[PATCH v4 0/7] ptrace: introduce PTRACE_SET_SYSCALL_INFO API

[PATCH v4 0/7] ptrace: introduce PTRACE_SET_SYSCALL_INFO API

[Dmitry V. Levin]

PTRACE_SET_SYSCALL_INFO is a generic ptrace API that complements
PTRACE_GET_SYSCALL_INFO by letting the ptracer modify details of
system calls the tracee is blocked in.

This API allows ptracers to obtain and modify system call details
in a straightforward and architecture-agnostic way.

Current implementation supports changing only those bits of system call
information that are used by strace, namely, syscall number, syscall
arguments, and syscall return value.

Support of changing additional details returned by PTRACE_GET_SYSCALL_INFO,
such as instruction pointer and stack pointer, could be added later if
needed, by using struct ptrace_syscall_info.flags to specify the additional
details that should be set.  Currently, "flags" and "reserved" fields of
struct ptrace_syscall_info must be initialized with zeroes; "arch",
"instruction_pointer", and "stack_pointer" fields are ignored.

PTRACE_SET_SYSCALL_INFO currently supports only PTRACE_SYSCALL_INFO_ENTRY,
PTRACE_SYSCALL_INFO_EXIT, and PTRACE_SYSCALL_INFO_SECCOMP operations.
Other operations could be added later if needed.

Ideally, PTRACE_SET_SYSCALL_INFO should have been introduced along with
PTRACE_GET_SYSCALL_INFO, but it didn't happen.  The last straw that
convinced me to implement PTRACE_SET_SYSCALL_INFO was apparent failure
to provide an API of changing the first system call argument on riscv
architecture [1].

ptrace(2) man page:

long ptrace(enum __ptrace_request request, pid_t pid, void *addr, void *data);
...
PTRACE_SET_SYSCALL_INFO
       Modify information about the system call that caused the stop.
       The "data" argument is a pointer to struct ptrace_syscall_info
       that specifies the system call information to be set.
       The "addr" argument should be set to sizeof(struct ptrace_syscall_info)).

[1] https://lore.kernel.org/all/59505464-c84a-403d-972f-d4b2055eeaac@gmail.com/

Notes:
    v4:
    * Split out syscall_set_return_value() for hexagon into a separate patch
    * s390: Change the style of syscall_set_arguments() implementation as
      requested
    * Add more Reviewed-by
    * v3: https://lore.kernel.org/all/20250128091445.GA8257@strace.io/

    v3:
    * powerpc: Submit syscall_set_return_value() fix for "sc" case separately
    * mips: Do not introduce erroneous argument truncation on mips n32,
      add a detailed description to the commit message of the
      mips_get_syscall_arg() change
    * ptrace: Add explicit padding to the end of struct ptrace_syscall_info,
      simplify obtaining of user ptrace_syscall_info,
      do not introduce PTRACE_SYSCALL_INFO_SIZE_VER0
    * ptrace: Change the return type of ptrace_set_syscall_info_* functions
      from "unsigned long" to "int"
    * ptrace: Add -ERANGE check to ptrace_set_syscall_info_exit(),
      add comments to -ERANGE checks
    * ptrace: Update comments about supported syscall stops
    * selftests: Extend set_syscall_info test, fix for mips n32
    * Add Tested-by and Reviewed-by

    v2:
    * Add patch to fix syscall_set_return_value() on powerpc
    * Add patch to fix mips_get_syscall_arg() on mips
    * Add syscall_set_return_value() implementation on hexagon
    * Add syscall_set_return_value() invocation to syscall_set_nr()
      on arm and arm64.
    * Fix syscall_set_nr() and mips_set_syscall_arg() on mips
    * Add a comment to syscall_set_nr() on arc, powerpc, s390, sh,
      and sparc
    * Remove redundant ptrace_syscall_info.op assignments in
      ptrace_get_syscall_info_*
    * Minor style tweaks in ptrace_get_syscall_info_op()
    * Remove syscall_set_return_value() invocation from
      ptrace_set_syscall_info_entry()
    * Skip syscall_set_arguments() invocation in case of syscall number -1
      in ptrace_set_syscall_info_entry() 
    * Split ptrace_syscall_info.reserved into ptrace_syscall_info.reserved
      and ptrace_syscall_info.flags
    * Use __kernel_ulong_t instead of unsigned long in set_syscall_info test

    v1:

Dmitry V. Levin (7):
  mips: fix mips_get_syscall_arg() for o32
  hexagon: add syscall_set_return_value()
  syscall.h: add syscall_set_arguments()
  syscall.h: introduce syscall_set_nr()
  ptrace_get_syscall_info: factor out ptrace_get_syscall_info_op
  ptrace: introduce PTRACE_SET_SYSCALL_INFO request
  selftests/ptrace: add a test case for PTRACE_SET_SYSCALL_INFO

