- 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
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
Clean up the variables in scripts/link-vmlinux.sh
- Specify the extra objects directly in vmlinux_link()
- Move the AS rule to kallsyms()
- Set kallsymso and btf_vmlinux_bin_o where they are generated
- Remove unneeded variable, kallsymso_prev
No functional change intended.
Signed-off-by: Masahiro Yamada <[email protected]>
---
scripts/link-vmlinux.sh | 48 +++++++++++++++++++----------------------
1 file changed, 22 insertions(+), 26 deletions(-)
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index 46ce5d04dbeb..b16967d33f1c 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -45,7 +45,6 @@ info()
# Link of vmlinux
# ${1} - output file
-# ${2}, ${3}, ... - optional extra .o files
vmlinux_link()
{
local output=${1}
@@ -101,7 +100,7 @@ vmlinux_link()
${ld} ${ldflags} -o ${output} \
${wl}--whole-archive ${objs} ${wl}--no-whole-archive \
${wl}--start-group ${libs} ${wl}--end-group \
- $@ ${ldlibs}
+ ${kallsymso} ${btf_vmlinux_bin_o} ${ldlibs}
}
# generate .BTF typeinfo from DWARF debuginfo
@@ -142,9 +141,11 @@ gen_btf()
et_rel='\1\0'
fi
printf "${et_rel}" | dd of=${2} conv=notrunc bs=1 seek=16 status=none
+
+ btf_vmlinux_bin_o=${2}
}
-# Create ${2} .S file with all symbols from the ${1} object file
+# Create ${2}.o file with all symbols from the ${1} object file
kallsyms()
{
local kallsymopt;
@@ -165,27 +166,25 @@ kallsyms()
kallsymopt="${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}"
+ mksysmap "${kallsyms_vmlinux}" "${kallsyms_vmlinux}.syms"
+ kallsyms "${kallsyms_vmlinux}.syms" "${kallsyms_vmlinux}"
}
# Create map file with all symbols from ${1}
@@ -223,19 +222,17 @@ fi
${MAKE} -f "${srctree}/scripts/Makefile.build" obj=init init/version-timestamp.o
-btf_vmlinux_bin_o=""
+kallsymso=
+btf_vmlinux_bin_o=
+
if is_enabled CONFIG_DEBUG_INFO_BTF; then
- btf_vmlinux_bin_o=.btf.vmlinux.bin.o
- if ! gen_btf .tmp_vmlinux.btf $btf_vmlinux_bin_o ; then
+ if ! gen_btf .tmp_vmlinux.btf .btf.vmlinux.bin.o ; then
echo >&2 "Failed to generate BTF for vmlinux"
echo >&2 "Try to disable CONFIG_DEBUG_INFO_BTF"
exit 1
fi
fi
-kallsymso=""
-kallsymso_prev=""
-kallsyms_vmlinux=""
if is_enabled CONFIG_KALLSYMS; then
# kallsyms support
@@ -262,10 +259,9 @@ if is_enabled CONFIG_KALLSYMS; then
# ${kallsymso}.
kallsyms_step 1
- kallsyms_step 2
+ size1=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso})
- # step 3
- size1=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso_prev})
+ kallsyms_step 2
size2=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso})
if [ $size1 -ne $size2 ] || [ -n "${KALLSYMS_EXTRA_PASS}" ]; then
@@ -273,7 +269,7 @@ if is_enabled CONFIG_KALLSYMS; then
fi
fi
-vmlinux_link vmlinux "${kallsymso}" ${btf_vmlinux_bin_o}
+vmlinux_link vmlinux
# fill in BTF IDs
if is_enabled CONFIG_DEBUG_INFO_BTF && is_enabled CONFIG_BPF; then
--
2.40.1
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 <[email protected]>
---
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
CONFIG_DEBUG_INFO_BTF=y requires one additional link step.
(.tmp_vmlinux.btf)
CONFIG_KALLSYMS=y requires two additional link steps.
