[PATCH bpf-next v12 1/2] libbpf: fix USDT SIB argument handling causing unrecognized register error

[PATCH bpf-next v12 1/2] libbpf: fix USDT SIB argument handling causing unrecognized register error

[Jiawei Zhao]

On x86-64, USDT arguments can be specified using Scale-Index-Base (SIB)
addressing, e.g. "1@-96(%rbp,%rax,8)". The current USDT implementation
in libbpf cannot parse this format, causing `bpf_program__attach_usdt()`
to fail with -ENOENT (unrecognized register).

This patch fixes this by implementing the necessary changes:
- add correct handling for SIB-addressed arguments in `bpf_usdt_arg`.
- add adaptive support to `__bpf_usdt_arg_type` and
  `__bpf_usdt_arg_spec` to represent SIB addressing parameters.

Signed-off-by: Jiawei Zhao <phoenix500526@163.com>
---
 tools/lib/bpf/usdt.bpf.h | 47 ++++++++++++++++++++++++++++++--
 tools/lib/bpf/usdt.c     | 58 ++++++++++++++++++++++++++++++++++++----
 2 files changed, 98 insertions(+), 7 deletions(-)

diff --git a/tools/lib/bpf/usdt.bpf.h b/tools/lib/bpf/usdt.bpf.h
index 2a7865c8e3fe..263168d57286 100644
--- a/tools/lib/bpf/usdt.bpf.h
+++ b/tools/lib/bpf/usdt.bpf.h
@@ -4,6 +4,7 @@
 #define __USDT_BPF_H__
 
 #include <linux/errno.h>
+#include <asm/byteorder.h>
 #include "bpf_helpers.h"
 #include "bpf_tracing.h"
 
@@ -34,13 +35,34 @@ enum __bpf_usdt_arg_type {
 	BPF_USDT_ARG_CONST,
 	BPF_USDT_ARG_REG,
 	BPF_USDT_ARG_REG_DEREF,
+	BPF_USDT_ARG_SIB,
 };
 
+/*
+ * This struct layout is designed specifically to be backwards/forward
+ * compatible between libbpf versions for ARG_CONST, ARG_REG, and
+ * ARG_REG_DEREF modes. ARG_SIB requires libbpf v1.7+.
+ */
 struct __bpf_usdt_arg_spec {
 	/* u64 scalar interpreted depending on arg_type, see below */
 	__u64 val_off;
 	/* arg location case, see bpf_usdt_arg() for details */
-	enum __bpf_usdt_arg_type arg_type;
+	enum __bpf_usdt_arg_type arg_type: 8;
+#if defined(__LITTLE_ENDIAN_BITFIELD)
+	/* index register offset within struct pt_regs (high 12 bits) */
+	__u16	idx_reg_off: 12,
+	/* scale factor for index register (1, 2, 4, or 8) (low 4 bits) */
+		scale: 4;
+#elif defined(__BIG_ENDIAN_BITFIELD)
+	/* scale factor for index register (1, 2, 4, or 8) (high 4 bits) */
+	__u16	scale: 4,
+	/* index register offset within struct pt_regs (low 12 bits) */
+		idx_reg_off: 12;
+#else
+#error "Please fix <asm/byteorder.h>"
+#endif
+	/* reserved for future use, keeps reg_off offset stable */
+	__u8 reserved;
 	/* offset of referenced register within struct pt_regs */
 	short reg_off;
 	/* whether arg should be interpreted as signed value */
@@ -149,7 +171,7 @@ int bpf_usdt_arg(struct pt_regs *ctx, __u64 arg_num, long *res)
 {
 	struct __bpf_usdt_spec *spec;
 	struct __bpf_usdt_arg_spec *arg_spec;
-	unsigned long val;
+	unsigned long val, idx;
 	int err, spec_id;
 
 	*res = 0;
@@ -202,6 +224,27 @@ int bpf_usdt_arg(struct pt_regs *ctx, __u64 arg_num, long *res)
 			return err;
 #if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 		val >>= arg_spec->arg_bitshift;
+#endif
+		break;
+	case BPF_USDT_ARG_SIB:
+		/* Arg is in memory addressed by SIB (Scale-Index-Base) mode
+		 * (e.g., "-1@-96(%rbp,%rax,8)" in USDT arg spec). We first
+		 * fetch the base register contents and the index register
+		 * contents from pt_regs. Then we calculate the final address
+		 * as base + (index * scale) + offset, and do a user-space
+		 * probe read to fetch the argument value.
+		 */
+		err = bpf_probe_read_kernel(&val, sizeof(val), (void *)ctx + arg_spec->reg_off);
+		if (err)
+			return err;
+		err = bpf_probe_read_kernel(&idx, sizeof(idx), (void *)ctx + arg_spec->idx_reg_off);
+		if (err)
+			return err;
+		err = bpf_probe_read_user(&val, sizeof(val), (void *)(val + (idx * arg_spec->scale) + arg_spec->val_off));
+		if (err)
+			return err;
+#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+		val >>= arg_spec->arg_bitshift;
 #endif
 		break;
 	default:
diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c
index 3373b9d45ac4..730a896a566b 100644
--- a/tools/lib/bpf/usdt.c
+++ b/tools/lib/bpf/usdt.c
@@ -9,6 +9,7 @@
 #include <unistd.h>
 #include <linux/ptrace.h>
 #include <linux/kernel.h>
+#include <asm/byteorder.h>
 
