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

[Nick Hudson <nick.hudson%gmx.co.uk@localhost>]

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 = 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 
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 
0   0 64
$