[Emacs-diffs] master ebecafb: Port new fingerprinting scheme to clang + LTO

[Paul Eggert]

branch: master
commit ebecafbd19e2ba55ba90bfc9f7de88f4742479ad
Author: Paul Eggert <address@hidden>
Commit: Paul Eggert <address@hidden>

    Port new fingerprinting scheme to clang + LTO
    
    * lib-src/make-fingerprint.c (main): Don't consider multiple
    instances of the fingerprint to be an error, as this can
    happen with clang and -flto.  Instead, replace all instances
    of the fingerprint.  There is a tiny chance that this will
    silently corrupt the Emacs executable.
    
    This patch suggests that we should go back to fingerprinting
    the inputs to the linker instead of its output, as the new
    fingerprinting scheme is unnecessarily complicated and this
    complexity reduces reliability. The old scheme (i.e., before
    commit 2019-05-14T23:31:address@hidden) was simpler
    and more portable and good enough, and it's looking like it
    would be less trouble in practice than the new scheme.
---
 lib-src/make-fingerprint.c | 32 ++++++++++++++------------------
 1 file changed, 14 insertions(+), 18 deletions(-)

diff --git a/lib-src/make-fingerprint.c b/lib-src/make-fingerprint.c
index 79bd007..5779e0d 100644
--- a/lib-src/make-fingerprint.c
+++ b/lib-src/make-fingerprint.c
@@ -140,29 +140,25 @@ main (int argc, char **argv)
     }
   else
     {
-      char *finger = memmem (buf, chunksz, fingerprint, sizeof fingerprint);
-      if (!finger)
-       {
-         fprintf (stderr, "%s: %s: missing fingerprint\n", prog, file);
-         return EXIT_FAILURE;
-       }
-      else if (memmem (finger + 1, buf + chunksz - (finger + 1),
-                      fingerprint, sizeof fingerprint))
-       {
-         fprintf (stderr, "%s: %s: two occurrences of fingerprint\n",
-                  prog, file);
-         return EXIT_FAILURE;
-       }
+      bool fingered = false;
 
-      if (fseeko (f, finger - buf, SEEK_SET) != 0)
+      for (char *finger = buf;
+          (finger = memmem (finger, buf + chunksz - finger,
+                            fingerprint, sizeof fingerprint));
+          finger++)
        {
-         perror (file);
-         return EXIT_FAILURE;
+         if (! (fseeko (f, finger - buf, SEEK_SET) == 0
+                && fwrite (digest, 1, sizeof digest, f) == sizeof digest))
+           {
+             perror (file);
+             return EXIT_FAILURE;
+           }
+         fingered = true;
        }
 
-      if (fwrite (digest, 1, sizeof digest, f) != sizeof digest)
+      if (!fingered)
        {
-         perror (file);
+         fprintf (stderr, "%s: %s: missing fingerprint\n", prog, file);
          return EXIT_FAILURE;
        }
     }