[PATCH 2/4] modpost: detect endianness on run-time

Masahiro Yamada
2024-07-27T07:45:38Z

Endianness is currently detected on compile-time, but we can defer this
until run-time. This change avoids re-executing scripts/mod/mk_elfconfig
even if modpost in the linux-headers package needs to be rebuilt for a
foreign architecture.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---

scripts/mod/mk_elfconfig.c | 19 -------------------
scripts/mod/modpost.c | 36 ++++++++++++++++++++++++++++++++++++
scripts/mod/modpost.h | 13 ++++---------
3 files changed, 40 insertions(+), 28 deletions(-)

diff --git a/scripts/mod/mk_elfconfig.c b/scripts/mod/mk_elfconfig.c
index aca96b3aada0..e8cee4e4bc73 100644
--- a/scripts/mod/mk_elfconfig.c
+++ b/scripts/mod/mk_elfconfig.c
@@ -8,7 +8,6 @@ int
main(int argc, char **argv)
{
unsigned char ei[EI_NIDENT];
- union { short s; char c[2]; } endian_test;

if (fread(ei, 1, EI_NIDENT, stdin) != EI_NIDENT) {
fprintf(stderr, "Error: input truncated\n");
@@ -28,24 +27,6 @@ main(int argc, char **argv)
default:
exit(1);
}
- switch (ei[EI_DATA]) {
- case ELFDATA2LSB:
- printf("#define KERNEL_ELFDATA ELFDATA2LSB\n");
- break;
- case ELFDATA2MSB:
- printf("#define KERNEL_ELFDATA ELFDATA2MSB\n");
- break;
- default:
- exit(1);
- }
-
- endian_test.s = 0x0102;
- if (memcmp(endian_test.c, "\x01\x02", 2) == 0)
- printf("#define HOST_ELFDATA ELFDATA2MSB\n");
- else if (memcmp(endian_test.c, "\x02\x01", 2) == 0)
- printf("#define HOST_ELFDATA ELFDATA2LSB\n");
- else
- exit(1);

return 0;
}
diff --git a/scripts/mod/modpost.c b/scripts/mod/modpost.c
index d16d0ace2775..f492fbeed300 100644
--- a/scripts/mod/modpost.c
+++ b/scripts/mod/modpost.c
@@ -50,6 +50,9 @@ static bool error_occurred;

static bool extra_warn;

+bool target_is_big_endian;
+bool host_is_big_endian;
+
/*
* Cut off the warnings when there are too many. This typically occurs when
* vmlinux is missing. ('make modules' without building vmlinux.)
@@ -438,6 +441,18 @@ static int parse_elf(struct elf_info *info, const char *filename)
/* Not an ELF file - silently ignore it */
return 0;
}
+
+ switch (hdr->e_ident[EI_DATA]) {
+ case ELFDATA2LSB:
+ target_is_big_endian = false;
+ break;
+ case ELFDATA2MSB:
+ target_is_big_endian = true;
+ break;
+ default:
+ fatal("kernel endian is unknown\n");
+ }
+
/* Fix endianness in ELF header */
hdr->e_type = TO_NATIVE(hdr->e_type);
hdr->e_machine = TO_NATIVE(hdr->e_machine);
@@ -2117,6 +2132,25 @@ struct dump_list {
const char *file;
};

+static void check_host_endian(void)
+{
+ static const union {
+ short s;
+ char c[2];
+ } endian_test = { .c = {0x01, 0x02} };
+
+ switch (endian_test.s) {
+ case 0x0102:
+ host_is_big_endian = true;
+ break;
+ case 0x0201:
+ host_is_big_endian = false;
+ break;
+ default:
+ fatal("Unknown host endian\n");
+ }
+}
+
int main(int argc, char **argv)
{
struct module *mod;
@@ -2181,6 +2215,8 @@ int main(int argc, char **argv)
}
}

+ check_host_endian();
+
list_for_each_entry_safe(dl, dl2, &dump_lists, list) {
read_dump(dl->file);
list_del(&dl->list);
diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
index 58197b34a3c8..54ba9431713f 100644
--- a/scripts/mod/modpost.h
+++ b/scripts/mod/modpost.h
@@ -62,15 +62,8 @@
x); \
})

-#if KERNEL_ELFDATA != HOST_ELFDATA
-
-#define TO_NATIVE(x) (bswap(x))
-
-#else /* endianness matches */
-
-#define TO_NATIVE(x) (x)
-
-#endif
+#define TO_NATIVE(x) \
+ (target_is_big_endian == host_is_big_endian ? x : bswap(x))

#define NOFAIL(ptr) do_nofail((ptr), #ptr)

@@ -187,6 +180,8 @@ void add_moddevtable(struct buffer *buf, struct module *mod);
void get_src_version(const char *modname, char sum[], unsigned sumlen);

/* from modpost.c */
+extern bool target_is_big_endian;
+extern bool host_is_big_endian;
char *read_text_file(const char *filename);
char *get_line(char **stringp);
void *sym_get_data(const struct elf_info *info, const Elf_Sym *sym);
--
2.43.0