On 2023-08-14 19:12, Qing Zhao wrote:
Hi, Sid,For the following testing case: #include <stdio.h> #define noinline __attribute__((__noinline__)) static void noinline alloc_buf_more (int index) { struct annotated { long foo; char b; char array[index]; long c; } q, *p; p = &q; printf("the__bdos of p->array whole max is %d \n", __builtin_dynamic_object_size(p->array, 0)); printf("the__bdos of p->array sub max is %d \n", __builtin_dynamic_object_size(p->array, 1)); printf("the__bdos of p->array whole min is %d \n", __builtin_dynamic_object_size(p->array, 2)); printf("the__bdos of p->array sub min is %d \n", __builtin_dynamic_object_size(p->array, 3)); return; } int main () { alloc_buf_more (10); return 0; } If I compile it with the latest upstream gcc and run it: /home/opc/Install/latest-d/bin/gcc -O t.c the__bdos of p->array whole max is 23 the__bdos of p->array sub max is 23 the__bdos of p->array whole min is 23 the__bdos of p->array sub min is 23 In which__builtin_dynamic_object_size(p->array, 0) and __builtin_dynamic_object_size(p->array, 1) return the same size, this seems wrong to me. There is one line in tree-object-size.cc might relate to this bug: (in the routine “addr_object_size”) 603 if (! TYPE_SIZE_UNIT (TREE_TYPE (var)) 604 || ! tree_fits_uhwi_p (TYPE_SIZE_UNIT (TREE_TYPE (var))) 605 || (pt_var_size && TREE_CODE (pt_var_size) == INTEGER_CST 606 && tree_int_cst_lt (pt_var_size, 607 TYPE_SIZE_UNIT (TREE_TYPE (var))))) 608 var = pt_var; I suspect that the above line 604 “ ! tree_fits_uhwi_p (TYPE_SIZE_UNIT (TREE_TYPE (var)))” relates to this bug, since the TYPESIZE of the VLA “array” is not a unsigned HOST_WIDE_INT, but we still can use its TYPESIZE for dynamic_object_size? What do you think?
Thanks, yes that doesn't work. I'm trying to revive the patch I had submitted earlier[1] in the year and fix this issue too in that process. In general the subobject size computation doesn't handle variable sizes at all; it depends on whole object+offset to get size information, which ends up working only for flex arrays at the end of objects.
Sid [1] https://gcc.gnu.org/pipermail/gcc-patches/2022-December/608914.html