 /* s8 will be marked as poison while it's a reg of riscv */
 #if defined(__riscv)
@@ -200,12 +201,23 @@ enum usdt_arg_type {
 	USDT_ARG_CONST,
 	USDT_ARG_REG,
 	USDT_ARG_REG_DEREF,
+	USDT_ARG_SIB,
 };
 
 /* should match exactly struct __bpf_usdt_arg_spec from usdt.bpf.h */
 struct usdt_arg_spec {
 	__u64 val_off;
-	enum usdt_arg_type arg_type;
+	enum usdt_arg_type arg_type: 8;
+#if defined(__LITTLE_ENDIAN_BITFIELD)
+	__u16	idx_reg_off: 12,
+		scale: 4;
+#elif defined(__BIG_ENDIAN_BITFIELD)
+	__u16	scale: 4,
+		idx_reg_off: 12;
+#else
+#error "Please fix <asm/byteorder.h>"
+#endif
+	__u8 reserved;     /* keep reg_off offset stable */
 	short reg_off;
 	bool arg_signed;
 	char arg_bitshift;
@@ -1283,11 +1295,46 @@ static int calc_pt_regs_off(const char *reg_name)
 
 static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg, int *arg_sz)
 {
-	char reg_name[16];
-	int len, reg_off;
-	long off;
+	char reg_name[16] = {0}, idx_reg_name[16] = {0};
+	int len, reg_off, idx_reg_off, scale = 1;
+	long off = 0;
+
+	if (sscanf(arg_str, " %d @ %ld ( %%%15[^,] , %%%15[^,] , %d ) %n",
+			   arg_sz, &off, reg_name, idx_reg_name, &scale, &len) == 5 ||
+		sscanf(arg_str, " %d @ ( %%%15[^,] , %%%15[^,] , %d ) %n",
+			   arg_sz, reg_name, idx_reg_name, &scale, &len) == 4 ||
+		sscanf(arg_str, " %d @ %ld ( %%%15[^,] , %%%15[^)] ) %n",
+			   arg_sz, &off, reg_name, idx_reg_name, &len) == 4 ||
+		sscanf(arg_str, " %d @ ( %%%15[^,] , %%%15[^)] ) %n",
+			   arg_sz, reg_name, idx_reg_name, &len) == 3
+		) {
+		/*
+		 * Scale Index Base case:
+		 * 1@-96(%rbp,%rax,8)
+		 * 1@(%rbp,%rax,8)
+		 * 1@-96(%rbp,%rax)
+		 * 1@(%rbp,%rax)
+		 */
+		arg->arg_type = USDT_ARG_SIB;
+		arg->val_off = off;
 
-	if (sscanf(arg_str, " %d @ %ld ( %%%15[^)] ) %n", arg_sz, &off, reg_name, &len) == 3) {
+		reg_off = calc_pt_regs_off(reg_name);
+		if (reg_off < 0)
+			return reg_off;
+		arg->reg_off = reg_off;
+
+		idx_reg_off = calc_pt_regs_off(idx_reg_name);
+		if (idx_reg_off < 0)
+			return idx_reg_off;
+		/* validate scale factor and set fields directly */
+		if (scale != 1 && scale != 2 && scale != 4 && scale != 8) {
+			pr_warn("usdt: invalid SIB scale %d, expected 1,2,4,8; defaulting to 1\n", scale);
+			return -EINVAL;
+		}
+		arg->idx_reg_off = idx_reg_off;
+		arg->scale = scale;
+	} else if (sscanf(arg_str, " %d @ %ld ( %%%15[^)] ) %n",
+				arg_sz, &off, reg_name, &len) == 3) {
 		/* Memory dereference case, e.g., -4@-20(%rbp) */
 		arg->arg_type = USDT_ARG_REG_DEREF;
 		arg->val_off = off;
@@ -1306,6 +1353,7 @@ static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec
 	} else if (sscanf(arg_str, " %d @ %%%15s %n", arg_sz, reg_name, &len) == 2) {
 		/* Register read case, e.g., -4@%eax */
 		arg->arg_type = USDT_ARG_REG;
+		/* register read has no memory offset */
 		arg->val_off = 0;
 
 		reg_off = calc_pt_regs_off(reg_name);
-- 
2.43.0

[PATCH bpf-next v12 0/2] libbpf: fix USDT SIB argument handling causing unrecognized register error

[Jiawei Zhao]

When using GCC on x86-64 to compile an usdt prog with -O1 or higher
optimization, the compiler will generate SIB addressing mode for global
array and PC-relative addressing mode for global variable,
e.g. "1@-96(%rbp,%rax,8)" and "-1@4+t1(%rip)".

