riscv's start.S includes a `.cfi_label dummy` directive in [1]. The comment above it says > use a dummy .cfi_label to force starting the FDE.` but as I understand it, `ENTRY (ENTRY_POINT)` macro includes a `.cfi_startproc`, which should already do the same thing as comment suggests. This directive was introduced in https://sourceware.org/bugzilla/show_bug.cgi?id=23125 , but the original patch in the first comment didn't include cfi_label and works as reported. Zig compilation gets stuck on this directive as clang doesn't support it [2]. Can I get some help to clarify this directive and whether it is okay to remove it? [1] https://github.com/bminor/glibc/blob/8c77e26ba8b360c851b2b9485bb4431aacc51ad1/sysdeps/riscv/start.S#L48 [2] https://github.com/ziglang/zig/issues/3340
btw, this issue originally opened at https://github.com/riscv-collab/riscv-gnu-toolchain/issues/1149 and I was suggested to report it here.
.cfi_startproc does *not* start the FDE. Without .cfi_label, the DW_CFA_undefined directive is part of the CIE. $ readelf -wf csu/start.o Contents of the .eh_frame section: 00000000 0000000000000014 00000000 CIE Version: 3 Augmentation: "zR" Code alignment factor: 1 Data alignment factor: -4 Return address column: 1 Augmentation data: 1b DW_CFA_def_cfa_register: r2 (sp) DW_CFA_undefined: r1 (ra) DW_CFA_nop DW_CFA_nop DW_CFA_nop 00000018 0000000000000014 0000001c FDE cie=00000000 pc=0000000000000002..000000000000002c DW_CFA_nop DW_CFA_nop DW_CFA_nop DW_CFA_nop DW_CFA_nop DW_CFA_nop DW_CFA_nop
(In reply to Andreas Schwab from comment #2) > .cfi_startproc does *not* start the FDE. Without .cfi_label, the > DW_CFA_undefined directive is part of the CIE. I find llvm assembler puts it into fde without needing .cfi_label. Is cfi_startproc meant to mark start of a function frame and fde is per function? rv64d-dev0 /tmp # llvm-mc --filetype=obj -o=test.o test.s rv64d-dev0 /tmp # objdump --dwarf test.o test.o: file format elf64-littleriscv Contents of the .eh_frame section: 00000000 0000000000000010 00000000 CIE Version: 1 Augmentation: "zR" Code alignment factor: 1 Data alignment factor: -8 Return address column: 1 Augmentation data: 1b DW_CFA_def_cfa: r2 (sp) ofs 0 00000014 0000000000000010 00000018 FDE cie=00000000 pc=000000000000001c..0000000000000020 DW_CFA_undefined: r1 (ra) DW_CFA_nop