When using -fstrict-aliasing the function LC1_f15 below gets miscompiled. More
precisely, the va_list object is only partially assigned. The system fails to
set the frame size or something similar. In the assembler I see
/* local function %F15 */
static cl_object LC1_f15(cl_narg narg, volatile cl_object *lex0, ...)
{
cl_object value0;
cl_object V1;
va_list args; va_start(args,lex0);
0: 48 8d 44 24 08 lea0x8(%rsp),%rax
5: 48 89 44 24 e0 mov%rax,-0x20(%rsp)
if (narg 1) {
a: ba 00 00 00 00 mov$0x0,%edx
f: 48 85 fftest %rdi,%rdi
12: 7e 1a jle2e LC1_f15+0x2e
V1=0;
} else {
V1= va_arg(args,cl_object);
14: 8b 44 24 d8 mov-0x28(%rsp),%eax
18: 83 f8 30cmp$0x30,%eax
Here we are reading -0x28(%rsp) which has not been set. The same code, with gcc
4.1 produces an assignment mov 0x10,-0x28(%rsp) that makes things right. The
preprocessed example follows.
# 1 /usr/lib/gcc/x86_64-linux-gnu/4.2.3/include/stdarg.h 1 3 4
# 43 /usr/lib/gcc/x86_64-linux-gnu/4.2.3/include/stdarg.h 3 4
typedef __builtin_va_list __gnuc_va_list;
# 105 /usr/lib/gcc/x86_64-linux-gnu/4.2.3/include/stdarg.h 3 4
typedef __gnuc_va_list va_list;
typedef long cl_fixnum;
typedef unsigned long cl_index;
typedef union cl_lispunion *cl_object;
typedef cl_fixnum cl_narg;
struct ecl_singlefloat {
float SFVAL;
};
struct ecl_stack_frame {
cl_object *bottom;
cl_object *top;
cl_object *stack;
};
union cl_lispunion {
struct ecl_singlefloat SF;
struct ecl_stack_frame frame;
};
struct cl_env_struct2 {
cl_index nvalues;
cl_object values[64];
};
extern struct cl_env_struct2 cl_env2;
static cl_object LC1_f15(cl_narg narg, volatile cl_object *lex0, ...)
{
cl_object value0;
cl_object V1;
va_list args; __builtin_va_start(args,lex0);
if (narg 1) {
V1=0;
} else {
V1= __builtin_va_arg(args,cl_object);
}
value0=V1; cl_env2.nvalues=1;
return value0;
}
cl_object LC2__g147(cl_object V1, cl_object V2, cl_object V3)
{
cl_object T0;
volatile cl_object lex0[1];
cl_object value0;
{
lex0[0]= V3;
value0=LC1_f15(1,lex0,MAKE_FIXNUM(-2688612)) ;
return value0;
}}
--
Summary: -fstrict-aliasing breaks __builtin_va_args
Product: gcc
Version: 4.2.3
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: juanjose dot garciaripoll at gmail dot com
GCC build triplet: x86_64-linux-gnu
GCC host triplet: x86_64-linux-gnu
GCC target triplet: x86_64-linux-gnu
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36255
