Re: [PATCH v3 2/6] powerpc/module: Handle caller-saved TOC in module linker
From: Christophe Leroy <hidden>
Date: 2022-10-05 19:19:56
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 ?
quoted hunk ↗ jump to hunk
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..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.
quoted hunk ↗ jump to hunk
+} + #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);