Re: lib/59652: DNS utilities core dump in -current

["Nick Hudson via gnats" <gnats-admin%NetBSD.org@localhost>]

The following reply was made to PR lib/59652; it has been noted by GNATS.

From: Nick Hudson <nick.hudson%gmx.co.uk@localhost>
To: gnats-bugs%netbsd.org@localhost, lib-bug-people%netbsd.org@localhost, gnats-admin%netbsd.org@localhost,
 netbsd-bugs%netbsd.org@localhost
Cc: 
Subject: Re: lib/59652: DNS utilities core dump in -current
Date: Sun, 21 Sep 2025 08:26:06 +0100

 I've analysed this and it's a compiler/linker bug.
 
 A cut down program of
 
 $ cat urcu.c
 typedef struct __pthread_st *pthread_t;
 pthread_t __libc_thr_self(void);
 
 struct cds_list_head {
   struct cds_list_head *next, *prev;
 };
 
 struct urcu_reader {
   unsigned long ctr;
 
   struct cds_list_head node __attribute__((aligned(64)));
 
   unsigned int registered:1;
 };
 
 __thread struct urcu_reader urcu_mb_reader;
 
 int
 main(void)
 {
          int ret =3D urcu_mb_reader.registered;
 
          return ret;
 }
 $
 
 
 The compiler generates the following code
 
 00000000 <main>:
     0:   03 60 08 bc     mfctl tr3,ret0
     4:   2b 80 00 00     addil L%0,ret0,r1
                          4: R_PARISC_TPREL21L    urcu_mb_reader
     8:   34 3c 00 00     ldo 0(r1),ret0
                          8: R_PARISC_TPREL14R    urcu_mb_reader
     c:   37 9c 00 90     ldo 48(ret0),ret0
    10:   0f 80 10 9c     ldw 0(ret0),ret0
    14:   e8 40 c0 00     bv r0(rp)
    18:   d3 9c 18 1f     extrw,u ret0,0,1,ret0
 
 
 which the linker resolves to a load from 0x40 + 0x4c (0x8c) relative to=20
 the TLS area
 
 000107b4 <main>:
     107b4:       03 60 08 bc     mfctl tr3,ret0
     107b8:       2b 80 00 00     addil L%0,ret0,r1
     107bc:       34 3c 00 80     ldo 40(r1),ret0
     107c0:       37 9c 00 90     ldo 48(ret0),ret0
     107c4:       0f 80 10 9c     ldw 0(ret0),ret0
     107c8:       e8 40 c0 00     bv r0(rp)
     107cc:       d3 9c 18 1f     extrw,u ret0,0,1,ret0
 
 
 which is outside the 0x80 bytes allocated.
 $ readelf -S urcu  | grep tbss
    [14] .tbss             NOBITS          00011000 001000 000080 00 WAT=20
 0   0 64
 $