[PATCH bpf-next v2 0/5] core_reloc fixes for s390

[PATCH bpf-next v2 0/5] core_reloc fixes for s390

[Ilya Leoshkevich]

v1: https://lore.kernel.org/bpf/20211021234653.643302-1-iii@linux.ibm.com/
v1 -> v2: Drop bpf_core_calc_field_relo() restructuring, split
          __BYTE_ORDER__ change.

Hi,

this series fixes test failures in core_reloc on s390.

Patches 1-4 replace __BYTE_ORDER with __BYTE_ORDER__ in order to fix an
endianness bug and make the code consistent.
Patch 5 fixes an endianness issue in test_core_reloc_mods.

Best regards,
Ilya

Ilya Leoshkevich (5):
  libbpf: Use __BYTE_ORDER__
  selftests/bpf: Use __BYTE_ORDER__
  samples: seccomp: use __BYTE_ORDER__
  selftests/seccomp: Use __BYTE_ORDER__
  selftests/bpf: Fix test_core_reloc_mods on big-endian machines

 samples/seccomp/bpf-helper.h                       |  8 ++++----
 tools/lib/bpf/bpf_core_read.h                      |  2 +-
 tools/lib/bpf/btf.c                                |  4 ++--
 tools/lib/bpf/btf_dump.c                           |  8 ++++----
 tools/lib/bpf/libbpf.c                             |  4 ++--
 tools/lib/bpf/linker.c                             | 12 ++++++------
 tools/lib/bpf/relo_core.c                          |  2 +-
 .../testing/selftests/bpf/prog_tests/btf_endian.c  |  6 +++---
 .../selftests/bpf/progs/test_core_reloc_mods.c     |  9 +++++++++
 tools/testing/selftests/bpf/test_sysctl.c          |  4 ++--
 tools/testing/selftests/bpf/verifier/ctx_skb.c     | 14 +++++++-------
 tools/testing/selftests/bpf/verifier/lwt.c         |  2 +-
 .../bpf/verifier/perf_event_sample_period.c        |  6 +++---
 tools/testing/selftests/seccomp/seccomp_bpf.c      |  6 +++---
 14 files changed, 48 insertions(+), 39 deletions(-)

-- 
2.31.1

[PATCH bpf-next v2 1/5] libbpf: Use __BYTE_ORDER__

[Ilya Leoshkevich]

__BYTE_ORDER is supposed to be defined by a libc, and __BYTE_ORDER__ -
by a compiler. bpf_core_read.h checks __BYTE_ORDER == __LITTLE_ENDIAN,
which is true if neither are defined, leading to incorrect behavior on
big-endian hosts if libc headers are not included, which is often the
case.

Instead of changing just this particular location, replace all
occurrences of __BYTE_ORDER with __BYTE_ORDER__ in libbpf code for
consistency.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 tools/lib/bpf/bpf_core_read.h |  2 +-
 tools/lib/bpf/btf.c           |  4 ++--
 tools/lib/bpf/btf_dump.c      |  8 ++++----
 tools/lib/bpf/libbpf.c        |  4 ++--
 tools/lib/bpf/linker.c        | 12 ++++++------
 tools/lib/bpf/relo_core.c     |  2 +-
 6 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/tools/lib/bpf/bpf_core_read.h b/tools/lib/bpf/bpf_core_read.h
index 09ebe3db5f2f..e4aa9996a550 100644
--- a/tools/lib/bpf/bpf_core_read.h
+++ b/tools/lib/bpf/bpf_core_read.h
@@ -40,7 +40,7 @@ enum bpf_enum_value_kind {
 #define __CORE_RELO(src, field, info)					      \
 	__builtin_preserve_field_info((src)->field, BPF_FIELD_##info)
 
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 #define __CORE_BITFIELD_PROBE_READ(dst, src, fld)			      \
 	bpf_probe_read_kernel(						      \
 			(void *)dst,				      \
diff --git a/tools/lib/bpf/btf.c b/tools/lib/bpf/btf.c
index ef924fc2c911..0c628c33e23b 100644
--- a/tools/lib/bpf/btf.c
+++ b/tools/lib/bpf/btf.c
@@ -538,9 +538,9 @@ int btf__set_pointer_size(struct btf *btf, size_t ptr_sz)
 
