[gPXE-devel] [PATCH] Run COM32 programs with a valid IDT
Stefan Hajnoczi
stefanha at gmail.com
Wed Jul 7 16:06:18 EDT 2010
On Wed, Jul 7, 2010 at 8:49 PM, Geoff Lywood <glywood at vmware.com> wrote:
> This patch adds a fair amount of code size... ~300 bytes I think. Is there some kind of script I can run that will tell me exactly how much it has changed?
$ size bin/com32.o
or
$ make bin/gpxe.hd.sizes
or
util/diffsize.pl
Take your pick!
Stefan
> I can see some obvious optimizations I can do to eliminate some of this added code, and I'll send out a new patch soon.
>
> Thanks,
> Geoff
>
>
>> -----Original Message-----
>> From: Stefan Hajnoczi [mailto:stefanha at gmail.com]
>> Sent: Wednesday, July 07, 2010 12:42 PM
>> To: Geoff Lywood
>> Cc: gpxe-devel at etherboot.org
>> Subject: Re: [gPXE-devel] [PATCH] Run COM32 programs with a valid IDT
>>
>> On Tue, Jun 29, 2010 at 2:18 AM, Geoff Lywood <glywood at vmware.com> wrote:
>> > COM32 binaries generally expect to run with interrupts enabled. Syslinux
>> does
>> > so, and COM32 programs will execute cli/sti pairs when running a
>> critical
>> > section, to provide mutual exclusion against BIOS interrupt handlers.
>> > Previously, under gPXE, the IDT was not valid, so any interrupt (e.g. a
>> timer
>> > tick) would generally cause the machine to triple fault.
>> >
>> > This change introduces code to:
>> > - Create a valid IDT at the same location that syslinux uses
>> > - Create an "interrupt jump buffer", which contains small pieces of code
>> that
>> > simply record the vector number and jump to a common handler
>> > - Thunk down to real mode and execute the BIOS's interrupt handler
>> whenever
>> > an interrupt is received in a COM32 program
>> > - Switch IDTs and enable/disable interrupts when context switching to
>> and from
>> > COM32 binaries
>> >
>> > Testing done:
>> > - Booted VMware ESX using a COM32 multiboot loader (mboot.c32)
>> > - Built with GDBSERIAL enabled, and tested breakpoints on int22 and
>> com32_irq
>> > - Put the following code in a COM32 program:
>> > asm volatile ( "sti" );
>> > while ( 1 );
>> > Before this change, the machine would triple fault immediately. After
>> this
>> > change, it hangs as expected. Under Bochs, it is possible to see the
>> > interrupt handler run, and the current time in the BIOS data area gets
>> > incremented.
>>
>> I think we should merge this patch as it enables mboot.c32. Thanks
>> for describing the testing you have done.
>>
>> I have skimmed the code but not reviewed in depth.
>>
>> Stefan
>>
>> > I have a feeling that Outlook is going to mangle this patch, so I'm
>> attaching it as well.
>> >
>> > VMware, Inc. is providing this patch to you under the terms of the GPL
>> version 2 and any later version. This patch is provided as is, with no
>> warranties or support. VMware disclaims all liability in connection with
>> the use/inability to use this patch. Any use of the attached is considered
>> acceptance of the above.
