[PATCH v4 2/6] powerpc/module: Handle caller-saved TOC in module linker

[Benjamin Gray <bgray@linux.ibm.com>]

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.

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

Signed-off-by: Benjamin Gray <bgray@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..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 */
 				value = stub_for_addr(sechdrs, value, me,
 						strtab + sym->st_name);
-- 
2.37.3