[PATCH] um: Allow building and running on older hosts

[Florian Fainelli <f.fainelli@gmail.com>]

Commit a78ff1112263 ("um: add extended processor state save/restore
support") and b6024b21fec8 ("um: extend fpstate to _xstate to support
YMM registers") forced the use of the x86 FP _xstate and
PTRACE_GETREGSET/SETREGSET. On older hosts, we would neither be able to
build UML nor run it anymore with these two commits applied because we
don't have definitions for struct _xstate nor these two ptrace requests.

We can determine at build time which fp context structure to check
against, just like we can keep using the old i387 fp save/restore if
PTRACE_GETRESET/SETREGSET are not defined.

Fixes: a78ff1112263 ("um: add extended processor state save/restore support")
Fixes: b6024b21fec8 ("um: extend fpstate to _xstate to support YMM registers")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
---
 arch/x86/um/os-Linux/registers.c | 13 +++++++++----
 arch/x86/um/user-offsets.c       |  4 ++++
 2 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/arch/x86/um/os-Linux/registers.c b/arch/x86/um/os-Linux/registers.c
index 00f54a91bb4b..502bd642e5c2 100644
--- a/arch/x86/um/os-Linux/registers.c
+++ b/arch/x86/um/os-Linux/registers.c
@@ -26,13 +26,14 @@ int save_i387_registers(int pid, unsigned long *fp_regs)
 
 int save_fp_registers(int pid, unsigned long *fp_regs)
 {
-	struct iovec iov;
-
 	if (have_xstate_support) {
+#ifdef PTRACE_GETREGSET
+		struct iovec iov;
 		iov.iov_base = fp_regs;
 		iov.iov_len = sizeof(struct _xstate);
 		if (ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov) < 0)
 			return -errno;
+#endif
 		return 0;
 	} else {
 		return save_i387_registers(pid, fp_regs);
@@ -48,13 +49,15 @@ int restore_i387_registers(int pid, unsigned long *fp_regs)
 
 int restore_fp_registers(int pid, unsigned long *fp_regs)
 {
-	struct iovec iov;
-
 	if (have_xstate_support) {
+#ifdef PTRACE_SETREGSET
+		struct iovec iov;
+
 		iov.iov_base = fp_regs;
 		iov.iov_len = sizeof(struct _xstate);
 		if (ptrace(PTRACE_SETREGSET, pid, NT_X86_XSTATE, &iov) < 0)
 			return -errno;
+#endif
 		return 0;
 	} else {
 		return restore_i387_registers(pid, fp_regs);
@@ -127,8 +130,10 @@ void arch_init_registers(int pid)
 
 	iov.iov_base = &fp_regs;
 	iov.iov_len = sizeof(struct _xstate);
+#ifdef PTRACE_GETREGSET
 	if (ptrace(PTRACE_GETREGSET, pid, NT_X86_XSTATE, &iov) == 0)
 		have_xstate_support = 1;
+#endif
 }
 #endif
 
diff --git a/arch/x86/um/user-offsets.c b/arch/x86/um/user-offsets.c
index cb3c22370cf5..8af0fb5d2780 100644
--- a/arch/x86/um/user-offsets.c
+++ b/arch/x86/um/user-offsets.c
@@ -50,7 +50,11 @@ void foo(void)
 	DEFINE(HOST_GS, GS);
 	DEFINE(HOST_ORIG_AX, ORIG_EAX);
 #else
+#if defined(PTRACE_GETREGSET) && defined(PTRACE_SETREGSET)
 	DEFINE(HOST_FP_SIZE, sizeof(struct _xstate) / sizeof(unsigned long));
+#else
+	DEFINE(HOST_FP_SIZE, sizeof(struct _fpstate) / sizeof(unsigned long));
+#endif
 	DEFINE_LONGS(HOST_BX, RBX);
 	DEFINE_LONGS(HOST_CX, RCX);
 	DEFINE_LONGS(HOST_DI, RDI);
-- 
2.12.2