>> >
>> > Signed-off-by: Geoff Lywood <glywood at vmware.com>
>> > ---
>> > src/arch/i386/image/com32.c | 73
>> +++++++++++++++++++++-
>> > src/arch/i386/include/comboot.h | 45 +++++++++++++
>> > src/arch/i386/interface/syslinux/com32_call.c | 17 +++++
>> > src/arch/i386/interface/syslinux/com32_wrapper.S | 28 ++++++++
>> > 4 files changed, 162 insertions(+), 1 deletions(-)
>> >
>> > diff --git a/src/arch/i386/image/com32.c b/src/arch/i386/image/com32.c
>> > index 6ab347c..0f01027 100644
>> > --- a/src/arch/i386/image/com32.c
>> > +++ b/src/arch/i386/image/com32.c
>> > @@ -42,6 +42,13 @@ FILE_LICENCE ( GPL2_OR_LATER );
>> >
>> > struct image_type com32_image_type __image_type ( PROBE_NORMAL );
>> >
>> > +struct idt_register com32_external_idtr = {
>> > + .limit = COM32_NUM_IDT_ENTRIES * sizeof ( struct idt_descriptor
>> ) - 1,
>> > + .base = COM32_IDT
>> > +};
>> > +
>> > +struct idt_register com32_internal_idtr;
>> > +
>> > /**
>> > * Execute COMBOOT image
>> > *
>> > @@ -89,9 +96,12 @@ static int com32_exec ( struct image *image ) {
>> > unregister_image ( image );
>> >
>> > __asm__ __volatile__ (
>> > + "sidt com32_internal_idtr\n\t"
>> > + "lidt com32_external_idtr\n\t" /* Set up
>> IDT */
>> > "movl %%esp, (com32_internal_esp)\n\t" /* Save
>> internal virtual address space ESP */
>> > "movl (com32_external_esp), %%esp\n\t" /* Switch
>> to COM32 ESP (top of available memory) */
>> > "call _virt_to_phys\n\t" /* Switch
>> to flat physical address space */
>> > + "sti\n\t" /* Enable
>> interrupts */
>> > "pushl %0\n\t" /* Pointer
>> to CDECL helper function */
>> > "pushl %1\n\t" /* Pointer
>> to FAR call helper function */
>> > "pushl %2\n\t" /* Size of
>> low memory bounce buffer */
>> > @@ -100,7 +110,9 @@ static int com32_exec ( struct image *image ) {
>> > "pushl %5\n\t" /* Pointer
>> to the command line arguments */
>> > "pushl $6\n\t" /* Number
>> of additional arguments */
>> > "call *%6\n\t" /* Execute
>> image */
>> > - "call _phys_to_virt\n\t" /* Switch
>> back to internal virtual address space */
>> > + "cli\n\t" /*
>> Disable interrupts */
>> > + "call _phys_to_virt\n\t" /* Switch
>> back to internal virtual address space */
>> > + "lidt com32_internal_idtr\n\t" /* Switch
>> back to internal IDT (for debugging) */
>> > "movl (com32_internal_esp), %%esp\n\t" /* Switch
>> back to internal stack */
>> > :
>> > :
>> > @@ -216,6 +228,60 @@ static int comboot_load_image ( struct image *image
>> ) {
>> > }
>> >
>> > /**
>> > + * Prepare COM32 Interrupt Descriptor Table and Interrupt Jump Buffer
>> > + * @v image COM32 image
>> > + * @ret rc Return status code
>> > + */
>> > +static int comboot_prepare_idt ( struct image * image ) {
>> > + struct idt_descriptor *idt;
>> > + struct ijb_entry *ijb;
>> > + physaddr_t com32_irq_wrapper_phys;
>> > + userptr_t buffer;
>> > + size_t memsz;
>> > + int i, rc;
>> > +
>> > + buffer = phys_to_user ( COM32_IDT );
>> > + memsz = COM32_NUM_IDT_ENTRIES * sizeof ( struct idt_descriptor
>> );
>> > + rc = prep_segment ( buffer, memsz, memsz );
>> > + if ( rc != 0 ) {
>> > + DBGC ( image, "COM32 %p: could not prepare IDT segment:
>> %s\n",
>> > + image, strerror ( rc ) );
