[Bug debug/56502] New: entry-value: Missing DW_AT_linkage_name for C<->C++ calls

[jan.kratochvil at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=56502

             Bug #: 56502
           Summary: entry-value: Missing DW_AT_linkage_name for C<->C++
                    calls
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: jan.kratochvil@redhat.com
            Target: x86_64-unknown-linux-gnu


Created attachment 29564
  --> http://gcc.gnu.org/bugzilla/attachment.cgi?id=29564
FSF GDB HEAD patch before it is upstreamed.

gcc-4.8.0-0.14.fc19.x86_64
gdb FSF HEAD with attached patch (reproducer does not work without patched GDB)

gcc -o extcall3.o -c extcall3.c -Wall -g -O2; g++ -o extcall extcall3.o
extcall{,2}.C -Wall -g -O2
gdb ./extcall -ex 'b a' -ex 'b b' -ex 'set debug entry-values 1' -ex r

Breakpoint 1, Cannot find function "f(int)" for a call site target at 0x4004ce
in main
(gdb) bt
#0  a (y=1) at extcall3.c:2
#1  0x00000000004004ce in main () at extcall.C:4
(gdb) c
[...]
(gdb) bt
#0  b (y=y@entry=2) at extcall2.C:2
#1  0x0000000000400607 in g (x=x@entry=42) at extcall2.C:3
#2  0x00000000004004d8 in main () at extcall.C:5

You can see the first case main->f->a is missing the tail call frame because:
  Cannot find function "f(int)" for a call site target at 0x4004ce in main
 <0><bb>: Abbrev Number: 1 (DW_TAG_compile_unit)
    <c0>   DW_AT_language    : 4        (C++)
    <c1>   DW_AT_name        : extcall.C
 <2><fa>: Abbrev Number: 3 (DW_TAG_GNU_call_site)
    <fb>   DW_AT_low_pc      : 0x4004ce
    <103>   DW_AT_abstract_origin: <0x12e>
 <1><12e>: Abbrev Number: 7 (DW_TAG_subprogram)
    <12f>   DW_AT_external    : 1
    <12f>   DW_AT_name        : f
    <133>   DW_AT_declaration : 1
 <2><137>: Abbrev Number: 8 (DW_TAG_formal_parameter)
    <138>   DW_AT_type        : <0x127>
 <2><13c>: Abbrev Number: 0

As <12e> is in C++ CU and it has no DW_AT_linkage_name GDB expects it is
"f(int)" but the C symbol is "f".

==> extcall.C <==
extern "C" { void f(int x); }
void g(int x);
int main() {
  f(42);
  g(42);
}

==> extcall2.C <==
static volatile int j;
static __attribute__((noinline, noclone)) void b(int y) { j=y; }
void g(int x) { b(2); }

==> extcall3.c <==
static volatile int i;
static __attribute__((noinline, noclone)) void a(int y) { i=y; }
void f(int x) { a(1); }