The current USDT implementation in libbpf cannot parse these two formats,
causing `bpf_program__attach_usdt()` to fail with -ENOENT
(unrecognized register).

This patch series adds support for SIB addressing mode in USDT probes.
The main changes include:
- add correct handling logic for SIB-addressed arguments in
  `parse_usdt_arg`.
- add an usdt_o2 test case to cover SIB addressing mode.

Testing shows that the SIB probe correctly generates 8@(%rcx,%rax,8) 
argument spec and passes all validation checks.

The modification history of this patch series:
Change since v1:
- refactor the code to make it more readable
- modify the commit message to explain why and how

Change since v2:
- fix the `scale` uninitialized error

Change since v3:
- force -O2 optimization for usdt.test.o to generate SIB addressing usdt
  and pass all test cases.

Change since v4:
- split the patch into two parts, one for the fix and the other for the
  test

Change since v5:
- Only enable optimization for x86 architecture to generate SIB addressing
  usdt argument spec.

Change since v6:
- Add an usdt_o2 test case to cover SIB addressing mode.
- Reinstate the usdt.c test case.

Change since v7:
- Refactor modifications to __bpf_usdt_arg_spec to avoid increasing its size,
  achieving better compatibility
- Fix some minor code style issues
- Refactor the usdt_o2 test case, removing semaphore and adding GCC attribute
  to force -O2 optimization

Change since v8:
- Refactor the usdt_o2 test case, using assembly to force SIB addressing mode.

Change since v9:
- Only enable the usdt_o2 test case on x86_64 and i386 architectures since the
  SIB addressing mode is only supported on x86_64 and i386.

Change since v10:
- Replace `__attribute__((optimize("O2")))` with `#pragma GCC optimize("O1")`
  to fix the issue where the optimized compilation condition works improperly. 
- Renamed test case usdt_o2 and relevant files name to usdt_o1 in that O1
  level optimization is enough to generate SIB addressing usdt argument spec.

Change since v11:
- Replace `STAP_PROBE1` with `STAP_PROBE_ASM`
- Use bit fields instead of bit shifting operations
- Merge the usdt_o1 test case into the usdt test case

Jiawei Zhao (2):
  libbpf: fix USDT SIB argument handling causing unrecognized register
    error
  selftests/bpf: Enrich subtest_basic_usdt case in selftests to cover
    SIB handling logic

 tools/lib/bpf/usdt.bpf.h                      | 47 ++++++++++++++-
 tools/lib/bpf/usdt.c                          | 58 +++++++++++++++++--
 tools/testing/selftests/bpf/prog_tests/usdt.c | 44 +++++++++++++-
 tools/testing/selftests/bpf/progs/test_usdt.c | 30 ++++++++++
 4 files changed, 170 insertions(+), 9 deletions(-)

-- 
2.43.0

[PATCH bpf-next v12 1/2] libbpf: fix USDT SIB argument handling causing unrecognized register error

[Jiawei Zhao]

On x86-64, USDT arguments can be specified using Scale-Index-Base (SIB)
addressing, e.g. "1@-96(%rbp,%rax,8)". The current USDT implementation
in libbpf cannot parse this format, causing `bpf_program__attach_usdt()`
to fail with -ENOENT (unrecognized register).

This patch fixes this by implementing the necessary changes:
- add correct handling for SIB-addressed arguments in `bpf_usdt_arg`.
- add adaptive support to `__bpf_usdt_arg_type` and
  `__bpf_usdt_arg_spec` to represent SIB addressing parameters.

