I have submitted:
https://bugs.llvm.org//show_bug.cgi?id=41050
for the clang 8 code generation problem of
no code for setting r2 appropriately before
the:
bl . . . <00000018.plt_call.__cxa_begin_catch@@CXXABI_1.3>
in unoptimized code ( no -O ). For the -O2 code:
ld r2,40(r1)
is present but is being skipped by the libunwind return
to the code: it returns to the just-following bl
instruction (like above) instead.
In both cases:
(gdb) x/32i 0x100007c0
0x100007c0 <00000018.plt_call.__cxa_begin_catch@@CXXABI_1.3>: std
r2,40(r1)
0x100007c4 <00000018.plt_call.__cxa_begin_catch@@CXXABI_1.3+4>: ld
r12,-32608(r2)
0x100007c8 <00000018.plt_call.__cxa_begin_catch@@CXXABI_1.3+8>: mtctr
r12
0x100007cc <00000018.plt_call.__cxa_begin_catch@@CXXABI_1.3+12>: ld
r11,-32592(r2)
0x100007d0 <00000018.plt_call.__cxa_begin_catch@@CXXABI_1.3+16>: ld
r2,-32600(r2)
0x100007d4 <00000018.plt_call.__cxa_begin_catch@@CXXABI_1.3+20>: bctr
0x100007d8 <00000018.plt_call.__cxa_begin_catch@@CXXABI_1.3+24>: .long
0x0
0x100007dc <00000018.plt_call.__cxa_begin_catch@@CXXABI_1.3+28>: .long
0x0
. . .
with an inappropriate r2 value leads to jumping to
inappropriate places.
The example source code was:
#include <exception>
int main(void)
{
try { throw std::exception(); }
catch (std::exception& e) {}
return 0;
}
Note:
This is from investigations of head -r345044 using
WITH_LLVM_LIBUNWIND= on powerpc64.
===
Mark Millard
marklmi at yahoo.com
( dsl-only.net went
away in early 2018-Mar)
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