[Bug debug/108600] Use DW_LNS_set_prologue_end
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108600
--- Comment #4 from Tom de Vries ---
(In reply to Tom de Vries from comment #0)
> Note that for for instance gdb test-case gdb.ada/ref_param.exp, this
> convention was broken for gcc 7.5.0 (and I don't know how much earlier), and
> my current guess is that it got fixed in gcc 11.1.0, by commit c029fcb5680
> ("Reset force_source_line in final.c").
Confirmed, see PR108615.
[Bug debug/108600] Use DW_LNS_set_prologue_end
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108600 --- Comment #3 from Tom de Vries --- (In reply to Tom de Vries from comment #2) > (In reply to Tom de Vries from comment #1) > > Created attachment 54371 [details] > > We probably don't want to emit in all cases, maybe limiting to > "dwarf_version >= 3", or "!dwarf_strict || dwarf_version >= 3". Let's see about dwarf_strict. Semantics: ... -gstrict-dwarf Disallow using extensions of later DWARF standard version than selected with -gdwarf-version. On most targets using non-conflicting DWARF extensions from later standard versions is allowed. ... For the -gas-loc-support case (gcc emitting .locs), even when passing -gdwarf-2, gas emits a v3 version .debug_line section (since binutils-2_32). And even if we'd fix that (I've filed https://sourceware.org/bugzilla/show_bug.cgi?id=30064), the way gas works is by bumping the dwarf version when encountering a feature that requires a higher version, so using end_prologue in a loc directive would then end up bumping dwarf_level to 3, bumping also the .debug_line version. For the -gno-as-loc-support case (gcc emitting .debug_line contribution), for -gdwarf-2 gcc indeed emits a v2 .debug_line section. But, that makes DW_LNS_set_prologue_end fall in the range of vendor specific extensions, and we can't conflict with that. Taking this all into account, I think it's better not to emit DW_LNS_set_prologue_end for -gdwarf-2 -gno-strict-dwarf.
[Bug debug/108600] Use DW_LNS_set_prologue_end
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108600 --- Comment #2 from Tom de Vries --- (In reply to Tom de Vries from comment #1) > Created attachment 54371 [details] We probably don't want to emit in all cases, maybe limiting to "dwarf_version >= 3", or "!dwarf_strict || dwarf_version >= 3".
[Bug debug/108600] Use DW_LNS_set_prologue_end
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108600 --- Comment #1 from Tom de Vries --- Created attachment 54371 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54371=edit tentative patch Tentative patch. For hello.c, for the -gas-loc-support case it gives us: ... $ gcc -g ~/hello.c -S -o- ... main: .LFB0: .file 1 "/home/vries/hello.c" .loc 1 5 1 .cfi_startproc pushq %rbp .cfi_def_cfa_offset 16 .cfi_offset 6, -16 movq%rsp, %rbp .cfi_def_cfa_register 6 .loc 1 6 3 prologue_end movl$.LC0, %edi ... And for the -gno-as-loc-support case: ... $ gcc -g ~/hello.c -c -gno-as-loc-support $ llvm-dwarfdump --debug-line hello.o ... AddressLine Column File ISA Discriminator Flags -- -- -- -- --- - - 0x 5 0 1 0 0 is_stmt 0x0004 6 1 1 0 0 is_stmt prologue_end 0x000e 8 3 1 0 0 is_stmt 0x0013 9 10 1 0 0 is_stmt 0x0015 9 1 1 0 0 is_stmt end_sequence ...
