Re: [PATCH v2] ftrace: speed up module enable by binary searching module symbols

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] ftrace: undeclared function is_ignored_kernel_symbol() breaks build
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commit 4bde25e1c49a34cddab8dbd106c29413a3f1f699
Author: Yaxiong Tian <tianyaxiong@kylinos.cn>

ftrace: speed up module enable by binary searching module symbols

This commit speeds up ftrace_module_enable() by collecting and sorting a
module's symbol addresses once and binary searching them to validate
ftrace records instead of linearly scanning the module symbol table for
each record.

> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index c7d74b33d36de..255e813fe70e1 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -26,6 +26,7 @@
>  #include <linux/uaccess.h>
>  #include <linux/bsearch.h>
>  #include <linux/module.h>
> +#include <linux/module_symbol.h>
>  #include <linux/ftrace.h>
>  #include <linux/sysctl.h>
>  #include <linux/slab.h>
> @@ -8034,8 +8035,129 @@ void ftrace_release_mod(struct module *mod)
>  	}
>  }
>  
> +#ifdef FTRACE_MCOUNT_MAX_OFFSET

[ ... ]

> +static struct ftrace_mod_syms *ftrace_mod_syms_alloc(struct module *mod)
> +{
> +	struct mod_kallsyms *kallsyms;
> +	struct ftrace_mod_syms *syms;
> +	unsigned int i, nr = 0;
> +
> +	/*
> +	 * mod->kallsyms stays valid until do_init_module() replaces it later
> +	 * in this thread, so no RCU read-side section is needed.
> +	 */
> +	kallsyms = rcu_dereference_raw(mod->kallsyms);
> +
> +	if (!kallsyms || kallsyms->num_symtab < 2)
> +		return NULL;
> +
> +	syms = kvmalloc(struct_size(syms, addr, kallsyms->num_symtab),
> +			GFP_KERNEL);
> +	if (!syms)
> +		return NULL;
> +
> +	/* The symbols find_kallsyms_symbol() would consider. */
> +	for (i = 1; i < kallsyms->num_symtab; i++) {
> +		const Elf_Sym *sym = &kallsyms->symtab[i];
> +		const char *name = kallsyms->strtab + sym->st_name;
> +
> +		if (sym->st_shndx == SHN_UNDEF || !*name ||
> +		    is_ignored_kernel_symbol(name))
> +			continue;

[Severity: Low]
Does this break the build on architectures defining FTRACE_MCOUNT_MAX_OFFSET
(such as x86 with CONFIG_HAVE_FENTRY or powerpc)?

ftrace_mod_syms_alloc() calls is_ignored_kernel_symbol(), which is not
declared or defined in any kernel header in this tree. In
include/linux/module_symbol.h, the helper is still named is_mapping_symbol():

include/linux/module_symbol.h:
static inline bool is_mapping_symbol(const char *str)
{
	if (str[0] == '.' && str[1] == 'L')
		return true;
	if (str[0] == 'L' && str[1] == '0')
		return true;
	return str[0] == '$';
}

and find_kallsyms_symbol() in kernel/module/kallsyms.c calls
is_mapping_symbol():

kernel/module/kallsyms.c:find_kallsyms_symbol() {
	...
		if (*kallsyms_symbol_name(kallsyms, i) == '\0' ||
		    is_mapping_symbol(kallsyms_symbol_name(kallsyms, i)))
			continue;
	...
}

Should ftrace_mod_syms_alloc() call is_mapping_symbol(name) here instead?

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Sashiko AI review · https://sashiko.dev/#/patchset/20261105031530.280442-1-tianyaxiong@kylinos.cn?part=1