kbuild: remove PROVIDE() for kallsyms symbols

This reimplements commit 951bcae6c5a0 ("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>

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 5703526d6ebf13bcca1d092edcffd0180db48bad..62b4cb0462e68b6d5198c1cc81b4937b3307cf8e 100644 (file)
--- 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- * definitions that will be superseded in the final link to avoid having to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 85480274fc8fb135b4d4aa7c17404c36f08af41d..925f2ab22639a194a2d0900c4d1984a8361999be 100644 (file)
--- 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 47978efe4797c2e90ce179596108836ee0e9b4b7..fa53b5eef5530db5ba3ef09becb7102045e41ee4 100644 (file)
--- 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 3d9d7257143a02734c01b0f43650cf7581758dc4..83d605ba7241ad34251184b177513587b269f093 100755 (executable)
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -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