bpf: support pre-2.25-binutils objcopy for vmlinux BTF

PATCH Superseded Stanislav Fomichev 4 participants 6 messages Nov 26, 2019 – Nov 27, 2019

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Stanislav Fomichev

author

2019-11-26 23:28 UTC #0 lore raw

PATCH v2 1/1 bpf: support pre-2.25-binutils objcopy for vmlinux BTF

If vmlinux BTF generation fails, but CONFIG_DEBUG_INFO_BTF is set, .BTF section of vmlinux is empty and kernel will prohibit BPF loading and return "in-kernel BTF is malformed".

--dump-section argument to binutils' objcopy was added in version 2.25. When using pre-2.25 binutils, BTF generation silently fails. Convert to --only-section which is present on pre-2.25 binutils.

Documentation/process/changes.rst states that binutils 2.21+ is supported, not sure those standards apply to BPF subsystem.

v2:
* exit and print an error if gen_btf fails (John Fastabend)

Cc Andrii Nakryiko <[email protected]>

Cc John Fastabend <[email protected]>

Fixes 341dfcf8d78ea ("btf: expose BTF info through sysfs")

Signed-off-by Stanislav Fomichev <[email protected]>

---
 scripts/link-vmlinux.sh | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

scripts/link-vmlinux.sh +6 -1

index 06495379fcd8..2998ddb323e3 100755
@@ -127,7 +127,8 @@ gen_btf()
 		cut -d, -f1 | cut -d' ' -f2)
 	bin_format=$(LANG=C ${OBJDUMP} -f ${1} | grep 'file format' | \
 		awk '{print $4}')
-	${OBJCOPY} --dump-section .BTF=.btf.vmlinux.bin ${1} 2>/dev/null
+	${OBJCOPY} --set-section-flags .BTF=alloc -O binary \
+		--only-section=.BTF ${1} .btf.vmlinux.bin 2>/dev/null
 	${OBJCOPY} -I binary -O ${bin_format} -B ${bin_arch} \
 		--rename-section .data=.BTF .btf.vmlinux.bin ${2}
 }

@@ -253,6 +254,10 @@ btf_vmlinux_bin_o=""
 if [ -n "${CONFIG_DEBUG_INFO_BTF}" ]; then
 	if gen_btf .tmp_vmlinux.btf .btf.vmlinux.bin.o ; then
 		btf_vmlinux_bin_o=.btf.vmlinux.bin.o
+	else
+		echo >&2 "Failed to generate BTF for vmlinux"
+		echo >&2 "Try to disable CONFIG_DEBUG_INFO_BTF"
+		exit 1
 	fi
 fi

Signature · 1 line

2.24.0.432.g9d3f5f5b63-goog

John Fastabend

2019-11-26 23:36 UTC #1 lore raw

Quoted 37 lines · Stanislav Fomichev

If vmlinux BTF generation fails, but CONFIG_DEBUG_INFO_BTF is set, .BTF section of vmlinux is empty and kernel will prohibit BPF loading and return "in-kernel BTF is malformed".
--dump-section argument to binutils' objcopy was added in version 2.25. When using pre-2.25 binutils, BTF generation silently fails. Convert to --only-section which is present on pre-2.25 binutils.
Documentation/process/changes.rst states that binutils 2.21+ is supported, not sure those standards apply to BPF subsystem.
v2:
* exit and print an error if gen_btf fails (John Fastabend)
Cc Andrii Nakryiko <[email protected]>
Cc John Fastabend <[email protected]>
Fixes 341dfcf8d78ea ("btf: expose BTF info through sysfs")
Signed-off-by Stanislav Fomichev <[email protected]>
---
 scripts/link-vmlinux.sh | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
scripts/link-vmlinux.sh +2 -1
index 06495379fcd8..2998ddb323e3 100755
@@ -127,7 +127,8 @@ gen_btf()
 		cut -d, -f1 | cut -d' ' -f2)
 	bin_format=$(LANG=C ${OBJDUMP} -f ${1} | grep 'file format' | \
 		awk '{print $4}')
-	${OBJCOPY} --dump-section .BTF=.btf.vmlinux.bin ${1} 2>/dev/null
+	${OBJCOPY} --set-section-flags .BTF=alloc -O binary \
+		--only-section=.BTF ${1} .btf.vmlinux.bin 2>/dev/null
 	${OBJCOPY} -I binary -O ${bin_format} -B ${bin_arch} \
 		--rename-section .data=.BTF .btf.vmlinux.bin ${2}
 }

scripts/link-vmlinux.sh btf_vmlinux_bin_o="" · line 259

Quoted 6 lines

scripts/link-vmlinux.sh +3 -0

@@ -253,6 +254,10 @@ btf_vmlinux_bin_o=""
 if [ -n "${CONFIG_DEBUG_INFO_BTF}" ]; then
 	if gen_btf .tmp_vmlinux.btf .btf.vmlinux.bin.o ; then
 		btf_vmlinux_bin_o=.btf.vmlinux.bin.o
+	else
+		echo >&2 "Failed to generate BTF for vmlinux"
+		echo >&2 "Try to disable CONFIG_DEBUG_INFO_BTF"

I think we should encourage upgrading binutils first? Maybe

"binutils 2.25+ required for BTF please upgrade or disable CONFIG_DEBUG_INFO_BTF"

otherwise I guess its going to be a bit mystical why it works in cases and not others to folks unfamiliar with the details.

