x86: Add a NT_X86_SEGBASES register set.

This register set contains the values of the fsbase and gsbase
registers.  Note that these registers can already be controlled
individually via ptrace(2) via MD operations, so the main reason for
adding this is to include these register values in core dumps.  In
particular, this will enable looking up the value of TLS variables
from core dumps in gdb.

The value of NT_X86_SEGBASES was chosen to match the value of
NT_386_TLS on Linux.  The notes serve similar purposes, but FreeBSD
will never dump a note equivalent to NT_386_TLS (which dumps a single
segment descriptor rather than a pair of addresses) and picking a
currently-unused value in the NT_X86_* range could result in a future
conflict.

Reviewed by:	markj
Differential Revision:	https://reviews.freebsd.org/D34650

1 files changed, 18 insertions, 0 deletions

diff --git a/sys/x86/include/reg.h b/sys/x86/include/reg.h
index 7be3e24850c3..e237b080be1c 100644
--- a/sys/x86/include/reg.h
+++ b/sys/x86/include/reg.h
@@ -86,6 +86,7 @@
 #define	__reg32		reg
 #define	__fpreg32	fpreg
 #define	__dbreg32	dbreg
+#define	__segbasereg32	segbasereg
 #else
 #define	__reg32		reg32
 #define	__reg64		reg
@@ -93,6 +94,8 @@
 #define	__fpreg64	fpreg
 #define	__dbreg32	dbreg32
 #define	__dbreg64	dbreg
+#define	__segbasereg32	segbasereg32
+#define	__segbasereg64	segbasereg
 #define	__HAVE_REG32
 #endif
 
@@ -236,12 +239,27 @@ struct __dbreg64 {
 #define	DBREG_DRX(d,x)	((d)->dr[(x)])	/* reference dr0 - dr7 by
 					   register number */
 
+/*
+ * Register set accessible via NT_X86_SEGBASES.
+ */
+struct __segbasereg32 {
+	__uint32_t	r_fsbase;
+	__uint32_t	r_gsbase;
+};
+
+struct __segbasereg64 {
+	__uint64_t	r_fsbase;
+	__uint64_t	r_gsbase;
+};
+
 #undef __reg32
 #undef __reg64
 #undef __fpreg32
 #undef __fpreg64
 #undef __dbreg32
 #undef __dbreg64
+#undef __segbasereg32
+#undef __segbasereg64
 
 #ifdef _KERNEL
 /*