>> > + return rc;
>> > + }
>> > +
>> > + buffer = phys_to_user ( COM32_IJB );
>> > + memsz = COM32_NUM_IDT_ENTRIES * sizeof ( struct ijb_entry );
>> > + rc = prep_segment ( buffer, memsz, memsz );
>> > + if ( rc != 0 ) {
>> > + DBGC ( image, "COM32 %p: could not prepare IJB segment:
>> %s\n",
>> > + image, strerror ( rc ) );
>> > + return rc;
>> > + }
>> > +
>> > + idt = phys_to_virt ( COM32_IDT );
>> > + ijb = phys_to_virt ( COM32_IJB );
>> > + com32_irq_wrapper_phys = virt_to_phys ( com32_irq_wrapper );
>> > +
>> > + for ( i = 0; i < COM32_NUM_IDT_ENTRIES; i++ ) {
>> > + uint32_t ijb_address = virt_to_phys ( &ijb[i] );
>> > +
>> > + idt[i].offset_low = ijb_address & 0xFFFF;
>> > + idt[i].selector = PHYSICAL_CS;
>> > + idt[i].flags = IDT_INTERRUPT_GATE_FLAGS;
>> > + idt[i].offset_high = ijb_address >> 16;
>> > +
>> > + ijb[i].pusha_instruction = IJB_PUSHA;
>> > + ijb[i].mov_instruction = IJB_MOV_AL_IMM8;
>> > + ijb[i].mov_value = i;
>> > + ijb[i].jump_instruction = IJB_JMP_REL32;
>> > + ijb[i].jump_destination = com32_irq_wrapper_phys -
>> > + virt_to_phys ( &ijb[i + 1] );
>> > + }
>> > +
>> > + return 0;
>> > +}
>> > +
>> > +/**
>> > * Prepare COM32 low memory bounce buffer
>> > * @v image COM32 image
>> > * @ret rc Return status code
>> > @@ -269,6 +335,11 @@ static int com32_load ( struct image *image ) {
>> > return rc;
>> > }
>> >
>> > + /* Set up IDT */
>> > + if ( ( rc = comboot_prepare_idt ( image ) ) != 0 ) {
>> > + return rc;
>> > + }
>> > +
>> > /* Prepare bounce buffer segment */
>> > if ( ( rc = comboot_prepare_bounce_buffer ( image ) ) != 0 ) {
>> > return rc;
>> > diff --git a/src/arch/i386/include/comboot.h
>> b/src/arch/i386/include/comboot.h
>> > index 1232f0a..ce6990d 100644
>> > --- a/src/arch/i386/include/comboot.h
>> > +++ b/src/arch/i386/include/comboot.h
>> > @@ -13,6 +13,50 @@ FILE_LICENCE ( GPL2_OR_LATER );
>> > #include <setjmp.h>
>> > #include <gpxe/in.h>
>> >
>> > +/** Descriptor in a 32-bit IDT */
>> > +struct idt_descriptor {
>> > + uint16_t offset_low;
>> > + uint16_t selector;
>> > + uint16_t flags;
>> > + uint16_t offset_high;
>> > +} PACKED;
>> > +
>> > +/** Operand for the LIDT instruction */
>> > +struct idt_register {
>> > + uint16_t limit;
>> > + uint32_t base;
>> > +} PACKED;
>> > +
>> > +/** Entry in the interrupt jump buffer */
>> > +struct ijb_entry {
>> > + uint8_t pusha_instruction;
>> > + uint8_t mov_instruction;
>> > + uint8_t mov_value;
>> > + uint8_t jump_instruction;
>> > + uint32_t jump_destination;
>> > +} PACKED;
>> > +
>> > +/** The x86 opcode for "pushal" */
>> > +#define IJB_PUSHA 0x60
>> > +
>> > +/** The x86 opcode for "movb $imm8,%al" */
>> > +#define IJB_MOV_AL_IMM8 0xB0
>> > +
>> > +/** The x86 opcode for "jmp rel32" */
>> > +#define IJB_JMP_REL32 0xE9
>> > +
>> > +/** Flags that specify a 32-bit interrupt gate with DPL=0 */
>> > +#define IDT_INTERRUPT_GATE_FLAGS 0x8E00
>> > +
>> > +/** Address of COM32 interrupt descriptor table */
>> > +#define COM32_IDT 0x100000
>> > +
>> > +/** Number of entries in a fully populated IDT */
>> > +#define COM32_NUM_IDT_ENTRIES 256
>> > +
>> > +/** Address of COM32 interrupt jump buffer */