 arch/arc/include/asm/syscall.h                |  25 +
 arch/arm/include/asm/syscall.h                |  37 ++
 arch/arm64/include/asm/syscall.h              |  29 +
 arch/csky/include/asm/syscall.h               |  13 +
 arch/hexagon/include/asm/syscall.h            |  21 +
 arch/loongarch/include/asm/syscall.h          |  15 +
 arch/m68k/include/asm/syscall.h               |   7 +
 arch/microblaze/include/asm/syscall.h         |   7 +
 arch/mips/include/asm/syscall.h               |  70 ++-
 arch/nios2/include/asm/syscall.h              |  16 +
 arch/openrisc/include/asm/syscall.h           |  13 +
 arch/parisc/include/asm/syscall.h             |  19 +
 arch/powerpc/include/asm/syscall.h            |  20 +
 arch/riscv/include/asm/syscall.h              |  16 +
 arch/s390/include/asm/syscall.h               |  21 +
 arch/sh/include/asm/syscall_32.h              |  24 +
 arch/sparc/include/asm/syscall.h              |  22 +
 arch/um/include/asm/syscall-generic.h         |  19 +
 arch/x86/include/asm/syscall.h                |  43 ++
 arch/xtensa/include/asm/syscall.h             |  18 +
 include/asm-generic/syscall.h                 |  30 +
 include/uapi/linux/ptrace.h                   |   7 +-
 kernel/ptrace.c                               | 179 +++++-
 tools/testing/selftests/ptrace/Makefile       |   2 +-
 .../selftests/ptrace/set_syscall_info.c       | 514 ++++++++++++++++++
 25 files changed, 1140 insertions(+), 47 deletions(-)
 create mode 100644 tools/testing/selftests/ptrace/set_syscall_info.c

-- 
ldv

[PATCH v4 2/7] hexagon: add syscall_set_return_value()

[Dmitry V. Levin]

hexagon is the only architecture that provides HAVE_ARCH_TRACEHOOK but
doesn't define syscall_set_return_value().  Since this function is going
to be needed on all HAVE_ARCH_TRACEHOOK architectures to implement
PTRACE_SET_SYSCALL_INFO API, add it on hexagon, too.

Signed-off-by: Dmitry V. Levin <ldv@strace.io>
---
 arch/hexagon/include/asm/syscall.h | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/hexagon/include/asm/syscall.h b/arch/hexagon/include/asm/syscall.h
index f6e454f18038..951ca0ed8376 100644
--- a/arch/hexagon/include/asm/syscall.h
+++ b/arch/hexagon/include/asm/syscall.h
@@ -45,6 +45,13 @@ static inline long syscall_get_return_value(struct task_struct *task,
 	return regs->r00;
 }
 
+static inline void syscall_set_return_value(struct task_struct *task,
+					    struct pt_regs *regs,
+					    int error, long val)
+{
+	regs->r00 = (long) error ?: val;
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	return AUDIT_ARCH_HEXAGON;
-- 
ldv

[PATCH v4 3/7] syscall.h: add syscall_set_arguments()

[Dmitry V. Levin]

This function is going to be needed on all HAVE_ARCH_TRACEHOOK
architectures to implement PTRACE_SET_SYSCALL_INFO API.

This partially reverts commit 7962c2eddbfe ("arch: remove unused
function syscall_set_arguments()") by reusing some of old
syscall_set_arguments() implementations.

Signed-off-by: Dmitry V. Levin <ldv@strace.io>
Tested-by: Charlie Jenkins <charlie@rivosinc.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
---
 arch/arc/include/asm/syscall.h        | 14 +++++++++++
 arch/arm/include/asm/syscall.h        | 13 ++++++++++
 arch/arm64/include/asm/syscall.h      | 13 ++++++++++
 arch/csky/include/asm/syscall.h       | 13 ++++++++++
 arch/hexagon/include/asm/syscall.h    |  7 ++++++
 arch/loongarch/include/asm/syscall.h  |  8 ++++++
 arch/mips/include/asm/syscall.h       | 32 ++++++++++++++++++++++++
 arch/nios2/include/asm/syscall.h      | 11 ++++++++
 arch/openrisc/include/asm/syscall.h   |  7 ++++++
 arch/parisc/include/asm/syscall.h     | 12 +++++++++
 arch/powerpc/include/asm/syscall.h    | 10 ++++++++
 arch/riscv/include/asm/syscall.h      |  9 +++++++
 arch/s390/include/asm/syscall.h       |  9 +++++++
 arch/sh/include/asm/syscall_32.h      | 12 +++++++++
 arch/sparc/include/asm/syscall.h      | 10 ++++++++
 arch/um/include/asm/syscall-generic.h | 14 +++++++++++
 arch/x86/include/asm/syscall.h        | 36 +++++++++++++++++++++++++++
 arch/xtensa/include/asm/syscall.h     | 11 ++++++++
 include/asm-generic/syscall.h         | 16 ++++++++++++
 19 files changed, 257 insertions(+)

diff --git a/arch/arc/include/asm/syscall.h b/arch/arc/include/asm/syscall.h
index 9709256e31c8..89c1e1736356 100644
--- a/arch/arc/include/asm/syscall.h
+++ b/arch/arc/include/asm/syscall.h
@@ -67,6 +67,20 @@ syscall_get_arguments(struct task_struct *task, struct pt_regs *regs,
 	}
 }
 