Signed-off-by: Jiawei Zhao <phoenix500526@163.com>
---
 tools/lib/bpf/usdt.bpf.h | 47 ++++++++++++++++++++++++++++++--
 tools/lib/bpf/usdt.c     | 58 ++++++++++++++++++++++++++++++++++++----
 2 files changed, 98 insertions(+), 7 deletions(-)

diff --git a/tools/lib/bpf/usdt.bpf.h b/tools/lib/bpf/usdt.bpf.h
index 2a7865c8e3fe..263168d57286 100644
--- a/tools/lib/bpf/usdt.bpf.h
+++ b/tools/lib/bpf/usdt.bpf.h
@@ -4,6 +4,7 @@
 #define __USDT_BPF_H__
 
 #include <linux/errno.h>
+#include <asm/byteorder.h>
 #include "bpf_helpers.h"
 #include "bpf_tracing.h"
 
@@ -34,13 +35,34 @@ enum __bpf_usdt_arg_type {
 	BPF_USDT_ARG_CONST,
 	BPF_USDT_ARG_REG,
 	BPF_USDT_ARG_REG_DEREF,
+	BPF_USDT_ARG_SIB,
 };
 
+/*
+ * This struct layout is designed specifically to be backwards/forward
+ * compatible between libbpf versions for ARG_CONST, ARG_REG, and
+ * ARG_REG_DEREF modes. ARG_SIB requires libbpf v1.7+.
+ */
 struct __bpf_usdt_arg_spec {
 	/* u64 scalar interpreted depending on arg_type, see below */
 	__u64 val_off;
 	/* arg location case, see bpf_usdt_arg() for details */
-	enum __bpf_usdt_arg_type arg_type;
+	enum __bpf_usdt_arg_type arg_type: 8;
+#if defined(__LITTLE_ENDIAN_BITFIELD)
+	/* index register offset within struct pt_regs (high 12 bits) */
+	__u16	idx_reg_off: 12,
+	/* scale factor for index register (1, 2, 4, or 8) (low 4 bits) */
+		scale: 4;
+#elif defined(__BIG_ENDIAN_BITFIELD)
+	/* scale factor for index register (1, 2, 4, or 8) (high 4 bits) */
+	__u16	scale: 4,
+	/* index register offset within struct pt_regs (low 12 bits) */
+		idx_reg_off: 12;
+#else
+#error "Please fix <asm/byteorder.h>"
+#endif
+	/* reserved for future use, keeps reg_off offset stable */
+	__u8 reserved;
 	/* offset of referenced register within struct pt_regs */
 	short reg_off;
 	/* whether arg should be interpreted as signed value */
@@ -149,7 +171,7 @@ int bpf_usdt_arg(struct pt_regs *ctx, __u64 arg_num, long *res)
 {
 	struct __bpf_usdt_spec *spec;
 	struct __bpf_usdt_arg_spec *arg_spec;
-	unsigned long val;
+	unsigned long val, idx;
 	int err, spec_id;
 
 	*res = 0;
@@ -202,6 +224,27 @@ int bpf_usdt_arg(struct pt_regs *ctx, __u64 arg_num, long *res)
 			return err;
 #if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 		val >>= arg_spec->arg_bitshift;
+#endif
+		break;
+	case BPF_USDT_ARG_SIB:
+		/* Arg is in memory addressed by SIB (Scale-Index-Base) mode
+		 * (e.g., "-1@-96(%rbp,%rax,8)" in USDT arg spec). We first
+		 * fetch the base register contents and the index register
+		 * contents from pt_regs. Then we calculate the final address
+		 * as base + (index * scale) + offset, and do a user-space
+		 * probe read to fetch the argument value.
+		 */
+		err = bpf_probe_read_kernel(&val, sizeof(val), (void *)ctx + arg_spec->reg_off);
+		if (err)
+			return err;
+		err = bpf_probe_read_kernel(&idx, sizeof(idx), (void *)ctx + arg_spec->idx_reg_off);
+		if (err)
+			return err;
+		err = bpf_probe_read_user(&val, sizeof(val), (void *)(val + (idx * arg_spec->scale) + arg_spec->val_off));
+		if (err)
+			return err;
+#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
+		val >>= arg_spec->arg_bitshift;
 #endif
 		break;
 	default:
diff --git a/tools/lib/bpf/usdt.c b/tools/lib/bpf/usdt.c
index 3373b9d45ac4..730a896a566b 100644
--- a/tools/lib/bpf/usdt.c
+++ b/tools/lib/bpf/usdt.c
@@ -9,6 +9,7 @@
 #include <unistd.h>
 #include <linux/ptrace.h>
 #include <linux/kernel.h>
+#include <asm/byteorder.h>
 
 /* s8 will be marked as poison while it's a reg of riscv */
 #if defined(__riscv)
@@ -200,12 +201,23 @@ enum usdt_arg_type {
 	USDT_ARG_CONST,
 	USDT_ARG_REG,
 	USDT_ARG_REG_DEREF,
+	USDT_ARG_SIB,
 };
 
