On Mon, 2022-10-10 at 11:29 +1100, Benjamin Gray wrote:

quoted

A function symbol may set a value in the st_other field to indicate
the TOC should be treated as caller-saved. The linker should
ensure> the
current TOC is saved before calling it and restore the TOC>
afterwards,
much like external calls.

As I suggested on the last revision, worth mentioning here that it's
the '.localentry <NAME>, 1' directive we're talking about here.

quoted

This is necessary for supporting V2 ABI static calls that do not
preserve the TOC.

Signed-off-by: Benjamin Gray <redacted>
---
 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..83a6f6e22e3b 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) == (1 <<>
STO_PPC64_LOCAL_BIT);
+}
+
 #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 */

Perhaps this comment should be updated to mention that there are non-
external but external-like calls?

Otherwise

Reviewed-by: Andrew Donnellan <redacted>

quoted

                                value = stub_for_addr(sechdrs,
value,> me,
                                                strtab +> sym-

quoted

st_name);

-- 
Andrew Donnellan    OzLabs, ADL Canberra
ajd@linux.ibm.com   IBM Australia Limited