Quoted 7 lines

scripts/link-vmlinux.sh +1 -0
+		exit 1
 	fi
 fi
 
Signature · 1 line
2.24.0.432.g9d3f5f5b63-goog

Stanislav Fomichev

2019-11-26 23:45 UTC #2 lore raw

Quoted 47 lines · John Fastabend

Quoted 37 lines · Stanislav Fomichev
If vmlinux BTF generation fails, but CONFIG_DEBUG_INFO_BTF is set, .BTF section of vmlinux is empty and kernel will prohibit BPF loading and return "in-kernel BTF is malformed".
--dump-section argument to binutils' objcopy was added in version 2.25. When using pre-2.25 binutils, BTF generation silently fails. Convert to --only-section which is present on pre-2.25 binutils.
Documentation/process/changes.rst states that binutils 2.21+ is supported, not sure those standards apply to BPF subsystem.
v2:
* exit and print an error if gen_btf fails (John Fastabend)
Cc Andrii Nakryiko <[email protected]>
Cc John Fastabend <[email protected]>
Fixes 341dfcf8d78ea ("btf: expose BTF info through sysfs")
Signed-off-by Stanislav Fomichev <[email protected]>
---
 scripts/link-vmlinux.sh | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
scripts/link-vmlinux.sh +2 -1
index 06495379fcd8..2998ddb323e3 100755
@@ -127,7 +127,8 @@ gen_btf()
 		cut -d, -f1 | cut -d' ' -f2)
 	bin_format=$(LANG=C ${OBJDUMP} -f ${1} | grep 'file format' | \
 		awk '{print $4}')
-	${OBJCOPY} --dump-section .BTF=.btf.vmlinux.bin ${1} 2>/dev/null
+	${OBJCOPY} --set-section-flags .BTF=alloc -O binary \
+		--only-section=.BTF ${1} .btf.vmlinux.bin 2>/dev/null
 	${OBJCOPY} -I binary -O ${bin_format} -B ${bin_arch} \
 		--rename-section .data=.BTF .btf.vmlinux.bin ${2}
 }
scripts/link-vmlinux.sh btf_vmlinux_bin_o="" · line 259
Quoted 6 lines
scripts/link-vmlinux.sh +3 -0
@@ -253,6 +254,10 @@ btf_vmlinux_bin_o=""
 if [ -n "${CONFIG_DEBUG_INFO_BTF}" ]; then
 	if gen_btf .tmp_vmlinux.btf .btf.vmlinux.bin.o ; then
 		btf_vmlinux_bin_o=.btf.vmlinux.bin.o
+	else
+		echo >&2 "Failed to generate BTF for vmlinux"
+		echo >&2 "Try to disable CONFIG_DEBUG_INFO_BTF"
I think we should encourage upgrading binutils first? Maybe

Quoted 4 lines

"binutils 2.25+ required for BTF please upgrade or disable CONFIG_DEBUG_INFO_BTF"
otherwise I guess its going to be a bit mystical why it works in cases and not others to folks unfamiliar with the details.

With the conversion from --dump-section to --only-section that I did in this patch, binutils 2.25+ is no longer a requirement. 2.21 (minimal version from Documentation/process/changes.rst) should work just fine.

