According to http://wiki.dwarfstd.org/index.php?title=Exception_Handling#Relationship_with_DWARF current GCC behavior for aarch64 simply violates DWARF standard that in turn doesn't define EH. p.s. I've also found a note that .eh_frame uses different numbering of registers than .debug_frame on PPC target (https://www.sourceware.org/ml/binutils/2009-10/msg00028.html) Alex On Fri, Oct 5, 2018 at 4:09 PM Alexander Fedotov <alfedotov@xxxxxxxxx> wrote: > > >>So I presume this is done to avoid wasting space with duplicate information. > Well yes, I had the same thought too. But seems like it is makes no > sense because you can disable/strip debug sections. > > But the major problem that I've seen is that non-GDB debugger expects > CFI in debug_frame section but not eh_frame. And their point is pretty > strong - eh_frame is just for EH, not for debugging. purposes. > GDB is smart enough to use this info from eh_frame but it is not > specified for architecture in documents (or I was unable to find it). > > > Alex > On Fri, Oct 5, 2018 at 3:33 PM Richard Earnshaw (lists) > <Richard.Earnshaw@xxxxxxx> wrote: > > > > On 05/10/18 13:27, Kyrill Tkachov wrote: > > > Hi Alex, > > > > > > I'm forwarding this to the gcc-help list which is the appropriate place > > > for this discussion. > > > gcc-bugs is for automated emails from the bug tracker and your mail is > > > likely to get lost in there. > > > > > > Thanks, > > > Kyrill > > > > > > On 05/10/18 13:24, Alexander Fedotov wrote: > > >> Hello > > >> > > >> I've noticed that for C++ translation unit GCC for aarch64 always > > >> emits CFI into eh_frame but never debug_frame even if debug > > >> information is enabled. Tried on GCC versions 6 to 8. > > >> DWARF for the ARM 64-bit architecture (AArch64) states that it must be > > >> debug_frame > > >> ((https://static.docs.arm.com/ihi0057/b/IHI0057B_aadwarf64.pdf) > > >> GAS supports emitting CFI to both sections by directive: .cfi_sections > > >> .debug_frame,.eh_frame > > >> > > >> At the same time gcc for arm emits CFI in both debug_frame and .ARM.exidx > > >> > > >> I'm aware about CFI for Exception Handling. But what the reason to not > > >> emit both ? > > >> Is there any implicit reason for that or it's just a bug ? > > > > On Arm, the .ARM.exidx data is insufficient for debugging, so we > > certainly need the additional information in the dwarf unwinding tables. > > On AArch64 that's not true, the information is complete enough for a > > debugger to use. So I presume this is done to avoid wasting space with > > duplicate information. > > > > What do other targets that use dwarf exception unwinding do? > > > > R. > > > > >> > > >> Steps to reproduce: > > >> > > >> cat > test.cpp <<EOF > > >> int foo() { > > >> return 0; > > >> } > > >> EOF > > >> > > >> ./aarch64-none-elf-gcc -c -g test.cpp -o test_cpp.o && > > >> ./aarch64-none-elf-objdump -g test_cpp.o | grep -B 3 "CIE" | grep > > >> "_frame" > > >> Contents of the .eh_frame section: > > >> > > >> While for C code it does: > > >> cat > test.c <<EOF > > >> int foo() { > > >> return 0; > > >> } > > >> EOF > > >> > > >> ./aarch64-none-elf-gcc -c -g test.c -o test_c.o && > > >> ./aarch64-none-elf-objdump -g test_c.o | grep -B 3 "CIE" | grep > > >> "_frame" > > >> Contents of the .debug_frame section: > > >> > > >> > > >> Alex > > > > > > > > -- > Best regards, > AF -- Best regards, AF
