[Bug 232387] head -r345558 (updated): system crash during kldload if_epair on powerpc64 (for more modern buildworld buildkernel toolchain experiments)

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=232387

--- Comment #16 from Mark Millard <marklmi26-fbsd at yahoo.com> ---
(In reply to Mark Millard from comment #15)

I added printing &DPCPU_NAME(epair_dpcpu) to:

static void
epair_dpcpu_init(void)

This and ddb use gives the following information for the
use of:

#define _DPCPU_PTR(b, n)                                                \
    (__typeof(DPCPU_NAME(n))*)((b) + (uintptr_t)&DPCPU_NAME(n))
. . .
#define DPCPU_ID_PTR(i, n)      _DPCPU_PTR(dpcpu_off[(i)], n)

(Typed from a picture:)

&DPCPU_NAME(epair_dpcpu)=0xe00000008fcee810

show dpcpu_off in ddb shows:

dpcpu_off[0]=0x1ffffffffecf6980
dpcpu_off[1]=0x2000000002adc980
dpcpu_off[2]=0x2000000002ada980
dpcpu_off[3]=0x2000000002ad8980

The failing virtual address was reported as:

virtual address = 0x8e9e5198
. . .
cpuid = 0

Then, checking:

0x1ffffffffecf6980+0xe00000008fcee810==0x8e9e5190

so 0x8 short. But:

<epair_modevent+0xd0> addi    r3,r22,24
<epair_modevent+0xd4> bl      <0000001b.plt_call._mtx_init>

and:

<_mtx_init+0x20> mr      r30,r3
. . .
<_mtx_init+0x60> addi    r3,r30,-24
<_mtx_init+0x64> clrldi  r7,r6,32
<_mtx_init+0x68> mr      r6,r8
<_mtx_init+0x6c> bl      <lock_init+0x8>

and:

<lock_init+0x140> stw     r4,8(r3)

So 0x8e9e5190+24-24+8==0x8e9e5198 (the failure address).


It appears to me that the dpcpu_off[i] figures
are expected to convert 0xc???_????_????_???? type
(direct-map) addresses to 0xe???_????_????_????
addresses but &DPCPU_NAME(epair_dpcpu) already was
a 0xe???_????_????_???? type of address. The result
overflowed/wrapped/truncated and was invalid.

This looks likely to be a problem for any kldload'd
.ko that uses a DPCPU_DEFINE and DPCPU_ID_PTR
similarly to (showing my printf addition as well):

struct epair_dpcpu {
        struct mtx      if_epair_mtx;           /* Per-CPU locking. */
        int             epair_drv_flags;        /* Per-CPU ``hw'' drv flags. */
        struct eid_list epair_ifp_drain_list;   /* Per-CPU list of ifps with
                                                 * data in the ifq. */
};
DPCPU_DEFINE(struct epair_dpcpu, epair_dpcpu);

static void
epair_dpcpu_init(void)
{
        struct epair_dpcpu *epair_dpcpu;
        struct eid_list *s;
        u_int cpuid;

printf("epair_dpcpu_init: &DPCPU_NAME(epair_dpcpu)=%p\n",
&DPCPU_NAME(epair_dpcpu));

        CPU_FOREACH(cpuid) {
                epair_dpcpu = DPCPU_ID_PTR(cpuid, epair_dpcpu);

                /* Initialize per-cpu lock. */
                EPAIR_LOCK_INIT(epair_dpcpu);
. . .

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