+static inline void
+syscall_set_arguments(struct task_struct *task, struct pt_regs *regs,
+		      unsigned long *args)
+{
+	unsigned long *inside_ptregs = &regs->r0;
+	unsigned int n = 6;
+	unsigned int i = 0;
+
+	while (n--) {
+		*inside_ptregs = args[i++];
+		inside_ptregs--;
+	}
+}
+
 static inline int
 syscall_get_arch(struct task_struct *task)
 {
diff --git a/arch/arm/include/asm/syscall.h b/arch/arm/include/asm/syscall.h
index fe4326d938c1..21927fa0ae2b 100644
--- a/arch/arm/include/asm/syscall.h
+++ b/arch/arm/include/asm/syscall.h
@@ -80,6 +80,19 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	memcpy(args, &regs->ARM_r0 + 1, 5 * sizeof(args[0]));
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	memcpy(&regs->ARM_r0, args, 6 * sizeof(args[0]));
+	/*
+	 * Also copy the first argument into ARM_ORIG_r0
+	 * so that syscall_get_arguments() would return it
+	 * instead of the previous value.
+	 */
+	regs->ARM_ORIG_r0 = regs->ARM_r0;
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	/* ARM tasks don't change audit architectures on the fly. */
diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
index ab8e14b96f68..76020b66286b 100644
--- a/arch/arm64/include/asm/syscall.h
+++ b/arch/arm64/include/asm/syscall.h
@@ -73,6 +73,19 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	memcpy(args, &regs->regs[1], 5 * sizeof(args[0]));
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	memcpy(&regs->regs[0], args, 6 * sizeof(args[0]));
+	/*
+	 * Also copy the first argument into orig_x0
+	 * so that syscall_get_arguments() would return it
+	 * instead of the previous value.
+	 */
+	regs->orig_x0 = regs->regs[0];
+}
+
 /*
  * We don't care about endianness (__AUDIT_ARCH_LE bit) here because
  * AArch64 has the same system calls both on little- and big- endian.
diff --git a/arch/csky/include/asm/syscall.h b/arch/csky/include/asm/syscall.h
index 0de5734950bf..30403f7a0487 100644
--- a/arch/csky/include/asm/syscall.h
+++ b/arch/csky/include/asm/syscall.h
@@ -59,6 +59,19 @@ syscall_get_arguments(struct task_struct *task, struct pt_regs *regs,
 	memcpy(args, &regs->a1, 5 * sizeof(args[0]));
 }
 
+static inline void
+syscall_set_arguments(struct task_struct *task, struct pt_regs *regs,
+		      const unsigned long *args)
+{
+	memcpy(&regs->a0, args, 6 * sizeof(regs->a0));
+	/*
+	 * Also copy the first argument into orig_x0
+	 * so that syscall_get_arguments() would return it
+	 * instead of the previous value.
+	 */
+	regs->orig_a0 = regs->a0;
+}
+
 static inline int
 syscall_get_arch(struct task_struct *task)
 {
diff --git a/arch/hexagon/include/asm/syscall.h b/arch/hexagon/include/asm/syscall.h
index 951ca0ed8376..1024a6548d78 100644
--- a/arch/hexagon/include/asm/syscall.h
+++ b/arch/hexagon/include/asm/syscall.h
@@ -33,6 +33,13 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	memcpy(args, &(&regs->r00)[0], 6 * sizeof(args[0]));
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 unsigned long *args)
+{
+	memcpy(&(&regs->r00)[0], args, 6 * sizeof(args[0]));
+}
+
 static inline long syscall_get_error(struct task_struct *task,
 				     struct pt_regs *regs)
 {
diff --git a/arch/loongarch/include/asm/syscall.h b/arch/loongarch/include/asm/syscall.h
index e286dc58476e..ff415b3c0a8e 100644
--- a/arch/loongarch/include/asm/syscall.h
+++ b/arch/loongarch/include/asm/syscall.h
@@ -61,6 +61,14 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	memcpy(&args[1], &regs->regs[5], 5 * sizeof(long));
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 unsigned long *args)
+{
+	regs->orig_a0 = args[0];
+	memcpy(&regs->regs[5], &args[1], 5 * sizeof(long));
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	return AUDIT_ARCH_LOONGARCH64;
diff --git a/arch/mips/include/asm/syscall.h b/arch/mips/include/asm/syscall.h
index b3f00ede8bb3..2dcc1d01b405 100644
--- a/arch/mips/include/asm/syscall.h
+++ b/arch/mips/include/asm/syscall.h
@@ -74,6 +74,23 @@ static inline void mips_get_syscall_arg(unsigned long *arg,
 #endif
 }
 
+static inline void mips_set_syscall_arg(unsigned long *arg,
+	struct task_struct *task, struct pt_regs *regs, unsigned int n)
+{
+#ifdef CONFIG_32BIT
+	switch (n) {
+	case 0: case 1: case 2: case 3:
+		regs->regs[4 + n] = *arg;
+		return;
+	case 4: case 5: case 6: case 7:
+		*arg = regs->pad0[n] = *arg;
+		return;
+	}
+#else
+	regs->regs[4 + n] = *arg;
+#endif
+}
+
 static inline long syscall_get_error(struct task_struct *task,
 				     struct pt_regs *regs)
 {
@@ -120,6 +137,21 @@ static inline void syscall_get_arguments(struct task_struct *task,
 		mips_get_syscall_arg(args++, task, regs, i++);
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 unsigned long *args)
+{
+	unsigned int i = 0;
+	unsigned int n = 6;
+
+	/* O32 ABI syscall() */
+	if (mips_syscall_is_indirect(task, regs))
+		i++;
+
+	while (n--)
+		mips_set_syscall_arg(args++, task, regs, i++);
+}
+
 extern const unsigned long sys_call_table[];
 extern const unsigned long sys32_call_table[];
 extern const unsigned long sysn32_call_table[];
diff --git a/arch/nios2/include/asm/syscall.h b/arch/nios2/include/asm/syscall.h
index fff52205fb65..526449edd768 100644
--- a/arch/nios2/include/asm/syscall.h
+++ b/arch/nios2/include/asm/syscall.h
@@ -58,6 +58,17 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	*args   = regs->r9;
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+	struct pt_regs *regs, const unsigned long *args)
+{
+	regs->r4 = *args++;
+	regs->r5 = *args++;
+	regs->r6 = *args++;
+	regs->r7 = *args++;
+	regs->r8 = *args++;
+	regs->r9 = *args;
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	return AUDIT_ARCH_NIOS2;
diff --git a/arch/openrisc/include/asm/syscall.h b/arch/openrisc/include/asm/syscall.h
index 903ed882bdec..e6383be2a195 100644
--- a/arch/openrisc/include/asm/syscall.h
+++ b/arch/openrisc/include/asm/syscall.h
@@ -57,6 +57,13 @@ syscall_get_arguments(struct task_struct *task, struct pt_regs *regs,
 	memcpy(args, &regs->gpr[3], 6 * sizeof(args[0]));
 }
 
