Re: [Tinycc-devel] core dump because stack overwritten

[Herman ten Brugge]

How about this patch:

--------------------------
--- a/tccgen.c        2019-10-22 19:52:48.761977245 +0200
+++ b/tccgen.c  2019-10-23 11:18:14.871290060 +0200
@@ -2627,7 +2627,9 @@ static void gen_cvt_ftoi1(int t)
         gfunc_call(1);
         vpushi(0);
         vtop->r = REG_IRET;
+#if !defined(TCC_TARGET_X86_64) /* REG_LRET only for VT_QLONG */
         vtop->r2 = REG_LRET;
+#endif
     } else {
         gen_cvt_ftoi(t);
     }
--------------------------
According to https://en.wikipedia.org/wiki/X86_calling_conventions the 
x86_64 only uses rax for 64 bits returns.

    Herman


On 2019-10-23 07:20, Christian Jullien wrote:
> I confirm your test case fails on Linux x64. It looks your patch pay attention 
> to PTR_SIZE == 4 (i.e. it now enters if only with 32bit processor).
> However, w.o. the patch I can't reproduce the core dump on aarch64 Linux nor with Windows 
> x64 which are also a 64bit processors. They both correctly display "42 42"
> No core dumps does not mean it works, memory may be corrupted somewhere else.
>
> Either your patch is only required for Linux x64 or there is something to 
> investigate more carefully.
>
> I can only test on different platforms but I'm unable to give you further 
> advices.
>
> M2c
>
> C.
>
> -----Original Message-----
> From: Tinycc-devel [mailto:tinycc-devel-bounces+eligis=address@hidden] On 
> Behalf Of Herman ten Brugge via Tinycc-devel
> Sent: Tuesday, October 22, 2019 22:15
> To: address@hidden
> Cc: Herman ten Brugge
> Subject: [Tinycc-devel] core dump because stack overwritten
>
> I have a small testcase:
>
> --------------
> #include <stdio.h>
> #include <stdlib.h>
> #include <inttypes.h>
>
> int
> main(void)
> {
>     struct tst_struct { uint64_t cnt; } *tst =
>       (struct tst_struct *) malloc (sizeof (struct tst_struct));
>
>     tst->cnt = 42;
>     printf ("%" PRIu64 " %" PRIu64 "\n", tst->cnt, (uint64_t) (tst->cnt /
> 1.0));
>     return 0;
> }
> ----------------
> when I compile this with tcc and run it I get a core dump. The problem
> is that the stack is overwritten.
> I have a fix.
>
> ------------------------
> --- a/tccgen.c  2019-10-22 19:52:48.761977245 +0200
> +++ b/tccgen.c  2019-10-22 22:08:08.465825842 +0200
> @@ -1203,7 +1203,7 @@ ST_FUNC void save_reg_upstack(int r, int
>                    }
>    #endif
>                    /* special long long case */
> -                if ((p->r2 & VT_VALMASK) < VT_CONST) {
> +                if (PTR_SIZE == 4 && (p->r2 & VT_VALMASK) < VT_CONST) {
>                        sv.c.i += PTR_SIZE;
>                        store(p->r2, &sv);
>                    }
> ---------------------
> But am not sure if this is the correct fix. The code generator is quite
> complex.
>
>       Herman
>
>
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