I'm trying to debug a program on a BeagleBone Black. Outside the debugger it produces an incorrect result but no SIGILL. It also runs OK under the debugger without a breakpoint. However it produces a SIGILL with a breakpoint set when stepping. The program and library does not use SIGILL-based cpu feature probes. However, I don't know what GDB is doing.
Under the debugger I am seeing:
(gdb) b main
Breakpoint 1 at 0x26f20: file test.cxx, line 22.
(gdb) r
Starting program: /home/cryptopp/test.exe
Breakpoint 1, main (argc=0x1, argv=0xbeffea54) at test.cxx:22
22 byte key[16] = {0};
(gdb) n
23 byte iv[12] = {0};
(gdb)
25 GCM<AES>::Encryption enc;
(gdb)
26 enc.SetKeyWithIV(key, 16, iv, 12);
(gdb)
28 std::string plain(0x00, 16);
(gdb)
Program received signal SIGILL, Illegal instruction.
0x00026d5c in std::basic_ostream<char, std::char_traits<char> >& std::endl<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&)
()
(gdb) n
Single stepping until exit from function _ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_,
which has no line number information.
Program terminated with signal SIGILL, Illegal instruction.
The program no longer exists.
And:
(gdb) shell echo _ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_ | c++filt
std::basic_ostream<char, std::char_traits<char> >& std::endl<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&)
I tried searching for this issue, but I have not been able to locate a hit. I'm getting too much noise.
Why am I experiencing a SIGILL when GDB sets a breakpoint, and how do I work around it?
NEON is the problem I am trying to investigate. Here's the command line used for the program and library:
$ echo $CXXFLAGS
-DDEBUG -g3 -O0 -march=armv7-a -mtune=cortex-a8 -mfpu=neon -mfloat-abi=hard
$ g++ $CXXFLAGS test.cxx ./libcryptopp.a -o test.exe
And:
$ gdb --version
GNU gdb (Debian 7.7.1+dfsg-5) 7.7.1
$ uname -a
Linux beaglebone 4.1.15-ti-rt-r40 #1 SMP PREEMPT RT Thu Jan 7 23:32:08 UTC 2016 armv7l GNU/Linux
$ cat /proc/cpuinfo
processor : 0
model name : ARMv7 Processor rev 2 (v7l)
BogoMIPS : 996.14
Features : half thumb fastmult vfp edsp thumbee neon vfpv3 tls vfpd32
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x3
CPU part : 0xc08
CPU revision : 2
Hardware : Generic AM33XX (Flattened Device Tree)
Revision : 0000
Serial : 0000000000000000
And:
Breakpoint 1, main (argc=0x1, argv=0xbeffea54) at test.cxx:22
22 byte key[16] = {0};
(gdb) n
23 byte iv[12] = {0};
(gdb)
25 GCM<AES>::Encryption enc;
(gdb)
26 enc.SetKeyWithIV(key, 16, iv, 12);
(gdb)
28 std::string plain(0x00, 16);
(gdb)
Program received signal SIGILL, Illegal instruction.
0x00026d5c in std::basic_ostream<char, std::char_traits<char> >& std::endl<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&)
()
(gdb) up
#1 0x00026f82 in main (argc=0x1, argv=0xbeffea54) at test.cxx:28
28 std::string plain(0x00, 16);
(gdb) disass
Dump of assembler code for function main(int, char**):
0x00026f10 <+0>: push {r4, r7, lr}
0x00026f12 <+2>: sub.w sp, sp, #916 ; 0x394
0x00026f16 <+6>: add r7, sp, #16
0x00026f18 <+8>: adds r3, r7, #4
0x00026f1a <+10>: str r0, [r3, #0]
0x00026f1c <+12>: mov r3, r7
0x00026f1e <+14>: str r1, [r3, #0]
0x00026f20 <+16>: add.w r3, r7, #692 ; 0x2b4
0x00026f24 <+20>: movs r2, #0
0x00026f26 <+22>: str r2, [r3, #0]
0x00026f28 <+24>: adds r3, #4
0x00026f2a <+26>: movs r2, #0
0x00026f2c <+28>: str r2, [r3, #0]
0x00026f2e <+30>: adds r3, #4
0x00026f30 <+32>: movs r2, #0
0x00026f32 <+34>: str r2, [r3, #0]
0x00026f34 <+36>: adds r3, #4
0x00026f36 <+38>: movs r2, #0
0x00026f38 <+40>: str r2, [r3, #0]
0x00026f3a <+42>: adds r3, #4
0x00026f3c <+44>: add.w r3, r7, #680 ; 0x2a8
0x00026f40 <+48>: movs r2, #0
---Type <return> to continue, or q <return> to quit---
0x00026f42 <+50>: str r2, [r3, #0]
0x00026f44 <+52>: adds r3, #4
0x00026f46 <+54>: movs r2, #0
0x00026f48 <+56>: str r2, [r3, #0]
0x00026f4a <+58>: adds r3, #4
0x00026f4c <+60>: movs r2, #0
0x00026f4e <+62>: str r2, [r3, #0]
0x00026f50 <+64>: adds r3, #4
0x00026f52 <+66>: add.w r3, r7, #240 ; 0xf0
0x00026f56 <+70>: mov r0, r3
0x00026f58 <+72>: bl 0x2a804 <CryptoPP::GCM_Final<CryptoPP::Rijndael, (CryptoPP::GCM_TablesOption)0, true>::GCM_Final()>
0x00026f5c <+76>: add.w r1, r7, #240 ; 0xf0
0x00026f60 <+80>: add.w r2, r7, #692 ; 0x2b4
0x00026f64 <+84>: add.w r4, r7, #680 ; 0x2a8
0x00026f68 <+88>: movs r3, #12
0x00026f6a <+90>: str r3, [sp, #0]
0x00026f6c <+92>: mov r0, r1
0x00026f6e <+94>: mov r1, r2
0x00026f70 <+96>: movs r2, #16
0x00026f72 <+98>: mov r3, r4
0x00026f74 <+100>: bl 0x2da0c <CryptoPP::SimpleKeyingInterface::SetKeyWithIV(unsigned char const*, unsigned int, unsigned char const*, unsigned int)>
---Type <return> to continue, or q <return> to quit---
0x00026f78 <+104>: add.w r3, r7, #708 ; 0x2c4
0x00026f7c <+108>: mov r0, r3
0x00026f7e <+110>: blx 0x26d58 <_ZSt4endlIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_+852>
=> 0x00026f82 <+114>: add.w r2, r7, #676 ; 0x2a4
0x00026f86 <+118>: add.w r3, r7, #708 ; 0x2c4
0x00026f8a <+122>: mov r0, r2
0x00026f8c <+124>: movs r1, #0
0x00026f8e <+126>: movs r2, #16
...