+static inline void
+syscall_set_arguments(struct task_struct *task, struct pt_regs *regs,
+		      const unsigned long *args)
+{
+	memcpy(&regs->gpr[3], args, 6 * sizeof(args[0]));
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	return AUDIT_ARCH_OPENRISC;
diff --git a/arch/parisc/include/asm/syscall.h b/arch/parisc/include/asm/syscall.h
index 00b127a5e09b..b146d0ae4c77 100644
--- a/arch/parisc/include/asm/syscall.h
+++ b/arch/parisc/include/asm/syscall.h
@@ -29,6 +29,18 @@ static inline void syscall_get_arguments(struct task_struct *tsk,
 	args[0] = regs->gr[26];
 }
 
+static inline void syscall_set_arguments(struct task_struct *tsk,
+					 struct pt_regs *regs,
+					 unsigned long *args)
+{
+	regs->gr[21] = args[5];
+	regs->gr[22] = args[4];
+	regs->gr[23] = args[3];
+	regs->gr[24] = args[2];
+	regs->gr[25] = args[1];
+	regs->gr[26] = args[0];
+}
+
 static inline long syscall_get_error(struct task_struct *task,
 				     struct pt_regs *regs)
 {
diff --git a/arch/powerpc/include/asm/syscall.h b/arch/powerpc/include/asm/syscall.h
index 422d7735ace6..521f279e6b33 100644
--- a/arch/powerpc/include/asm/syscall.h
+++ b/arch/powerpc/include/asm/syscall.h
@@ -114,6 +114,16 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	}
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	memcpy(&regs->gpr[3], args, 6 * sizeof(args[0]));
+
+	/* Also copy the first argument into orig_gpr3 */
+	regs->orig_gpr3 = args[0];
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	if (is_tsk_32bit_task(task))
diff --git a/arch/riscv/include/asm/syscall.h b/arch/riscv/include/asm/syscall.h
index 121fff429dce..8d389ba995c8 100644
--- a/arch/riscv/include/asm/syscall.h
+++ b/arch/riscv/include/asm/syscall.h
@@ -66,6 +66,15 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	memcpy(args, &regs->a1, 5 * sizeof(args[0]));
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	regs->orig_a0 = args[0];
+	args++;
+	memcpy(&regs->a1, args, 5 * sizeof(regs->a1));
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 #ifdef CONFIG_64BIT
diff --git a/arch/s390/include/asm/syscall.h b/arch/s390/include/asm/syscall.h
index 27e3d804b311..0e3296a32e6a 100644
--- a/arch/s390/include/asm/syscall.h
+++ b/arch/s390/include/asm/syscall.h
@@ -78,6 +78,15 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	args[0] = regs->orig_gpr2 & mask;
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	regs->orig_gpr2 = args[0];
+	for (int n = 1; n < 6; n++)
+		regs->gprs[2 + n] = args[n];
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 #ifdef CONFIG_COMPAT
diff --git a/arch/sh/include/asm/syscall_32.h b/arch/sh/include/asm/syscall_32.h
index d87738eebe30..cb51a7528384 100644
--- a/arch/sh/include/asm/syscall_32.h
+++ b/arch/sh/include/asm/syscall_32.h
@@ -57,6 +57,18 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	args[0] = regs->regs[4];
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	regs->regs[1] = args[5];
+	regs->regs[0] = args[4];
+	regs->regs[7] = args[3];
+	regs->regs[6] = args[2];
+	regs->regs[5] = args[1];
+	regs->regs[4] = args[0];
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	int arch = AUDIT_ARCH_SH;
diff --git a/arch/sparc/include/asm/syscall.h b/arch/sparc/include/asm/syscall.h
index 20c109ac8cc9..62a5a78804c4 100644
--- a/arch/sparc/include/asm/syscall.h
+++ b/arch/sparc/include/asm/syscall.h
@@ -117,6 +117,16 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	}
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	unsigned int i;
+
+	for (i = 0; i < 6; i++)
+		regs->u_regs[UREG_I0 + i] = args[i];
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 #if defined(CONFIG_SPARC64) && defined(CONFIG_COMPAT)
diff --git a/arch/um/include/asm/syscall-generic.h b/arch/um/include/asm/syscall-generic.h
index 172b74143c4b..2984feb9d576 100644
--- a/arch/um/include/asm/syscall-generic.h
+++ b/arch/um/include/asm/syscall-generic.h
@@ -62,6 +62,20 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	*args   = UPT_SYSCALL_ARG6(r);
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	struct uml_pt_regs *r = &regs->regs;
+
+	UPT_SYSCALL_ARG1(r) = *args++;
+	UPT_SYSCALL_ARG2(r) = *args++;
+	UPT_SYSCALL_ARG3(r) = *args++;
+	UPT_SYSCALL_ARG4(r) = *args++;
+	UPT_SYSCALL_ARG5(r) = *args++;
+	UPT_SYSCALL_ARG6(r) = *args;
+}
+
 /* See arch/x86/um/asm/syscall.h for syscall_get_arch() definition. */
 