 /* should match exactly struct __bpf_usdt_arg_spec from usdt.bpf.h */
 struct usdt_arg_spec {
 	__u64 val_off;
-	enum usdt_arg_type arg_type;
+	enum usdt_arg_type arg_type: 8;
+#if defined(__LITTLE_ENDIAN_BITFIELD)
+	__u16	idx_reg_off: 12,
+		scale: 4;
+#elif defined(__BIG_ENDIAN_BITFIELD)
+	__u16	scale: 4,
+		idx_reg_off: 12;
+#else
+#error "Please fix <asm/byteorder.h>"
+#endif
+	__u8 reserved;     /* keep reg_off offset stable */
 	short reg_off;
 	bool arg_signed;
 	char arg_bitshift;
@@ -1283,11 +1295,46 @@ static int calc_pt_regs_off(const char *reg_name)
 
 static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec *arg, int *arg_sz)
 {
-	char reg_name[16];
-	int len, reg_off;
-	long off;
+	char reg_name[16] = {0}, idx_reg_name[16] = {0};
+	int len, reg_off, idx_reg_off, scale = 1;
+	long off = 0;
+
+	if (sscanf(arg_str, " %d @ %ld ( %%%15[^,] , %%%15[^,] , %d ) %n",
+			   arg_sz, &off, reg_name, idx_reg_name, &scale, &len) == 5 ||
+		sscanf(arg_str, " %d @ ( %%%15[^,] , %%%15[^,] , %d ) %n",
+			   arg_sz, reg_name, idx_reg_name, &scale, &len) == 4 ||
+		sscanf(arg_str, " %d @ %ld ( %%%15[^,] , %%%15[^)] ) %n",
+			   arg_sz, &off, reg_name, idx_reg_name, &len) == 4 ||
+		sscanf(arg_str, " %d @ ( %%%15[^,] , %%%15[^)] ) %n",
+			   arg_sz, reg_name, idx_reg_name, &len) == 3
+		) {
+		/*
+		 * Scale Index Base case:
+		 * 1@-96(%rbp,%rax,8)
+		 * 1@(%rbp,%rax,8)
+		 * 1@-96(%rbp,%rax)
+		 * 1@(%rbp,%rax)
+		 */
+		arg->arg_type = USDT_ARG_SIB;
+		arg->val_off = off;
 
-	if (sscanf(arg_str, " %d @ %ld ( %%%15[^)] ) %n", arg_sz, &off, reg_name, &len) == 3) {
+		reg_off = calc_pt_regs_off(reg_name);
+		if (reg_off < 0)
+			return reg_off;
+		arg->reg_off = reg_off;
+
+		idx_reg_off = calc_pt_regs_off(idx_reg_name);
+		if (idx_reg_off < 0)
+			return idx_reg_off;
+		/* validate scale factor and set fields directly */
+		if (scale != 1 && scale != 2 && scale != 4 && scale != 8) {
+			pr_warn("usdt: invalid SIB scale %d, expected 1,2,4,8; defaulting to 1\n", scale);
+			return -EINVAL;
+		}
+		arg->idx_reg_off = idx_reg_off;
+		arg->scale = scale;
+	} else if (sscanf(arg_str, " %d @ %ld ( %%%15[^)] ) %n",
+				arg_sz, &off, reg_name, &len) == 3) {
 		/* Memory dereference case, e.g., -4@-20(%rbp) */
 		arg->arg_type = USDT_ARG_REG_DEREF;
 		arg->val_off = off;
@@ -1306,6 +1353,7 @@ static int parse_usdt_arg(const char *arg_str, int arg_num, struct usdt_arg_spec
 	} else if (sscanf(arg_str, " %d @ %%%15s %n", arg_sz, reg_name, &len) == 2) {
 		/* Register read case, e.g., -4@%eax */
 		arg->arg_type = USDT_ARG_REG;
+		/* register read has no memory offset */
 		arg->val_off = 0;
 
 		reg_off = calc_pt_regs_off(reg_name);
-- 
2.43.0

[PATCH bpf-next v12 2/2] selftests/bpf: Enrich subtest_basic_usdt case in selftests to cover SIB handling logic

[Jiawei Zhao]

When using GCC on x86-64 to compile an usdt prog with -O1 or higher
optimization, the compiler will generate SIB addressing mode for global
array and PC-relative addressing mode for global variable,
e.g. "1@-96(%rbp,%rax,8)" and "-1@4+t1(%rip)".

In this patch:
- enrich subtest_basic_usdt test case to cover SIB addressing usdt argument spec
  handling logic

Signed-off-by: Jiawei Zhao <phoenix500526@163.com>
---
 tools/testing/selftests/bpf/prog_tests/usdt.c | 44 ++++++++++++++++++-
 tools/testing/selftests/bpf/progs/test_usdt.c | 30 +++++++++++++
 2 files changed, 72 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/usdt.c b/tools/testing/selftests/bpf/prog_tests/usdt.c
index 9057e983cc54..c04b416aa4a8 100644
--- a/tools/testing/selftests/bpf/prog_tests/usdt.c
+++ b/tools/testing/selftests/bpf/prog_tests/usdt.c
@@ -25,6 +25,10 @@ unsigned short test_usdt0_semaphore SEC(".probes");
 unsigned short test_usdt3_semaphore SEC(".probes");
 unsigned short test_usdt12_semaphore SEC(".probes");
 
