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([2001:af0:8000:1409:193:86:92:181]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49cf7736132sm466320805e9.12.2026.09.09.06.57.55 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 09 Sep 2026 06:57:56 -0700 (PDT) Message-ID: <3bd2f451-cbe4-4ef4-a552-81ea227fb15b@suse.com> Date: Wed, 9 Sep 2026 15:57:55 +0200 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 3/4] module: introduce SH_ENTSIZE_STANDALONE for separately allocated sections To: Hao Ge Cc: Luis Chamberlain , Daniel Gomez , Sami Tolvanen , Aaron Tomlin , Suren Baghdasaryan , Andrew Morton , linux-modules@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Sashiko , stable@vger.kernel.org References: <20260908092412.115953-1-hao.ge@linux.dev> <20260908092412.115953-4-hao.ge@linux.dev> <76b5edbb-8231-41d0-9e7b-f965af13c324@suse.com> <7dbba23e-5530-43c4-9c44-20108cd0cef5@linux.dev> Content-Language: en-US From: Petr Pavlu In-Reply-To: <7dbba23e-5530-43c4-9c44-20108cd0cef5@linux.dev> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/9/26 3:08 PM, Hao Ge wrote: > On 9/9/26 20:47, Hao Ge wrote: >> On 9/9/26 19:30, Petr Pavlu wrote: >>> On 9/8/26 11:24 AM, Hao Ge wrote: >>>> SHF_ALLOC means, per the ELF spec, that a section occupies memory >>>> during process execution. Some module sections occupy memory >>>> outside the regular module layout, for example the percpu section >>>> with its per-CPU allocations. The loader currently excludes such >>>> a section from the layout by clearing its SHF_ALLOC, which >>>> overloads the flag with a loader-internal meaning. >>>> apply_relocations() needs a special case for the section, and >>>> find_sec(".data..percpu") returns different results before and >>>> after layout_and_allocate(). >>>> >>>> Introduce SH_ENTSIZE_STANDALONE to mark sections with a separate >>>> allocation. The percpu section is its first user. layout_sections() >>>> and move_module() skip marked sections, and apply_relocations() goes >>>> back to testing only SHF_ALLOC. Based on a patch by Petr Pavlu [1]. >>>> >>>> .data..percpu keeps SHF_ALLOC, so it would now show up under >>>> /sys/module/*/sections/. The section has one instance per CPU and no >>>> single address to report, and the entry never existed before, so >>>> skip it in add_sect_attrs(). add_notes_attrs() indexes its attrs[] >>>> array and skips it too. No functional change otherwise. >>>> >>>> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression") >>>> Reported-by: Sashiko >>>> Link: https://lore.kernel.org/all/499bb60c-c6e3-43a3-bd92-95a0567ece5e@suse.com/ [1] >>>> Suggested-by: Petr Pavlu >>>> Cc: stable@vger.kernel.org >>>> Signed-off-by: Hao Ge >>>> --- >>>> [...] >>>> diff --git a/kernel/module/kallsyms.c b/kernel/module/kallsyms.c >>>> index 0fc11e45df9b..49190deae61e 100644 >>>> --- a/kernel/module/kallsyms.c >>>> +++ b/kernel/module/kallsyms.c >>>> @@ -76,7 +76,7 @@ static char elf_type(const Elf_Sym *sym, const struct load_info *info) >>>> } >>>> static bool is_core_symbol(const Elf_Sym *src, const Elf_Shdr *sechdrs, >>>> - unsigned int shnum, unsigned int pcpundx) >>>> + unsigned int shnum) >>>> { >>>> const Elf_Shdr *sec; >>>> enum mod_mem_type type; >>>> @@ -86,11 +86,6 @@ static bool is_core_symbol(const Elf_Sym *src, const Elf_Shdr *sechdrs, >>>> !src->st_name) >>>> return false; >>>> -#ifdef CONFIG_KALLSYMS_ALL >>>> - if (src->st_shndx == pcpundx) >>>> - return true; >>>> -#endif >>>> - >>>> sec = sechdrs + src->st_shndx; >>>> type = sec->sh_entsize >> SH_ENTSIZE_TYPE_SHIFT; >>>> if (!