On Tue, Apr 20, 2021 at 12:20:06PM +0000, Lucier, Bradley J via Gcc wrote:
> I’m seeing an “Illegal Instruction” fault and don’t quite know how to
> generate a proper bug report yet.
>
> This is the compiler:
>
> [Bradleys-Mac-mini:~] lucier% /usr/local/gcc-10.3.0/bin/gcc -v
> Using built-in specs.
> COLLECT_GCC=/usr/local/gcc-10.3.0/bin/gcc
> COLLECT_LTO_WRAPPER=/usr/local/gcc-10.3.0/libexec/gcc/x86_64-apple-darwin19.6.0/10.3.0/lto-wrapper
> Target: x86_64-apple-darwin19.6.0
> Configured with: ../../gcc-10.3.0/configure --prefix=/usr/local/gcc-10.3.0
> --enable-languages=c --disable-multilib --enable-checking=release
> --with-sysroot=/Library/Developer/CommandLineTools/SDKs/MacOSX.sdk
> Thread model: posix
> Supported LTO compression algorithms: zlib
> gcc version 10.3.0 (GCC)
>
> This is the crash report from the console:
>
> Exception Type: EXC_BAD_INSTRUCTION (SIGILL)
> Exception Codes: 0x000000000000000c, 0x0000000000000000
> Exception Note: EXC_CORPSE_NOTIFY
>
> Termination Signal: Illegal instruction: 4
> Termination Reason: Namespace SIGNAL, Code 0x4
> Terminating Process: exc handler [98080]
>
> Application Specific Information:
> dyld2 mode
>
> Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
> 0 libgambit.dylib 0x000000010dfaf010
> ___SCMOBJ_to_NONNULLSTRING + 1520 (c_intf.c:3280)
>
> This is the disassembled code (arrow points to crash point):
>
> (lldb) di -s 0x0000000103d60000 -c 10
> libgambit.dylib`___SCMOBJ_to_NONNULLSTRING:
> 0x103d60000 <+1504>: jl 0x103d60026 ; <+1542> at
> c_intf.c:3282:9
> 0x103d60002 <+1506>: orb %al, 0x31(%rbp)
> 0x103d60005 <+1509>: shlb %cl, 0x2e(%rsi)
Does GCC ever generate this last instruction (a variable shift of a
byte in memory!)? Even the next to last (register to memory) is only
generated infrequently.
First thing to do would be to start the disassembly earlier, or even at
the beginning of the function, because I believe that the address you
gave is not an instruction boundary, and in this case the output of the
disassembler is nonsense until it resynchronizes on a real boundary.
Regards,
Gabriel
> 0x103d60008 <+1512>: nopl (%rax,%rax)
> -> 0x103d60010 <+1520>: movl (%rbp,%r10,4), %esi
> 0x103d60015 <+1525>: callq 0x103fba9a0 ; symbol stub for:
> ___UTF_8_put
> 0x103d6001a <+1530>: movq %r10, %rax
> 0x103d6001d <+1533>: addq $0x1, %r10
> 0x103d60021 <+1537>: cmpq %r12, %rax
> 0x103d60024 <+1540>: jne 0x103d60010 ; <+1520> at
> c_intf.c:3280:173
>
> I don’t know why that particular instruction is “Illegal”.
>
> Can someone suggest a way forward?
>
> Thanks.
>
> Brad
