[llvm-dev] Inexplicable ASAN report. Code generation bug?

[Greg Stark via llvm-dev]

On Thu, Nov 12, 2015 at 8:42 PM, Kostya Serebryany <kcc at google.com> wrote:
> 2 questions:
> - Do you see this with the fresh llvm trunk?
> - Can you prepare a minimized example?

Pretty recent, I updated a couple days ago. I tried to minimize the
attached but at the same time I didn't want to lose too many unions
and casts in case it didn't trigger any more.

$ clang -fsanitize=address  -Wall numeric-asan-test.c
$ ./a.out
VARSIZE 6
NDIGITS 0
WEIGHT 0
SIGN 0
DSCALE 0
$ clang -fsanitize=address -O2  -Wall numeric-asan-test.c
$ ./a.out
VARSIZE 6
=================================================================
==19982==ERROR: AddressSanitizer: heap-buffer-overflow on address
0x60200000eff4 at pc 0x0000004d4986 bp 0x7ffe14e2cb90 sp
0x7ffe14e2cb88
READ of size 4 at 0x60200000eff4 thread T0
    #0 0x4d4985 in main (/home/stark/src/a.out+0x4d4985)
    #1 0x7f6360f40b44 in __libc_start_main
/tmp/buildd/glibc-2.19/csu/libc-start.c:287
    #2 0x41a935 in _start (/home/stark/src/a.out+0x41a935)

0x60200000eff6 is located 0 bytes to the right of 6-byte region
[0x60200000eff0,0x60200000eff6)
allocated by thread T0 here:
    #0 0x4abceb in __interceptor_malloc
/home/stark/src/llvm/projects/compiler-rt/lib/asan/asan_malloc_linux.cc:40:3
    #1 0x4d479e in main (/home/stark/src/a.out+0x4d479e)

SUMMARY: AddressSanitizer: heap-buffer-overflow
(/home/stark/src/a.out+0x4d4985) in main
Shadow bytes around the buggy address:
  0x0c047fff9da0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9db0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9dc0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9dd0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9de0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
=>0x0c047fff9df0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa[06]fa
  0x0c047fff9e00: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9e10: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9e20: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9e30: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9e40: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
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
  Heap right redzone:      fb
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack partial redzone:   f4
  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
==19982==ABORTING



-- 
greg
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