 #endif	/* __UM_SYSCALL_GENERIC_H */
diff --git a/arch/x86/include/asm/syscall.h b/arch/x86/include/asm/syscall.h
index 7c488ff0c764..b9c249dd9e3d 100644
--- a/arch/x86/include/asm/syscall.h
+++ b/arch/x86/include/asm/syscall.h
@@ -90,6 +90,18 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	args[5] = regs->bp;
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	regs->bx = args[0];
+	regs->cx = args[1];
+	regs->dx = args[2];
+	regs->si = args[3];
+	regs->di = args[4];
+	regs->bp = args[5];
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	return AUDIT_ARCH_I386;
@@ -121,6 +133,30 @@ static inline void syscall_get_arguments(struct task_struct *task,
 	}
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+# ifdef CONFIG_IA32_EMULATION
+	if (task->thread_info.status & TS_COMPAT) {
+		regs->bx = *args++;
+		regs->cx = *args++;
+		regs->dx = *args++;
+		regs->si = *args++;
+		regs->di = *args++;
+		regs->bp = *args;
+	} else
+# endif
+	{
+		regs->di = *args++;
+		regs->si = *args++;
+		regs->dx = *args++;
+		regs->r10 = *args++;
+		regs->r8 = *args++;
+		regs->r9 = *args;
+	}
+}
+
 static inline int syscall_get_arch(struct task_struct *task)
 {
 	/* x32 tasks should be considered AUDIT_ARCH_X86_64. */
diff --git a/arch/xtensa/include/asm/syscall.h b/arch/xtensa/include/asm/syscall.h
index 5ee974bf8330..f9a671cbf933 100644
--- a/arch/xtensa/include/asm/syscall.h
+++ b/arch/xtensa/include/asm/syscall.h
@@ -68,6 +68,17 @@ static inline void syscall_get_arguments(struct task_struct *task,
 		args[i] = regs->areg[reg[i]];
 }
 
+static inline void syscall_set_arguments(struct task_struct *task,
+					 struct pt_regs *regs,
+					 const unsigned long *args)
+{
+	static const unsigned int reg[] = XTENSA_SYSCALL_ARGUMENT_REGS;
+	unsigned int i;
+
+	for (i = 0; i < 6; ++i)
+		regs->areg[reg[i]] = args[i];
+}
+
 asmlinkage long xtensa_rt_sigreturn(void);
 asmlinkage long xtensa_shmat(int, char __user *, int);
 asmlinkage long xtensa_fadvise64_64(int, int,
diff --git a/include/asm-generic/syscall.h b/include/asm-generic/syscall.h
index 5a80fe728dc8..0f7b9a493de7 100644
--- a/include/asm-generic/syscall.h
+++ b/include/asm-generic/syscall.h
@@ -117,6 +117,22 @@ void syscall_set_return_value(struct task_struct *task, struct pt_regs *regs,
 void syscall_get_arguments(struct task_struct *task, struct pt_regs *regs,
 			   unsigned long *args);
 
+/**
+ * syscall_set_arguments - change system call parameter value
+ * @task:	task of interest, must be in system call entry tracing
+ * @regs:	task_pt_regs() of @task
+ * @args:	array of argument values to store
+ *
+ * Changes 6 arguments to the system call.
+ * The first argument gets value @args[0], and so on.
+ *
+ * It's only valid to call this when @task is stopped for tracing on
+ * entry to a system call, due to %SYSCALL_WORK_SYSCALL_TRACE or
+ * %SYSCALL_WORK_SYSCALL_AUDIT.
+ */
+void syscall_set_arguments(struct task_struct *task, struct pt_regs *regs,
+			   const unsigned long *args);
+
 /**
  * syscall_get_arch - return the AUDIT_ARCH for the current system call
  * @task:	task of interest, must be blocked
-- 
ldv

[PATCH v4 4/7] syscall.h: introduce syscall_set_nr()

[Dmitry V. Levin]

Similar to syscall_set_arguments() that complements
syscall_get_arguments(), introduce syscall_set_nr()
that complements syscall_get_nr().

syscall_set_nr() is going to be needed along with
syscall_set_arguments() on all HAVE_ARCH_TRACEHOOK
architectures to implement PTRACE_SET_SYSCALL_INFO API.

Signed-off-by: Dmitry V. Levin <ldv@strace.io>
Tested-by: Charlie Jenkins <charlie@rivosinc.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
---
 arch/arc/include/asm/syscall.h        | 11 +++++++++++
 arch/arm/include/asm/syscall.h        | 24 ++++++++++++++++++++++++
 arch/arm64/include/asm/syscall.h      | 16 ++++++++++++++++
 arch/hexagon/include/asm/syscall.h    |  7 +++++++
 arch/loongarch/include/asm/syscall.h  |  7 +++++++
 arch/m68k/include/asm/syscall.h       |  7 +++++++
 arch/microblaze/include/asm/syscall.h |  7 +++++++
 arch/mips/include/asm/syscall.h       | 14 ++++++++++++++
 arch/nios2/include/asm/syscall.h      |  5 +++++
 arch/openrisc/include/asm/syscall.h   |  6 ++++++
 arch/parisc/include/asm/syscall.h     |  7 +++++++
 arch/powerpc/include/asm/syscall.h    | 10 ++++++++++
 arch/riscv/include/asm/syscall.h      |  7 +++++++
 arch/s390/include/asm/syscall.h       | 12 ++++++++++++
 arch/sh/include/asm/syscall_32.h      | 12 ++++++++++++
 arch/sparc/include/asm/syscall.h      | 12 ++++++++++++
 arch/um/include/asm/syscall-generic.h |  5 +++++
 arch/x86/include/asm/syscall.h        |  7 +++++++
 arch/xtensa/include/asm/syscall.h     |  7 +++++++
 include/asm-generic/syscall.h         | 14 ++++++++++++++
 20 files changed, 197 insertions(+)

diff --git a/arch/arc/include/asm/syscall.h b/arch/arc/include/asm/syscall.h
index 89c1e1736356..728d625a10f1 100644
--- a/arch/arc/include/asm/syscall.h
+++ b/arch/arc/include/asm/syscall.h
@@ -23,6 +23,17 @@ syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 		return -1;
 }
 
