* [PATCH 2/3] kbuild: remove PROVIDE() for kallsyms symbols
2024-05-22 11:47 [PATCH 0/3] kbuild: remove PROVIDE() and refactor vmlinux_link steps Masahiro Yamada
@ 2024-05-22 11:47 ` Masahiro Yamada
2024-05-23 9:31 ` Ard Biesheuvel
2024-05-28 9:42 ` [PATCH 0/3] kbuild: remove PROVIDE() and refactor vmlinux_link steps Jiri Olsa
1 sibling, 1 reply; 5+ messages in thread
From: Masahiro Yamada @ 2024-05-22 11:47 UTC (permalink / raw)
To: linux-kbuild
Cc: linux-kernel, bpf, Ard Biesheuvel, Masahiro Yamada, Arnd Bergmann,
Nathan Chancellor, Nicolas Schier, linux-arch
This reimplements commit 951bcae6c5a0 ("kallsyms: Avoid weak references
for kallsyms symbols").
I am not a big fan of PROVIDE() because it always satisfies the linker
even in situations that should result in a link error. In other words,
it can potentially shift a compile-time error into a run-time error.
Duplicating kallsyms_* in vmlinux.lds.h also reduces maintainability.
As an alternative solution, this commit prepends one more kallsyms step.
KSYMS .tmp_vmlinux.kallsyms0.S # added
AS .tmp_vmlinux.kallsyms0.o # added
LD .tmp_vmlinux.btf
BTF .btf.vmlinux.bin.o
LD .tmp_vmlinux.kallsyms1
NM .tmp_vmlinux.kallsyms1.syms
KSYMS .tmp_vmlinux.kallsyms1.S
AS .tmp_vmlinux.kallsyms1.o
LD .tmp_vmlinux.kallsyms2
NM .tmp_vmlinux.kallsyms2.syms
KSYMS .tmp_vmlinux.kallsyms2.S
AS .tmp_vmlinux.kallsyms2.o
LD vmlinux
Step 0 takes /dev/null as input, and generates .tmp_vmlinux.kallsyms0.o,
which has a valid kallsyms format with the empty symbol list, and can be
linked to vmlinux. Since it is really small, the added compile-time cost
is negligible.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
---
include/asm-generic/vmlinux.lds.h | 19 -------------------
kernel/kallsyms_internal.h | 5 -----
scripts/kallsyms.c | 6 ------
scripts/link-vmlinux.sh | 10 ++++++++--
4 files changed, 8 insertions(+), 32 deletions(-)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 5703526d6ebf..62b4cb0462e6 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -451,30 +451,11 @@
#endif
#endif
-/*
- * Some symbol definitions will not exist yet during the first pass of the
- * link, but are guaranteed to exist in the final link. Provide preliminary
- * definitions that will be superseded in the final link to avoid having to
- * rely on weak external linkage, which requires a GOT when used in position
- * independent code.
- */
-#define PRELIMINARY_SYMBOL_DEFINITIONS \
- PROVIDE(kallsyms_addresses = .); \
- PROVIDE(kallsyms_offsets = .); \
- PROVIDE(kallsyms_names = .); \
- PROVIDE(kallsyms_num_syms = .); \
- PROVIDE(kallsyms_relative_base = .); \
- PROVIDE(kallsyms_token_table = .); \
- PROVIDE(kallsyms_token_index = .); \
- PROVIDE(kallsyms_markers = .); \
- PROVIDE(kallsyms_seqs_of_names = .);
-
/*
* Read only Data
*/
#define RO_DATA(align) \
. = ALIGN((align)); \
- PRELIMINARY_SYMBOL_DEFINITIONS \
.rodata : AT(ADDR(.rodata) - LOAD_OFFSET) { \
__start_rodata = .; \
*(.rodata) *(.rodata.*) \
diff --git a/kernel/kallsyms_internal.h b/kernel/kallsyms_internal.h
index 85480274fc8f..925f2ab22639 100644
--- a/kernel/kallsyms_internal.h
+++ b/kernel/kallsyms_internal.h
@@ -4,11 +4,6 @@
#include <linux/types.h>
-/*
- * These will be re-linked against their real values during the second link
- * stage. Preliminary values must be provided in the linker script using the
- * PROVIDE() directive so that the first link stage can complete successfully.
