elf: Report when found libraries are rejected [BZ #25669]

When debugging library loading issues with `LD_DEBUG`, it can be
frustrating to see logs for files in a directory are searched, but the
target library is skipped over without any indication of why. Add
reporting to all paths which reject a library as `ENOENT`.

Originally created for minimum-OS version detection, but that has since
been removed in b46d250656 (Remove kernel version check, 2022-02-21).
The remaining codepaths are still useful.

Signed-off-by: Ben Boeckel <ben.boeckel@kitware.com>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

diff --git a/elf/dl-load.c b/elf/dl-load.c
index 891b44966c524b7f8cd1c14e3f8abab15bba1fa8..674bae2cbbcaea9bf4ca217f6c2ad32297a42afd 100644 (file)
--- a/elf/dl-load.c
+++ b/elf/dl-load.c
@@ -1633,6 +1633,8 @@ open_verify (const char *name, int fd,
                 32-bit and 64-bit binaries can be run this might
                 happen.  */
              *found_other_class = true;
+             if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS))
+               _dl_debug_printf ("    (incompatible ELF class)\n");
              __close_nocancel (fd);
              __set_errno (ENOENT);
              return -1;
@@ -1671,6 +1673,8 @@ open_verify (const char *name, int fd,
        }
       if (! __glibc_likely (elf_machine_matches_host (ehdr)))
        {
+         if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS))
+           _dl_debug_printf ("    (incompatible ELF machine)\n");
          __close_nocancel (fd);
          __set_errno (ENOENT);
          return -1;
@@ -1706,12 +1710,19 @@ open_verify (const char *name, int fd,
                            (phdr, ehdr->e_phnum, fbp->buf, fbp->len,
                             loader, fd)))
        {
+         if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS))
+           _dl_debug_printf ("    (incompatible ELF headers with the host)\n");
          __close_nocancel (fd);
          __set_errno (ENOENT);
          return -1;
        }
 
     }
+  else
+    {
+      if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS))
+       _dl_debug_printf ("    (no such file)\n");
+    }
 
   return fd;
 }
@@ -1822,6 +1833,11 @@ open_path (const char *name, size_t namelen, int mode,
                  /* The shared object cannot be tested for being SUID
                     or this bit is not set.  In this case we must not
                     use this object.  */
+                 if (__glibc_unlikely (GLRO(dl_debug_mask) & DL_DEBUG_LIBS))
+                   _dl_debug_printf ("  refusing to load file=%s, the shared "
+                                     "object cannot be tested for being "
+                                     "SUID or the bit is not set\n",
+                                     buf);
                  __close_nocancel (fd);
                  fd = -1;
                  /* We simply ignore the file, signal this by setting