Commit c442db3f authored by Masahiro Yamada's avatar Masahiro Yamada
Browse files

kbuild: remove PROVIDE() for kallsyms symbols 



This reimplements commit 951bcae6 ("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: default avatarMasahiro Yamada <masahiroy@kernel.org>
Acked-by: default avatarArd Biesheuvel <ardb@kernel.org>
Reviewed-by: default avatarNicolas Schier <nicolas@fjasle.eu>
parent ddf41329

include/asm-generic/vmlinux.lds.h

+0 −19
Original line number Diff line number Diff line
@@ -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 * definitions that will be superseded in the final link to avoid having to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.*)					\

kernel/kallsyms_internal.h

+0 −5
Original line number Diff line number Diff line
@@ -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[];

scripts/kallsyms.c

+0 −6
Original line number Diff line number Diff line
@@ -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)

scripts/link-vmlinux.sh

+7 −2
Original line number Diff line number Diff line
@@ -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