Re: [PATCH] objtool: fix objtool regression on x32 systems

Peter Zijlstra
2022-05-16T15:41:51Z

On Mon, May 16, 2022 at 11:06:36AM -0400, Mikulas Patocka wrote:
> The patch 4abff6d48dbc ("objtool: Fix code relocs vs weak symbols") makes
> the kernel unbootable. The patch c087c6e7b551 ("objtool: Fix type of
> reloc::addend") attempts to fix it by replacing 'int' with 'long'.
>
> However, we may be running on a system with x32 ABI and 'long' on x32 is
> 32-bit, thus the patch c087c6e7b551 doesn't really change anything and we
> still end up with miscompiled kernel. This patch replaces 'long' with
> 'long long', so that the 64-bit kernel is correctly compiled on a x32
> system.

Hurmph.. you're building a 64bit kernel on a x32 hosted machine? And
this is the *only* thing that goes sideways?

I suspect quite a bit of objtool assumes LP64 and won't quite work right
on ILP32 and we've just been lucky so far.

> Index: linux-2.6/tools/objtool/elf.c
> ===================================================================
> --- linux-2.6.orig/tools/objtool/elf.c 2022-05-16 16:20:49.000000000 +0200
> +++ linux-2.6/tools/objtool/elf.c 2022-05-16 16:22:21.000000000 +0200
> @@ -546,7 +546,7 @@ static struct section *elf_create_reloc_
> int reltype);
>
> int elf_add_reloc(struct elf *elf, struct section *sec, unsigned long offset,
> - unsigned int type, struct symbol *sym, long addend)
> + unsigned int type, struct symbol *sym, long long addend)
> {
> struct reloc *reloc;
>
> Index: linux-2.6/tools/objtool/include/objtool/elf.h
> ===================================================================
> --- linux-2.6.orig/tools/objtool/include/objtool/elf.h 2022-05-16 16:07:54.000000000 +0200
> +++ linux-2.6/tools/objtool/include/objtool/elf.h 2022-05-16 16:22:45.000000000 +0200
> @@ -73,7 +73,7 @@ struct reloc {
> struct symbol *sym;
> unsigned long offset;
> unsigned int type;
> - long addend;
> + long long addend;
> int idx;
> bool jump_table_start;
> };
> @@ -135,7 +135,7 @@ struct elf *elf_open_read(const char *na
> struct section *elf_create_section(struct elf *elf, const char *name, unsigned int sh_flags, size_t entsize, int nr);
>
> int elf_add_reloc(struct elf *elf, struct section *sec, unsigned long offset,
> - unsigned int type, struct symbol *sym, long addend);
> + unsigned int type, struct symbol *sym, long long addend);
> int elf_add_reloc_to_insn(struct elf *elf, struct section *sec,
> unsigned long offset, unsigned int type,
> struct section *insn_sec, unsigned long insn_off);
>

I think I much prefer s64 there instead of 'long long'. But really I
think all of objtool needs a bit of an audit to see what types need be
used.