s390: add USER_STACKTRACE support

Use the perf_callchain_user() code as blueprint to also add support for
USER_STACKTRACE. To describe how to use this cite the commit message of the
LoongArch implementation which came with commit 4d7bf939df08 ("LoongArch:
Add USER_STACKTRACE support"), but replace -fno-omit-frame-pointer option
with the s390 specific -mbackchain option:
====================================================================== To
get the best stacktrace output, you can compile your userspace programs
with frame pointers (at least glibc + the app you are tracing).

1, export "CC = gcc -mbackchain";
2, compile your programs with "CC";
3, use uprobe to get stacktrace output.

...
     echo 'p:malloc /usr/lib64/libc.so.6:0x0a4704 size=%r2:u64' > uprobe_events
     echo 'p:free /usr/lib64/libc.so.6:0x0a4d50 ptr=%r2:u64' >> uprobe_events
     echo 'comm == "demo"' > ./events/uprobes/malloc/filter
     echo 'comm == "demo"' > ./events/uprobes/free/filter
     echo 1 > ./options/userstacktrace
     echo 1 > ./options/sym-userobj
...
======================================================================

Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index b0d67ac..3bec98d 100644 (file)
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -236,6 +236,7 @@ config S390
        select THREAD_INFO_IN_TASK
        select TRACE_IRQFLAGS_SUPPORT
        select TTY
+       select USER_STACKTRACE_SUPPORT
        select VIRT_CPU_ACCOUNTING
        select ZONE_DMA
        # Note: keep the above list sorted alphabetically

diff --git a/arch/s390/kernel/stacktrace.c b/arch/s390/kernel/stacktrace.c
index 0787010..94f440e 100644 (file)
--- a/arch/s390/kernel/stacktrace.c
+++ b/arch/s390/kernel/stacktrace.c
@@ -6,9 +6,12 @@
  */
 
 #include <linux/stacktrace.h>
+#include <linux/uaccess.h>
+#include <linux/compat.h>
 #include <asm/stacktrace.h>
 #include <asm/unwind.h>
 #include <asm/kprobes.h>
+#include <asm/ptrace.h>
 
 void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
                     struct task_struct *task, struct pt_regs *regs)
@@ -58,3 +61,43 @@ int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry,
                return -EINVAL;
        return 0;
 }
+
+void arch_stack_walk_user(stack_trace_consume_fn consume_entry, void *cookie,
+                         const struct pt_regs *regs)
+{
+       struct stack_frame_user __user *sf;
+       unsigned long ip, sp;
+       bool first = true;
+
+       if (is_compat_task())
+               return;
+       if (!consume_entry(cookie, instruction_pointer(regs)))
+               return;
+       sf = (void __user *)user_stack_pointer(regs);
+       pagefault_disable();
+       while (1) {
+               if (__get_user(sp, &sf->back_chain))
+                       break;
+               if (__get_user(ip, &sf->gprs[8]))
+                       break;
+               if (ip & 0x1) {
+                       /*
+                        * If the instruction address is invalid, and this
+                        * is the first stack frame, assume r14 has not
+                        * been written to the stack yet. Otherwise exit.
+                        */
+                       if (first && !(regs->gprs[14] & 0x1))
+                               ip = regs->gprs[14];
+                       else
+                               break;
+               }
+               if (!consume_entry(cookie, ip))
+                       break;
+               /* Sanity check: ABI requires SP to be aligned 8 bytes. */
+               if (!sp || sp & 0x7)
+                       break;
+               sf = (void __user *)sp;
+               first = false;
+       }
+       pagefault_enable();
+}