Re: [PATCH 3/6] powerpc/module: Optimise nearby branches in ELF V2 ABI stub
From: Christophe Leroy <hidden>
Date: 2022-09-19 06:12:26
Le 16/09/2022 à 08:23, Benjamin Gray a écrit :
quoted hunk ↗ jump to hunk
Inserts a direct branch to the stub target when possible, replacing the mtctr/btctr sequence. The load into r12 could potentially be skipped too, but that change would need to refactor the arguments to indicate that the address does not have a separate local entry point. This helps the static call implementation, where modules calling their own trampolines are called through this stub and the trampoline is easily within range of a direct branch. Signed-off-by: Benjamin Gray <redacted> --- arch/powerpc/kernel/module_64.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c index 3656476097c2..03ab28d86008 100644 --- a/arch/powerpc/kernel/module_64.c +++ b/arch/powerpc/kernel/module_64.c@@ -432,8 +432,17 @@ static inline int create_stub(const Elf64_Shdr *sechdrs, return create_ftrace_stub(entry, addr, me); for (i = 0; i < ARRAY_SIZE(ppc64_stub_insns); i++) { - if (patch_instruction(&entry->jump[i], - ppc_inst(ppc64_stub_insns[i]))) + ppc_inst_t inst = ppc_inst(ppc64_stub_insns[i]); + + // Replace the indirect branch with a direct branch where possible + if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V2) && i == 4) { + ppc_inst_t direct;
Add blank line here.
+ if (create_branch(&direct, (void*) entry + (i * 4), addr, 0) == 0) {No braces for single lines if statement.
+ inst = direct; + } + } + + if (patch_instruction(&entry->jump[i], inst)) return 0; }