Re: [patch] Verify byte-by-byte if both files are the same on "remote:" [Re: [rfc] False separate debuginfo warning with "remote:"

Jan Kratochvil
2011-10-10T20:22:11Z

On Mon, 10 Oct 2011 15:47:57 +0200, Ulrich Weigand wrote:
> >From an API simplicity point of view, I'd somewhat prefer for the function to
> rewind the file position itself instead of requiring the caller to do it ...

done, yes, I had some wrong performance assumptions.

> > @@ -1345,25 +1359,35 @@ separate_debug_file_exists (const char *name, unsigned long crc,
> > negatives. */
> >
> > if (bfd_stat (abfd, &abfd_stat) == 0
> > - && bfd_stat (parent_objfile->obfd, &parent_stat) == 0
> > - && abfd_stat.st_dev == parent_stat.st_dev
> > - && abfd_stat.st_ino == parent_stat.st_ino
> > - && abfd_stat.st_ino != 0)
> > + && abfd_stat.st_ino != 0
> > + && bfd_stat (parent_objfile->obfd, &parent_stat) == 0)
> > {
> > - bfd_close (abfd);
> > - return 0;
> > + if (abfd_stat.st_dev == parent_stat.st_dev
> > + && abfd_stat.st_ino == parent_stat.st_ino)
> > + {
> > + bfd_close (abfd);
> > + return 0;
> > + }
> > + verified_as_different = 1;
> > }
> > + else
> > + verified_as_different = 0;
>
> So this no longer handles the st_ino == 0 case. I think we still need to do
> that, to cope with filesystems (e.g. on Windows?) where stat works, but does
> not provide inode numbers ... Two files with zero st_ino should not be
> considered equal.

I believe the code is right. st_ino == 0 will verified_as_different = 0,
therefore this code does not make any assumption about such files.

FYI I reordered the condition for some negligible btter performance.

> As another performance optimization, maybe it would make sense to cache
> the parent's CRC (e.g. in the objfile) to avoid redundant computation?

OK, done.

No regressions on {x86_64,x86_64-m32,i686}-fedora16pre-linux-gnu.

Thanks,
Jan

gdb/
2011-10-10 Jan Kratochvil <jan.kratochvil@redhat.com>

Fix separate debuginfo warning with "remote:" access.
* objfiles.h (struct objfile): New fields crc32 and crc32_p.
* symfile.c (get_file_crc): New function with the code moved from ...
(separate_debug_file_exists): ... this function, specifically variables
buffer and count. New variable verified_as_different, set it. Remove
file_crc initialization. Verify also if both files are not the same
manually, if needed.

--- a/gdb/objfiles.h
+++ b/gdb/objfiles.h
@@ -244,6 +244,11 @@ struct objfile

long mtime;

+ /* Cached 32-bit CRC as computed by gnu_debuglink_crc32. CRC32 is valid
+ iff CRC32_P. */
+ unsigned long crc32;
+ int crc32_p;
+
/* Obstack to hold objects that should be freed when we load a new symbol
table from this object file. */

--- a/gdb/symfile.c
+++ b/gdb/symfile.c
@@ -1310,15 +1310,52 @@ get_debug_link_info (struct objfile *objfile, unsigned long *crc32_out)
return contents;
}

+/* Return 32-bit CRC for ABFD. If successful store it to *FILE_CRC_RETURN and
+ return 1. Otherwise print a warning and return 0. ABFD seek position is
+ not preserved. */
+
+static int
+get_file_crc (bfd *abfd, unsigned long *file_crc_return)
+{
+ unsigned long file_crc = 0;
+
+ if (bfd_seek (abfd, 0, SEEK_SET) != 0)
+ {
+ warning (_("Problem reading \"%s\" for CRC: %s"),
+ bfd_get_filename (abfd), bfd_errmsg (bfd_get_error ()));
+ return 0;
+ }
+
+ for (;;)
+ {
+ gdb_byte buffer[8 * 1024];
+ bfd_size_type count;
+
+ count = bfd_bread (buffer, sizeof (buffer), abfd);
+ if (count == (bfd_size_type) -1)
+ {
+ warning (_("Problem reading \"%s\" for CRC: %s"),
+ bfd_get_filename (abfd), bfd_errmsg (bfd_get_error ()));
+ return 0;
+ }
+ if (count == 0)
+ break;
+ file_crc = gnu_debuglink_crc32 (file_crc, buffer, count);
+ }
+
+ *file_crc_return = file_crc;
+ return 1;
+}
+
static int
separate_debug_file_exists (const char *name, unsigned long crc,
struct objfile *parent_objfile)
{
- unsigned long file_crc = 0;
+ unsigned long file_crc;
+ int file_crc_p;
bfd *abfd;
- gdb_byte buffer[8*1024];
- int count;
struct stat parent_stat, abfd_stat;
+ int verified_as_different;

/* Find a separate debug info file as if symbols would be present in
PARENT_OBJFILE itself this function would not be called. .gnu_debuglink
@@ -1345,25 +1382,46 @@ separate_debug_file_exists (const char *name, unsigned long crc,
negatives. */

if (bfd_stat (abfd, &abfd_stat) == 0
- && bfd_stat (parent_objfile->obfd, &parent_stat) == 0
- && abfd_stat.st_dev == parent_stat.st_dev
- && abfd_stat.st_ino == parent_stat.st_ino
- && abfd_stat.st_ino != 0)
+ && abfd_stat.st_ino != 0
+ && bfd_stat (parent_objfile->obfd, &parent_stat) == 0)
{
- bfd_close (abfd);
- return 0;
+ if (abfd_stat.st_dev == parent_stat.st_dev
+ && abfd_stat.st_ino == parent_stat.st_ino)
+ {
+ bfd_close (abfd);
+ return 0;
+ }
+ verified_as_different = 1;
}
+ else
+ verified_as_different = 0;

- while ((count = bfd_bread (buffer, sizeof (buffer), abfd)) > 0)
- file_crc = gnu_debuglink_crc32 (file_crc, buffer, count);
+ file_crc_p = get_file_crc (abfd, &file_crc);

bfd_close (abfd);

+ if (!file_crc_p)
+ return 0;
+
if (crc != file_crc)
{
- warning (_("the debug information found in \"%s\""
- " does not match \"%s\" (CRC mismatch).\n"),
- name, parent_objfile->name);
+ /* If one (or both) the files are accessed for example the via "remote:"
+ gdbserver way it does not support the bfd_stat operation. Verify
+ whether those two files are not the same manually. */
+
+ if (!verified_as_different && !parent_objfile->crc32_p)
+ {
+ parent_objfile->crc32_p = get_file_crc (parent_objfile->obfd,
+ &parent_objfile->crc32);
+ if (!parent_objfile->crc32_p)
+ return 0;
+ }
+
+ if (verified_as_different || parent_objfile->crc32 != crc)
+ warning (_("the debug information found in \"%s\""
+ " does not match \"%s\" (CRC mismatch).\n"),
+ name, parent_objfile->name);
+
return 0;
}