Andrii Nakryiko

2019-11-26 23:47 UTC #3 lore raw

Quoted 48 lines · Stanislav Fomichev

Quoted 47 lines · John Fastabend
Quoted 37 lines · Stanislav Fomichev
If vmlinux BTF generation fails, but CONFIG_DEBUG_INFO_BTF is set, .BTF section of vmlinux is empty and kernel will prohibit BPF loading and return "in-kernel BTF is malformed".
--dump-section argument to binutils' objcopy was added in version 2.25. When using pre-2.25 binutils, BTF generation silently fails. Convert to --only-section which is present on pre-2.25 binutils.
Documentation/process/changes.rst states that binutils 2.21+ is supported, not sure those standards apply to BPF subsystem.
v2:
* exit and print an error if gen_btf fails (John Fastabend)
Cc Andrii Nakryiko <[email protected]>
Cc John Fastabend <[email protected]>
Fixes 341dfcf8d78ea ("btf: expose BTF info through sysfs")
Signed-off-by Stanislav Fomichev <[email protected]>
---
  scripts/link-vmlinux.sh | 7 ++++++-
  1 file changed, 6 insertions(+), 1 deletion(-)
scripts/link-vmlinux.sh +2 -1
index 06495379fcd8..2998ddb323e3 100755
@@ -127,7 +127,8 @@ gen_btf()
  		cut -d, -f1 | cut -d' ' -f2)
  	bin_format=$(LANG=C ${OBJDUMP} -f ${1} | grep 'file format' | \
  		awk '{print $4}')
-	${OBJCOPY} --dump-section .BTF=.btf.vmlinux.bin ${1} 2>/dev/null
+	${OBJCOPY} --set-section-flags .BTF=alloc -O binary \
+		--only-section=.BTF ${1} .btf.vmlinux.bin 2>/dev/null
  	${OBJCOPY} -I binary -O ${bin_format} -B ${bin_arch} \
  		--rename-section .data=.BTF .btf.vmlinux.bin ${2}
  }
scripts/link-vmlinux.sh btf_vmlinux_bin_o="" · line 259
Quoted 6 lines
scripts/link-vmlinux.sh +3 -0
@@ -253,6 +254,10 @@ btf_vmlinux_bin_o=""
  if [ -n "${CONFIG_DEBUG_INFO_BTF}" ]; then
  	if gen_btf .tmp_vmlinux.btf .btf.vmlinux.bin.o ; then
  		btf_vmlinux_bin_o=.btf.vmlinux.bin.o
+	else
+		echo >&2 "Failed to generate BTF for vmlinux"
+		echo >&2 "Try to disable CONFIG_DEBUG_INFO_BTF"
I think we should encourage upgrading binutils first? Maybe

Quoted 8 lines

Quoted 4 lines
"binutils 2.25+ required for BTF please upgrade or disable CONFIG_DEBUG_INFO_BTF"
otherwise I guess its going to be a bit mystical why it works in cases and not others to folks unfamiliar with the details.
With the conversion from --dump-section to --only-section that I did in this patch, binutils 2.25+ is no longer a requirement. 2.21 (minimal version from Documentation/process/changes.rst) should work just fine.

Yeah, instead it's better to mention that pahole v1.13+ is required.

Quoted 1 line

Stanislav Fomichev

2019-11-27 00:04 UTC #4 lore raw

Quoted 51 lines · Andrii Nakryiko

Quoted 50 lines · Stanislav Fomichev
Quoted 49 lines · John Fastabend
Quoted 37 lines · Stanislav Fomichev
If vmlinux BTF generation fails, but CONFIG_DEBUG_INFO_BTF is set, .BTF section of vmlinux is empty and kernel will prohibit BPF loading and return "in-kernel BTF is malformed".
--dump-section argument to binutils' objcopy was added in version 2.25. When using pre-2.25 binutils, BTF generation silently fails. Convert to --only-section which is present on pre-2.25 binutils.
Documentation/process/changes.rst states that binutils 2.21+ is supported, not sure those standards apply to BPF subsystem.
v2:
* exit and print an error if gen_btf fails (John Fastabend)
Cc Andrii Nakryiko <[email protected]>
Cc John Fastabend <[email protected]>
Fixes 341dfcf8d78ea ("btf: expose BTF info through sysfs")
Signed-off-by Stanislav Fomichev <[email protected]>
---
  scripts/link-vmlinux.sh | 7 ++++++-
  1 file changed, 6 insertions(+), 1 deletion(-)
scripts/link-vmlinux.sh +2 -1
index 06495379fcd8..2998ddb323e3 100755
@@ -127,7 +127,8 @@ gen_btf()
  		cut -d, -f1 | cut -d' ' -f2)
  	bin_format=$(LANG=C ${OBJDUMP} -f ${1} | grep 'file format' | \
  		awk '{print $4}')
-	${OBJCOPY} --dump-section .BTF=.btf.vmlinux.bin ${1} 2>/dev/null
+	${OBJCOPY} --set-section-flags .BTF=alloc -O binary \
+		--only-section=.BTF ${1} .btf.vmlinux.bin 2>/dev/null
  	${OBJCOPY} -I binary -O ${bin_format} -B ${bin_arch} \
  		--rename-section .data=.BTF .btf.vmlinux.bin ${2}
  }
scripts/link-vmlinux.sh btf_vmlinux_bin_o="" · line 259
Quoted 6 lines
scripts/link-vmlinux.sh +3 -0
@@ -253,6 +254,10 @@ btf_vmlinux_bin_o=""
  if [ -n "${CONFIG_DEBUG_INFO_BTF}" ]; then
  	if gen_btf .tmp_vmlinux.btf .btf.vmlinux.bin.o ; then
  		btf_vmlinux_bin_o=.btf.vmlinux.bin.o
+	else
+		echo >&2 "Failed to generate BTF for vmlinux"
+		echo >&2 "Try to disable CONFIG_DEBUG_INFO_BTF"
I think we should encourage upgrading binutils first? Maybe
"binutils 2.25+ required for BTF please upgrade or disable CONFIG_DEBUG_INFO_BTF"

