+++ Andrii Nakryiko [09/11/20 17:19 -0800]:
[snipped]
diff --git a/kernel/module.c b/kernel/module.c
index a4fa44a652a7..f2996b02ab2e 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -380,6 +380,35 @@ static void *section_objs(const struct load_info *info,
return (void *)info->sechdrs[sec].sh_addr;
}
+/* Find a module section: 0 means not found. Ignores SHF_ALLOC flag. */
+static unsigned int find_any_sec(const struct load_info *info, const char *name)
+{
+ unsigned int i;
+
+ for (i = 1; i < info->hdr->e_shnum; i++) {
+ Elf_Shdr *shdr = &info->sechdrs[i];
+ if (strcmp(info->secstrings + shdr->sh_name, name) == 0)
+ return i;
+ }
+ return 0;
+}
+
+/*
+ * Find a module section, or NULL. Fill in number of "objects" in section.
+ * Ignores SHF_ALLOC flag.
+ */
+static __maybe_unused void *any_section_objs(const struct load_info *info,
+ const char *name,
+ size_t object_size,
+ unsigned int *num)
+{
+ unsigned int sec = find_any_sec(info, name);
+
+ /* Section 0 has sh_addr 0 and sh_size 0. */
+ *num = info->sechdrs[sec].sh_size / object_size;
+ return (void *)info->sechdrs[sec].sh_addr;
+}
+
Hm, I see this patchset has already been applied to bpf-next, but I
guess that doesn't preclude any follow-up patches :-)
I am not a huge fan of the code duplication here, and also the fact
that they're only called in one place. any_section_objs() and
find_any_sec() are pretty much identical to section_objs() and
find_sec(), other than the fact the former drops the SHF_ALLOC check.
Moreover, since it appears that the ".BTF" section is not marked
SHF_ALLOC, I think this will leave mod->btf_data as a dangling pointer
after the module is done loading and the module's load_info has been
deallocated, since SHF_ALLOC sections are not allocated nor copied to
the module's final location in memory.
Why not simply mark the ".BTF" section in the module SHF_ALLOC? We
already do some sh_flags rewriting in rewrite_section_headers(). Then
the module loader knows to keep the section in memory and you can use
section_objs(). And since the .BTF section stays in module memory,
that might save you the memcpy() to btf->data in btf_parse_module()
(unless that is still needed for some reason).
Thanks,
Jessica
/* Provided by the linker */
extern const struct kernel_symbol __start___ksymtab[];
extern const struct kernel_symbol __stop___ksymtab[];
@@ -3250,6 +3279,9 @@ static int find_module_sections(struct module *mod, struct load_info *info)
sizeof(*mod->bpf_raw_events),
&mod->num_bpf_raw_events);
#endif
+#ifdef CONFIG_DEBUG_INFO_BTF_MODULES
+ mod->btf_data = any_section_objs(info, ".BTF", 1, &mod->btf_data_size);
+#endif
#ifdef CONFIG_JUMP_LABEL
mod->jump_entries = section_objs(info, "__jump_table",
sizeof(*mod->jump_entries),
--
2.24.1
