linux-kernel - Re: [PATCH v3 11/25] powerpc/ftrace: Make __ftrace_make

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Date:   Tue, 09 Aug 2022 11:55:42 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Michael Ellerman <mpe@...erman.id.au>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        llvm@...ts.linux.dev, nathan@...nel.org, omosnacek@...il.com
Subject: Re: [PATCH v3 11/25] powerpc/ftrace: Make __ftrace_make_{nop/call}()
 common to PPC32 and PPC64

Nick Desaulniers wrote:
> Christ...that's not what I meant to send; sorry, mutt is giving me
> bizarro errors today so I can't insert myself into threads using the
> usual incantation I have in the past.  What I meant to send was:
> 
> Christophe,
> Ondrej reported a regression with ftrace when building w/ clang
> bisected to this commit. Can you PTAL?
> https://github.com/ClangBuiltLinux/linux/issues/1682

Thanks for the report. That was my doing - I tend to miss the fact that 
clang doesn't support -mprofile-kernel. Can you check if the below patch 
fixes it for you?

- Naveen

---
diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
index cb158c32b50b99..7b85c3b460a3c0 100644
--- a/arch/powerpc/kernel/trace/ftrace.c
+++ b/arch/powerpc/kernel/trace/ftrace.c
@@ -393,11 +393,11 @@ int ftrace_make_nop(struct module *mod,
  */
 static bool expected_nop_sequence(void *ip, ppc_inst_t op0, ppc_inst_t op1)
 {
-       if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V1))
+       if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS))
+               return ppc_inst_equal(op0, ppc_inst(PPC_RAW_NOP()));
+       else
                return ppc_inst_equal(op0, ppc_inst(PPC_RAW_BRANCH(8))) &&
                       ppc_inst_equal(op1, ppc_inst(PPC_INST_LD_TOC));
-       else
-               return ppc_inst_equal(op0, ppc_inst(PPC_RAW_NOP()));
 }
 
 static int
@@ -412,7 +412,7 @@ __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
        if (copy_inst_from_kernel_nofault(op, ip))
                return -EFAULT;
 
-       if (IS_ENABLED(CONFIG_PPC64_ELF_ABI_V1) &&
+       if (!IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS) &&
            copy_inst_from_kernel_nofault(op + 1, ip + 4))
                return -EFAULT;