Re: [PATCH 12/17] powerpc/ftrace: Simplify ftrace_make_call()

[Christophe Leroy <christophe.leroy@csgroup.eu>]

Le 19/06/2023 à 11:47, Naveen N Rao a écrit :
> Now that we validate the ftrace location during initialization in
> ftrace_init_nop(), we can simplify ftrace_make_call() to replace the nop
> without worrying about the instructions surrounding the ftrace location.
> Note that we continue to ensure that we have a nop at the ftrace
> location before patching it.
> 
> Signed-off-by: Naveen N Rao <naveen@kernel.org>

Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>

> ---
>   arch/powerpc/kernel/trace/ftrace.c | 187 +++++------------------------
>   1 file changed, 31 insertions(+), 156 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/trace/ftrace.c b/arch/powerpc/kernel/trace/ftrace.c
> index 05153a1038fdff..6ea8b90246a540 100644
> --- a/arch/powerpc/kernel/trace/ftrace.c
> +++ b/arch/powerpc/kernel/trace/ftrace.c
> @@ -129,162 +129,6 @@ static unsigned long find_ftrace_tramp(unsigned long ip)
>   	return 0;
>   }
>   
> -#ifdef CONFIG_MODULES
> -/*
> - * Examine the existing instructions for __ftrace_make_call.
> - * They should effectively be a NOP, and follow formal constraints,
> - * depending on the ABI. Return false if they don't.
> - */
> -static bool expected_nop_sequence(void *ip, ppc_inst_t op0, ppc_inst_t op1)
> -{
> -	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));
> -}
> -
> -static int
> -__ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
> -{
> -	ppc_inst_t op[2];
> -	void *ip = (void *)rec->ip;
> -	unsigned long entry, ptr, tramp;
> -	struct module *mod = rec->arch.mod;
> -
> -	/* read where this goes */
> -	if (copy_inst_from_kernel_nofault(op, ip))
> -		return -EFAULT;
> -
> -	if (!IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS) &&
> -	    copy_inst_from_kernel_nofault(op + 1, ip + 4))
> -		return -EFAULT;
> -
> -	if (!expected_nop_sequence(ip, op[0], op[1])) {
> -		pr_err("Unexpected call sequence at %p: %08lx %08lx\n", ip,
> -		       ppc_inst_as_ulong(op[0]), ppc_inst_as_ulong(op[1]));
> -		return -EINVAL;
> -	}
> -
> -	/* If we never set up ftrace trampoline(s), then bail */
> -	if (!mod->arch.tramp ||
> -	    (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS) && !mod->arch.tramp_regs)) {
> -		pr_err("No ftrace trampoline\n");
> -		return -EINVAL;
> -	}
> -
> -	if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS) && rec->flags & FTRACE_FL_REGS)
> -		tramp = mod->arch.tramp_regs;
> -	else
> -		tramp = mod->arch.tramp;
> -
> -	if (module_trampoline_target(mod, tramp, &ptr)) {
> -		pr_err("Failed to get trampoline target\n");
> -		return -EFAULT;
> -	}
> -
> -	pr_devel("trampoline target %lx", ptr);
> -
> -	entry = ppc_global_function_entry((void *)addr);
> -	/* This should match what was called */
> -	if (ptr != entry) {
> -		pr_err("addr %lx does not match expected %lx\n", ptr, entry);
> -		return -EINVAL;
> -	}
> -
> -	if (patch_branch(ip, tramp, BRANCH_SET_LINK)) {
> -		pr_err("REL24 out of range!\n");
> -		return -EINVAL;
> -	}
> -
> -	return 0;
> -}
> -#else
> -static int __ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
> -{
> -	return 0;
> -}
> -#endif /* CONFIG_MODULES */
> -
> -static int __ftrace_make_call_kernel(struct dyn_ftrace *rec, unsigned long addr)
> -{
> -	ppc_inst_t op;
> -	void *ip = (void *)rec->ip;
> -	unsigned long tramp, entry, ptr;
> -
> -	/* Make sure we're being asked to patch branch to a known ftrace addr */
