Hi all,
I have a bit of a strange one. I'm not after a full solution, just any
hints that quickly come to mind :)
After a few simple patches I have a build of mongodb for aarch64 (built
with gcc-4.8). However, all of the test binaries that the build spits
out immediately segfault. gdb-ing shows that they segfault inside this
macro:
TSP_DECLARE(OwnedOstreamVector, threadOstreamCache);
This expands to:
# define TSP_DECLARE(T,p) \
extern __thread T* _ ## p; \
template<> inline T* TSP<T>::get() const { return _ ## p; } \
extern TSP<T> p;
And indeed, it's mongo::TSP<mongo::OwnedPointerVector<...> >::get()
const that we're segfaulting in. This is the disassembly of this
function (at -O0) with the faulting instruction marked:
0x00000000004b4b6c <+0>: stp x29, x30, [sp,#-32]!
0x00000000004b4b70 <+4>: mov x29, sp
0x00000000004b4b74 <+8>: str x0, [x29,#16]
0x00000000004b4b78 <+12>: adrp x0, 0x64c000
0x00000000004b4b7c <+16>: ldr x0, [x0,#776]
0x00000000004b4b80 <+20>: nop
0x00000000004b4b84 <+24>: nop
0x00000000004b4b88 <+28>: mrs x1, tpidr_el0
0x00000000004b4b8c <+32>: add x0, x1, x0
=> 0x00000000004b4b90 <+36>: ldr x0, [x0]
0x00000000004b4b94 <+40>: ldp x29, x30, [sp],#32
0x00000000004b4b98 <+44>: ret
And the registers:
(gdb) info registers
x0 0x7fb863fd70 548554407280
x1 0x7fb7ff76f0 548547819248
x2 0x0 0
x3 0x7fb7fc11b8 548547596728
x4 0x1 1
x5 0x0 0
x6 0x50 80
x7 0x0 0
x8 0x0 0
x9 0x6165727473676f4c 7018141438804717388
x10 0x0 0
x11 0x0 0
x12 0x2 2
x13 0x10 16
x14 0x0 0
x15 0x7fb7e5e590 548546143632
x16 0x64b3d8 6599640
x17 0x7fb7f667d0 548547225552
x18 0x7fffffdab0 549755804336
x19 0x7fffffed50 549755809104
x20 0xb 11
x21 0xb 11
x22 0x6500b0 6619312
x23 0x650070 6619248
x24 0x7fffffff 2147483647
x25 0x64db40 6609728
x26 0x7fffffeda0 549755809184
x27 0x653d00 6634752
x28 0x7fffffe750 549755807568
x29 0x7fffffe4d0 549755806928
x30 0x4b4ed4 4935380
sp 0x7fffffe4d0 0x7fffffe4d0
pc 0x4b4b90 0x4b4b90
<mongo::TSP<mongo::OwnedPointerVector<std::basic_ostringstream<char,
std::char_traits<char>, std::allocator<char> > > >::get() const+36>
cpsr 0x20000000 536870912
fpsr 0x0 0
fpcr 0x0 0
If I recompile this object file without -fPIC, it works.
I guess I see three things that could be wrong:
1) The operand to "adrp x0, 0x64c000"[1]
2) The operand to "ldr x0, [x0,#776]"
3) The value of tpidr_el0
Oh, and I guess:
4) The setup of tls has gone wrong and the address in x0 _ought_ to be
accessible but isn't for some reason.
Any hints on which of these seems mostly likely to be the culprit?
Chers,
mwh
[1] FWIW, objdump reports 0x64c000 as "_GLOBAL_OFFSET_TABLE_+0x2d0", not
sure why that doesn't show up in gdb's disassembly).
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