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

[Christian Jullien]

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


_______________________________________________
Tinycc-devel mailing list
address@hidden
https://lists.nongnu.org/mailman/listinfo/tinycc-devel