https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115965
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |INVALID
Status|UNCONFIRMED |RESOLVED
--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Nathan Teodosio from comment #5)
> In none of them. Or am I overlooking a buffer overrun here?
You definitely are overlooking one.
for (size_t i = 0; i < size; i += hn::Lanes(d)) {
hn::Store(x, d, x_array + i);
hn::Lanes(d) is 4.
so you are storing 0,1,2,3 and then 4,5,6,7 . Except there are only 5 elements
of x_array so 5,6,7 stores is broken.
>In any case I fail to see why that would be dependent on which of the array
>definitions in main come first.
Because -fstack-protector-all only checks one place in the stack rather than
after each array. So the order of the arrays on the stack for a tie breaker is
the order of how the user order was. So it just happens to be at the end you
get the stack smasher error.
With -fsanitize=address all arrays have a redzone and you get the following
eror message and that is indepdent of the order of arrays since all load/stores
are checked.
=================================================================
==1==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x782bede00030
at pc 0x000000401b3e bp 0x7ffeb05deab0 sp 0x7ffeb05deaa8
READ of size 16 at 0x782bede00030 thread T0
#0 0x401b3d in _mm_load_si128(long long __vector(2) const*)
/opt/compiler-explorer/gcc-trunk-20240717/lib/gcc/x86_64-linux-gnu/15.0.0/include/emmintrin.h:701
#1 0x401b3d in Load<hwy::N_SSE2::Simd<int, 4, 0> >
/opt/compiler-explorer/libs/highway/trunk/hwy/ops/x86_128-inl.h:2069
#2 0x401311 in MulAddLoop(int const*, int const*, unsigned long, int*)
/app/example.cpp:11
#3 0x401954 in main /app/example.cpp:22
#4 0x782befa29d8f (/lib/x86_64-linux-gnu/libc.so.6+0x29d8f) (BuildId:
490fef8403240c91833978d494d39e537409b92e)
#5 0x782befa29e3f in __libc_start_main
(/lib/x86_64-linux-gnu/libc.so.6+0x29e3f) (BuildId:
490fef8403240c91833978d494d39e537409b92e)
#6 0x401104 in _start (/app/output.s+0x401104) (BuildId:
4af5893bdf93a048dba77151f2e0b5e5a0ee46bd)
Address 0x782bede00030 is located in stack of thread T0 at offset 48 in frame
#0 0x4014cf in main /app/example.cpp:18
This frame has 3 object(s):
[32, 52) 'a' (line 19) <== Memory access at offset 48 partially overflows
this variable
[96, 116) 'b' (line 19)
[160, 180) 'c' (line 20)
HINT: this may be a false positive if your program uses some custom stack
unwind mechanism, swapcontext or vfork
(longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-buffer-overflow
/opt/compiler-explorer/gcc-trunk-20240717/lib/gcc/x86_64-linux-gnu/15.0.0/include/emmintrin.h:701
in _mm_load_si128(long long __vector(2) const*)
Shadow bytes around the buggy address:
0x782beddffd80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x782beddffe00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x782beddffe80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x782beddfff00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x782beddfff80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x782bede00000: f1 f1 f1 f1 00 00[04]f2 f2 f2 f2 f2 00 00 04 f2
0x782bede00080: f2 f2 f2 f2 00 00 04 f3 f3 f3 f3 f3 00 00 00 00
0x782bede00100: f1 f1 f1 f1 f1 f1 01 f2 00 00 f2 f2 f8 f8 f2 f2
0x782bede00180: f8 f8 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00
0x782bede00200: f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5 f5
0x782bede00280: f5 f5 f5 f5 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
==1==ABORTING
