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kbuild: remove PROVIDE() for kallsyms symbols

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This reimplements commit 951bcae6c5 ("kallsyms: Avoid weak references
for kallsyms symbols") because I am not a big fan of PROVIDE().

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>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>
This commit is contained in:
Masahiro Yamada 2024-06-10 20:25:17 +09:00
parent ddf4132983
commit c442db3f49
4 changed files with 7 additions and 32 deletions
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19
include/asm-generic/vmlinux.lds.h
View File

@ -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* definitions that will be superseded in the final link to avoid having to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.*) \

5
kernel/kallsyms_internal.h
View File

@ -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[];

6
scripts/kallsyms.c
View File

@ -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)

9
scripts/link-vmlinux.sh
View File

@ -227,6 +227,10 @@ btf_vmlinux_bin_o=
kallsymso=
strip_debug=
if is_enabled CONFIG_KALLSYMS; then
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"
@ -239,9 +243,10 @@ 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