https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71951
--- Comment #12 from Icenowy Zheng <icenowy at aosc dot io> --- (In reply to Wilco from comment #11) > (In reply to Icenowy Zheng from comment #10) > > In my environment (glibc 2.25, and both the building scripts of glibc and > > gcc have -fomit-frame-pointer automatically enabled), this bug is not fully > > resolved yet. > > > > With GCC upgraded to 6.4.0, GDB debugger started to work correctly. (With > > GCC 6.3.0 GDB cannot even work and segfault at unwind code in libgcc). > > > > However, if I still build GCC with -fomit-frame-pointer in CFLAGS, the > > backtrace() function of glibc cannot work, and segfault at line 240 of > > libgcc/unwind-dw2.c . > > > > By reading the source code, I think the unwind code is still trying to get > > CFA from the register x29, and when debugging I found that the x29 register > > in the unwind context is 0 (because of -fomit-frame-pointer), so line 240 is > > dereferencing a NULL pointer, so it segfaulted. > > > > Maybe the behavior that accessing x29 register to get CFA is not correct? > > Well if everything built with -fomit-frame-pointer then it is definitely > wrong to read x29. Can you give more info similar to comment #3? I didn't remember a lot as this issue is already fixed in our build system by removing -fomit-frame-pointer. But I remember part of the stacktrace: _Unwind_GetGR(index=29) at libgcc/unwind-dw2.c:240 <= segfault here _Unwind_GetPtr(index=29) at libgcc/unwind-dw2.c:251 uw_update_context_1() at libgcc/unwind-dw2.c:1410 _Unwind_Backtrace() at libgcc/unwind.inc (line number forgot) backtrace() in libc.so.6
