linux(4): Add elf_hwcap2 to x86

On x86 Linux via AT_HWCAP2 the user controlled (by tunables) processor
capabilities are exposed.

Reviewed by:
Differential Revision:	https://reviews.freebsd.org/D41165
MFC after:		2 weeks

sys/amd64/linux/linux_sysvec.c

@@ -233,7 +233,7 @@ linux64_arch_copyout_auxargs(struct image_params *imgp, Elf_Auxinfo **pos)
 
 	AUXARGS_ENTRY((*pos), LINUX_AT_SYSINFO_EHDR, linux_vdso_base);
 	AUXARGS_ENTRY((*pos), LINUX_AT_HWCAP, cpu_feature);
-	AUXARGS_ENTRY((*pos), LINUX_AT_HWCAP2, 0);
+	AUXARGS_ENTRY((*pos), LINUX_AT_HWCAP2, linux_x86_elf_hwcap2());
 	AUXARGS_ENTRY((*pos), LINUX_AT_PLATFORM, PTROUT(linux_platform));
 }
 

sys/amd64/linux32/linux32_sysvec.c

@@ -146,7 +146,7 @@ linux32_arch_copyout_auxargs(struct image_params *imgp, Elf_Auxinfo **pos)
 	AUXARGS_ENTRY((*pos), LINUX_AT_SYSINFO, __kernel_vsyscall);
 	AUXARGS_ENTRY((*pos), LINUX_AT_SYSINFO_EHDR, linux_vdso_base);
 	AUXARGS_ENTRY((*pos), LINUX_AT_HWCAP, cpu_feature);
-	AUXARGS_ENTRY((*pos), LINUX_AT_HWCAP2, 0);
+	AUXARGS_ENTRY((*pos), LINUX_AT_HWCAP2, linux_x86_elf_hwcap2());
 	AUXARGS_ENTRY((*pos), LINUX_AT_PLATFORM, PTROUT(linux_platform));
 }
 

sys/i386/linux/linux.h

@@ -94,7 +94,7 @@ typedef struct {
 /*
  * Miscellaneous
  */
-#define LINUX_AT_COUNT		21	/* Count of used aux entry types.
+#define LINUX_AT_COUNT		22	/* Count of used aux entry types.
 					 * Keep this synchronized with
 					 * linux_copyout_auxargs() code.
 					 */

sys/i386/linux/linux_sysvec.c

@@ -145,6 +145,7 @@ linux32_arch_copyout_auxargs(struct image_params *imgp, Elf_Auxinfo **pos)
 	AUXARGS_ENTRY((*pos), LINUX_AT_SYSINFO_EHDR, linux_vdso_base);
 	AUXARGS_ENTRY((*pos), LINUX_AT_SYSINFO, __kernel_vsyscall);
 	AUXARGS_ENTRY((*pos), LINUX_AT_HWCAP, cpu_feature);
+	AUXARGS_ENTRY((*pos), LINUX_AT_HWCAP2, linux_x86_elf_hwcap2());
 	AUXARGS_ENTRY((*pos), LINUX_AT_PLATFORM, PTROUT(linux_platform));
 }
 

sys/x86/linux/linux_x86.c

@@ -31,7 +31,9 @@ __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
 #include <sys/signal.h>
+#include <x86/specialreg.h>
 #include <x86/trap.h>
+#include <x86/x86_var.h>
 
 #include <x86/linux/linux_x86.h>
 
@@ -96,4 +98,18 @@ bsd_to_linux_trapcode(int code)
 
 	return (code < nitems(_bsd_to_linux_trapcode) ?
 	    _bsd_to_linux_trapcode[code] : LINUX_T_UNKNOWN);
-}
+}
+
+u_int
+linux_x86_elf_hwcap2(void)
+{
+	static u_int elf_hwcap2 = 0;
+	static bool elf_hwcap2_valid = false;
+
+	if (!elf_hwcap2_valid) {
+		if ((cpu_stdext_feature & CPUID_STDEXT_FSGSBASE) != 0)
+			elf_hwcap2 |= LINUX_HWCAP2_FSGSBASE;
+		elf_hwcap2_valid = true;
+	}
+	return (elf_hwcap2);
+}

sys/x86/linux/linux_x86.h

@@ -32,10 +32,16 @@
 #define	LINUX_VDSO_CPU_RDPID		1
 #define	LINUX_VDSO_CPU_RDTSCP		2
 
+/* More machine dependent hints about processor capabilities. */
+#define	LINUX_HWCAP2_RING3MWAIT		0x00000001
+#define	LINUX_HWCAP2_FSGSBASE		0x00000002
+
 int	linux_vdso_tsc_selector_idx(void);
 int	linux_vdso_cpu_selector_idx(void);
 
 int	linux_translate_traps(int, int);
 int	bsd_to_linux_trapcode(int);
 
+u_int	linux_x86_elf_hwcap2(void);
+
 #endif /* _X86_INCLUDE_LINUX_LINUX_X86_H_ */