On Thu, Feb 13, 2014 at 5:52 PM, Renato Golin <renato.golin at linaro.org> wrote:> On 13 February 2014 13:47, Evgeniy Stepanov <eugenis at google.com> wrote: >> Hm, I see that -funwind-tables on arm-linux-androideabi target >> replaces this "cantunwind" with a proper unwind table. >> Hence http://llvm-reviews.chandlerc.com/D2762. > > If Android is using EHABI (I think it is), the default now is to > output full tables all the time, everywhere. This will change to be > the same as x86 soon.It does use EHABI, but at r201326: $ cat 1.cc int f() {} $ ./bin/clang++ -target arm-linux-androideabi 1.cc -c $ readelf -u 1.o 0x0 <_Z1fv>: 0x1 [cantunwind] $ ./bin/clang++ -target arm-linux-androideabi 1.cc -c -funwind-tables $ readelf -u 1.o 0x0 <_Z1fv>: 0x8000b0b0 Compact model 0 0x00 vsp = vsp + 4 0xb0 finish 0xb0 finish
Hi Evgeniy, I have run in to the some unwind handling table issue recently. After some investigation, I believe that the correct behavior is to generate [cantunwind] with and without the -funwind-tables. Thus, I am afraid that -funwind-tables might not be a good solution for your use case. (i.e. your program might fall in an infinite loop during stack unwinding.) I will send the details for discussion ASAP. Sincerely, Logan On Thu, Feb 13, 2014 at 10:03 PM, Evgeniy Stepanov <eugenis at google.com>wrote:> On Thu, Feb 13, 2014 at 5:52 PM, Renato Golin <renato.golin at linaro.org> > wrote: > > On 13 February 2014 13:47, Evgeniy Stepanov <eugenis at google.com> wrote: > >> Hm, I see that -funwind-tables on arm-linux-androideabi target > >> replaces this "cantunwind" with a proper unwind table. > >> Hence http://llvm-reviews.chandlerc.com/D2762. > > > > If Android is using EHABI (I think it is), the default now is to > > output full tables all the time, everywhere. This will change to be > > the same as x86 soon. > > It does use EHABI, but at r201326: > $ cat 1.cc > int f() {} > $ ./bin/clang++ -target arm-linux-androideabi 1.cc -c > $ readelf -u 1.o > 0x0 <_Z1fv>: 0x1 [cantunwind] > $ ./bin/clang++ -target arm-linux-androideabi 1.cc -c -funwind-tables > $ readelf -u 1.o > 0x0 <_Z1fv>: 0x8000b0b0 > Compact model 0 > 0x00 vsp = vsp + 4 > 0xb0 finish > 0xb0 finish > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev >-------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20140215/3f9170f4/attachment.html>
I'd love to hear more details. Are you saying that this infinite loop is a limitation of EHABI table format, and not something that can be fixed in the compiler? Meanwhile, please notice that gcc behavior matches current clang behavior that I described above. We would not want to create an incompatibility. On Fri, Feb 14, 2014 at 8:42 PM, Logan Chien <tzuhsiang.chien at gmail.com> wrote:> Hi Evgeniy, > > I have run in to the some unwind handling table issue recently. After some > investigation, I believe that the correct behavior is to generate > [cantunwind] with and without the -funwind-tables. Thus, I am afraid that > -funwind-tables might not be a good solution for your use case. (i.e. your > program might fall in an infinite loop during stack unwinding.) > > I will send the details for discussion ASAP. > > Sincerely, > Logan > > > On Thu, Feb 13, 2014 at 10:03 PM, Evgeniy Stepanov <eugenis at google.com> > wrote: >> >> On Thu, Feb 13, 2014 at 5:52 PM, Renato Golin <renato.golin at linaro.org> >> wrote: >> > On 13 February 2014 13:47, Evgeniy Stepanov <eugenis at google.com> wrote: >> >> Hm, I see that -funwind-tables on arm-linux-androideabi target >> >> replaces this "cantunwind" with a proper unwind table. >> >> Hence http://llvm-reviews.chandlerc.com/D2762. >> > >> > If Android is using EHABI (I think it is), the default now is to >> > output full tables all the time, everywhere. This will change to be >> > the same as x86 soon. >> >> It does use EHABI, but at r201326: >> $ cat 1.cc >> int f() {} >> $ ./bin/clang++ -target arm-linux-androideabi 1.cc -c >> $ readelf -u 1.o >> 0x0 <_Z1fv>: 0x1 [cantunwind] >> $ ./bin/clang++ -target arm-linux-androideabi 1.cc -c -funwind-tables >> $ readelf -u 1.o >> 0x0 <_Z1fv>: 0x8000b0b0 >> Compact model 0 >> 0x00 vsp = vsp + 4 >> 0xb0 finish >> 0xb0 finish >> _______________________________________________ >> LLVM Developers mailing list >> LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu >> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev > > > > _______________________________________________ > LLVM Developers mailing list > LLVMdev at cs.uiuc.edu http://llvm.cs.uiuc.edu > http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev >