Le 05/10/2022 à 07:32, Benjamin Gray a écrit :
> The callee may set a field in st_other to 1 to indicate r2 should be
> treated as caller-saved. This means a trampoline must be used to save
> the current TOC before calling it and restore it afterwards, much like
> external calls.
The 'callee', what is that here in that context ?
Don't you mean the 'linker' instead ?
>
> This is necessary for supporting V2 ABI static calls that do not
> preserve the TOC.
>
> Signed-off-by: Benjamin Gray <bg...@linux.ibm.com>
> ---
> arch/powerpc/kernel/module_64.c | 14 +++++++++++++-
> 1 file changed, 13 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
> index 7e45dc98df8a..4d816f7785b4 100644
> --- a/arch/powerpc/kernel/module_64.c
> +++ b/arch/powerpc/kernel/module_64.c
> @@ -55,6 +55,12 @@ static unsigned int local_entry_offset(const Elf64_Sym
> *sym)
> * of function and try to derive r2 from it). */
> return PPC64_LOCAL_ENTRY_OFFSET(sym->st_other);
> }
> +
> +static bool need_r2save_stub(unsigned char st_other)
> +{
> + return ((st_other & STO_PPC64_LOCAL_MASK) >> STO_PPC64_LOCAL_BIT) == 1;
I would have writen :
return st_other & STO_PPC64_LOCAL_MASK == 1 << STO_PPC64_LOCAL_BIT;
But it is just a matter of preference, so up to you.
> +}
> +
> #else
>
> static func_desc_t func_desc(unsigned long addr)
> @@ -66,6 +72,11 @@ static unsigned int local_entry_offset(const Elf64_Sym
> *sym)
> return 0;
> }
>
> +static bool need_r2save_stub(unsigned char st_other)
> +{
> + return false;
> +}
> +
> void *dereference_module_function_descriptor(struct module *mod, void *ptr)
> {
> if (ptr < (void *)mod->arch.start_opd ||
> @@ -632,7 +643,8 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,
> case R_PPC_REL24:
> /* FIXME: Handle weak symbols here --RR */
> if (sym->st_shndx == SHN_UNDEF ||
> - sym->st_shndx == SHN_LIVEPATCH) {
> + sym->st_shndx == SHN_LIVEPATCH ||
> + need_r2save_stub(sym->st_other)) {
> /* External: go via stub */
> value = stub_for_addr(sechdrs, value, me,
> strtab + sym->st_name);
