[RFC PATCH v1 24/25] unwind_user/eh_frame/s390: Enable eh_frame unwinding on s390

[Jens Remus]

The unwind user eh_frame implementation works well with GCC and Clang
generated code on s390.  Enable it.

Signed-off-by: Jens Remus <jremus@xxxxxxxxxxxxx>
---
 arch/s390/Kconfig                            |  1 +
 arch/s390/include/asm/unwind_user.h          | 71 ++++++++++++++++++++
 arch/s390/include/asm/unwind_user_eh_frame.h | 24 +++++++
 3 files changed, 96 insertions(+)
 create mode 100644 arch/s390/include/asm/unwind_user.h
 create mode 100644 arch/s390/include/asm/unwind_user_eh_frame.h

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 84404e6778d5..fa229ac92d5a 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -251,6 +251,7 @@ config S390
 	select HAVE_SOFTIRQ_ON_OWN_STACK
 	select HAVE_STACKPROTECTOR if CC_HAS_STACKPROTECTOR_GLOBAL
 	select HAVE_SYSCALL_TRACEPOINTS
+	select HAVE_UNWIND_USER_EH_FRAME
 	select HAVE_VIRT_CPU_ACCOUNTING
 	select HAVE_VIRT_CPU_ACCOUNTING_IDLE
 	select HOTPLUG_SMT
diff --git a/arch/s390/include/asm/unwind_user.h b/arch/s390/include/asm/unwind_user.h
new file mode 100644
index 000000000000..41ff0b477626
--- /dev/null
+++ b/arch/s390/include/asm/unwind_user.h
@@ -0,0 +1,71 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_S390_UNWIND_USER_H
+#define _ASM_S390_UNWIND_USER_H
+
+#include <linux/sched/task_stack.h>
+#include <linux/types.h>
+#include <asm/fpu.h>
+
+#ifdef CONFIG_UNWIND_USER
+
+static inline int unwind_user_word_size(struct pt_regs *regs)
+{
+	return 8;
+}
+
+static inline int unwind_user_get_ra_reg(unsigned long *val)
+{
+	struct pt_regs *regs = task_pt_regs(current);
+	*val = regs->gprs[14];
+	return 0;
+}
+#define unwind_user_get_ra_reg unwind_user_get_ra_reg
+
+static inline unsigned long __s390_dwarf_fpr_to_fpr(unsigned int regnum)
+{
+	unsigned int fpr;
+
+	/*
+	 * Convert from s390 DWARF floating-point register number (16..31)
+	 * to floating-point register number (0..15): left rotate the least
+	 * significant three bits and then return the least significant four
+	 * bits.
+	 */
+	fpr  = (regnum & 3) << 1;
+	fpr |= (regnum & 4) >> 2;
+	fpr |= (regnum & 8);
+	return fpr;
+}
+
+static inline unsigned long __s390_get_dwarf_fpr(unsigned int regnum)
+{
+	struct fpu *fpu = &current->thread.ufpu;
+
+	save_user_fpu_regs();
+	return fpu->vxrs[__s390_dwarf_fpr_to_fpr(regnum)].high;
+}
+
+static inline int unwind_user_get_reg(unsigned long *val, unsigned int regnum)
+{
+	if (regnum <= 15) {
+		/* DWARF register numbers 0..15 */
+		struct pt_regs *regs = task_pt_regs(current);
+		*val = regs->gprs[regnum];
+		return 0;
+	} else if (regnum <= 31) {
+		/* DWARF register numbers 16..31 */
+		*val = __s390_get_dwarf_fpr(regnum);
+		return 0;
+	}
+
+	pr_debug("%s (%d): %s(%u): unsupported register number\n",
+		 current->comm, current->pid, __func__, regnum);
+	return -EINVAL;
+}
+#define unwind_user_get_reg unwind_user_get_reg
+
+#endif /* CONFIG_UNWIND_USER */
+
+#include <asm-generic/unwind_user.h>
+
+#endif /* _ASM_S390_UNWIND_USER_H */
diff --git a/arch/s390/include/asm/unwind_user_eh_frame.h b/arch/s390/include/asm/unwind_user_eh_frame.h
new file mode 100644
index 000000000000..842d9f7c3d80
--- /dev/null
+++ b/arch/s390/include/asm/unwind_user_eh_frame.h
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_S390_UNWIND_USER_EH_FRAME_H
+#define _ASM_S390_UNWIND_USER_EH_FRAME_H
+
+#define EH_FRAME_REG_SP	15	/* designated stack pointer register */
+#define EH_FRAME_REG_FP	11	/* "preferred" frame pointer register */
+#define EH_FRAME_REG_RA	14	/* designaged return address register */
+
+/* Instructions must be 2-byte aligned */
+#define EH_FRAME_MAX_CODE_ALIGN 2
+
+/* CFA is defined as SP at call site + 160, so that SP = CFA - 160 */
+#define EH_FRAME_SP_VAL_OFFSET -160
+
+/* SP may be saved on the stack or in a register */
+static inline bool eh_frame_reject_sp_rule(void)
+{
+	return false;
+}
+#define eh_frame_reject_sp_rule eh_frame_reject_sp_rule
+
+#include <asm-generic/unwind_user_eh_frame.h>
+
+#endif /* _ASM_S390_UNWIND_USER_EH_FRAME_H */
-- 
2.53.0