[Bug lto/98912] New: valgrind error in default_elf_asm_output_ascii

[Bug lto/98912] New: valgrind error in default_elf_asm_output_ascii

[dcb314 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98912

            Bug ID: 98912
           Summary: valgrind error in default_elf_asm_output_ascii
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: lto
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dcb314 at hotmail dot com
                CC: marxin at gcc dot gnu.org
  Target Milestone: ---

Created attachment 50105
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=50105&action=edit
fortran source code

For the attached fortran source code file, compiled as follows:

$ /home/dcb/gcc/results.20210131.valgrind/bin/gfortran -flto=auto getfname.f

does this:

==29891== Conditional jump or move depends on uninitialised value(s)
==29891==    at 0xF68B43: default_elf_asm_output_ascii(_IO_FILE*, char const*,
u
nsigned int) (varasm.c:8285)
==29891==    by 0xF68A8F: assemble_string(char const*, int) (varasm.c:2069)
==29891==    by 0xAAA5EF: lhd_append_data(void const*, unsigned long, void*)
(la
nghooks.c:823)
==29891==    by 0xAFC984: produce_lto_section (lto-streamer-out.c:2675)

[Bug lto/98912] valgrind error in default_elf_asm_output_ascii

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98912

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-02-01
             Status|UNCONFIRMED                 |WAITING

--- Comment #1 from Martin Liška <marxin at gcc dot gnu.org> ---
Hm, this one is about streaming of 

  lto_section s
    = { LTO_major_version, LTO_minor_version, slim_object, 0 };
  s.set_compression (compression);
  lto_write_data (&s, sizeof s);

where sizeof s == 8.

I cannot reproduce it..

[Bug lto/98912] valgrind error in default_elf_asm_output_ascii

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98912

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jakub at gcc dot gnu.org

--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Well, lto_section is 8 byte long struct containing 2 ushort fields, 1 uchar,
one byte padding (on most hosts) and one ushort field.
So bet valgrind is complaining about streaming the padding...

[Bug lto/98912] valgrind error in default_elf_asm_output_ascii

[dcb314 at hotmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98912

--- Comment #3 from David Binderman <dcb314 at hotmail dot com> ---
For varasm.c line 8285 is

          for (p = s; p < limit && *p != '\0'; p++)

So either the limit is wrong or there are some un-init bytes in
the string. My money is on option 2 ;->

Maybe a suitable first step would be to produce some debug output,
(maybe fprintf on stderr ?) of the parameters to default_elf_asm_output_ascii,
i.e s and len.

Whichever of s or len that valgrind detects would be the culprit.

[Bug lto/98912] valgrind error in default_elf_asm_output_ascii

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98912

--- Comment #4 from Martin Liška <marxin at gcc dot gnu.org> ---
(In reply to Jakub Jelinek from comment #2)
> Well, lto_section is 8 byte long struct containing 2 ushort fields, 1 uchar,
> one byte padding (on most hosts) and one ushort field.
> So bet valgrind is complaining about streaming the padding...

I bet it's complaining about the padding.
Please test the following debugging patch:

diff --git a/gcc/lto-streamer-out.c b/gcc/lto-streamer-out.c
index 405f3bfc56c..d96a7ee3ec8 100644
--- a/gcc/lto-streamer-out.c
+++ b/gcc/lto-streamer-out.c
@@ -2672,6 +2672,10 @@ produce_lto_section ()
   lto_section s
     = { LTO_major_version, LTO_minor_version, slim_object, 0 };
   s.set_compression (compression);
+  char *ptr = (char *)&s;
+  for (unsigned i = 0; i < sizeof s; i++)
+    fprintf (stderr, "v[%d]=%d\n", i, ptr[i]);
+  fprintf (stderr, "\n");
   lto_write_data (&s, sizeof s);
   lto_end_section ();
   destroy_output_block (ob);

with GCC 10 the object is constructed in the following way:

  MEM <char[4]> [(struct lto_section *)&s + 2B] = {};
  s.major_version = 9;
  s.slim_object = prephitmp_911;
  s.flags = 1;

and that covers all bytes in the struct.

[Bug lto/98912] valgrind error in default_elf_asm_output_ascii

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98912

--- Comment #5 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
How exactly it is gimplified depends on the target, optimization level etc.
Anyway, I'd suggest just to add a unsigned char padding; to the structure, that
seems easiest.

[Bug lto/98912] valgrind error in default_elf_asm_output_ascii

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98912

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |marxin at gcc dot gnu.org
             Status|WAITING                     |ASSIGNED

--- Comment #6 from Martin Liška <marxin at gcc dot gnu.org> ---
All right, I'll send patch for it.

[Bug lto/98912] valgrind error in default_elf_asm_output_ascii

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98912

--- Comment #7 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Martin Liska <marxin@gcc.gnu.org>:

https://gcc.gnu.org/g:84110515b93a6709de24240d6658ac207db5129f

commit r11-7057-g84110515b93a6709de24240d6658ac207db5129f
Author: Martin Liska <mliska@suse.cz>
Date:   Wed Feb 3 10:53:32 2021 +0100

    Fill up padding in lto_section struct.

    gcc/ChangeLog:

            PR lto/98912
            * lto-streamer-out.c (produce_lto_section): Fill up missing
            padding.
            * lto-streamer.h (struct lto_section): Add _padding field.

[Bug lto/98912] valgrind error in default_elf_asm_output_ascii

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98912

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED

--- Comment #8 from Martin Liška <marxin at gcc dot gnu.org> ---
Should be fixed now.