Quoted 8 lines

Quoted 6 lines
Quoted 2 lines
otherwise I guess its going to be a bit mystical why it works in cases and not others to folks unfamiliar with the details.
With the conversion from --dump-section to --only-section that I did in this patch, binutils 2.25+ is no longer a requirement. 2.21 (minimal version from Documentation/process/changes.rst) should work just fine.
Yeah, instead it's better to mention that pahole v1.13+ is required.

We already have most of the messages about missing pahole or wrong version:
https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/scripts/link-vmlinux.sh#n111
https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/scripts/link-vmlinux.sh#n117

They are 'info' though, but it seems logical to drop -s from make arguments if someone wants to debug further.

Andrii Nakryiko

Acked-by

2019-11-27 00:27 UTC #5 lore raw

Quoted 59 lines · Stanislav Fomichev

Quoted 58 lines · Andrii Nakryiko
Quoted 56 lines · Stanislav Fomichev
Quoted 47 lines · John Fastabend
Quoted 37 lines · Stanislav Fomichev
If vmlinux BTF generation fails, but CONFIG_DEBUG_INFO_BTF is set, .BTF section of vmlinux is empty and kernel will prohibit BPF loading and return "in-kernel BTF is malformed".
--dump-section argument to binutils' objcopy was added in version 2.25. When using pre-2.25 binutils, BTF generation silently fails. Convert to --only-section which is present on pre-2.25 binutils.
Documentation/process/changes.rst states that binutils 2.21+ is supported, not sure those standards apply to BPF subsystem.
v2:
* exit and print an error if gen_btf fails (John Fastabend)
Cc Andrii Nakryiko <[email protected]>
Cc John Fastabend <[email protected]>
Fixes 341dfcf8d78ea ("btf: expose BTF info through sysfs")
Signed-off-by Stanislav Fomichev <[email protected]>
---
   scripts/link-vmlinux.sh | 7 ++++++-
   1 file changed, 6 insertions(+), 1 deletion(-)
scripts/link-vmlinux.sh +2 -1
index 06495379fcd8..2998ddb323e3 100755
@@ -127,7 +127,8 @@ gen_btf()
   		cut -d, -f1 | cut -d' ' -f2)
   	bin_format=$(LANG=C ${OBJDUMP} -f ${1} | grep 'file format' | \
   		awk '{print $4}')
-	${OBJCOPY} --dump-section .BTF=.btf.vmlinux.bin ${1} 2>/dev/null
+	${OBJCOPY} --set-section-flags .BTF=alloc -O binary \
+		--only-section=.BTF ${1} .btf.vmlinux.bin 2>/dev/null
   	${OBJCOPY} -I binary -O ${bin_format} -B ${bin_arch} \
   		--rename-section .data=.BTF .btf.vmlinux.bin ${2}
   }
scripts/link-vmlinux.sh btf_vmlinux_bin_o="" · line 259
Quoted 6 lines
scripts/link-vmlinux.sh +3 -0
@@ -253,6 +254,10 @@ btf_vmlinux_bin_o=""
   if [ -n "${CONFIG_DEBUG_INFO_BTF}" ]; then
   	if gen_btf .tmp_vmlinux.btf .btf.vmlinux.bin.o ; then
   		btf_vmlinux_bin_o=.btf.vmlinux.bin.o
+	else
+		echo >&2 "Failed to generate BTF for vmlinux"
+		echo >&2 "Try to disable CONFIG_DEBUG_INFO_BTF"
I think we should encourage upgrading binutils first? Maybe
Quoted 4 lines
"binutils 2.25+ required for BTF please upgrade or disable CONFIG_DEBUG_INFO_BTF"
otherwise I guess its going to be a bit mystical why it works in cases and not others to folks unfamiliar with the details.
With the conversion from --dump-section to --only-section that I did in this patch, binutils 2.25+ is no longer a requirement. 2.21 (minimal version from Documentation/process/changes.rst) should work just fine.

Quoted 8 lines

Quoted 1 line
Yeah, instead it's better to mention that pahole v1.13+ is required.
We already have most of the messages about missing pahole or wrong version:
https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/scripts/link-vmlinux.sh#n111
https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/scripts/link-vmlinux.sh#n117
They are 'info' though, but it seems logical to drop -s from make arguments if someone wants to debug further.

Fair enough. Please add back my Tested-by: tag.

Acked-by Andrii Nakryiko <[email protected]>