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[PATCH] Fix search_path to fill stat_buf when given an absolute pathname


From: Mark H Weaver
Subject: [PATCH] Fix search_path to fill stat_buf when given an absolute pathname
Date: Wed, 01 Feb 2012 16:47:00 -0500

Hello all,

David Pirotte has been experiencing a problem where (reload-module ...)
was failing to trigger a recompilation even after the source file has
been modified.  We did some debugging, and discovered that when
'compiled_is_fresh' is called during the failed reload, the
'stat_source' structure contains garbage.

My investigation revealed a flaw in 'search_path'.  Although it is not
mentioned in the header comment, it is clearly supposed to fill the
'stat_buf' whenever it is successful (scm_primitive_load_path assumes
that it will, anyway).

The problem is that there's a case when 'search_path' leaves the
'stat_buf' uninitialized.  If the provided 'filename' is an absolute
pathname, then it simply returns this pathname unchanged without
touching the 'stat_buf'.  This is bad, because 'scm_primitive_load_path'
proceeds to pass this uninitialized 'stat_buf' to 'compiled_is_fresh'.

I've attached a patch to (hopefully) fix this problem.  Unfortunately,
David tells me that this doesn't solve his reload issue, so unless he
made a mistake in testing it, I guess there's another bug still lurking,
or perhaps this fix is incorrect.

Reviews solicited.

    Thanks,
      Mark


>From b3e8ae048d87ab28c90b1c1c635a5116ee6f080c Mon Sep 17 00:00:00 2001
From: Mark H Weaver <address@hidden>
Date: Wed, 1 Feb 2012 16:35:32 -0500
Subject: [PATCH] Fix search_path to fill stat_buf when given an absolute
 pathname

* libguile/load.c (search_path): When the provided 'filename' is an
  absolute pathname, perform a 'stat' on that pathname to fill the
  'stat_buf'.  Previously, 'stat_buf' was left uninitialized in this
  case, even though 'scm_primitive_load_path' assumes that 'stat_buf'
  will be filled.  Update the header comment to explicitly specify that
  'stat_buf' will be filled.  Also 'goto end' in a few failure cases
  instead of replicating its code.
---
 libguile/load.c |   21 ++++++++++-----------
 1 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/libguile/load.c b/libguile/load.c
index 0076218..ae9e4bd 100644
--- a/libguile/load.c
+++ b/libguile/load.c
@@ -419,8 +419,9 @@ scm_c_string_has_an_ext (char *str, size_t len, SCM 
extensions)
 
 /* Search PATH for a directory containing a file named FILENAME.
    The file must be readable, and not a directory.
-   If we find one, return its full filename; otherwise, return #f.
+   If we find one, return its full pathname; otherwise, return #f.
    If FILENAME is absolute, return it unchanged.
+   We also fill *stat_buf corresponding to the returned pathname.
    If given, EXTENSIONS is a list of strings; for each directory 
    in PATH, we search for FILENAME concatenated with each EXTENSION.  */
 static SCM
@@ -445,7 +446,7 @@ search_path (SCM path, SCM filename, SCM extensions, SCM 
require_exts,
   filename_len = strlen (filename_chars);
   scm_dynwind_free (filename_chars);
 
-  /* If FILENAME is absolute, return it unchanged.  */
+  /* If FILENAME is absolute and is still valid, return it unchanged.  */
 #ifdef __MINGW32__
   if (((filename_len >= 1) && 
        (filename_chars[0] == '/' || filename_chars[0] == '\\')) ||
@@ -457,14 +458,13 @@ search_path (SCM path, SCM filename, SCM extensions, SCM 
require_exts,
   if (filename_len >= 1 && filename_chars[0] == '/')
 #endif
     {
-      SCM res = filename;
-      if (scm_is_true (require_exts) &&
-          !scm_c_string_has_an_ext (filename_chars, filename_len,
+      if ((scm_is_false (require_exts) ||
+           scm_c_string_has_an_ext (filename_chars, filename_len,
                                     extensions))
-        res = SCM_BOOL_F;
-
-      scm_dynwind_end ();
-      return res;
+          && stat (filename_chars, stat_buf) == 0
+          && !(stat_buf->st_mode & S_IFDIR))
+        result = filename;
+      goto end;
     }
 
   /* If FILENAME has an extension, don't try to add EXTENSIONS to it.  */
@@ -483,8 +483,7 @@ search_path (SCM path, SCM filename, SCM extensions, SCM 
require_exts,
               {
                 /* This filename has an extension, but not one of the right
                    ones... */
-                scm_dynwind_end ();
-                return SCM_BOOL_F;
+                goto end;
               }
            /* This filename already has an extension, so cancel the
                list of extensions.  */
-- 
1.7.5.4


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