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SubjectRe: [PATCH v2 2/2] kallsyms: ignore arm mapping symbols when loading module
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On 29/10/2021 07:50, Lexi Shao wrote:
> Arm modules contains mapping symbols(e.g. $a $d) which are ignored in
> module_kallsyms_on_each_symbol. However, these symbols are still
> displayed when catting /proc/kallsyms. This confuses tools(e.g. perf)
> that resolves kernel symbols with address using information from
> /proc/kallsyms. See discussion in Link:
> https://lore.kernel.org/all/c7dfbd17-85fd-b914-b90f-082abc64c9d1@arm.com/
>
> Being left out in vmlinux(see scripts/kallsyms.c is_ignored_symbol) and
> kernelspace API implies that these symbols are not used in any cases.
> So we can ignore them in the first place by not adding them to module
> kallsyms.
>
> Signed-off-by: Lexi Shao <shaolexi@huawei.com>


I tested this and it has removed the $ symbols from kallsyms where I saw
them before.

Reviewed-by: James Clark <james.clark@arm.com>

> ---
> kernel/module.c | 19 +++++++++++--------
> 1 file changed, 11 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/module.c b/kernel/module.c
> index 5c26a76e800b..b30cbbe144c7 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -2662,16 +2662,22 @@ static char elf_type(const Elf_Sym *sym, const struct load_info *info)
> return '?';
> }
>
> -static bool is_core_symbol(const Elf_Sym *src, const Elf_Shdr *sechdrs,
> - unsigned int shnum, unsigned int pcpundx)
> +static inline int is_arm_mapping_symbol(const char *str);
> +static bool is_core_symbol(const Elf_Sym *src, const struct load_info *info)
> {
> const Elf_Shdr *sec;
> + const Elf_Shdr *sechdrs = info->sechdrs;
> + unsigned int shnum = info->hdr->e_shnum;
> + unsigned int pcpundx = info->index.pcpu;
>
> if (src->st_shndx == SHN_UNDEF
> || src->st_shndx >= shnum
> || !src->st_name)
> return false;
>
> + if (is_arm_mapping_symbol(&info->strtab[src->st_name]))
> + return false;
> +
> #ifdef CONFIG_KALLSYMS_ALL
> if (src->st_shndx == pcpundx)
> return true;
> @@ -2714,8 +2720,7 @@ static void layout_symtab(struct module *mod, struct load_info *info)
> /* Compute total space required for the core symbols' strtab. */
> for (ndst = i = 0; i < nsrc; i++) {
> if (i == 0 || is_livepatch_module(mod) ||
> - is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum,
> - info->index.pcpu)) {
> + is_core_symbol(src+i, info)) {
> strtab_size += strlen(&info->strtab[src[i].st_name])+1;
> ndst++;
> }
> @@ -2778,8 +2783,7 @@ static void add_kallsyms(struct module *mod, const struct load_info *info)
> for (ndst = i = 0; i < mod->kallsyms->num_symtab; i++) {
> mod->kallsyms->typetab[i] = elf_type(src + i, info);
> if (i == 0 || is_livepatch_module(mod) ||
> - is_core_symbol(src+i, info->sechdrs, info->hdr->e_shnum,
> - info->index.pcpu)) {
> + is_core_symbol(src+i, info)) {
> mod->core_kallsyms.typetab[ndst] =
> mod->kallsyms->typetab[i];
> dst[ndst] = src[i];
> @@ -4246,8 +4250,7 @@ static const char *find_kallsyms_symbol(struct module *mod,
> * We ignore unnamed symbols: they're uninformative
> * and inserted at a whim.
> */
> - if (*kallsyms_symbol_name(kallsyms, i) == '\0'
> - || is_arm_mapping_symbol(kallsyms_symbol_name(kallsyms, i)))
> + if (*kallsyms_symbol_name(kallsyms, i) == '\0')
> continue;
>
> if (thisval <= addr && thisval > bestval) {
>

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