[PATCH 22/23] task_current_syscall

Roland McGrath
2008-07-17T07:36:35Z

This adds the new function task_current_syscall() on machines where the
asm/syscall.h interface is supported (CONFIG_HAVE_ARCH_TRACEHOOK).
It's exported for modules to use in the future. This function safely
samples the state of a blocked thread to collect what system call it
is blocked in, and the six system call argument registers.

Signed-off-by: Roland McGrath <roland@redhat.com>
---
include/linux/ptrace.h | 4 ++
lib/Makefile | 2 +
lib/syscall.c | 75 ++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 81 insertions(+), 0 deletions(-)

diff --git a/include/linux/ptrace.h b/include/linux/ptrace.h
index ed69c03..fd31756 100644
--- a/include/linux/ptrace.h
+++ b/include/linux/ptrace.h
@@ -314,6 +314,10 @@ static inline void user_enable_block_step(struct task_struct *task)
#define arch_ptrace_stop(code, info) do { } while (0)
#endif

+extern int task_current_syscall(struct task_struct *target, long *callno,
+ unsigned long args[6], unsigned int maxargs,
+ unsigned long *sp, unsigned long *pc);
+
#endif

#endif
diff --git a/lib/Makefile b/lib/Makefile
index 2c62a9c..0dd88c4 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -82,6 +82,8 @@ lib-$(CONFIG_GENERIC_BUG) += bug.o

obj-$(CONFIG_HAVE_LMB) += lmb.o

+obj-$(CONFIG_HAVE_ARCH_TRACEHOOK) += syscall.o
+
hostprogs-y := gen_crc32table
clean-files := crc32table.h

diff --git a/lib/syscall.c b/lib/syscall.c
new file mode 100644
index 0000000..a4f7067
--- /dev/null
+++ b/lib/syscall.c
@@ -0,0 +1,75 @@
+#include <linux/ptrace.h>
+#include <linux/sched.h>
+#include <linux/module.h>
+#include <asm/syscall.h>
+
+static int collect_syscall(struct task_struct *target, long *callno,
+ unsigned long args[6], unsigned int maxargs,
+ unsigned long *sp, unsigned long *pc)
+{
+ struct pt_regs *regs = task_pt_regs(target);
+ if (unlikely(!regs))
+ return -EAGAIN;
+
+ *sp = user_stack_pointer(regs);
+ *pc = instruction_pointer(regs);
+
+ *callno = syscall_get_nr(target, regs);
+ if (*callno != -1L && maxargs > 0)
+ syscall_get_arguments(target, regs, 0, maxargs, args);
+
+ return 0;
+}
+
+/**
+ * task_current_syscall - Discover what a blocked task is doing.
+ * @target: thread to examine
+ * @callno: filled with system call number or -1
+ * @args: filled with @maxargs system call arguments
+ * @maxargs: number of elements in @args to fill
+ * @sp: filled with user stack pointer
+ * @pc: filled with user PC
+ *
+ * If @target is blocked in a system call, returns zero with *@callno
+ * set to the the call's number and @args filled in with its arguments.
+ * Registers not used for system call arguments may not be available and
+ * it is not kosher to use &struct user_regset calls while the system
+ * call is still in progress. Note we may get this result if @target
+ * has finished its system call but not yet returned to user mode, such
+ * as when it's stopped for signal handling or syscall exit tracing.
+ *
+ * If @target is blocked in the kernel during a fault or exception,
+ * returns zero with *@callno set to -1 and does not fill in @args.
+ * If so, it's now safe to examine @target using &struct user_regset
+ * get() calls as long as we're sure @target won't return to user mode.
+ *
+ * Returns -%EAGAIN if @target does not remain blocked.
+ *
+ * Returns -%EINVAL if @maxargs is too large (maximum is six).
+ */
+int task_current_syscall(struct task_struct *target, long *callno,
+ unsigned long args[6], unsigned int maxargs,
+ unsigned long *sp, unsigned long *pc)
+{
+ long state;
+ unsigned long ncsw;
+
+ if (unlikely(maxargs > 6))
+ return -EINVAL;
+
+ if (target == current)
+ return collect_syscall(target, callno, args, maxargs, sp, pc);
+
+ state = target->state;
+ if (unlikely(!state))
+ return -EAGAIN;
+
+ ncsw = wait_task_inactive(target, state);
+ if (unlikely(!ncsw) ||
+ unlikely(collect_syscall(target, callno, args, maxargs, sp, pc)) ||
+ unlikely(wait_task_inactive(target, state) != ncsw))
+ return -EAGAIN;
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(task_current_syscall);