On 2015-01-12 09:26, Pavel Dovgaluk wrote: >> From: Jan Kiszka [mailto:jan.kis...@siemens.com] >> On 2014-10-22 13:38, Pavel Dovgalyuk wrote: >>> This patch fixes instructions counting when execution is stopped on >>> breakpoint (e.g. set from gdb). Without a patch extra instruction is >>> translated >>> and icount is incremented by invalid value (which equals to number of >>> executed instructions + 1). >>> >>> Signed-off-by: Pavel Dovgalyuk <pavel.dovga...@ispras.ru> >>> --- >>> target-i386/translate.c | 3 ++- >>> 1 files changed, 2 insertions(+), 1 deletions(-) >>> >>> diff --git a/target-i386/translate.c b/target-i386/translate.c >>> index 1284173..193cf9f 100644 >>> --- a/target-i386/translate.c >>> +++ b/target-i386/translate.c >>> @@ -8000,7 +8000,7 @@ static inline void >>> gen_intermediate_code_internal(X86CPU *cpu, >>> if (bp->pc == pc_ptr && >>> !((bp->flags & BP_CPU) && (tb->flags & HF_RF_MASK))) { >>> gen_debug(dc, pc_ptr - dc->cs_base); >>> - break; >>> + goto done_generating; >>> } >>> } >>> } >>> @@ -8049,6 +8049,7 @@ static inline void >>> gen_intermediate_code_internal(X86CPU *cpu, >>> break; >>> } >>> } >>> +done_generating: >>> if (tb->cflags & CF_LAST_IO) >>> gen_io_end(); >>> gen_tb_end(tb, num_insns); >>> >>> >>> >> >> Didn't looked into why, just bisected that this patch breaks at least >> certain guest-originated break- or watchpoints in TCG mode. Can be >> triggered by booting a Linux kernel with kgdb self-tests enabled. The >> result is some false reporting of a host-originated debug stop to >> gdb_set_stop_cpu while gdbserver_state is NULL -> SEGV. > > It seems that kernel sets some hardware breakpoints and QEMU tries to process > them with GDB stub. Modifying gdb_set_stop_cpu should help: > > diff --git a/gdbstub.c b/gdbstub.c > index e4a1a79..e8ef546 100644 > --- a/gdbstub.c > +++ b/gdbstub.c > @@ -1202,8 +1202,10 @@ static int gdb_handle_packet(GDBState *s, const char > *line_buf) > > void gdb_set_stop_cpu(CPUState *cpu) > { > - gdbserver_state->c_cpu = cpu; > - gdbserver_state->g_cpu = cpu; > + if (gdbserver_state) { > + gdbserver_state->c_cpu = cpu; > + gdbserver_state->g_cpu = cpu; > + } > } > > #ifndef CONFIG_USER_ONLY
I think this would only cure a symptom, but it doesn't explain why we now hit cpu_handle_guest_debug which we do not before the patch: (gdb) bt #0 gdb_set_stop_cpu (cpu=cpu@entry=0x55555663ac40) at /data/qemu/gdbstub.c:1193 #1 0x000055555562dfdf in cpu_handle_guest_debug (cpu=0x55555663ac40) at /data/qemu/cpus.c:636 #2 tcg_exec_all () at /data/qemu/cpus.c:1389 #3 qemu_tcg_cpu_thread_fn (arg=<optimized out>) at /data/qemu/cpus.c:1033 #4 0x00007ffff2c3d0a4 in start_thread () from /lib64/libpthread.so.0 #5 0x00007fffeea4a7fd in clone () from /lib64/libc.so.6 Jan -- Siemens AG, Corporate Technology, CT RTC ITP SES-DE Corporate Competence Center Embedded Linux