 static bool is_host_big_endian(void)
 {
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 	return false;
-#elif __BYTE_ORDER == __BIG_ENDIAN
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 	return true;
 #else
 # error "Unrecognized __BYTE_ORDER__"
diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index 8e05ab44c22a..17db62b5002e 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -1576,11 +1576,11 @@ static int btf_dump_get_bitfield_value(struct btf_dump *d,
 	/* Bitfield value retrieval is done in two steps; first relevant bytes are
 	 * stored in num, then we left/right shift num to eliminate irrelevant bits.
 	 */
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 	for (i = t->size - 1; i >= 0; i--)
 		num = num * 256 + bytes[i];
 	nr_copy_bits = bit_sz + bits_offset;
-#elif __BYTE_ORDER == __BIG_ENDIAN
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 	for (i = 0; i < t->size; i++)
 		num = num * 256 + bytes[i];
 	nr_copy_bits = t->size * 8 - bits_offset;
@@ -1700,10 +1700,10 @@ static int btf_dump_int_data(struct btf_dump *d,
 		/* avoid use of __int128 as some 32-bit platforms do not
 		 * support it.
 		 */
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 		lsi = ints[0];
 		msi = ints[1];
-#elif __BYTE_ORDER == __BIG_ENDIAN
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 		lsi = ints[1];
 		msi = ints[0];
 #else
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 604abe00785f..cd6132c5a416 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -1299,10 +1299,10 @@ static int bpf_object__elf_init(struct bpf_object *obj)
 
 static int bpf_object__check_endianness(struct bpf_object *obj)
 {
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 	if (obj->efile.ehdr->e_ident[EI_DATA] == ELFDATA2LSB)
 		return 0;
-#elif __BYTE_ORDER == __BIG_ENDIAN
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 	if (obj->efile.ehdr->e_ident[EI_DATA] == ELFDATA2MSB)
 		return 0;
 #else
diff --git a/tools/lib/bpf/linker.c b/tools/lib/bpf/linker.c
index 7bf658fbda80..ce0800e61dc7 100644
--- a/tools/lib/bpf/linker.c
+++ b/tools/lib/bpf/linker.c
@@ -323,12 +323,12 @@ static int init_output_elf(struct bpf_linker *linker, const char *file)
 
 	linker->elf_hdr->e_machine = EM_BPF;
 	linker->elf_hdr->e_type = ET_REL;
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 	linker->elf_hdr->e_ident[EI_DATA] = ELFDATA2LSB;
-#elif __BYTE_ORDER == __BIG_ENDIAN
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 	linker->elf_hdr->e_ident[EI_DATA] = ELFDATA2MSB;
 #else
-#error "Unknown __BYTE_ORDER"
+#error "Unknown __BYTE_ORDER__"
 #endif
 
 	/* STRTAB */
@@ -538,12 +538,12 @@ static int linker_load_obj_file(struct bpf_linker *linker, const char *filename,
 				const struct bpf_linker_file_opts *opts,
 				struct src_obj *obj)
 {
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 	const int host_endianness = ELFDATA2LSB;
-#elif __BYTE_ORDER == __BIG_ENDIAN
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 	const int host_endianness = ELFDATA2MSB;
 #else
-#error "Unknown __BYTE_ORDER"
+#error "Unknown __BYTE_ORDER__"
 #endif
 	int err = 0;
 	Elf_Scn *scn;
diff --git a/tools/lib/bpf/relo_core.c b/tools/lib/bpf/relo_core.c
index 4016ed492d0c..b5b8956a1be8 100644
--- a/tools/lib/bpf/relo_core.c
+++ b/tools/lib/bpf/relo_core.c
@@ -662,7 +662,7 @@ static int bpf_core_calc_field_relo(const char *prog_name,
 			*validate = true; /* signedness is never ambiguous */
 		break;
 	case BPF_FIELD_LSHIFT_U64:
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 		*val = 64 - (bit_off + bit_sz - byte_off  * 8);
 #else
 		*val = (8 - byte_sz) * 8 + (bit_off - byte_off * 8);
-- 
2.31.1

[PATCH bpf-next v2 2/5] selftests/bpf: Use __BYTE_ORDER__

[Ilya Leoshkevich]