(sec->sh_flags & SHF_ALLOC) >>>> @@ -131,8 +126,7 @@ 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->sechdrs, info->hdr->e_shnum)) { >>>> strtab_size += strlen(&info->strtab[src[i].st_name]) + 1; >>>> ndst++; >>>> } >>>> @@ -199,8 +193,7 @@ void add_kallsyms(struct module *mod, const struct load_info *info) >>>> for (ndst = i = 0; i < kallsyms->num_symtab; i++) { >>>> 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->sechdrs, info->hdr->e_shnum)) { >>>> ssize_t ret; >>>> mod->core_kallsyms.typetab[ndst] = >>> FTR These changes in kernel/module/kallsyms.c have a conflict with the >>> series "Ignore local labels and mapping symbols during module load" [1], >>> which is currently queued on modules-next, but it should be >>> straightforward to resolve. >>> >>>> diff --git a/kernel/module/sysfs.c b/kernel/module/sysfs.c >>>> index 01c65d608873..f64170344e69 100644 >>>> --- a/kernel/module/sysfs.c >>>> +++ b/kernel/module/sysfs.c >>>> @@ -62,6 +62,15 @@ static void free_sect_attrs(struct module_sect_attrs *sect_attrs) >>>> kfree(sect_attrs); >>>> } >>>> +/* >>>> + * .data..percpu has a separate allocation per CPU and no single >>>> + * address to report. >>>> + */ >>>> +static bool sect_visible(const struct load_info *info, unsigned int i) >>>> +{ >>>> + return !sect_empty(&info->sechdrs[i]) && i != info->index.pcpu; >>>> +} >>>> + >>>> static int add_sect_attrs(struct module *mod, const struct load_info *info) >>>> { >>>> struct module_sect_attrs *sect_attrs; >>>> @@ -72,7 +81,7 @@ static int add_sect_attrs(struct module *mod, const struct load_info *info) >>>> /* Count loaded sections and allocate structures */ >>>> for (i = 0; i < info->hdr->e_shnum; i++) >>>> - if (!sect_empty(&info->sechdrs[i])) >>>> + if (sect_visible(info, i)) >>>> nloaded++; >>>> sect_attrs = kzalloc_flex(*sect_attrs, attrs, nloaded); >>>> if (!sect_attrs) >>>> @@ -92,7 +101,7 @@ static int add_sect_attrs(struct module *mod, const struct load_info *info) >>>> for (i = 0; i < info->hdr->e_shnum; i++) { >>>> Elf_Shdr *sec = &info->sechdrs[i]; >>>> - if (sect_empty(sec)) >>>> + if (!sect_visible(info, i)) >>>> continue; >>>> sysfs_bin_attr_init(sattr); >>>> sattr->attr.name = >>>> @@ -181,7 +190,7 @@ static int add_notes_attrs(struct module *mod, const struct load_info *info) >>>> nattr = ¬es_attrs->attrs[0]; >>>> for (loaded = i = 0; i < info->hdr->e_shnum; ++i) { >>>> - if (sect_empty(&info->sechdrs[i])) >>>> + if (!sect_visible(info, i)) >>>> continue; >>>> if (info->sechdrs[i].sh_type == SHT_NOTE) { >>>> sysfs_bin_attr_init(nattr); >>> add_notes_attrs() has two sect_empty() calls. Both should be changed to >>> sect_visible(). >> >> >> I kept this part unmodified to preserve the loop's original intent. >> >> This loop counts SHT_NOTE sections. >> >> SHT_NOTE refers to ELF note sections, which hold non-executable >> >> metadata such as build ID and ABI info. >> >> I wonder if we could keep the current implementation. >> >> As noted in the comment above, the top part counts SHT_NOTE sections >> >> and allocates structures, while the lower logic handles control of node attributes. >> >> >> WDYT? >> >> > > Sorry, I've reconsidered this. I think changing it to sect_visible would be better. > > sect_visible stands for the count of externally visible note attributes, so the code > > above and below can align with each other. > > > Sorry for the noise. No worries. One problem with continuing to use sect_empty() in the first loop is that it could overallocate the number of required entries if a module contains an SHT_NOTE section named .data..percpu. That shouldn't happen, but we can trivially avoid it by using sect_visible() there as well. Using the same condition in both loops also makes the code generally simpler to understand. -- Cheers, Petr