--- /dev/null
+From 90ceddcb495008ac8ba7a3dce297841efcd7d584 Mon Sep 17 00:00:00 2001
+From: Fangrui Song <maskray@google.com>
+Date: Wed, 18 Mar 2020 15:27:46 -0700
+Subject: bpf: Support llvm-objcopy for vmlinux BTF
+
+From: Fangrui Song <maskray@google.com>
+
+commit 90ceddcb495008ac8ba7a3dce297841efcd7d584 upstream.
+
+Simplify gen_btf logic to make it work with llvm-objcopy. The existing
+'file format' and 'architecture' parsing logic is brittle and does not
+work with llvm-objcopy/llvm-objdump.
+
+'file format' output of llvm-objdump>=11 will match GNU objdump, but
+'architecture' (bfdarch) may not.
+
+.BTF in .tmp_vmlinux.btf is non-SHF_ALLOC. Add the SHF_ALLOC flag
+because it is part of vmlinux image used for introspection. C code
+can reference the section via linker script defined __start_BTF and
+__stop_BTF. This fixes a small problem that previous .BTF had the
+SHF_WRITE flag (objcopy -I binary -O elf* synthesized .data).
+
+Additionally, `objcopy -I binary` synthesized symbols
+_binary__btf_vmlinux_bin_start and _binary__btf_vmlinux_bin_stop (not
+used elsewhere) are replaced with more commonplace __start_BTF and
+__stop_BTF.
+
+Add 2>/dev/null because GNU objcopy (but not llvm-objcopy) warns
+"empty loadable segment detected at vaddr=0xffffffff81000000, is this intentional?"
+
+We use a dd command to change the e_type field in the ELF header from
+ET_EXEC to ET_REL so that lld will accept .btf.vmlinux.bin.o. Accepting
+ET_EXEC as an input file is an extremely rare GNU ld feature that lld
+does not intend to support, because this is error-prone.
+
+The output section description .BTF in include/asm-generic/vmlinux.lds.h
+avoids potential subtle orphan section placement issues and suppresses
+--orphan-handling=warn warnings.
+
+Fixes: df786c9b9476 ("bpf: Force .BTF section start to zero when dumping from vmlinux")
+Fixes: cb0cc635c7a9 ("powerpc: Include .BTF section")
+Reported-by: Nathan Chancellor <natechancellor@gmail.com>
+Signed-off-by: Fangrui Song <maskray@google.com>
+Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
+Tested-by: Stanislav Fomichev <sdf@google.com>
+Tested-by: Andrii Nakryiko <andriin@fb.com>
+Reviewed-by: Stanislav Fomichev <sdf@google.com>
+Reviewed-by: Kees Cook <keescook@chromium.org>
+Acked-by: Andrii Nakryiko <andriin@fb.com>
+Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
+Link: https://github.com/ClangBuiltLinux/linux/issues/871
+Link: https://lore.kernel.org/bpf/20200318222746.173648-1-maskray@google.com
+Signed-off-by: Maria Teguiani <teguiani@google.com>
+Tested-by: Matthias Maennich <maennich@google.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+
+---
+ arch/powerpc/kernel/vmlinux.lds.S | 6 ------
+ include/asm-generic/vmlinux.lds.h | 22 +++++++++++++++++++---
+ kernel/bpf/sysfs_btf.c | 11 +++++------
+ scripts/link-vmlinux.sh | 24 ++++++++++--------------
+ 4 files changed, 34 insertions(+), 29 deletions(-)
+
+--- a/arch/powerpc/kernel/vmlinux.lds.S
++++ b/arch/powerpc/kernel/vmlinux.lds.S
+@@ -326,12 +326,6 @@ SECTIONS
+ *(.branch_lt)
+ }
+
+-#ifdef CONFIG_DEBUG_INFO_BTF
+- .BTF : AT(ADDR(.BTF) - LOAD_OFFSET) {
+- *(.BTF)
+- }
+-#endif
+-
+ .opd : AT(ADDR(.opd) - LOAD_OFFSET) {
+ __start_opd = .;
+ KEEP(*(.opd))
+--- a/include/asm-generic/vmlinux.lds.h
++++ b/include/asm-generic/vmlinux.lds.h
+@@ -496,10 +496,12 @@
+ __start___modver = .; \
+ KEEP(*(__modver)) \
+ __stop___modver = .; \
+- . = ALIGN((align)); \
+- __end_rodata = .; \
+ } \
+- . = ALIGN((align));
++ \
++ BTF \
++ \
++ . = ALIGN((align)); \
++ __end_rodata = .;
+
+ /* RODATA & RO_DATA provided for backward compatibility.
