On Thu, Oct 13, 2016 at 07:57:41PM +0200, Denys Vlasenko wrote: > On 10/13/2016 02:46 PM, Josh Poimboeuf wrote: > > On Tue, Oct 11, 2016 at 10:38:42PM +0200, Arnd Bergmann wrote: > > > 0000000000000000 <snic_log_q_error>: > > > 0: 55 push %rbp > > > 1: 48 89 e5 mov %rsp,%rbp > > > 4: 53 push %rbx > > > 5: 48 89 fb mov %rdi,%rbx > > > 8: 48 83 ec 08 sub $0x8,%rsp > > > c: e8 00 00 00 00 callq 11 <snic_log_q_error+0x11> > > > d: R_X86_64_PC32 __sanitizer_cov_trace_pc-0x4 > > > 11: 8b 03 mov (%rbx),%eax > > > 13: 85 c0 test %eax,%eax > > > 15: 75 11 jne 28 <snic_log_q_error+0x28> > > > 17: 48 83 c4 08 add $0x8,%rsp > > > 1b: 5b pop %rbx > > > 1c: 5d pop %rbp > > > 1d: e9 00 00 00 00 jmpq 22 <snic_log_q_error+0x22> > > > 1e: R_X86_64_PC32 __sanitizer_cov_trace_pc-0x4 > > > 22: 66 0f 1f 44 00 00 nopw 0x0(%rax,%rax,1) > > > 28: e8 00 00 00 00 callq 2d <snic_log_q_error+0x2d> > > > 29: R_X86_64_PC32 __sanitizer_cov_trace_pc-0x4 > > > 2d: 48 8b 7b 10 mov 0x10(%rbx),%rdi > > > 31: e8 00 00 00 00 callq 36 <snic_log_q_error+0x36> > > > 32: R_X86_64_PC32 ioread32-0x4 > > > 36: 89 05 00 00 00 00 mov %eax,0x0(%rip) # 3c > > > <snic_log_q_error+0x3c> > > > 38: R_X86_64_PC32 snic_log_q_error_err_status-0x4 > > > 3c: 83 3b 01 cmpl $0x1,(%rbx) > > > 3f: 76 d6 jbe 17 <snic_log_q_error+0x17> > > > 41: e8 00 00 00 00 callq 46 <snic_log_q_error+0x46> > > > 42: R_X86_64_PC32 __sanitizer_cov_trace_pc-0x4 > > > > I opened a bug: > > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77966 > > > > Surprisingly, it's really "not a bug". The only way you can end up in this > branch > is if you have a bug and run off the end of wq[1] array member: i.e. > if snic->wq_count >= 2. (See gcc BZ for smaller example) > > It's debatable whether it's okay for gcc to just let buggy code to run off > and execute something random. It is surely surprising, and not debug-friendly. > > An option to emit a crashing instruction (HLT, INT3, that sort of thing) > instead of just stopping code generation might be useful.
Ah, you're right. IMO it's still a gcc bug though. Instead of following a bad pointer, it would instead start executing some random function. That takes "undefined behavior" to a new level. -- Josh