+static inline void
+syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
+{
+	/*
+	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
+	 * the target task is stopped for tracing on entering syscall, so
+	 * there is no need to have the same check syscall_get_nr() has.
+	 */
+	regs->r8 = nr;
+}
+
 static inline void
 syscall_rollback(struct task_struct *task, struct pt_regs *regs)
 {
diff --git a/arch/arm/include/asm/syscall.h b/arch/arm/include/asm/syscall.h
index 21927fa0ae2b..18b102a30741 100644
--- a/arch/arm/include/asm/syscall.h
+++ b/arch/arm/include/asm/syscall.h
@@ -68,6 +68,30 @@ static inline void syscall_set_return_value(struct task_struct *task,
 	regs->ARM_r0 = (long) error ? error : val;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	if (nr == -1) {
+		task_thread_info(task)->abi_syscall = -1;
+		/*
+		 * When the syscall number is set to -1, the syscall will be
+		 * skipped.  In this case the syscall return value has to be
+		 * set explicitly, otherwise the first syscall argument is
+		 * returned as the syscall return value.
+		 */
+		syscall_set_return_value(task, regs, -ENOSYS, 0);
+		return;
+	}
+	if ((IS_ENABLED(CONFIG_AEABI) && !IS_ENABLED(CONFIG_OABI_COMPAT))) {
+		task_thread_info(task)->abi_syscall = nr;
+		return;
+	}
+	task_thread_info(task)->abi_syscall =
+		(task_thread_info(task)->abi_syscall & ~__NR_SYSCALL_MASK) |
+		(nr & __NR_SYSCALL_MASK);
+}
+
 #define SYSCALL_MAX_ARGS 7
 
 static inline void syscall_get_arguments(struct task_struct *task,
diff --git a/arch/arm64/include/asm/syscall.h b/arch/arm64/include/asm/syscall.h
index 76020b66286b..712daa90e643 100644
--- a/arch/arm64/include/asm/syscall.h
+++ b/arch/arm64/include/asm/syscall.h
@@ -61,6 +61,22 @@ static inline void syscall_set_return_value(struct task_struct *task,
 	regs->regs[0] = val;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->syscallno = nr;
+	if (nr == -1) {
+		/*
+		 * When the syscall number is set to -1, the syscall will be
+		 * skipped.  In this case the syscall return value has to be
+		 * set explicitly, otherwise the first syscall argument is
+		 * returned as the syscall return value.
+		 */
+		syscall_set_return_value(task, regs, -ENOSYS, 0);
+	}
+}
+
 #define SYSCALL_MAX_ARGS 6
 
 static inline void syscall_get_arguments(struct task_struct *task,
diff --git a/arch/hexagon/include/asm/syscall.h b/arch/hexagon/include/asm/syscall.h
index 1024a6548d78..70637261817a 100644
--- a/arch/hexagon/include/asm/syscall.h
+++ b/arch/hexagon/include/asm/syscall.h
@@ -26,6 +26,13 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return regs->r06;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->r06 = nr;
+}
+
 static inline void syscall_get_arguments(struct task_struct *task,
 					 struct pt_regs *regs,
 					 unsigned long *args)
diff --git a/arch/loongarch/include/asm/syscall.h b/arch/loongarch/include/asm/syscall.h
index ff415b3c0a8e..81d2733f7b94 100644
--- a/arch/loongarch/include/asm/syscall.h
+++ b/arch/loongarch/include/asm/syscall.h
@@ -26,6 +26,13 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return regs->regs[11];
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->regs[11] = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {
diff --git a/arch/m68k/include/asm/syscall.h b/arch/m68k/include/asm/syscall.h
index d1453e850cdd..bf84b160c2eb 100644
--- a/arch/m68k/include/asm/syscall.h
+++ b/arch/m68k/include/asm/syscall.h
@@ -14,6 +14,13 @@ static inline int syscall_get_nr(struct task_struct *task,
 	return regs->orig_d0;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->orig_d0 = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {
diff --git a/arch/microblaze/include/asm/syscall.h b/arch/microblaze/include/asm/syscall.h
index 5eb3f624cc59..b5b6b91fae3e 100644
--- a/arch/microblaze/include/asm/syscall.h
+++ b/arch/microblaze/include/asm/syscall.h
@@ -14,6 +14,13 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return regs->r12;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->r12 = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {
diff --git a/arch/mips/include/asm/syscall.h b/arch/mips/include/asm/syscall.h
index 2dcc1d01b405..1cd25306cc13 100644
--- a/arch/mips/include/asm/syscall.h
+++ b/arch/mips/include/asm/syscall.h
@@ -41,6 +41,20 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return task_thread_info(task)->syscall;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	/*
+	 * New syscall number has to be assigned to regs[2] because
+	 * syscall_trace_entry() loads it from there unconditionally.
+	 *
+	 * Consequently, if the syscall was indirect and nr != __NR_syscall,
+	 * then after this assignment the syscall will cease to be indirect.
+	 */
+	task_thread_info(task)->syscall = regs->regs[2] = nr;
+}
+
 static inline void mips_syscall_update_nr(struct task_struct *task,
 					  struct pt_regs *regs)
 {
diff --git a/arch/nios2/include/asm/syscall.h b/arch/nios2/include/asm/syscall.h
index 526449edd768..8e3eb1d689bb 100644
--- a/arch/nios2/include/asm/syscall.h
+++ b/arch/nios2/include/asm/syscall.h
@@ -15,6 +15,11 @@ static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 	return regs->r2;
 }
 