Use the compiler-defined __BYTE_ORDER__ instead of the libc-defined
__BYTE_ORDER for consistency.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 .../testing/selftests/bpf/prog_tests/btf_endian.c  |  6 +++---
 tools/testing/selftests/bpf/test_sysctl.c          |  4 ++--
 tools/testing/selftests/bpf/verifier/ctx_skb.c     | 14 +++++++-------
 tools/testing/selftests/bpf/verifier/lwt.c         |  2 +-
 .../bpf/verifier/perf_event_sample_period.c        |  6 +++---
 5 files changed, 16 insertions(+), 16 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/btf_endian.c b/tools/testing/selftests/bpf/prog_tests/btf_endian.c
index 2653cc482df4..8afbf3d0b89a 100644
--- a/tools/testing/selftests/bpf/prog_tests/btf_endian.c
+++ b/tools/testing/selftests/bpf/prog_tests/btf_endian.c
@@ -7,12 +7,12 @@
 #include <bpf/btf.h>
 
 void test_btf_endian() {
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 	enum btf_endianness endian = BTF_LITTLE_ENDIAN;
-#elif __BYTE_ORDER == __BIG_ENDIAN
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 	enum btf_endianness endian = BTF_BIG_ENDIAN;
 #else
-#error "Unrecognized __BYTE_ORDER"
+#error "Unrecognized __BYTE_ORDER__"
 #endif
 	enum btf_endianness swap_endian = 1 - endian;
 	struct btf *btf = NULL, *swap_btf = NULL;
diff --git a/tools/testing/selftests/bpf/test_sysctl.c b/tools/testing/selftests/bpf/test_sysctl.c
index a20a919244c0..a3bb6d399daa 100644
--- a/tools/testing/selftests/bpf/test_sysctl.c
+++ b/tools/testing/selftests/bpf/test_sysctl.c
@@ -124,7 +124,7 @@ static struct sysctl_test tests[] = {
 		.descr = "ctx:write sysctl:write read ok narrow",
 		.insns = {
 			/* u64 w = (u16)write & 1; */
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 			BPF_LDX_MEM(BPF_H, BPF_REG_7, BPF_REG_1,
 				    offsetof(struct bpf_sysctl, write)),
 #else
@@ -184,7 +184,7 @@ static struct sysctl_test tests[] = {
 		.descr = "ctx:file_pos sysctl:read read ok narrow",
 		.insns = {
 			/* If (file_pos == X) */
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 			BPF_LDX_MEM(BPF_B, BPF_REG_7, BPF_REG_1,
 				    offsetof(struct bpf_sysctl, file_pos)),
 #else
diff --git a/tools/testing/selftests/bpf/verifier/ctx_skb.c b/tools/testing/selftests/bpf/verifier/ctx_skb.c
index 9e1a30b94197..83cecfbd6739 100644
--- a/tools/testing/selftests/bpf/verifier/ctx_skb.c
+++ b/tools/testing/selftests/bpf/verifier/ctx_skb.c
@@ -502,7 +502,7 @@
 	"check skb->hash byte load permitted",
 	.insns = {
 	BPF_MOV64_IMM(BPF_REG_0, 0),
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 	BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_1,
 		    offsetof(struct __sk_buff, hash)),
 #else
@@ -537,7 +537,7 @@
 	"check skb->hash byte load permitted 3",
 	.insns = {
 	BPF_MOV64_IMM(BPF_REG_0, 0),
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 	BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_1,
 		    offsetof(struct __sk_buff, hash) + 3),
 #else
@@ -646,7 +646,7 @@
 	"check skb->hash half load permitted",
 	.insns = {
 	BPF_MOV64_IMM(BPF_REG_0, 0),
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 	BPF_LDX_MEM(BPF_H, BPF_REG_0, BPF_REG_1,
 		    offsetof(struct __sk_buff, hash)),
 #else
@@ -661,7 +661,7 @@
 	"check skb->hash half load permitted 2",
 	.insns = {
 	BPF_MOV64_IMM(BPF_REG_0, 0),
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 	BPF_LDX_MEM(BPF_H, BPF_REG_0, BPF_REG_1,
 		    offsetof(struct __sk_buff, hash) + 2),
 #else
@@ -676,7 +676,7 @@
 	"check skb->hash half load not permitted, unaligned 1",
 	.insns = {
 	BPF_MOV64_IMM(BPF_REG_0, 0),
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 	BPF_LDX_MEM(BPF_H, BPF_REG_0, BPF_REG_1,
 		    offsetof(struct __sk_buff, hash) + 1),
 #else
@@ -693,7 +693,7 @@
 	"check skb->hash half load not permitted, unaligned 3",
 	.insns = {
 	BPF_MOV64_IMM(BPF_REG_0, 0),
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 	BPF_LDX_MEM(BPF_H, BPF_REG_0, BPF_REG_1,
 		    offsetof(struct __sk_buff, hash) + 3),
 #else
@@ -951,7 +951,7 @@
 	"check skb->data half load not permitted",
 	.insns = {
 	BPF_MOV64_IMM(BPF_REG_0, 0),
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 	BPF_LDX_MEM(BPF_H, BPF_REG_0, BPF_REG_1,
 		    offsetof(struct __sk_buff, data)),
 #else
diff --git a/tools/testing/selftests/bpf/verifier/lwt.c b/tools/testing/selftests/bpf/verifier/lwt.c
index 2cab6a3966bb..5c8944d0b091 100644
--- a/tools/testing/selftests/bpf/verifier/lwt.c
+++ b/tools/testing/selftests/bpf/verifier/lwt.c
@@ -174,7 +174,7 @@
 	"check skb->tc_classid half load not permitted for lwt prog",
 	.insns = {
 	BPF_MOV64_IMM(BPF_REG_0, 0),
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 	BPF_LDX_MEM(BPF_H, BPF_REG_0, BPF_REG_1,
 		    offsetof(struct __sk_buff, tc_classid)),
 #else
diff --git a/tools/testing/selftests/bpf/verifier/perf_event_sample_period.c b/tools/testing/selftests/bpf/verifier/perf_event_sample_period.c
index 471c1a5950d8..d8a9b1a1f9a2 100644
--- a/tools/testing/selftests/bpf/verifier/perf_event_sample_period.c
+++ b/tools/testing/selftests/bpf/verifier/perf_event_sample_period.c
@@ -2,7 +2,7 @@
 	"check bpf_perf_event_data->sample_period byte load permitted",
 	.insns = {
 	BPF_MOV64_IMM(BPF_REG_0, 0),
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 	BPF_LDX_MEM(BPF_B, BPF_REG_0, BPF_REG_1,
 		    offsetof(struct bpf_perf_event_data, sample_period)),
 #else
@@ -18,7 +18,7 @@
 	"check bpf_perf_event_data->sample_period half load permitted",
 	.insns = {
 	BPF_MOV64_IMM(BPF_REG_0, 0),
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 	BPF_LDX_MEM(BPF_H, BPF_REG_0, BPF_REG_1,
 		    offsetof(struct bpf_perf_event_data, sample_period)),
 #else
@@ -34,7 +34,7 @@
 	"check bpf_perf_event_data->sample_period word load permitted",
 	.insns = {
 	BPF_MOV64_IMM(BPF_REG_0, 0),
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 	BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
 		    offsetof(struct bpf_perf_event_data, sample_period)),
 #else
-- 
2.31.1

