Re: llvm19 lld issue

On 14 Nov 2024, at 13:44, Michal Meloun <mmel@FreeBSD.org> wrote:
> 
> While searching for the cause of armv7 kernel corruption after updating to llvm19 lld, I came across an interesting problem.
> 
> - The linker script does not list all generated sections. Specifically, the data sections created by the linker set are not listed.
> 
> - The linker can place these orphaned sections in any location (OK, with some restrictions). See https://maskray.me/blog/2024-06-02-understanding-orphan-sections.
> 
> - Creating symbols outside a section is fragile and subject to error; the linker may place an orphaned section between the symbol definition and the following section.
> 
> We ran into this problem many years ago, see https://github.com/freebsd/freebsd-src/commit/6e764e36da019837d90e3b4b712871ee4442637a. Unfortunately, we didn't fix it completely then, and we have to address the same corruption again.
> 
> I think we should be strict in this area and use '--orphan-handling=error' for kernel linking. However, I'm not sure we can handle linker sets gracefully.
> 
> Any comments, contrary opinion or better solution ? Does anyone know how to properly list all linker sets (mainly but not only 'set_<foo>_set') in linker script and which section is appropriate for them ? .rodata?

I tried adding --orphan-handler=error, and on buildkernel (even for amd64) I get pretty soon:

--- all_subdir_accf_data ---
ld: error: accf_data.o:(.data) is being placed in '.data'
ld: error: accf_data.o:(set_modmetadata_set) is being placed in 'set_modmetadata_set'
ld: error: accf_data.o:(set_sysinit_set) is being placed in 'set_sysinit_set'
ld: error: accf_data.o:(.debug_loc) is being placed in '.debug_loc'
ld: error: accf_data.o:(.debug_abbrev) is being placed in '.debug_abbrev'
ld: error: accf_data.o:(.debug_info) is being placed in '.debug_info'
ld: error: accf_data.o:(.debug_ranges) is being placed in '.debug_ranges'
ld: error: accf_data.o:(.debug_str) is being placed in '.debug_str'
ld: error: accf_data.o:(.comment) is being placed in '.comment'
ld: error: accf_data.o:(.debug_frame) is being placed in '.debug_frame'
ld: error: accf_data.o:(.debug_line) is being placed in '.debug_line'
ld: error: accf_data.o:(.llvm_addrsig) is being placed in '.llvm_addrsig'
ld: error: accf_data.o:(.SUNW_ctf) is being placed in '.SUNW_ctf'
ld: error: <internal>:(.note.gnu.build-id) is being placed in '.note.gnu.build-id'
ld: error: <internal>:(.note.GNU-stack) is being placed in '.note.GNU-stack'
ld: error: <internal>:(.symtab) is being placed in '.symtab'
ld: error: <internal>:(.shstrtab) is being placed in '.shstrtab'
ld: error: <internal>:(.strtab) is being placed in '.strtab'
--- all_subdir_aic7xxx ---
--- all_subdir_aic7xxx/ahc ---
--- machine ---
machine -> /home/dim/src/freebsd/src/sys/amd64/include
--- all_subdir_accf_data ---
*** [accf_data.ko.full] Error code 1


Not sure if those are all really orphaned, though?

-Dimitry