+static inline void syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
+{
+	regs->r2 = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				struct pt_regs *regs)
 {
diff --git a/arch/openrisc/include/asm/syscall.h b/arch/openrisc/include/asm/syscall.h
index e6383be2a195..5e037d9659c5 100644
--- a/arch/openrisc/include/asm/syscall.h
+++ b/arch/openrisc/include/asm/syscall.h
@@ -25,6 +25,12 @@ syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 	return regs->orig_gpr11;
 }
 
+static inline void
+syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
+{
+	regs->orig_gpr11 = nr;
+}
+
 static inline void
 syscall_rollback(struct task_struct *task, struct pt_regs *regs)
 {
diff --git a/arch/parisc/include/asm/syscall.h b/arch/parisc/include/asm/syscall.h
index b146d0ae4c77..c11222798ab2 100644
--- a/arch/parisc/include/asm/syscall.h
+++ b/arch/parisc/include/asm/syscall.h
@@ -17,6 +17,13 @@ static inline long syscall_get_nr(struct task_struct *tsk,
 	return regs->gr[20];
 }
 
+static inline void syscall_set_nr(struct task_struct *tsk,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->gr[20] = nr;
+}
+
 static inline void syscall_get_arguments(struct task_struct *tsk,
 					 struct pt_regs *regs,
 					 unsigned long *args)
diff --git a/arch/powerpc/include/asm/syscall.h b/arch/powerpc/include/asm/syscall.h
index 521f279e6b33..7505dcfed247 100644
--- a/arch/powerpc/include/asm/syscall.h
+++ b/arch/powerpc/include/asm/syscall.h
@@ -39,6 +39,16 @@ static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 		return -1;
 }
 
+static inline void syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
+{
+	/*
+	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
+	 * the target task is stopped for tracing on entering syscall, so
+	 * there is no need to have the same check syscall_get_nr() has.
+	 */
+	regs->gpr[0] = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {
diff --git a/arch/riscv/include/asm/syscall.h b/arch/riscv/include/asm/syscall.h
index 8d389ba995c8..a5281cdf2b10 100644
--- a/arch/riscv/include/asm/syscall.h
+++ b/arch/riscv/include/asm/syscall.h
@@ -30,6 +30,13 @@ static inline int syscall_get_nr(struct task_struct *task,
 	return regs->a7;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->a7 = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {
diff --git a/arch/s390/include/asm/syscall.h b/arch/s390/include/asm/syscall.h
index 0e3296a32e6a..db6ca55564ff 100644
--- a/arch/s390/include/asm/syscall.h
+++ b/arch/s390/include/asm/syscall.h
@@ -24,6 +24,18 @@ static inline long syscall_get_nr(struct task_struct *task,
 		(regs->int_code & 0xffff) : -1;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	/*
+	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
+	 * the target task is stopped for tracing on entering syscall, so
+	 * there is no need to have the same check syscall_get_nr() has.
+	 */
+	regs->int_code = (regs->int_code & ~0xffff) | (nr & 0xffff);
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {
diff --git a/arch/sh/include/asm/syscall_32.h b/arch/sh/include/asm/syscall_32.h
index cb51a7528384..7027d87d901d 100644
--- a/arch/sh/include/asm/syscall_32.h
+++ b/arch/sh/include/asm/syscall_32.h
@@ -15,6 +15,18 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return (regs->tra >= 0) ? regs->regs[3] : -1L;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	/*
+	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
+	 * the target task is stopped for tracing on entering syscall, so
+	 * there is no need to have the same check syscall_get_nr() has.
+	 */
+	regs->regs[3] = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {
diff --git a/arch/sparc/include/asm/syscall.h b/arch/sparc/include/asm/syscall.h
index 62a5a78804c4..b0233924d323 100644
--- a/arch/sparc/include/asm/syscall.h
+++ b/arch/sparc/include/asm/syscall.h
@@ -25,6 +25,18 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return (syscall_p ? regs->u_regs[UREG_G1] : -1L);
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	/*
+	 * Unlike syscall_get_nr(), syscall_set_nr() can be called only when
+	 * the target task is stopped for tracing on entering syscall, so
+	 * there is no need to have the same check syscall_get_nr() has.
+	 */
+	regs->u_regs[UREG_G1] = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {
diff --git a/arch/um/include/asm/syscall-generic.h b/arch/um/include/asm/syscall-generic.h
index 2984feb9d576..bcd73bcfe577 100644
--- a/arch/um/include/asm/syscall-generic.h
+++ b/arch/um/include/asm/syscall-generic.h
@@ -21,6 +21,11 @@ static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 	return PT_REGS_SYSCALL_NR(regs);
 }
 