[PATCH bpf-next v2 3/5] samples: seccomp: use __BYTE_ORDER__

[Ilya Leoshkevich]

Use the compiler-defined __BYTE_ORDER__ instead of the libc-defined
__BYTE_ORDER for consistency.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 samples/seccomp/bpf-helper.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/samples/seccomp/bpf-helper.h b/samples/seccomp/bpf-helper.h
index 0cc9816fe8e8..417e48a4c4df 100644
--- a/samples/seccomp/bpf-helper.h
+++ b/samples/seccomp/bpf-helper.h
@@ -62,9 +62,9 @@ void seccomp_bpf_print(struct sock_filter *filter, size_t count);
 #define EXPAND(...) __VA_ARGS__
 
 /* Ensure that we load the logically correct offset. */
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 #define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)])
-#elif __BYTE_ORDER == __BIG_ENDIAN
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 #define LO_ARG(idx) offsetof(struct seccomp_data, args[(idx)]) + sizeof(__u32)
 #else
 #error "Unknown endianness"
@@ -85,10 +85,10 @@ void seccomp_bpf_print(struct sock_filter *filter, size_t count);
 #elif __BITS_PER_LONG == 64
 
 /* Ensure that we load the logically correct offset. */
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 #define ENDIAN(_lo, _hi) _lo, _hi
 #define HI_ARG(idx) offsetof(struct seccomp_data, args[(idx)]) + sizeof(__u32)
-#elif __BYTE_ORDER == __BIG_ENDIAN
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 #define ENDIAN(_lo, _hi) _hi, _lo
 #define HI_ARG(idx) offsetof(struct seccomp_data, args[(idx)])
 #endif
-- 
2.31.1

