Hello everybody, We faced stack unwinding failures during working with libunwind for ARM. libunwind fails to unwind stack using UNW_ARM_METHOD_DWARF when there is ARM vfpv3/NEON register in stack, because libunwind cannot interpret ARM vfpv3/NEON registers(D0~D15) in .debug_frame section written in DWARF format.
These failure are observed while developing dotnet/coreclr using libunwind and clang-3.6. You can find more details at https://github.com/dotnet/coreclr/issues/6698 . For example, libunwind cannot interpret below .debug_frame section, because libunwind doesn't recognize "r264" in "DW_CFA_offset_extended: r264 at cfa-48" which means "d8 register is at cfa-48". (d8 is ARM vfpv3/NEON 64-bit registers which is alias of s16 and s17 registers.) 001644d8 0000002c 00163dc4 FDE cie=00163dc4 pc=0024da6c..0024dccc DW_CFA_advance_loc: 4 to 0024da70 DW_CFA_def_cfa_offset: 36 DW_CFA_offset: r14 at cfa-4 DW_CFA_offset: r11 at cfa-8 DW_CFA_offset: r10 at cfa-12 DW_CFA_offset: r9 at cfa-16 DW_CFA_offset: r8 at cfa-20 DW_CFA_offset: r7 at cfa-24 DW_CFA_offset: r6 at cfa-28 DW_CFA_offset: r5 at cfa-32 DW_CFA_offset: r4 at cfa-36 DW_CFA_advance_loc: 2 to 0024da72 DW_CFA_def_cfa: r7 ofs 24 DW_CFA_advance_loc: 6 to 0024da78 DW_CFA_offset_extended: r264 at cfa-48 DW_CFA_nop DW_CFA_nop ... omitted ... Above .debug_section is generated from below aseembly which is generated from clang 3.6. ... omitted ... .Ltmp2030: .cfi_offset r4, -36 .setfp r7, sp, #12 add r7, sp, #12 .Ltmp2031: .cfi_def_cfa r7, 24 .pad #4 sub sp, #4 .vsave {d8} vpush {d8} .Ltmp2032: .cfi_offset d8, -48 .pad #296 ... omitted ... ARM vpfv3/NEON registers are defined in "DWARF for the ARM architecture" and register number is from r256 to r287. http://infocenter.arm.com/help/topic/com.arm.doc.ihi0040b/IHI0040B_aadwarf.pdf I'm going to post a patch for D0~D15 register support for ARM DWARF. Is it ok to add these feature to libunwind ? At least, the patch worked with my libunwinding failure case from dotnet/coreclr mentioned above. Best regards, Hyung-Kyu Choi Hyung-Kyu Choi (1): Support ARM VFP-v3/Neon 64-bit registers in DWARF src/dwarf/Gparser.c | 23 ++++++++++++++++++++++- 1 file changed, 22 insertions(+), 1 deletion(-) -- 1.9.1 _______________________________________________ Libunwind-devel mailing list [email protected] https://lists.nongnu.org/mailman/listinfo/libunwind-devel
