https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97599
Bug ID: 97599
Summary: [8/9/10/11 Regression] missing unspecified_parameters
DIE in DWARF for functions with variable arguments
Product: gcc
Version: 11.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: debug
Assignee: unassigned at gcc dot gnu.org
Reporter: jakub at gcc dot gnu.org
CC: aldyh at gcc dot gnu.org, woodard at redhat dot com
Depends on: 71855
Target Milestone: ---
Target: x86-64-Linux
+++ This bug was initially created as a clone of Bug #71855 +++
Since PR71855, we emit bad debug info e.g. for
#include <stdarg.h>
static __attribute__((noinline)) int
foo (int unused, int args, ...)
{
va_list ap;
int ret = 0;
va_start (ap, args);
if (args)
ret = va_arg (ap, int);
va_end (ap);
return ret;
}
int
bar (int x)
{
return foo (0, 0) + foo (0, 1, 1) + foo (0, 1, 3) + foo (0, 0) + foo (0, 0,
4);
}
Also, with LTO:
#include <stdarg.h>
void
foo (int args, ...)
{
va_list ap;
va_start (ap, args);
va_end (ap);
}
gcc -shared -g -fpic -flto test.c
As written in https://bugzilla.redhat.com/show_bug.cgi?id=1891787 , it seems it
isn't enough to rely on the DW_TAG_unspecified_parameters DIE being present
among the abstract origin DIE of the DW_TAG_subprogram's children; the debug
info consumer can't know if the clone of that original function is really still
variadic, or if e.g. the variadic-ness has been removed.
For the non-LTO case, it is I think fairly easy to do, subr_die != old_die
should be true if it is a fresh new DIE, but I'm afraid for in_lto_p we don't
really know easily if it is a fresh new DIE or not.
As we have nothing to lookup in the hash tables to find out cheaply if it is
there or not already, the following is a painful way of doing that.
Thoughts on that?
--- gcc/dwarf2out.c.jj 2020-10-26 10:53:56.000000000 +0100
+++ gcc/dwarf2out.c 2020-10-27 17:56:07.249711468 +0100
@@ -23365,6 +23365,35 @@ gen_subprogram_die (tree decl, dw_die_re
else if (DECL_INITIAL (decl) == NULL_TREE)
gen_unspecified_parameters_die (decl, subr_die);
}
+ else if (prototype_p (TREE_TYPE (decl))
+ && stdarg_p (TREE_TYPE (decl)))
+ {
+ /* Emit DW_TAG_unspecified_parameters even in late DWARF,
+ but ensure to do it only when it isn't present already.
+ If subr_die != old_die, this is a new DIE to which it
+ should be added, otherwise if in_lto_p, we don't really
+ know if it is a freshly created one or something older,
+ so look it up. */
+ bool emit = subr_die != old_die;
+ if (!emit && in_lto_p)
+ {
+ dw_die_ref c;
+ emit = true;
+ FOR_EACH_CHILD (subr_die, c,
+ do
+ {
+ if (c->die_tag
+ == DW_TAG_unspecified_parameters)
+ {
+ emit = false;
+ break;
+ }
+ }
+ while (0));
+ }
+ if (emit)
+ gen_unspecified_parameters_die (decl, subr_die);
+ }
}
if (subr_die != old_die)
Referenced Bugs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71855
[Bug 71855] duplicate unspecified_parameters DIE in DWARF for functions with
variable arguments