(.tmp_vmlinux.kallsyms1 and .tmp_vmlinux.kallsyms2)
Enabling both requires three additional link steps.
When CONFIG_DEBUG_INFO_BTF=y and CONFIG_KALLSYMS=y, the build step looks
as follows:
KSYMS .tmp_vmlinux.kallsyms0.S
AS .tmp_vmlinux.kallsyms0.o
LD .tmp_vmlinux.btf # temp vmlinux for BTF
BTF .btf.vmlinux.bin.o
LD .tmp_vmlinux.kallsyms1 # temp vmlinux for kallsyms step 1
NM .tmp_vmlinux.kallsyms1.syms
KSYMS .tmp_vmlinux.kallsyms1.S
AS .tmp_vmlinux.kallsyms1.o
LD .tmp_vmlinux.kallsyms2 # temp vmlinux for kallsyms step 2
NM .tmp_vmlinux.kallsyms2.syms
KSYMS .tmp_vmlinux.kallsyms2.S
AS .tmp_vmlinux.kallsyms2.o
LD vmlinux # final vmlinux
This is redundant because the BTF generation and the kallsyms step 1 can
be performed against the same temporary vmlinux.
When both CONFIG_DEBUG_INFO_BTF and CONFIG_KALLSYMS are enabled, we can
reduce the number of link steps.
The build step will look as follows:
KSYMS .tmp_vmlinux0.kallsyms.S
AS .tmp_vmlinux0.kallsyms.o
LD .tmp_vmlinux1 # temp vmlinux for BTF and kallsyms step 1
BTF .tmp_vmlinux1.btf.o
NM .tmp_vmlinux1.syms
KSYMS .tmp_vmlinux1.kallsyms.S
AS .tmp_vmlinux1.kallsyms.o
LD .tmp_vmlinux2 # temp vmlinux for kallsyms step 2
NM .tmp_vmlinux2.syms
KSYMS .tmp_vmlinux2.kallsyms.S
AS .tmp_vmlinux2.kallsyms.o
LD vmlinux # final link
Signed-off-by: Masahiro Yamada <[email protected]>
---
scripts/link-vmlinux.sh | 45 +++++++++++++++++++++--------------------
1 file changed, 23 insertions(+), 22 deletions(-)
diff --git a/scripts/link-vmlinux.sh b/scripts/link-vmlinux.sh
index fe7db9a265ca..ea004aae6ce5 100755
--- a/scripts/link-vmlinux.sh
+++ b/scripts/link-vmlinux.sh
@@ -105,10 +105,10 @@ vmlinux_link()
# generate .BTF typeinfo from DWARF debuginfo
# ${1} - vmlinux image
-# ${2} - file to dump raw BTF data into
gen_btf()
{
local pahole_ver
+ local btf_data=${1}.btf.o
if ! [ -x "$(command -v ${PAHOLE})" ]; then
echo >&2 "BTF: ${1}: pahole (${PAHOLE}) is not available"
@@ -121,18 +121,16 @@ gen_btf()
return 1
fi
- vmlinux_link ${1}
-
- info "BTF" ${2}
+ info BTF "${btf_data}"
