[PATCH v4 08/12] s390/ptrace: Provide frame_pointer()

[Jens Remus <jremus@linux.ibm.com>]

On s390 64-bit the s390x ELF ABI [1] designates register 11 as the
"preferred" frame pointer (FP) register in user space.

[1]: s390x ELF ABI, https://github.com/IBM/s390x-abi/releases

Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---

Notes (jremus):
    Changes in v4:
    - Split out "while at it" changes into separate commit that can go
      upstream independently. (Heiko)
    
    Changes in RFC v2:
    - Separate provide frame_pointer() into this new commit.

 arch/s390/include/asm/ptrace.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/s390/include/asm/ptrace.h b/arch/s390/include/asm/ptrace.h
index e6ec0ccf3d73..8f18d00b5fdb 100644
--- a/arch/s390/include/asm/ptrace.h
+++ b/arch/s390/include/asm/ptrace.h
@@ -250,6 +250,12 @@ static __always_inline unsigned long user_stack_pointer(const struct pt_regs *re
 	return regs->gprs[15];
 }
 
+static __always_inline unsigned long frame_pointer(const struct pt_regs *regs)
+{
+	/* Return ABI-designated "preferred" frame-pointer register value. */
+	return regs->gprs[11];
+}
+
 static __always_inline unsigned long regs_get_register(const struct pt_regs *regs,
 						       unsigned int offset)
 {
-- 
2.51.0