[Bug symtab/18148] New: Definitions with DW_AT_const_value never make it into the psymtabs

[Bug symtab/18148] New: Definitions with DW_AT_const_value never make it into the psymtabs

[wingo at igalia dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=18148

            Bug ID: 18148
           Summary: Definitions with DW_AT_const_value never make it into
                    the psymtabs
           Product: gdb
           Version: HEAD
            Status: NEW
          Severity: normal
          Priority: P2
         Component: symtab
          Assignee: unassigned at sourceware dot org
          Reporter: wingo at igalia dot com

LLVM will not allocate storage for the "foo" in "static const int foo = 1". 
Instead it inlines the value at the use sites, and emits a DW_TAG_variable with
DW_AT_const_value for the definition of "foo".

GCC will allocate storage for both at -O0 but at -O2 the same problem exists.

Unfortunately, partial debug info (PDI) instances without a location don't get
added to the psymtabs table.  That means that if you do the following:

   cat <<EOF > one.c
static const int one = 1;

extern int fetch_two (void);

int main (int argc, char *argv[]) 
{
  return one + fetch_two ();
}
EOF
   cat <<EOF > two.c
static const int two = 2;

int fetch_two (void)
{
  return two;
}
EOF
   gcc -g -O2 -c -o one.o one.c
   gcc -g -O2 -c -o two.o two.c
   gcc -g -o test one.o two.o
   gdb ./test

Then at the GDB prompt:

   (gdb) p one
   $1 = 1
   (gdb) p two
   No symbol "two" in current context.

The reason we can get "one" and not "two" is because the symtab for one.c has
been expanded, when we went to look for main.  If we expand the compilation
unit for two.c and flush the symbol cache, if on GDB trunk:

   (gdb) mt expand foo.c
   # only needed on trunk
   (gdb) mt flush-symbol-cache
   (gdb) print two
   $2 = 2

The ultimate cause is that dwarf2read.c:add_partial_symbol punts if the symbol
has no location, thinking it's a declaration and not a definition.  Well if it
has a DT_AT_const_value, it might be a definition too.  Patch coming tomorrow.

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[Bug symtab/18148] Definitions with DW_AT_const_value never make it into the psymtabs

[cvs-commit at gcc dot gnu.org]

https://sourceware.org/bugzilla/show_bug.cgi?id=18148

--- Comment #1 from cvs-commit at gcc dot gnu.org <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Andy Wingo <wingo@sourceware.org>:

https://sourceware.org/git/gitweb.cgi?p=binutils-gdb.git;h=ff908ebf8612a737d9e168eca0604ff6c97556bc

commit ff908ebf8612a737d9e168eca0604ff6c97556bc
Author: Andy Wingo <wingo@igalia.com>
Date:   Thu Mar 26 19:41:15 2015 +0100

    Properly intern constants into psymtab

    Variables with a DW_AT_const_value but without a DW_AT_location were not
    getting added to the partial symbol table.  They are added to the full
    symbol table, however, when the compilation unit's psymtabs are
    expanded.

    Before:

       (gdb) p one
       No symbol "one" in current context.
       (gdb) mt flush-symbol-cache
       (gdb) mt expand one.c
       (gdb) p one
       $1 = 1

    After:

       (gdb) p one
       $1 = 1

    To the user it's pretty strange, as depending on whether tab completion
    has forced expansion of all CUs or not the lookup might succeed, or not
    if the failure was already added to the symbol cache.

    This commit simply makes sure to add constants to the partial symbol
    tables.

    gdb/testsuite/ChangeLog:

        PR symtab/18148
        * gdb.dwarf2/dw2-intercu.S (one, two): Add variables that have a
        const_value but not a location.
        * gdb.dwarf2/dw2-intercu.exp: Add tests that constants without
        location defined in non-main CUs are visible.

    gdb/ChangeLog:

        PR symtab/18148
        * dwarf2read.c (struct partial_die_info): Add has_const_value
        member.
        (add_partial_symbol): Don't punt on symbols that have const_value
        attributes.
        (read_partial_die): Detect DW_AT_const_value.

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[Bug symtab/18148] Definitions with DW_AT_const_value never make it into the psymtabs

[dje at google dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=18148

dje at google dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|                            |dje at google dot com
         Resolution|---                         |FIXED

--- Comment #2 from dje at google dot com ---
Patch committed.

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