[Bug sanitizer/105714] New: ASan in gcc trunk missed a buffer-overflow at -Os

[shaohua.li at inf dot ethz.ch]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105714

            Bug ID: 105714
           Summary: ASan in gcc trunk missed a buffer-overflow at -Os
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: sanitizer
          Assignee: unassigned at gcc dot gnu.org
          Reporter: shaohua.li at inf dot ethz.ch
                CC: dodji at gcc dot gnu.org, dvyukov at gcc dot gnu.org,
                    jakub at gcc dot gnu.org, kcc at gcc dot gnu.org, marxin at gcc dot gnu.org
  Target Milestone: ---

For the following code, `gcc-trunk -Os -fsanitize=address` reported nothing,
however other opt levels reported the global buffer-overflow at the end of
function g().

Initially, I thought it might due to optimization at -Os, but I indeed found
the overflowed buffer be loaded in the assembly code and gcc-11 -Os did not
miss this bug: https://godbolt.org/z/r4rhM8bjz 

$cat a.c
struct a {
  int x
};
struct a b[2];
struct a *c = b, *d = b;
int e;

int g() {
  for (e = 0; e < 1; e++) {
    int i[1];
    i;
  }
  for (int h = 0; h < 3; h++)
    *c = *d;
  *c = *(b+3);
  return c->x;
}

void main() { 
    g(); 
}
$
$gcc-trunk -Os -fsanitize=address a.c && ./a.out
$
$gcc-trunk -O3 -fsanitize=address a.c && ./a.out
==12272==ERROR: AddressSanitizer: global-buffer-overflow on address
0x0000004042ac at pc 0x00000040132a bp 0x7ffdbc905820 sp 0x7ffdbc905818
READ of size 4 at 0x0000004042ac thread T0
    #0 0x401329 in g /local/home/shaoli/a.c:15
    #1 0x7fc367b2f082 in __libc_start_main
(/lib/x86_64-linux-gnu/libc.so.6+0x24082) (BuildId:
1878e6b475720c7c51969e69ab2d276fae6d1dee)
    #2 0x40111d in _start (/local/home/shaoli/a.out+0x40111d)

0x0000004042ac is located 4 bytes to the right of global variable 'b' defined
in 'a.c:4:10' (0x4042a0) of size 8
SUMMARY: AddressSanitizer: global-buffer-overflow /local/home/shaoli/a.c:15 in
g
Shadow bytes around the buggy address:
  0x000080078800: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x000080078810: 00 f9 f9 f9 f9 f9 f9 f9 00 f9 f9 f9 f9 f9 f9 f9
  0x000080078820: 00 00 00 00 00 00 00 00 f9 f9 f9 f9 f9 f9 f9 f9
  0x000080078830: f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9 f9
  0x000080078840: f9 f9 f9 f9 f9 f9 f9 f9 00 00 00 00 04 f9 f9 f9
=>0x000080078850: f9 f9 f9 f9 00[f9]f9 f9 f9 f9 f9 f9 00 00 00 00
  0x000080078860: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x000080078870: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x000080078880: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x000080078890: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0000800788a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==12272==ABORTING