> -	entry = ppc_global_function_entry((void *)ftrace_caller);
> -	ptr = ppc_global_function_entry((void *)addr);
> -
> -	if (ptr != entry && IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_REGS))
> -		entry = ppc_global_function_entry((void *)ftrace_regs_caller);
> -
> -	if (ptr != entry) {
> -		pr_err("Unknown ftrace addr to patch: %ps\n", (void *)ptr);
> -		return -EINVAL;
> -	}
> -
> -	/* Make sure we have a nop */
> -	if (copy_inst_from_kernel_nofault(&op, ip)) {
> -		pr_err("Unable to read ftrace location %p\n", ip);
> -		return -EFAULT;
> -	}
> -
> -	if (!ppc_inst_equal(op, ppc_inst(PPC_RAW_NOP()))) {
> -		pr_err("Unexpected call sequence at %p: %08lx\n",
> -		       ip, ppc_inst_as_ulong(op));
> -		return -EINVAL;
> -	}
> -
> -	tramp = find_ftrace_tramp((unsigned long)ip);
> -	if (!tramp) {
> -		pr_err("No ftrace trampolines reachable from %ps\n", ip);
> -		return -EINVAL;
> -	}
> -
> -	if (patch_branch(ip, tramp, BRANCH_SET_LINK)) {
> -		pr_err("Error patching branch to ftrace tramp!\n");
> -		return -EINVAL;
> -	}
> -
> -	return 0;
> -}
> -
> -int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
> -{
> -	unsigned long ip = rec->ip;
> -	ppc_inst_t old, new;
> -
> -	/*
> -	 * If the calling address is more that 24 bits away,
> -	 * then we had to use a trampoline to make the call.
> -	 * Otherwise just update the call site.
> -	 */
> -	if (test_24bit_addr(ip, addr)) {
> -		/* within range */
> -		old = ppc_inst(PPC_RAW_NOP());
> -		new = ftrace_call_replace(ip, addr, 1);
> -		return ftrace_modify_code(ip, old, new);
> -	} else if (core_kernel_text(ip)) {
> -		return __ftrace_make_call_kernel(rec, addr);
> -	} else if (!IS_ENABLED(CONFIG_MODULES)) {
> -		/* We should not get here without modules */
> -		return -EINVAL;
> -	}
> -
> -	/*
> -	 * Out of range jumps are called from modules.
> -	 * Being that we are converting from nop, it had better
> -	 * already have a module defined.
> -	 */
> -	if (!rec->arch.mod) {
> -		pr_err("No module loaded\n");
> -		return -EINVAL;
> -	}
> -
> -	return __ftrace_make_call(rec, addr);
> -}
> -
>   #ifdef CONFIG_DYNAMIC_FTRACE_WITH_REGS
>   #ifdef CONFIG_MODULES
>   static int
> @@ -419,6 +263,37 @@ int ftrace_modify_call(struct dyn_ftrace *rec, unsigned long old_addr,
>   }
>   #endif
>   
> +int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
> +{
> +	unsigned long tramp, ip = rec->ip;
> +	ppc_inst_t old, new;
> +	struct module *mod;
> +
> +	old = ppc_inst(PPC_RAW_NOP());
> +	if (is_offset_in_branch_range(addr - ip)) {
> +		/* Within range */
> +		new = ftrace_create_branch_inst(ip, addr, 1);
> +		return ftrace_modify_code(ip, old, new);
> +	} else if (core_kernel_text(ip)) {
> +		/* We would be branching to one of our ftrace tramps */
> +		tramp = find_ftrace_tramp(ip);
> +		if (!tramp) {
> +			pr_err("0x%lx: No ftrace trampolines reachable\n", ip);
> +			return -EINVAL;
> +		}
> +		new = ftrace_create_branch_inst(ip, tramp, 1);
> +		return ftrace_modify_code(ip, old, new);
> +	} else if (IS_ENABLED(CONFIG_MODULES)) {
> +		/* Module code would be going to one of the module stubs */
> +		mod = rec->arch.mod;
> +		tramp = (addr == (unsigned long)ftrace_caller ? mod->arch.tramp : mod->arch.tramp_regs);
> +		new = ftrace_create_branch_inst(ip, tramp, 1);
> +		return ftrace_modify_code(ip, old, new);
> +	}
> +
> +	return -EINVAL;
> +}
> +
>   int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec, unsigned long addr)
>   {
>   	unsigned long tramp, ip = rec->ip;