x86_64: further cleanup of 32-bit compat syscall mechanisms

AMD only supports "syscall" from 32-bit compat usermode. Intel and Centaur(?) only support "sysenter" from 32-bit compat usermode.

Set the X86 feature bits accordingly, and set up the vdso in accordance with those bits. On the offchance we run on in a 64-bit environment which supports neither syscall nor sysenter from 32-bit mode, then fall back to the int $0x80 vdso.

---

arch/x86/kernel/cpu/amd_64.c    |    2 ++
arch/x86/kernel/cpu/common_64.c |    3 ---
arch/x86/vdso/Makefile          |    2 +-
arch/x86/vdso/vdso32-setup.c    |   19 +++++++++----------
arch/x86/vdso/vdso32.S          |   13 ++++++++-----
arch/x86/xen/setup.c            |   10 +++++++---
include/asm-x86/vdso.h          |    8 ++++++++
7 files changed, 35 insertions(+), 22 deletions(-)

===================================================================

@@ -115,6 +115,8 @@ static void __cpuinit early_init_amd(str

	/* c->x86_power is 8000_0007 edx. Bit 8 is constant TSC */
	if (c->x86_power & (1<<8))
		set_cpu_cap(c, X86_FEATURE_CONSTANT_TSC);

+
+ set_cpu_cap(c, X86_FEATURE_SYSCALL32);
}

static void __cpuinit init_amd(struct cpuinfo_x86 *c)
===================================================================

@@ -315,9 +315,6 @@ static void __cpuinit early_identify_cpu

	if (c->extended_cpuid_level >= 0x80000007)
		c->x86_power = cpuid_edx(0x80000007);

- /* Assume all 64-bit CPUs support 32-bit syscall */
- set_cpu_cap(c, X86_FEATURE_SYSCALL32);
-

	if (c->x86_vendor != X86_VENDOR_UNKNOWN &&
	    cpu_devs[c->x86_vendor]->c_early_init)
		cpu_devs[c->x86_vendor]->c_early_init(c);

===================================================================

@@ -62,7 +62,7 @@ endef

# Build multiple 32-bit vDSO images to choose from at boot time. #
obj-$(VDSO32-y) += vdso32-syms.lds
-vdso32.so-$(CONFIG_X86_32) += int80
+vdso32.so-$(VDSO32-y) += int80
vdso32.so-$(CONFIG_COMPAT) += syscall
vdso32.so-$(VDSO32-y) += sysenter

===================================================================

@@ -193,17 +193,12 @@ static __init void relocate_vdso(Elf32_E

	}
}

-/*
- * These symbols are defined by vdso32.S to mark the bounds
- * of the ELF DSO images included therein.
- */
-extern const char vdso32_default_start, vdso32_default_end; -extern const char vdso32_sysenter_start, vdso32_sysenter_end; static struct page *vdso32_pages[1];

#ifdef CONFIG_X86_64

#define vdso32_sysenter() (boot_cpu_has(X86_FEATURE_SYSENTER32))
+#define vdso32_syscall() (boot_cpu_has(X86_FEATURE_SYSCALL32))

/* May not be __init: called during resume */
void syscall32_cpu_init(void)
@@ -226,6 +221,7 @@ static inline void map_compat_vdso(int m #else /* CONFIG_X86_32 */

#define vdso32_sysenter() (boot_cpu_has(X86_FEATURE_SEP))
+#define vdso32_syscall() (0)

void enable_sep_cpu(void)
{
@@ -296,12 +292,15 @@ int __init sysenter_setup(void)

	gate_vma_init();

#endif

- if (!vdso32_sysenter()) {
- vsyscall = &vdso32_default_start;
- vsyscall_len = &vdso32_default_end - &vdso32_default_start;
- } else {
+ if (vdso32_syscall()) {
+ vsyscall = &vdso32_syscall_start;
+ vsyscall_len = &vdso32_syscall_end - &vdso32_syscall_start;

+	} else if (vdso32_sysenter()){
		vsyscall = &vdso32_sysenter_start;
		vsyscall_len = &vdso32_sysenter_end - &vdso32_sysenter_start;
+	} else {
+		vsyscall = &vdso32_int80_start;
+		vsyscall_len = &vdso32_int80_end - &vdso32_int80_start;
	}

	memcpy(syscall_page, vsyscall, vsyscall_len);

===================================================================

@@ -2,14 +2,17 @@
 

__INITDATA

- .globl vdso32_default_start, vdso32_default_end
-vdso32_default_start:
-#ifdef CONFIG_X86_32
+ .globl vdso32_int80_start, vdso32_int80_end
+vdso32_int80_start:

	.incbin "arch/x86/vdso/vdso32-int80.so"

-#else
+vdso32_int80_end:
+
+ .globl vdso32_syscall_start, vdso32_syscall_end
+vdso32_syscall_start:
+#ifdef CONFIG_COMPAT

	.incbin "arch/x86/vdso/vdso32-syscall.so"

#endif
-vdso32_default_end:
+vdso32_syscall_end:

.globl vdso32_sysenter_start, vdso32_sysenter_end
vdso32_sysenter_start:
===================================================================

@@ -83,12 +83,16 @@ static void xen_idle(void)
 

/*
* Set the bit indicating "nosegneg" library variants should be used.
+ * We only need to bother in pure 32-bit mode; compat 32-bit processes
+ * can have un-truncated segments, so wrapping around is allowed. */
static void __init fiddle_vdso(void)
{
-#if defined(CONFIG_X86_32) || defined(CONFIG_IA32_EMULATION)
- extern const char vdso32_default_start;
- u32 *mask = VDSO32_SYMBOL(&vdso32_default_start, NOTE_MASK);
+#ifdef CONFIG_X86_32
+ u32 *mask;
+ mask = VDSO32_SYMBOL(&vdso32_int80_start, NOTE_MASK);
+ *mask |= 1 << VDSO_NOTE_NONEGSEG_BIT;

+	mask = VDSO32_SYMBOL(&vdso32_sysenter_start, NOTE_MASK);
	*mask |= 1 << VDSO_NOTE_NONEGSEG_BIT;

#endif
}
===================================================================

@@ -36,4 +36,12 @@ extern void __user __kernel_sigreturn;

extern void __user __kernel_sigreturn;
extern void __user __kernel_rt_sigreturn;

+/*
+ * These symbols are defined by vdso32.S to mark the bounds
+ * of the ELF DSO images included therein.
+ */
+extern const char vdso32_int80_start, vdso32_int80_end; +extern const char vdso32_syscall_start, vdso32_syscall_end; +extern const char vdso32_sysenter_start, vdso32_sysenter_end; +
#endif /* asm-x86/vdso.h */

-hpa

Have these been applied to anything yet?

J

Just applied them to xen-64bit, thanks!

-hpa