+#if ((defined(__x86_64__) || defined(__i386__)) && defined(__GNUC__) && !defined(__clang__))
+unsigned short test_usdt_sib_semaphore SEC(".probes");
+#endif
+
 static void __always_inline trigger_func(int x) {
 	long y = 42;
 
@@ -40,12 +44,29 @@ static void __always_inline trigger_func(int x) {
 	}
 }
 
+#if ((defined(__x86_64__) || defined(__i386__)) && defined(__GNUC__) && !defined(__clang__))
+static __attribute__((optimize("O1"))) void trigger_sib_spec(void)
+{
+	/* Base address + offset + (index * scale) */
+	/* Force SIB addressing with inline assembly */
+	asm volatile(
+		"# probe point with memory access\n"
+		STAP_PROBE_ASM(test, usdt_sib, -2@(%%rdx,%%rax,2))
+		"# end probe point"
+		:
+		: "d"(nums), "a"(0)
+		: "memory"
+	);
+}
+#endif
+
 static void subtest_basic_usdt(void)
 {
 	LIBBPF_OPTS(bpf_usdt_opts, opts);
 	struct test_usdt *skel;
 	struct test_usdt__bss *bss;
 	int err, i;
+	const __u64 expected_cookie = 0xcafedeadbeeffeed;
 
 	skel = test_usdt__open_and_load();
 	if (!ASSERT_OK_PTR(skel, "skel_open"))
@@ -59,20 +80,29 @@ static void subtest_basic_usdt(void)
 		goto cleanup;
 
 	/* usdt0 won't be auto-attached */
-	opts.usdt_cookie = 0xcafedeadbeeffeed;
+	opts.usdt_cookie = expected_cookie;
 	skel->links.usdt0 = bpf_program__attach_usdt(skel->progs.usdt0,
 						     0 /*self*/, "/proc/self/exe",
 						     "test", "usdt0", &opts);
 	if (!ASSERT_OK_PTR(skel->links.usdt0, "usdt0_link"))
 		goto cleanup;
 
+#if ((defined(__x86_64__) || defined(__i386__)) && defined(__GNUC__) && !defined(__clang__))
+	opts.usdt_cookie = expected_cookie;
+	skel->links.usdt_sib = bpf_program__attach_usdt(skel->progs.usdt_sib,
+								0 /*self*/, "/proc/self/exe",
+								"test", "usdt_sib", &opts);
+	if (!ASSERT_OK_PTR(skel->links.usdt_sib, "usdt_sib_link"))
+		goto cleanup;
+#endif
+
 	trigger_func(1);
 
 	ASSERT_EQ(bss->usdt0_called, 1, "usdt0_called");
 	ASSERT_EQ(bss->usdt3_called, 1, "usdt3_called");
 	ASSERT_EQ(bss->usdt12_called, 1, "usdt12_called");
 
-	ASSERT_EQ(bss->usdt0_cookie, 0xcafedeadbeeffeed, "usdt0_cookie");
+	ASSERT_EQ(bss->usdt0_cookie, expected_cookie, "usdt0_cookie");
 	ASSERT_EQ(bss->usdt0_arg_cnt, 0, "usdt0_arg_cnt");
 	ASSERT_EQ(bss->usdt0_arg_ret, -ENOENT, "usdt0_arg_ret");
 	ASSERT_EQ(bss->usdt0_arg_size, -ENOENT, "usdt0_arg_size");
@@ -156,6 +186,16 @@ static void subtest_basic_usdt(void)
 	ASSERT_EQ(bss->usdt3_args[1], 42, "usdt3_arg2");
 	ASSERT_EQ(bss->usdt3_args[2], (uintptr_t)&bla, "usdt3_arg3");
 
+#if ((defined(__x86_64__) || defined(__i386__)) && defined(__GNUC__) && !defined(__clang__))
+	trigger_sib_spec();
+	ASSERT_EQ(bss->usdt_sib_called, 1, "usdt_sib_called");
+	ASSERT_EQ(bss->usdt_sib_cookie, expected_cookie, "usdt_sib_cookie");
+	ASSERT_EQ(bss->usdt_sib_arg_cnt, 1, "usdt_sib_arg_cnt");
+	ASSERT_EQ(bss->usdt_sib_arg, nums[0], "usdt_sib_arg");
+	ASSERT_EQ(bss->usdt_sib_arg_ret, 0, "usdt_sib_arg_ret");
+	ASSERT_EQ(bss->usdt_sib_arg_size, sizeof(nums[0]), "usdt_sib_arg_size");
+#endif
+
 cleanup:
 	test_usdt__destroy(skel);
 }
diff --git a/tools/testing/selftests/bpf/progs/test_usdt.c b/tools/testing/selftests/bpf/progs/test_usdt.c
index 096488f47fbc..b5f883bca66b 100644
--- a/tools/testing/selftests/bpf/progs/test_usdt.c
+++ b/tools/testing/selftests/bpf/progs/test_usdt.c
@@ -107,4 +107,34 @@ int BPF_USDT(usdt12, int a1, int a2, long a3, long a4, unsigned a5,
 	return 0;
 }
 