>> > +#define COM32_IJB 0x100800
>> > +
>> > /** Segment used for COMBOOT PSP and image */
>> > #define COMBOOT_PSP_SEG 0x07C0
>> >
>> > @@ -109,6 +153,7 @@ extern void unhook_comboot_interrupts ( );
>> > extern void com32_intcall_wrapper ( );
>> > extern void com32_farcall_wrapper ( );
>> > extern void com32_cfarcall_wrapper ( );
>> > +extern void com32_irq_wrapper ( );
>> >
>> > /* Resolve a hostname to an (IPv4) address */
>> > extern int comboot_resolv ( const char *name, struct in_addr *address
>> );
>> > diff --git a/src/arch/i386/interface/syslinux/com32_call.c
>> b/src/arch/i386/interface/syslinux/com32_call.c
>> > index d2c3f91..d271cc7 100644
>> > --- a/src/arch/i386/interface/syslinux/com32_call.c
>> > +++ b/src/arch/i386/interface/syslinux/com32_call.c
>> > @@ -188,3 +188,20 @@ int __asmcall com32_cfarcall ( uint32_t proc,
>> physaddr_t stack, size_t stacksz )
>> >
>> > return eax;
>> > }
>> > +
>> > +/**
>> > + * IRQ handler
>> > + */
>> > +void __asmcall com32_irq ( uint32_t vector ) {
>> > + uint32_t *ivt_entry = phys_to_virt( vector * 4 );
>> > +
>> > + __asm__ __volatile__ (
>> > + REAL_CODE ( "pushfw\n\t"
>> > + "pushw %%cs\n\t"
>> > + "pushw $com32_irq_return\n\t"
>> > + "pushl %0\n\t"
>> > + "retf\n"
>> > + "com32_irq_return:\n\t" )
>> > + : /* no outputs */
>> > + : "r" ( *ivt_entry ) );
>> > +}
>> > diff --git a/src/arch/i386/interface/syslinux/com32_wrapper.S
>> b/src/arch/i386/interface/syslinux/com32_wrapper.S
>> > index 5c5bd13..84d1571 100644
>> > --- a/src/arch/i386/interface/syslinux/com32_wrapper.S
>> > +++ b/src/arch/i386/interface/syslinux/com32_wrapper.S
>> > @@ -22,6 +22,26 @@ FILE_LICENCE ( GPL2_OR_LATER )
>> > .arch i386
>> > .code32
>> >
>> > + /*
>> > + * This code is entered after running the following sequence out
>> of
>> > + * the interrupt jump buffer:
>> > + *
>> > + * pushal
>> > + * movb $vector, %al
>> > + * jmp com32_irq_wrapper
>> > + */
>> > +
>> > + .globl com32_irq_wrapper
>> > +com32_irq_wrapper:
>> > +
>> > + movzxb %al,%eax
>> > + pushl %eax
>> > + movl $com32_irq, %eax
>> > + call com32_wrapper
>> > + popl %eax
>> > + popal
>> > + iret
>> > +
>> > .globl com32_farcall_wrapper
>> > com32_farcall_wrapper:
>> >
>> > @@ -43,10 +63,14 @@ com32_intcall_wrapper:
>> > /*jmp com32_wrapper*/ /* fall through */
>> >
>> > com32_wrapper:
>> > + cli
>> >
>> > /* Switch to internal virtual address space */
>> > call _phys_to_virt
>> >
>> > + /* Switch to internal IDT (if we have one for debugging) */
>> > + lidt com32_internal_idtr
>> > +
>> > mov %eax, (com32_helper_function)
>> >
>> > /* Save external COM32 stack pointer */
>> > @@ -74,9 +98,13 @@ com32_wrapper:
>> > movl %esp, (com32_internal_esp)
>> > movl (com32_external_esp), %esp
>> >
>> > + /* Switch to com32 IDT */
>> > + lidt com32_external_idtr
>> > +
>> > /* Switch to external flat physical address space */
>> > call _virt_to_phys
>> >
>> > + sti
>> > ret
>> >
>> >
>> > _______________________________________________
>> > gPXE-devel mailing list
>> > gPXE-devel at etherboot.org
>> > http://etherboot.org/mailman/listinfo/gpxe-devel
>> >
>> >
>
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