LLVM_OBJCOPY="${OBJCOPY}" ${PAHOLE} -J ${PAHOLE_FLAGS} ${1}
- # Create ${2} which contains just .BTF section but no symbols. Add
+ # Create ${btf_data} which contains just .BTF section but no symbols. Add
# SHF_ALLOC because .BTF will be part of the vmlinux image. --strip-all
# deletes all symbols including __start_BTF and __stop_BTF, which will
# be redefined in the linker script. Add 2>/dev/null to suppress GNU
# objcopy warnings: "empty loadable segment detected at ..."
${OBJCOPY} --only-section=.BTF --set-section-flags .BTF=alloc,readonly \
- --strip-all ${1} ${2} 2>/dev/null
+ --strip-all ${1} "${btf_data}" 2>/dev/null
# Change e_type to ET_REL so that it can be used to link final vmlinux.
# GNU ld 2.35+ and lld do not allow an ET_EXEC input.
if is_enabled CONFIG_CPU_BIG_ENDIAN; then
@@ -140,9 +138,9 @@ gen_btf()
else
et_rel='\1\0'
fi
- printf "${et_rel}" | dd of=${2} conv=notrunc bs=1 seek=16 status=none
+ printf "${et_rel}" | dd of="${btf_data}" conv=notrunc bs=1 seek=16 status=none
- btf_vmlinux_bin_o=${2}
+ btf_vmlinux_bin_o=${btf_data}
}
# Create ${2}.o file with all symbols from the ${1} object file
@@ -176,15 +174,13 @@ kallsyms()
kallsymso=${2}.o
}
-# Perform one step in kallsyms generation, including temporary linking of
-# vmlinux.
-kallsyms_step()
+# Perform kallsyms for the given temporary vmlinux.
+sysmap_and_kallsyms()
{
- kallsyms_vmlinux=.tmp_vmlinux.kallsyms${1}
+ mksysmap "${1}" "${1}.syms"
+ kallsyms "${1}.syms" "${1}.kallsyms"
- vmlinux_link "${kallsyms_vmlinux}"
- mksysmap "${kallsyms_vmlinux}" "${kallsyms_vmlinux}.syms"
- kallsyms "${kallsyms_vmlinux}.syms" "${kallsyms_vmlinux}"
+ kallsyms_sysmap=${1}.syms
}
# Create map file with all symbols from ${1}
@@ -226,12 +222,15 @@ kallsymso=
btf_vmlinux_bin_o=
if is_enabled CONFIG_KALLSYMS; then
- # kallsyms step 0
- kallsyms /dev/null .tmp_vmlinux.kallsyms0
+ kallsyms /dev/null .tmp_vmlinux0.kallsyms
+fi
+
+if is_enabled CONFIG_KALLSYMS || is_enabled CONFIG_DEBUG_INFO_BTF; then
+ vmlinux_link .tmp_vmlinux1
fi
if is_enabled CONFIG_DEBUG_INFO_BTF; then
- if ! gen_btf .tmp_vmlinux.btf .btf.vmlinux.bin.o ; then
+ if ! gen_btf .tmp_vmlinux1; then
echo >&2 "Failed to generate BTF for vmlinux"
echo >&2 "Try to disable CONFIG_DEBUG_INFO_BTF"
exit 1
@@ -264,14 +263,16 @@ if is_enabled CONFIG_KALLSYMS; then
# a) Verify that the System.map from vmlinux matches the map from
# ${kallsymso}.
- kallsyms_step 1
+ sysmap_and_kallsyms .tmp_vmlinux1
size1=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso})
- kallsyms_step 2
+ vmlinux_link .tmp_vmlinux2
+ sysmap_and_kallsyms .tmp_vmlinux2
size2=$(${CONFIG_SHELL} "${srctree}/scripts/file-size.sh" ${kallsymso})
if [ $size1 -ne $size2 ] || [ -n "${KALLSYMS_EXTRA_PASS}" ]; then
- kallsyms_step 3
+ vmlinux_link .tmp_vmlinux3
+ sysmap_and_kallsyms .tmp_vmlinux3
fi
fi
@@ -295,7 +296,7 @@ fi
# step a (see comment above)
if is_enabled CONFIG_KALLSYMS; then
- if ! cmp -s System.map ${kallsyms_vmlinux}.syms; then
+ if ! cmp -s System.map ${kallsyms_sysmap}; then
echo >&2 Inconsistent kallsyms data
echo >&2 'Try "make KALLSYMS_EXTRA_PASS=1" as a workaround'
exit 1
--
2.40.1
On Wed, 22 May 2024 at 13:48, Masahiro Yamada <[email protected]> wrote:
>
> 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.
>
I don't disagree. However, I did realize that, in this particular
case, we could at least make the preliminary symbol definitions
conditional on CONFIG_KALLSYMS rather than always providing them.
This approach is also fine with me, though.
> 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.
