[RFC PATCH v1 20/25] unwind_user/eh_frame/x86: Enable eh_frame unwinding on x86

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

The x86-64 .eh_frame implementation works well with GCC and Clang
generated code.  Enable it.

Signed-off-by: Jens Remus <jremus@linux.ibm.com>
---
 arch/x86/Kconfig                            |  1 +
 arch/x86/include/asm/unwind_user.h          | 40 +++++++++++++++++++++
 arch/x86/include/asm/unwind_user_eh_frame.h | 22 ++++++++++++
 3 files changed, 63 insertions(+)
 create mode 100644 arch/x86/include/asm/unwind_user_eh_frame.h

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index bdad90f210e4..fe7919915084 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -300,6 +300,7 @@ config X86
 	select HAVE_SYSCALL_TRACEPOINTS
 	select HAVE_UACCESS_VALIDATION		if HAVE_OBJTOOL
 	select HAVE_UNSTABLE_SCHED_CLOCK
+	select HAVE_UNWIND_USER_EH_FRAME	if X86_64
 	select HAVE_UNWIND_USER_FP		if X86_64
 	select HAVE_USER_RETURN_NOTIFIER
 	select HAVE_GENERIC_VDSO
diff --git a/arch/x86/include/asm/unwind_user.h b/arch/x86/include/asm/unwind_user.h
index c96645c824d1..df1966bcb0f6 100644
--- a/arch/x86/include/asm/unwind_user.h
+++ b/arch/x86/include/asm/unwind_user.h
@@ -4,6 +4,7 @@
 
 #ifdef CONFIG_UNWIND_USER
 
+#include <linux/sched/task_stack.h>
 #include <asm/ptrace.h>
 #include <asm/uprobes.h>
 
@@ -15,6 +16,45 @@ static inline int unwind_user_word_size(struct pt_regs *regs)
 	return user_64bit_mode(regs) ? 8 : 4;
 }
 
+#ifdef CONFIG_X86_64
+
+static inline int unwind_user_get_reg(unsigned long *val, unsigned int regnum)
+{
+	struct pt_regs *regs = task_pt_regs(current);
+
+	/* TODO: eh_frame is currently limited to x86-64 */
+	if (!user_64bit_mode(regs))
+		return -EINVAL;
+
+	switch (regnum) {
+	/* DWARF register numbers 0..15 */
+	case  0: *val = regs->ax; break;
+	case  1: *val = regs->dx; break;
+	case  2: *val = regs->cx; break;
+	case  3: *val = regs->bx; break;
+	case  4: *val = regs->si; break;
+	case  5: *val = regs->di; break;
+	case  6: *val = regs->bp; break;
+	case  7: *val = regs->sp; break;
+	case  8: *val = regs->r8; break;
+	case  9: *val = regs->r9; break;
+	case 10: *val = regs->r10; break;
+	case 11: *val = regs->r11; break;
+	case 12: *val = regs->r12; break;
+	case 13: *val = regs->r13; break;
+	case 14: *val = regs->r14; break;
+	case 15: *val = regs->r15; break;
+	default:
+		pr_debug("%s (%d): %s(%u): unsupported register number\n",
+			 current->comm, current->pid, __func__, regnum);
+		return -EINVAL;
+	}
+	return 0;
+}
+#define unwind_user_get_reg unwind_user_get_reg
+
+#endif /* CONFIG_X86_64 */
+
 #endif /* CONFIG_UNWIND_USER */
 
 #ifdef CONFIG_HAVE_UNWIND_USER_FP
diff --git a/arch/x86/include/asm/unwind_user_eh_frame.h b/arch/x86/include/asm/unwind_user_eh_frame.h
new file mode 100644
index 000000000000..fdccbda2fe4b
--- /dev/null
+++ b/arch/x86/include/asm/unwind_user_eh_frame.h
@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_X86_UNWIND_USER_EH_FRAME_H
+#define _ASM_X86_UNWIND_USER_EH_FRAME_H
+
+#ifdef CONFIG_X86_64
+
+#define EH_FRAME_REG_SP	7	/* designated stack pointer register */
+#define EH_FRAME_REG_FP	6	/* designated frame pointer register */
+#define EH_FRAME_REG_RA	16	/* (pseudo) return address register */
+
+/* Instructions must be 1-byte aligned */
+#define EH_FRAME_MAX_CODE_ALIGN 1
+
+/* Stack grows towards lower addresses and SP must be 8-byte aligned */
+#define EH_FRAME_MIN_DATA_ALIGN -8
+#define EH_FRAME_MAX_DATA_ALIGN -1
+
+#endif
+
+#include <asm-generic/unwind_user_eh_frame.h>
+
+#endif /* _ASM_X86_UNWIND_USER_EH_FRAME_H */
-- 
2.53.0