- */
extern const unsigned long kallsyms_addresses[];
extern const int kallsyms_offsets[];
extern const u8 kallsyms_names[];
diff --git a/scripts/kallsyms.c b/scripts/kallsyms.c
index 47978efe4797..fa53b5eef553 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -259,12 +259,6 @@ static void shrink_table(void)
}
}
table_cnt = pos;
-
- /* When valid symbol is not registered, exit to error */
- if (!table_cnt) {
- fprintf(stderr, "No valid symbol.\n");
- exit(1);
- }
}
static void read_map(const char *in)
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index b16967d33f1c..fe7db9a265ca 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -225,6 +225,11 @@ ${MAKE} -f "${srctree}/scripts/Makefile.build" obj=init init/version-timestamp.o
kallsymso=
btf_vmlinux_bin_o=
+if is_enabled CONFIG_KALLSYMS; then
+ # kallsyms step 0
+ kallsyms /dev/null .tmp_vmlinux.kallsyms0
+fi
+
if is_enabled CONFIG_DEBUG_INFO_BTF; then
if ! gen_btf .tmp_vmlinux.btf .btf.vmlinux.bin.o ; then
echo >&2 "Failed to generate BTF for vmlinux"
@@ -237,9 +242,10 @@ if is_enabled CONFIG_KALLSYMS; then
# kallsyms support
# Generate section listing all symbols and add it into vmlinux
- # It's a three step process:
+ # It's a four step process:
+ # 0) Generate a dummy __kallsyms with empty symbol list.
# 1) Link .tmp_vmlinux.kallsyms1 so it has all symbols and sections,
- # but __kallsyms is empty.
+ # with a dummy __kallsyms.
# Running kallsyms on that gives us .tmp_kallsyms1.o with
# the right size
# 2) Link .tmp_vmlinux.kallsyms2 so it now has a __kallsyms section of
--
2.40.1
^ permalink raw reply related [flat|nested] 5+ messages in thread* Re: [PATCH 0/3] kbuild: remove PROVIDE() and refactor vmlinux_link steps
2024-05-22 11:47 [PATCH 0/3] kbuild: remove PROVIDE() and refactor vmlinux_link steps Masahiro Yamada
2024-05-22 11:47 ` [PATCH 2/3] kbuild: remove PROVIDE() for kallsyms symbols Masahiro Yamada
@ 2024-05-28 9:42 ` Jiri Olsa
1 sibling, 0 replies; 5+ messages in thread
From: Jiri Olsa @ 2024-05-28 9:42 UTC (permalink / raw)
To: Masahiro Yamada
Cc: linux-kbuild, linux-kernel, bpf, Ard Biesheuvel, Arnd Bergmann,
Nathan Chancellor, Nicolas Schier, linux-arch
On Wed, May 22, 2024 at 08:47:52PM +0900, Masahiro Yamada wrote:
>
> - Remove PROVIDE() in the linker script
> - Merge temporary vmlinux link steps for BTF and kallsyms
>
>
>
> Masahiro Yamada (3):
> kbuild: refactor variables in scripts/link-vmlinux.sh
> kbuild: remove PROVIDE() for kallsyms symbols
> kbuild: merge temp vmlinux for CONFIG_DEBUG_INFO_BTF and
> CONFIG_KALLSYMS
lgtm, fyi I ran bpf CI on top of this change and passed
https://github.com/kernel-patches/bpf/pull/7104
jirka
>
> include/asm-generic/vmlinux.lds.h | 19 -------
> kernel/kallsyms_internal.h | 5 --
> scripts/kallsyms.c | 6 ---
> scripts/link-vmlinux.sh | 87 ++++++++++++++++---------------
> 4 files changed, 45 insertions(+), 72 deletions(-)
>
> --
> 2.40.1
>
>
^ permalink raw reply [flat|nested] 5+ messages in thread