[PATCH 4/4] kbuild: remove PROVIDE() for kallsyms symbols
From: Masahiro Yamada
Date: Mon May 20 2024 - 08:43:30 EST
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.
I shuffled scripts/link-vmlinux.sh to prepend one more kallsyms step.
The following logs illustrates how it works.
[Before]
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
[After]
KSYMS .tmp_vmlinux.kallsyms0.S # added
AS .tmp_vmlinux.kallsyms0.o # added
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 zero symbols, and can be linked
to vmlinux. Since it is really small, the added compile-time cost is
negligible.
Signed-off-by: Masahiro Yamada <masahiroy@xxxxxxxxxx>
---
include/asm-generic/vmlinux.lds.h | 19 -------------
kernel/kallsyms_internal.h | 5 ----
scripts/kallsyms.c | 6 -----
scripts/link-vmlinux.sh | 45 ++++++++++++++++---------------
4 files changed, 24 insertions(+), 51 deletions(-)
diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 870753fbb123..9752eb420ffa 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -448,30 +448,11 @@
#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- * definitions that will be superseded in the final link to avoid having to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 653b92f6d4c8..6b90f52fd707 100644
--- a/scripts/kallsyms.c
+++ b/scripts/kallsyms.c
@@ -246,12 +246,6 @@ 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 7aca51b24e9f..242a92e24f20 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -165,27 +165,25 @@ kallsyms()
kallsymopt="${kallsymopt} --lto-clang"
fi
- info KSYMS ${2}
- scripts/kallsyms ${kallsymopt} ${1} > ${2}
+ info KSYMS "${2}.S"
+ scripts/kallsyms ${kallsymopt} "${1}" > "${2}.S"
+
+ info AS "${2}.o"
+ ${CC} ${NOSTDINC_FLAGS} ${LINUXINCLUDE} ${KBUILD_CPPFLAGS} \
+ ${KBUILD_AFLAGS} ${KBUILD_AFLAGS_KERNEL} \
+ -c -o "${2}.o" "${2}.S"
+ kallsymso=${2}.o
}
# Perform one step in kallsyms generation, including temporary linking of
# vmlinux.
kallsyms_step()
{
- kallsymso_prev=${kallsymso}
kallsyms_vmlinux=.tmp_vmlinux.kallsyms${1}
- kallsymso=${kallsyms_vmlinux}.o
- kallsyms_S=${kallsyms_vmlinux}.S
- vmlinux_link ${kallsyms_vmlinux} "${kallsymso_prev}" ${btf_vmlinux_bin_o}
- mksysmap ${kallsyms_vmlinux} ${kallsyms_vmlinux}.syms
- kallsyms ${kallsyms_vmlinux}.syms ${kallsyms_S}
-
- info AS ${kallsymso}
- ${CC} ${NOSTDINC_FLAGS} ${LINUXINCLUDE} ${KBUILD_CPPFLAGS} \
- ${KBUILD_AFLAGS} ${KBUILD_AFLAGS_KERNEL} \
- -c -o ${kallsymso} ${kallsyms_S}
+ vmlinux_link "${kallsyms_vmlinux}" "${kallsymso}" "${btf_vmlinux_bin_o}"
+ mksysmap "${kallsyms_vmlinux}" "${kallsyms_vmlinux}.syms"
+ kallsyms "${kallsyms_vmlinux}.syms" "${kallsyms_vmlinux}"
}
# Create map file with all symbols from ${1}
@@ -235,15 +233,15 @@ if is_enabled CONFIG_DEBUG_INFO_BTF; then
fi
kallsymso=""
-kallsymso_prev=""
-kallsyms_vmlinux=""
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, which has zero symbols, but a valid
+ # format.
# 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
@@ -262,13 +260,18 @@ if is_enabled CONFIG_KALLSYMS; then
# a) Verify that the System.map from vmlinux matches the map from
# ${kallsymso}.
- kallsyms_step 1
- kallsyms_step 2
+ # step 0
+ kallsyms /dev/null .tmp_vmlinux.kallsyms0
- # step 3
- size1=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso_prev})
+ # step 1
+ kallsyms_step 1
+ size1=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso})
+
+ # step 2
+ kallsyms_step 2
size2=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso})
+ # step 3
if [ $size1 -ne $size2 ] || [ -n "${KALLSYMS_EXTRA_PASS}" ]; then
kallsyms_step 3
fi
--
2.40.1