Re: [Tinycc-devel] nocode_wanted does not work

[Sergey Korshunoff]

The previous trace is wrong, sorry

A correct place is

 else if (tok == '{') {
    if (const_wanted)
        tcc_error("expected constant");
    /* save all registers */
    save_regs(0); <<<<<<<<<<<<<<<
    /* statement _expression_ : we do not accept break/continue
       inside as GCC does */
    block(NULL, NULL, NULL, NULL, 0, 1);
    skip(')');
} else {
    gexpr();
    skip(')');
}

This is a save_regs(0) which generate a code when nocode_wanted=1

When

  if(!nocode_wanted)

    save_regs(0);

then there is no error messages but a test program still hangs

2016-04-03 14:17 GMT+03:00 Sergey Korshunoff <address@hidden>:

> Or at least fail with an explanatory
> message if o() is called while nocode_wanted is set?

I can not grock what is wrong (where is the error). But is starts in
block.c: 5001 when ({}) is used.

antoo # gdb tcc
(gdb) set args vla_label_fix_problem.c
(gdb) b check_nocode_wanted
Breakpoint 1 at 0x806193a: file i386-gen.c, line 118.
(gdb) r
Starting program: /usr/local/bin/tcc vla_label_fix_problem.c
Breakpoint 1, check_nocode_wanted () at i386-gen.c:118
118         if (nocode_wanted)
(gdb) bt
#0  check_nocode_wanted () at i386-gen.c:118
#1  0x08061960 in o (c=184) at i386-gen.c:124
#2  0x08061dbd in load (r=0, sv=0x80742b8) at i386-gen.c:269
#3  0x08050c95 in gv (rc=1) at tccgen.c:979
#4  0x08054882 in vstore () at tccgen.c:2752
#5  0x08059b06 in init_putv (type=0xbfeb2c18, sec=0x0, c=4294967292, v=0, expr_type=2) at tccgen.c:5559
#6  0x0805a3ce in decl_initializer (type=0xbfeb2c18, sec=0x0, c=4294967292, first=1, size_only=0) at tccgen.c:5867
#7  0x0805a9f7 in decl_initializer_alloc (type=0xbfeb2c18, ad=0xbfeb2bf0, r=306, has_init=1, v=1169, scope=50)
    at tccgen.c:6102
#8  0x0805b7a6 in decl0 (l=50, is_for_loop_init=0) at tccgen.c:6522
#9  0x0805b80e in decl (l=50) at tccgen.c:6541
#10 0x08058534 in label_or_decl (l=50) at tccgen.c:4919
#11 0x08058819 in block (bsym=0x0, csym=0x0, case_sym=0x0, def_sym=0x0, case_reg=0, is_expr=0) at tccgen.c:5001
#12 0x0805ade4 in gen_function (sym=0x8d931c4) at tccgen.c:6216
#13 0x0805b5a9 in decl0 (l=48, is_for_loop_init=0) at tccgen.c:6468
#14 0x0805b80e in decl (l=48) at tccgen.c:6541
#15 0x08068882 in tcc_compile (s1=0x8d86008) at libtcc.c:976
#16 0x08069374 in tcc_add_file_internal (s1=0x8d86008, filename=0x8d94241 "vla_label_fix_problem.c", flags=1, filetype=2)
    at libtcc.c:1384
#17 0x08069581 in tcc_add_file (s=0x8d86008, filename=0x8d94241 "vla_label_fix_problem.c", filetype=2) at libtcc.c:1476
#18 0x0806b63a in main (argc=2, argv=0xbfeb31f4) at tcc.c:326
(gdb).

block.c: 5001
        while (tok != '}') {
            label_or_decl(VT_LOCAL);
            if (tok != '}') {
                if (is_expr)
                    vpop();
                block(bsym, csym, case_sym, def_sym, case_reg, is_expr);
            }
        }

2016-04-03 12:13 GMT+03:00 Edmund Grimley Evans <address@hidden>:

> Hi! The following test hangs when compiled with tcc after 737f98421
>       tccgen.c: Bug fix for 992cbda and 3ff77a1: set nocode_wanted.
>       tests/tests2/78_vla_label.*: Add test

The change introduced at 737f98421 depends on "nocode_wanted" working.
But it doesn't work, of course. It's broken probably in lots of ways,
but in particular a "do" loop will generate code when it shouldn't. So
another instance of the same bug is demonstrated by this:

int main()
{
    return sizeof( ({ do { } while (1); }), 0 );
}

(So the bug perhaps only affects statement expressions, which are not
part of standard C.)

I wonder, how feasible is it to find every place in tccgen.c where a
back-end function like gjmp might be called and ensure that it won't
be called when nocode_wanted is set? Could this be done more
systematically at a lower level? Or at least fail with an explanatory
message if o() is called while nocode_wanted is set?

Edmund

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