+
+int usdt_sib_called;
+u64 usdt_sib_cookie;
+int usdt_sib_arg_cnt;
+int usdt_sib_arg_ret;
+u64 usdt_sib_arg;
+int usdt_sib_arg_size;
+
+// Note: usdt_sib is only tested on x86-related architectures, so it requires
+// manual attach since auto-attach will panic tests under other architectures
+SEC("usdt")
+int usdt_sib(struct pt_regs *ctx)
+{
+	long tmp;
+
+	if (my_pid != (bpf_get_current_pid_tgid() >> 32))
+		return 0;
+
+	__sync_fetch_and_add(&usdt_sib_called, 1);
+
+	usdt_sib_cookie = bpf_usdt_cookie(ctx);
+	usdt_sib_arg_cnt = bpf_usdt_arg_cnt(ctx);
+
+	usdt_sib_arg_ret = bpf_usdt_arg(ctx, 0, &tmp);
+	usdt_sib_arg = (short)tmp;
+	usdt_sib_arg_size = bpf_usdt_arg_size(ctx, 0);
+
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.43.0

Re: [PATCH bpf-next v12 0/2] libbpf: fix USDT SIB argument handling causing unrecognized register error

[Jiri Olsa]

On Thu, Aug 21, 2025 at 03:27:10PM +0000, Jiawei Zhao wrote:
> When using GCC on x86-64 to compile an usdt prog with -O1 or higher
> optimization, the compiler will generate SIB addressing mode for global
> array and PC-relative addressing mode for global variable,
> e.g. "1@-96(%rbp,%rax,8)" and "-1@4+t1(%rip)".
> 
> The current USDT implementation in libbpf cannot parse these two formats,
> causing `bpf_program__attach_usdt()` to fail with -ENOENT
> (unrecognized register).
> 
> This patch series adds support for SIB addressing mode in USDT probes.
> The main changes include:
> - add correct handling logic for SIB-addressed arguments in
>   `parse_usdt_arg`.
> - add an usdt_o2 test case to cover SIB addressing mode.
> 
> Testing shows that the SIB probe correctly generates 8@(%rcx,%rax,8) 
> argument spec and passes all validation checks.
> 
> The modification history of this patch series:
> Change since v1:
> - refactor the code to make it more readable
> - modify the commit message to explain why and how
> 
> Change since v2:
> - fix the `scale` uninitialized error
> 
> Change since v3:
> - force -O2 optimization for usdt.test.o to generate SIB addressing usdt
>   and pass all test cases.
> 
> Change since v4:
> - split the patch into two parts, one for the fix and the other for the
>   test
> 
> Change since v5:
> - Only enable optimization for x86 architecture to generate SIB addressing
>   usdt argument spec.
> 
> Change since v6:
> - Add an usdt_o2 test case to cover SIB addressing mode.
> - Reinstate the usdt.c test case.
> 
> Change since v7:
> - Refactor modifications to __bpf_usdt_arg_spec to avoid increasing its size,
>   achieving better compatibility
> - Fix some minor code style issues
> - Refactor the usdt_o2 test case, removing semaphore and adding GCC attribute
>   to force -O2 optimization
> 
> Change since v8:
> - Refactor the usdt_o2 test case, using assembly to force SIB addressing mode.
> 
> Change since v9:
> - Only enable the usdt_o2 test case on x86_64 and i386 architectures since the
>   SIB addressing mode is only supported on x86_64 and i386.
> 
> Change since v10:
> - Replace `__attribute__((optimize("O2")))` with `#pragma GCC optimize("O1")`
>   to fix the issue where the optimized compilation condition works improperly. 
> - Renamed test case usdt_o2 and relevant files name to usdt_o1 in that O1
>   level optimization is enough to generate SIB addressing usdt argument spec.
> 
> Change since v11:
> - Replace `STAP_PROBE1` with `STAP_PROBE_ASM`
> - Use bit fields instead of bit shifting operations
> - Merge the usdt_o1 test case into the usdt test case

hi,
I can see patchset v12 twice with different stats.. this one's the latter,
but you might want to resend with new version

jirka


> 
> Jiawei Zhao (2):
>   libbpf: fix USDT SIB argument handling causing unrecognized register
>     error
>   selftests/bpf: Enrich subtest_basic_usdt case in selftests to cover
>     SIB handling logic
> 
>  tools/lib/bpf/usdt.bpf.h                      | 47 ++++++++++++++-
>  tools/lib/bpf/usdt.c                          | 58 +++++++++++++++++--
>  tools/testing/selftests/bpf/prog_tests/usdt.c | 44 +++++++++++++-
>  tools/testing/selftests/bpf/progs/test_usdt.c | 30 ++++++++++
>  4 files changed, 170 insertions(+), 9 deletions(-)
> 
> -- 
> 2.43.0
> 
> 