>
OK, so the number of linker invocations is the same, right? The
difference is that the kallsyms symbol references are satisfied by a
dummy object?
That seems reasonable to me.
For the series,
Acked-by: Ard Biesheuvel <[email protected]>
On Thu, May 23, 2024 at 6:32 PM Ard Biesheuvel <[email protected]> wrote:
>
> On Wed, 22 May 2024 at 13:48, Masahiro Yamada <[email protected]> wrote:
> >
> > 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.
> >
>
> I don't disagree. However, I did realize that, in this particular
> case, we could at least make the preliminary symbol definitions
> conditional on CONFIG_KALLSYMS rather than always providing them.
Fair enough. I am fine with dropping this statement.
>
> This approach is also fine with me, though.
>
>
> > 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.
> >
>
> OK, so the number of linker invocations is the same, right? The
> difference is that the kallsyms symbol references are satisfied by a
> dummy object?
Correct.
In 3/3, I even reduce the number of link steps
when both CONFIG_DEBUG_INFO_BTF and CONFIG_KALLSYMS are enabled.
>
> That seems reasonable to me.
>
> For the series,
>
> Acked-by: Ard Biesheuvel <[email protected]>
>
--
Best Regards
Masahiro Yamada
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
>
>
On Wed, May 22, 2024 at 4:48 AM Masahiro Yamada <[email protected]> wrote:
>
> CONFIG_DEBUG_INFO_BTF=y requires one additional link step.
> (.tmp_vmlinux.btf)
>
> CONFIG_KALLSYMS=y requires two additional link steps.
> (.tmp_vmlinux.kallsyms1 and .tmp_vmlinux.kallsyms2)
>
> Enabling both requires three additional link steps.
>
> When CONFIG_DEBUG_INFO_BTF=y and CONFIG_KALLSYMS=y, the build step looks
> as follows:
>
> KSYMS .tmp_vmlinux.kallsyms0.S
> AS .tmp_vmlinux.kallsyms0.o
> LD .tmp_vmlinux.btf # temp vmlinux for BTF
> BTF .btf.vmlinux.bin.o
> LD .tmp_vmlinux.kallsyms1 # temp vmlinux for kallsyms step 1
> NM .tmp_vmlinux.kallsyms1.syms
> KSYMS .tmp_vmlinux.kallsyms1.S
> AS .tmp_vmlinux.kallsyms1.o
> LD .tmp_vmlinux.kallsyms2 # temp vmlinux for kallsyms step 2
> NM .tmp_vmlinux.kallsyms2.syms
> KSYMS .tmp_vmlinux.kallsyms2.S
> AS .tmp_vmlinux.kallsyms2.o
> LD vmlinux # final vmlinux
>
> This is redundant because the BTF generation and the kallsyms step 1 can
> be performed against the same temporary vmlinux.
>
> When both CONFIG_DEBUG_INFO_BTF and CONFIG_KALLSYMS are enabled, we can
> reduce the number of link steps.
>
> The build step will look as follows:
>
> KSYMS .tmp_vmlinux0.kallsyms.S
> AS .tmp_vmlinux0.kallsyms.o
> LD .tmp_vmlinux1 # temp vmlinux for BTF and kallsyms step 1
> BTF .tmp_vmlinux1.btf.o
> NM .tmp_vmlinux1.syms
> KSYMS .tmp_vmlinux1.kallsyms.S
> AS .tmp_vmlinux1.kallsyms.o
> LD .tmp_vmlinux2 # temp vmlinux for kallsyms step 2
> NM .tmp_vmlinux2.syms
> KSYMS .tmp_vmlinux2.kallsyms.S
> AS .tmp_vmlinux2.kallsyms.o
> LD vmlinux # final link
>
> Signed-off-by: Masahiro Yamada <[email protected]>
> ---
>
LGTM, thanks!
Acked-by: Andrii Nakryiko <[email protected]>
> scripts/link-vmlinux.sh | 45 +++++++++++++++++++++--------------------
> 1 file changed, 23 insertions(+), 22 deletions(-)
>
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