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SubjectAMD Geode NOPL emulation for kernel 2.6.36-rc2
Hi,
I have received many mails asking to refresh the patch so I decided to
post them on the public mailing list
In this version such feature is configurable via a kernel config option

Signed-off-by: Matteo Croce <matteo@openwrt.org>

--- a/arch/x86/kernel/Makefile 2010-08-27 00:27:50.101261000 +0200
+++ b/arch/x86/kernel/Makefile 2010-08-27 00:31:11.391261002 +0200
@@ -88,6 +88,8 @@
obj-$(CONFIG_APB_TIMER) += apb_timer.o

obj-$(CONFIG_K8_NB) += k8.o
+obj-$(CONFIG_GEODE_NOPL) += nopl_emu.o
+obj-$(CONFIG_GEODE_NOPL) += nopl_emu.o
obj-$(CONFIG_DEBUG_RODATA_TEST) += test_rodata.o
obj-$(CONFIG_DEBUG_NX_TEST) += test_nx.o

--- a/arch/x86/kernel/cpu/amd.c 2010-08-27 00:27:50.161261000 +0200
+++ b/arch/x86/kernel/cpu/amd.c 2010-08-27 00:34:13.371261000 +0200
@@ -137,11 +137,15 @@
return;
}

+#ifdef CONFIG_GEODE_NOPL
if (c->x86_model == 10) {
- /* AMD Geode LX is model 10 */
- /* placeholder for any needed mods */
+ /* Geode only lacks the NOPL instruction to be i686,
+ but we can promote it to a i686 class cpu
+ and emulate NOPLs in the exception handler*/
+ boot_cpu_data.x86 = 6;
return;
}
+#endif
}

static void __cpuinit amd_k7_smp_check(struct cpuinfo_x86 *c)
--- a/arch/x86/kernel/entry_32.S 2010-08-27 00:27:50.051261000 +0200
+++ b/arch/x86/kernel/entry_32.S 2010-08-27 00:57:35.531261000 +0200
@@ -978,7 +978,11 @@
RING0_INT_FRAME
pushl $0
CFI_ADJUST_CFA_OFFSET 4
+#ifdef CONFIG_GEODE_NOPL
+ pushl $do_nopl_emu
+#else
pushl $do_invalid_op
+#endif
CFI_ADJUST_CFA_OFFSET 4
jmp error_code
CFI_ENDPROC
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ b/arch/x86/kernel/nopl_emu.c 2010-08-27 00:27:57.881261002 +0200
@@ -0,0 +1,110 @@
+/*
+ * linux/arch/x86/kernel/nopl_emu.c
+ *
+ * Copyright (C) 2002 Willy Tarreau
+ * Copyright (C) 2010 Matteo Croce
+ */
+
+#include <asm/processor.h>
+#include <asm/traps.h>
+
+/* This code can be used to allow the AMD Geode to hopefully correctly execute
+ * some code which was originally compiled for an i686, by emulating NOPL,
+ * the only missing i686 instruction in the CPU
+ *
+ * Willy Tarreau <willy@meta-x.org>
+ * Matteo Croce <technoboy85@gmail.com>
+ */
+
+static inline int do_1f(u8 *ip)
+{
+ int length = 3;
+ switch (*ip) {
+ case 0x84:
+ if (!ip[5])
+ length++;
+ else
+ return 0;
+ case 0x80:
+ if (!ip[4] && !ip[3])
+ length += 2;
+ else
+ return 0;
+ case 0x44:
+ if (!ip[2])
+ length++;
+ else
+ return 0;
+ case 0x40:
+ if (!ip[1])
+ length++;
+ else
+ return 0;
+ case 0x00:
+ return length;
+ }
+ return 0;
+}
+
+static inline int do_0f(u8 *ip)
+{
+ if (*ip == 0x1f)
+ return do_1f(ip + 1);
+ return 0;
+}
+
+static inline int do_66(u8 *ip)
+{
+ if (*ip == 0x90)
+ return 2;
+ if (*ip == 0x0f) {
+ int res = do_0f(ip + 1);
+ if (res)
+ return res + 1;
+ else
+ return 0;
+ }
+ return 0;
+}
+
+static inline int do_start(u8 *ip)
+{
+ if (*ip == 0x0f)
+ return do_0f(ip + 1);
+ if (*ip == 0x66)
+ return do_66(ip + 1);
+ return 0;
+}
+
+/* [do_nopl_emu] is called by exception 6 after an invalid opcode has been
+ * encountered. It will try to emulate it by doing nothing,
+ * and will send a SIGILL or SIGSEGV to the process if not possible.
+ * the NOPL can have variable length opcodes:
+
+bytes number opcode
+ 2 66 90
+ 3 0f 1f 00
+ 4 0f 1f 40 00
+ 5 0f 1f 44 00 00
+ 6 66 0f 1f 44 00 00
+ 7 0f 1f 80 00 00 00 00
+ 8 0f 1f 84 00 00 00 00 00
+ 9 66 0f 1f 84 00 00 00 00 00
+*/
+void do_nopl_emu(struct pt_regs *regs, long error_code)
+{
+ u8 *ip = (u8 *)instruction_pointer(regs);
+ int res = do_start(ip);
+
+ if (res) {
+ int i = 0;
+ do {
+ ip += res;
+ i++;
+ res = do_start(ip);
+ } while(res);
+ printk(KERN_DEBUG "geode_nopl: emulated %d instructions\n", i);
+ regs->ip = (typeof(regs->ip))ip;
+ } else
+ do_invalid_op(regs, error_code);
+}

--
Matteo Croce
OpenWrt developer
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