RFA: unbreak typedefed bitfield

Vladimir Prus
2009-12-18T12:41:41Z

GDB presently crashes on any attempt to get a value of a bitfield that
has typedefed type. The bugzilla report is here:

http://sourceware.org/bugzilla/show_bug.cgi?id=10884

An easier reproducer is this program:

typedef unsigned int uint;

struct Data {
int alloc;
int begin;
int end;
uint sharable : 1;
};

int main()
{
Data d = {1, 2, 3, 1};
return 0;
}

and this session:

~"Breakpoint 1, main () at div.cpp:13\n"
~"13\t Data d = {1, 2, 3, 1};\n"
*stopped,frame={addr="0x0804849a",func="main",args=[],file="div.cpp",fullname="/home/ghost/Build/gdb-git/gdb/div.cpp",line="13"},thread-id="1",stopped-threads="all",core="1"
(gdb)
n
&"n\n"
&"During symbol reading, incomplete CFI data; unspecified registers (e.g., eax) at 0x8048497.\n"
^running
*running,thread-id="1"
(gdb)
~"14\t return 0;\n"
*stopped,frame={addr="0x080484b9",func="main",args=[],file="div.cpp",fullname="/home/ghost/Build/gdb-git/gdb/div.cpp",line="14"},thread-id="1",stopped-threads="all",core="1"
(gdb)
-var-create V * d
^done,name="V",numchild="1",value="{...}",type="Data",thread-id="1",has_more="0"
(gdb)
-var-list-children V
^done,numchild="1",children=[child={name="V.public",exp="public",numchild="4",thread-id="1"}],has_more="0"
(gdb)
-var-list-children --all-values V.public

Program received signal SIGFPE, Arithmetic exception.
0x0813add3 in value_primitive_field (arg1=0x8644840, offset=0, fieldno=3, arg_type=0x85a9d7c) at /home/ghost/Work/CodeSourcery/Projects/egdb/gdb-git/gdb/value.c:1892
1892 if ((bitpos % container_bitsize) + v->bitsize <= container_bitsize

And here's a trivial patch to fix this problem. I would claim this clearly indicates a design bug in GDB
type mechanism -- and it bites us repeatedly, but I'm not ready to propose a specific way to fix it, yet.

OK to commit?

- Volodya

--- a/gdb/value.c
+++ b/gdb/value.c
@@ -1873,6 +1873,7 @@ value_primitive_field (struct value *arg1, int offset,

CHECK_TYPEDEF (arg_type);
type = TYPE_FIELD_TYPE (arg_type, fieldno);
+ check_typedef (type);

/* Handle packed fields */