH must be <= %lu but saw: %llu\n",
+ ULONG_MAX, epoch);
+ else if (epoch < ret)
+ /* Only override if directory is newer */
+ ret = (int) epoch;
+ }
+
+ return ret;
+}
+
+static int64_t
+FcDirChecksumNano (struct stat *statb)
+{
+#ifdef HAVE_STRUCT_STAT_ST_MTIM
+ /* No nanosecond component to parse */
+ if (getenv("SOURCE_DATE_EPOCH"))
+ return 0;
+ return statb->st_mtim.tv_nsec;
+#else
+ return 0;
+#endif
+}
+
/*
* Validate a cache file by reading the header and checking
* the magic number and the size field
@@ -1007,10 +1055,10 @@ FcDirCacheValidateHelper (FcConfig *config, int fd, struct stat *fd_stat, struct
ret = FcFalse;
else if (fd_stat->st_size != c.size)
ret = FcFalse;
- else if (c.checksum != (int) dir_stat->st_mtime)
+ else if (c.checksum != FcDirChecksum (dir_stat))
ret = FcFalse;
#ifdef HAVE_STRUCT_STAT_ST_MTIM
- else if (c.checksum_nano != dir_stat->st_mtim.tv_nsec)
+ else if (c.checksum_nano != FcDirChecksumNano (dir_stat))
ret = FcFalse;
#endif
return ret;
@@ -1086,10 +1134,8 @@ FcDirCacheBuild (FcFontSet *set, const FcChar8 *dir, struct stat *dir_stat, FcSt
cache->magic = FC_CACHE_MAGIC_ALLOC;
cache->version = FC_CACHE_VERSION_NUMBER;
cache->size = serialize->size;
- cache->checksum = (int) dir_stat->st_mtime;
-#ifdef HAVE_STRUCT_STAT_ST_MTIM
- cache->checksum_nano = dir_stat->st_mtim.tv_nsec;
-#endif
+ cache->checksum = FcDirChecksum (dir_stat);
+ cache->checksum_nano = FcDirChecksumNano (dir_stat);
/*
* Serialize directory name
--
2.17.0
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