Date: Tue, 7 Mar 2023 02:26:00 -0800 From: Mark Millard <marklmi@yahoo.com> To: Lorenzo Salvadore <developer@lorenzosalvadore.it>, Brooks Davis <brooks@FreeBSD.org> Cc: "salvadore@freebsd.org" <salvadore@FreeBSD.org>, FreeBSD Mailing List <freebsd-ports@freebsd.org> Subject: Re: armv7 lang/gcc12 "no bootstrap" build via system clang 15.0.7 based poudriere build ends up stuck in a small loop Message-ID: <B703089D-0EA6-49D4-96F9-69C09B0FF23C@yahoo.com> In-Reply-To: <EB917CA9-CC67-4F79-8EBD-6BE82B021D45@yahoo.com> References: <F536BC00-49D3-41F8-A328-EA10FD21E1DC.ref@yahoo.com> <F536BC00-49D3-41F8-A328-EA10FD21E1DC@yahoo.com> <2HOLCFE6Z_cOyGycU4ZBU7Lf6kcqohVx7tiLiRLzdjMEc6a8DFeH1IaJqdPNJOqFVTh1MGE7_UUJLcg2gg0UbTZIHZl72NbaNEsqrJwJ3xA=@lorenzosalvadore.it> <93707ED2-F529-49DE-A018-794827F56247@yahoo.com> <7AA0AE73-87CC-4B26-92B2-A0EC4281F429@yahoo.com> <480C8278-DC30-40D6-AED2-F52F59E78EBC@yahoo.com> <EB917CA9-CC67-4F79-8EBD-6BE82B021D45@yahoo.com>
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Below is a small example C source showing the clang 15+ armv7
problem that leads to the unbounded looping in later code in
the lang/gcc12+ builds: a data structure is mis-initialized,
breaking its invariant properties used by the later code
structure.
# more partition.c
// Minor varation of part of some gcc source code!
// For system-clang 15: cc -g -O2 partition.c ; ./a.out
// For devel/llvm16: clang16 -g -O2 partition.c ; ./a.out
#include <stdio.h>
#define NUM_ELEMENTS 32
struct partition_elem
{
struct partition_elem* next;
int class_element;
unsigned class_count;
};
typedef struct partition_def
{
int num_elements;
struct partition_elem elements[NUM_ELEMENTS];
} *partition;
struct partition_def partition_storage;
partition
partition_new (int num_elements)
{
int e;
if (NUM_ELEMENTS < num_elements) num_elements =3D NUM_ELEMENTS;
partition part=3D &partition_storage;
part->num_elements =3D num_elements;
for (e =3D 0; e < num_elements; ++e)
{
part->elements[e].class_element =3D e;
part->elements[e].next =3D &(part->elements[e]);
part->elements[e].class_count =3D 1;
}
for (e =3D 0; e < num_elements; ++e)
printf("%d: %p : next?: =
%p\n",e,(void*)&part->elements[e],(void*)part->elements[e].next);
return part;
}
int main(void)
{
partition part;
part=3D partition_new(NUM_ELEMENTS);
return !part;
}
In the output below, note the blocks of 4 "next"
values that do not change. Each should match the
earlier hexadecimal value on the same line: point
back to same element of the array. 3 of 4 do not.
# cc -g -O2 partition.c
# ./a.out
0: 0x40a84 : next?: 0x40a84
1: 0x40a90 : next?: 0x40a84
2: 0x40a9c : next?: 0x40a84
3: 0x40aa8 : next?: 0x40a84
4: 0x40ab4 : next?: 0x40ab4
5: 0x40ac0 : next?: 0x40ab4
6: 0x40acc : next?: 0x40ab4
7: 0x40ad8 : next?: 0x40ab4
8: 0x40ae4 : next?: 0x40ae4
9: 0x40af0 : next?: 0x40ae4
10: 0x40afc : next?: 0x40ae4
11: 0x40b08 : next?: 0x40ae4
12: 0x40b14 : next?: 0x40b14
13: 0x40b20 : next?: 0x40b14
14: 0x40b2c : next?: 0x40b14
15: 0x40b38 : next?: 0x40b14
16: 0x40b44 : next?: 0x40b44
17: 0x40b50 : next?: 0x40b44
18: 0x40b5c : next?: 0x40b44
19: 0x40b68 : next?: 0x40b44
20: 0x40b74 : next?: 0x40b74
21: 0x40b80 : next?: 0x40b74
22: 0x40b8c : next?: 0x40b74
23: 0x40b98 : next?: 0x40b74
24: 0x40ba4 : next?: 0x40ba4
25: 0x40bb0 : next?: 0x40ba4
26: 0x40bbc : next?: 0x40ba4
27: 0x40bc8 : next?: 0x40ba4
28: 0x40bd4 : next?: 0x40bd4
29: 0x40be0 : next?: 0x40bd4
30: 0x40bec : next?: 0x40bd4
31: 0x40bf8 : next?: 0x40bd4
Turns out that the -O2 is important: no other that I
tried got the problem, including -O3 not getting the
problem. lang/gcc12+ builds happen to use -O2 , at
least in my environment.
-g is not required for the problem.
=3D=3D=3D
Mark Millard
marklmi at yahoo.com
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