[PATCH bpf-next v2 4/5] selftests/seccomp: Use __BYTE_ORDER__

[Ilya Leoshkevich]

Use the compiler-defined __BYTE_ORDER__ instead of the libc-defined
__BYTE_ORDER for consistency.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 tools/testing/selftests/seccomp/seccomp_bpf.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
index 1d64891e6492..d425688cf59c 100644
--- a/tools/testing/selftests/seccomp/seccomp_bpf.c
+++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
@@ -276,12 +276,12 @@ int seccomp(unsigned int op, unsigned int flags, void *args)
 }
 #endif
 
-#if __BYTE_ORDER == __LITTLE_ENDIAN
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 #define syscall_arg(_n) (offsetof(struct seccomp_data, args[_n]))
-#elif __BYTE_ORDER == __BIG_ENDIAN
+#elif __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 #define syscall_arg(_n) (offsetof(struct seccomp_data, args[_n]) + sizeof(__u32))
 #else
-#error "wut? Unknown __BYTE_ORDER?!"
+#error "wut? Unknown __BYTE_ORDER__?!"
 #endif
 
 #define SIBLING_EXIT_UNKILLED	0xbadbeef
-- 
2.31.1

[PATCH bpf-next v2 5/5] selftests/bpf: Fix test_core_reloc_mods on big-endian machines

[Ilya Leoshkevich]

This is the same as commit d164dd9a5c08 ("selftests/bpf: Fix
test_core_autosize on big-endian machines"), but for
test_core_reloc_mods.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
---
 tools/testing/selftests/bpf/progs/test_core_reloc_mods.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/test_core_reloc_mods.c b/tools/testing/selftests/bpf/progs/test_core_reloc_mods.c
index 8b533db4a7a5..b2ded497572a 100644
--- a/tools/testing/selftests/bpf/progs/test_core_reloc_mods.c
+++ b/tools/testing/selftests/bpf/progs/test_core_reloc_mods.c
@@ -42,7 +42,16 @@ struct core_reloc_mods {
 	core_reloc_mods_substruct_t h;
 };
 
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
 #define CORE_READ(dst, src) bpf_core_read(dst, sizeof(*(dst)), src)
+#else
+#define CORE_READ(dst, src) ({ \
+	int __sz = sizeof(*(dst)) < sizeof(*(src)) ? sizeof(*(dst)) : \
+						     sizeof(*(src)); \
+	bpf_core_read((char *)(dst) + sizeof(*(dst)) - __sz, __sz, \
+		      (const char *)(src) + sizeof(*(src)) - __sz); \
+})
+#endif
 
 SEC("raw_tracepoint/sys_enter")
 int test_core_mods(void *ctx)
-- 
2.31.1

Re: [PATCH bpf-next v2 1/5] libbpf: Use __BYTE_ORDER__

[Daniel Borkmann]

On 10/25/21 3:12 PM, Ilya Leoshkevich wrote:
> __BYTE_ORDER is supposed to be defined by a libc, and __BYTE_ORDER__ -
> by a compiler. bpf_core_read.h checks __BYTE_ORDER == __LITTLE_ENDIAN,
> which is true if neither are defined, leading to incorrect behavior on
> big-endian hosts if libc headers are not included, which is often the
> case.
> 
> Instead of changing just this particular location, replace all
> occurrences of __BYTE_ORDER with __BYTE_ORDER__ in libbpf code for
> consistency.

ACK, that is definitely broken as is - we had similar issue back then with the
bpf_{htons,ntohs}() helpers, details: 78a5a93c1eeb ("bpf, tests: fix endianness
selection").

The bpf_core_read.h change I would split out as a separate commit along with a
proper Fixes tag so it could potentially be cherry-picked easier (since the
remainder in here is a cleanup for consistency and not used out of the BPF prog
where this issue exists).

> Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
> ---
>   tools/lib/bpf/bpf_core_read.h |  2 +-
>   tools/lib/bpf/btf.c           |  4 ++--
>   tools/lib/bpf/btf_dump.c      |  8 ++++----
>   tools/lib/bpf/libbpf.c        |  4 ++--
>   tools/lib/bpf/linker.c        | 12 ++++++------
>   tools/lib/bpf/relo_core.c     |  2 +-
>   6 files changed, 16 insertions(+), 16 deletions(-)

Thanks,
Daniel