Re:Re: [PATCH bpf-next v12 0/2] libbpf: fix USDT SIB argument handling causing unrecognized register error

[赵佳炜]

Ok, done.







At 2025-08-22 21:17:55, "Jiri Olsa" <olsajiri@gmail.com> wrote:
>On Thu, Aug 21, 2025 at 03:27:10PM +0000, Jiawei Zhao wrote:
>> When using GCC on x86-64 to compile an usdt prog with -O1 or higher
>> optimization, the compiler will generate SIB addressing mode for global
>> array and PC-relative addressing mode for global variable,
>> e.g. "1@-96(%rbp,%rax,8)" and "-1@4+t1(%rip)".
>> 
>> The current USDT implementation in libbpf cannot parse these two formats,
>> causing `bpf_program__attach_usdt()` to fail with -ENOENT
>> (unrecognized register).
>> 
>> This patch series adds support for SIB addressing mode in USDT probes.
>> The main changes include:
>> - add correct handling logic for SIB-addressed arguments in
>>   `parse_usdt_arg`.
>> - add an usdt_o2 test case to cover SIB addressing mode.
>> 
>> Testing shows that the SIB probe correctly generates 8@(%rcx,%rax,8) 
>> argument spec and passes all validation checks.
>> 
>> The modification history of this patch series:
>> Change since v1:
>> - refactor the code to make it more readable
>> - modify the commit message to explain why and how
>> 
>> Change since v2:
>> - fix the `scale` uninitialized error
>> 
>> Change since v3:
>> - force -O2 optimization for usdt.test.o to generate SIB addressing usdt
>>   and pass all test cases.
>> 
>> Change since v4:
>> - split the patch into two parts, one for the fix and the other for the
>>   test
>> 
>> Change since v5:
>> - Only enable optimization for x86 architecture to generate SIB addressing
>>   usdt argument spec.
>> 
>> Change since v6:
>> - Add an usdt_o2 test case to cover SIB addressing mode.
>> - Reinstate the usdt.c test case.
>> 
>> Change since v7:
>> - Refactor modifications to __bpf_usdt_arg_spec to avoid increasing its size,
>>   achieving better compatibility
>> - Fix some minor code style issues
>> - Refactor the usdt_o2 test case, removing semaphore and adding GCC attribute
>>   to force -O2 optimization
>> 
>> Change since v8:
>> - Refactor the usdt_o2 test case, using assembly to force SIB addressing mode.
>> 
>> Change since v9:
>> - Only enable the usdt_o2 test case on x86_64 and i386 architectures since the
>>   SIB addressing mode is only supported on x86_64 and i386.
>> 
>> Change since v10:
>> - Replace `__attribute__((optimize("O2")))` with `#pragma GCC optimize("O1")`
>>   to fix the issue where the optimized compilation condition works improperly. 
>> - Renamed test case usdt_o2 and relevant files name to usdt_o1 in that O1
>>   level optimization is enough to generate SIB addressing usdt argument spec.
>> 
>> Change since v11:
>> - Replace `STAP_PROBE1` with `STAP_PROBE_ASM`
>> - Use bit fields instead of bit shifting operations
>> - Merge the usdt_o1 test case into the usdt test case
>
>hi,
>I can see patchset v12 twice with different stats.. this one's the latter,
>but you might want to resend with new version
>
>jirka
>
>
>> 
>> Jiawei Zhao (2):
>>   libbpf: fix USDT SIB argument handling causing unrecognized register
>>     error
>>   selftests/bpf: Enrich subtest_basic_usdt case in selftests to cover
>>     SIB handling logic
>> 
>>  tools/lib/bpf/usdt.bpf.h                      | 47 ++++++++++++++-
>>  tools/lib/bpf/usdt.c                          | 58 +++++++++++++++++--
>>  tools/testing/selftests/bpf/prog_tests/usdt.c | 44 +++++++++++++-
>>  tools/testing/selftests/bpf/progs/test_usdt.c | 30 ++++++++++
>>  4 files changed, 170 insertions(+), 9 deletions(-)
>> 
>> -- 
>> 2.43.0
>> 
>>