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?
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:[email protected]] > Sent: Wednesday, July 07, 2010 12:42 PM > To: Geoff Lywood > Cc: [email protected] > Subject: Re: [gPXE-devel] [PATCH] Run COM32 programs with a valid IDT > > On Tue, Jun 29, 2010 at 2:18 AM, Geoff Lywood <[email protected]> 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 <[email protected]> > > --- > > 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 > > [email protected] > > http://etherboot.org/mailman/listinfo/gpxe-devel > > > > _______________________________________________ gPXE-devel mailing list [email protected] http://etherboot.org/mailman/listinfo/gpxe-devel