+static inline void syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr)
+{
+	PT_REGS_SYSCALL_NR(regs) = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {
diff --git a/arch/x86/include/asm/syscall.h b/arch/x86/include/asm/syscall.h
index b9c249dd9e3d..c10dbb74cd00 100644
--- a/arch/x86/include/asm/syscall.h
+++ b/arch/x86/include/asm/syscall.h
@@ -38,6 +38,13 @@ static inline int syscall_get_nr(struct task_struct *task, struct pt_regs *regs)
 	return regs->orig_ax;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->orig_ax = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {
diff --git a/arch/xtensa/include/asm/syscall.h b/arch/xtensa/include/asm/syscall.h
index f9a671cbf933..7db3b489c8ad 100644
--- a/arch/xtensa/include/asm/syscall.h
+++ b/arch/xtensa/include/asm/syscall.h
@@ -28,6 +28,13 @@ static inline long syscall_get_nr(struct task_struct *task,
 	return regs->syscall;
 }
 
+static inline void syscall_set_nr(struct task_struct *task,
+				  struct pt_regs *regs,
+				  int nr)
+{
+	regs->syscall = nr;
+}
+
 static inline void syscall_rollback(struct task_struct *task,
 				    struct pt_regs *regs)
 {
diff --git a/include/asm-generic/syscall.h b/include/asm-generic/syscall.h
index 0f7b9a493de7..e33fd4e783c1 100644
--- a/include/asm-generic/syscall.h
+++ b/include/asm-generic/syscall.h
@@ -37,6 +37,20 @@ struct pt_regs;
  */
 int syscall_get_nr(struct task_struct *task, struct pt_regs *regs);
 
+/**
+ * syscall_set_nr - change the system call a task is executing
+ * @task:	task of interest, must be blocked
+ * @regs:	task_pt_regs() of @task
+ * @nr:		system call number
+ *
+ * Changes the system call number @task is about to execute.
+ *
+ * It's only valid to call this when @task is stopped for tracing on
+ * entry to a system call, due to %SYSCALL_WORK_SYSCALL_TRACE or
+ * %SYSCALL_WORK_SYSCALL_AUDIT.
+ */
+void syscall_set_nr(struct task_struct *task, struct pt_regs *regs, int nr);
+
 /**
  * syscall_rollback - roll back registers after an aborted system call
  * @task:	task of interest, must be in system call exit tracing
-- 
ldv

Re: [PATCH v4 0/7] ptrace: introduce PTRACE_SET_SYSCALL_INFO API

[Alexander Gordeev]

On Mon, Feb 03, 2025 at 08:58:49AM +0200, Dmitry V. Levin wrote:

Hi Dmitry,

> PTRACE_SET_SYSCALL_INFO is a generic ptrace API that complements
> PTRACE_GET_SYSCALL_INFO by letting the ptracer modify details of
> system calls the tracee is blocked in.
...

FWIW, I am getting these on s390:

# ./tools/testing/selftests/ptrace/set_syscall_info 
TAP version 13
1..1
# Starting 1 tests from 1 test cases.
#  RUN           global.set_syscall_info ...
# set_syscall_info.c:87:set_syscall_info:Expected exp_entry->nr (-1) == info->entry.nr (65535)
# set_syscall_info.c:88:set_syscall_info:wait #3: PTRACE_GET_SYSCALL_INFO #2: syscall nr mismatch
# set_syscall_info: Test terminated by assertion
#          FAIL  global.set_syscall_info
not ok 1 global.set_syscall_info
# FAILED: 0 / 1 tests passed.
# Totals: pass:0 fail:1 xfail:0 xpass:0 skip:0 error:0

I remember one of the earlier versions (v1 or v2) was working for me.

Thanks!

Re: [PATCH v4 0/7] ptrace: introduce PTRACE_SET_SYSCALL_INFO API

[Dmitry V. Levin]

On Mon, Feb 03, 2025 at 10:29:37AM +0100, Alexander Gordeev wrote:
> On Mon, Feb 03, 2025 at 08:58:49AM +0200, Dmitry V. Levin wrote:
> 
> Hi Dmitry,
> 
> > PTRACE_SET_SYSCALL_INFO is a generic ptrace API that complements
> > PTRACE_GET_SYSCALL_INFO by letting the ptracer modify details of
> > system calls the tracee is blocked in.
> ...
> 
> FWIW, I am getting these on s390:
> 
> # ./tools/testing/selftests/ptrace/set_syscall_info 
> TAP version 13
> 1..1
> # Starting 1 tests from 1 test cases.
> #  RUN           global.set_syscall_info ...
> # set_syscall_info.c:87:set_syscall_info:Expected exp_entry->nr (-1) == info->entry.nr (65535)
> # set_syscall_info.c:88:set_syscall_info:wait #3: PTRACE_GET_SYSCALL_INFO #2: syscall nr mismatch
> # set_syscall_info: Test terminated by assertion
> #          FAIL  global.set_syscall_info
> not ok 1 global.set_syscall_info
> # FAILED: 0 / 1 tests passed.
> # Totals: pass:0 fail:1 xfail:0 xpass:0 skip:0 error:0
> 
> I remember one of the earlier versions (v1 or v2) was working for me.
> 
> Thanks!

In v3, this test was extended to check whether PTRACE_GET_SYSCALL_INFO
called immediately after PTRACE_SET_SYSCALL_INFO returns the same syscall
number, and on s390 it apparently doesn't, thanks to its implementation
of syscall_get_nr() that returns 0xffff in this case.

To workaround this, we could either change syscall_get_nr() to return -1
in this case, or add an #ifdef __s390x__ exception to the test.

What would you prefer?


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ldv