------- Comment #3 from matz at gcc dot gnu dot org 2006-09-21 13:40 -------
Hmpf. I wonder if there's any tool to really inspect the unwind info, like
it is possible for dwarf. But readelf doesn't help very much:
% readelf -wf a.out
<nothing, no wonder, it's no dwarf>
% readelf -u a.out
...
<_Z4doItv>: [0x4000000000000b00-0x4000000000003ce0], info at +0x87b0
v1, flags=0x0 (), len=40 bytes
R2:prologue_gr(mask=[psp],grsave=r119,rlen=49)
P5:frgr_mem(grmask=[r4,r5,r6,r7],frmask=[f2,f3,f4,f5,f16,f17,f18,f19,f20,f21,f22,f23,f24,f25,f26,f27,f28,f29,f30,f31])
P4:spill_mask(imask=[---,---,---,---,rr-,rr-,-f-,ff-,ff-,ff-,ff-,ff-,ff-,ff-,ff-,ff-,f])
P7:mem_stack_v(t=3)
P7:unat_when(t=7)
P7:unat_psprel(pspoff=0x10-0x180)
P7:pfs_when(t=9)
P7:pfs_psprel(pspoff=0x10-0x178)
P7:rp_when(t=18)
P7:rp_psprel(pspoff=0x10-0x148)
R3:body(rlen=2345)
R1:prologue(rlen=0)
R1:prologue(rlen=0)
<_Z4testv>: [0x4000000000003ce0-0x4000000000003db0], info at +0x87e0
v1, flags=0x3 ( ehandler uhandler), len=16 bytes
R2:prologue_gr(mask=[rp,ar.pfs,psp],grsave=r32,rlen=5)
P7:pfs_when(t=0)
P7:mem_stack_v(t=1)
P7:rp_when(t=4)
R3:body(rlen=34)
B2:epilogue(t=2,ecount=0)
R1:prologue(rlen=0)
R1:prologue(rlen=0)
R1:prologue(rlen=0)
I traced the things in libunwind a bit, and know that the one writing the
wrong location of R4-7 into context->loc is the IA64_INSN_ADD_PSP_NAT
unwind script instruction, interpreted in _ULia64_find_save_locs (in
run_script actually). And it happens while context still is set to the
doIt() function. But I have no idea, how that script is generated,
or how it relates to the assembler file. For instance, the start of doIt()
has this code:
.save.g 0x1
.mem.offset 344, 0 //
st8.spill [r18] = r4, 16 //,
;;
.save.g 0x2
.mem.offset 336, 0 //
st8.spill [r17] = r5, 16 //,
.save.g 0x4
.mem.offset 328, 0 //
st8.spill [r18] = r6, 16 //,
;;
.save.g 0x8
.mem.offset 320, 0 //
st8.spill [r17] = r7, 16 //,
I assume (because there are no explicit unwind sections in the assembler
source) that these .save.g and .mem.offset somehow are pseudo instructions
which somehow produce unwind info. But I'm at a loss here.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29166