+ * All archs are supposed to use RO_DATA() */
+@@ -589,6 +591,20 @@
+ }
+
+ /*
++ * .BTF
++ */
++#ifdef CONFIG_DEBUG_INFO_BTF
++#define BTF \
++ .BTF : AT(ADDR(.BTF) - LOAD_OFFSET) { \
++ __start_BTF = .; \
++ *(.BTF) \
++ __stop_BTF = .; \
++ }
++#else
++#define BTF
++#endif
++
++/*
+ * Init task
+ */
+ #define INIT_TASK_DATA_SECTION(align) \
+--- a/kernel/bpf/sysfs_btf.c
++++ b/kernel/bpf/sysfs_btf.c
+@@ -9,15 +9,15 @@
+ #include <linux/sysfs.h>
+
+ /* See scripts/link-vmlinux.sh, gen_btf() func for details */
+-extern char __weak _binary__btf_vmlinux_bin_start[];
+-extern char __weak _binary__btf_vmlinux_bin_end[];
++extern char __weak __start_BTF[];
++extern char __weak __stop_BTF[];
+
+ static ssize_t
+ btf_vmlinux_read(struct file *file, struct kobject *kobj,
+ struct bin_attribute *bin_attr,
+ char *buf, loff_t off, size_t len)
+ {
+- memcpy(buf, _binary__btf_vmlinux_bin_start + off, len);
++ memcpy(buf, __start_BTF + off, len);
+ return len;
+ }
+
+@@ -30,15 +30,14 @@ static struct kobject *btf_kobj;
+
+ static int __init btf_vmlinux_init(void)
+ {
+- if (!_binary__btf_vmlinux_bin_start)
++ if (!__start_BTF)
+ return 0;
+
+ btf_kobj = kobject_create_and_add("btf", kernel_kobj);
+ if (!btf_kobj)
+ return -ENOMEM;
+
+- bin_attr_btf_vmlinux.size = _binary__btf_vmlinux_bin_end -
+- _binary__btf_vmlinux_bin_start;
++ bin_attr_btf_vmlinux.size = __stop_BTF - __start_BTF;
+
+ return sysfs_create_bin_file(btf_kobj, &bin_attr_btf_vmlinux);
+ }
+--- a/scripts/link-vmlinux.sh
++++ b/scripts/link-vmlinux.sh
+@@ -113,9 +113,6 @@ vmlinux_link()
+ gen_btf()
+ {
+ local pahole_ver
+- local bin_arch
+- local bin_format
+- local bin_file
+
+ if ! [ -x "$(command -v ${PAHOLE})" ]; then
+ echo >&2 "BTF: ${1}: pahole (${PAHOLE}) is not available"
+@@ -133,17 +130,16 @@ gen_btf()
+ info "BTF" ${2}
+ LLVM_OBJCOPY=${OBJCOPY} ${PAHOLE} -J ${1}
+
+- # dump .BTF section into raw binary file to link with final vmlinux
+- bin_arch=$(LANG=C ${OBJDUMP} -f ${1} | grep architecture | \
+- cut -d, -f1 | cut -d' ' -f2)
+- bin_format=$(LANG=C ${OBJDUMP} -f ${1} | grep 'file format' | \
+- awk '{print $4}')
+- bin_file=.btf.vmlinux.bin
+- ${OBJCOPY} --change-section-address .BTF=0 \
+- --set-section-flags .BTF=alloc -O binary \
+- --only-section=.BTF ${1} $bin_file
+- ${OBJCOPY} -I binary -O ${bin_format} -B ${bin_arch} \
+- --rename-section .data=.BTF $bin_file ${2}
++ # Create ${2} 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} ${2} 2>/dev/null
++ # Change e_type to ET_REL so that it can be used to link final vmlinux.
++ # Unlike GNU ld, lld does not allow an ET_EXEC input.
++ printf '\1' | dd of=${2} conv=notrunc bs=1 seek=16 status=none
+ }
+
+ # Create ${2} .o file with all symbols from the ${1} object file
projects / thirdparty / kernel / stable-queue.git / commitdiff
