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[comboot] Allow for tail recursion of COMBOOT images
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Multi-level menus via COMBOOT rely on the COMBOOT program being able
to exit and invoke a new COMBOOT program (the next menu).  This works,
but rapidly (within about five iterations) runs out of space in gPXE's
internal stack, since each new image is executed in a new function
context.

Fix by allowing tail recursion between images; an image can now
specify a replacement image for itself, and image_exec() will perform
the necessary tail recursion.
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Michael Brown committed Feb 17, 2009
1 parent 349868b commit 8904cd5
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Showing 8 changed files with 176 additions and 111 deletions.
40 changes: 23 additions & 17 deletions src/arch/i386/image/com32.c
View file
Expand Up @@ -70,20 +70,20 @@ static int com32_exec ( struct image *image ) {
}

DBGC ( image, "COM32 %p: available memory top = 0x%x\n",
image, (int)avail_mem_top );
image, avail_mem_top );

assert ( avail_mem_top != 0 );

com32_external_esp = phys_to_virt ( avail_mem_top );

/* Hook COMBOOT API interrupts */
hook_comboot_interrupts( );
hook_comboot_interrupts();

/* Temporarily de-register image, so that a "boot" command
* doesn't throw us into an execution loop. Hold a reference
* to avoid the image's being freed.
/* Unregister image, so that a "boot" command doesn't
* throw us into an execution loop. We never
* reregister ourselves; COMBOOT images expect to be
* removed on exit.
*/
image_get ( image );
unregister_image ( image );

__asm__ __volatile__ (
Expand Down Expand Up @@ -111,25 +111,31 @@ static int com32_exec ( struct image *image ) {
/* %6 */ "r" ( COM32_START_PHYS )
:
"memory" );
DBGC ( image, "COM32 %p: returned\n", image );
break;

case COMBOOT_RETURN_RUN_KERNEL:
DBGC ( image, "COM32 %p: returned to run kernel...\n", image );
comboot_run_kernel ( );
case COMBOOT_EXIT:
DBGC ( image, "COM32 %p: exited\n", image );
break;

case COMBOOT_RETURN_EXIT:
case COMBOOT_EXIT_RUN_KERNEL:
DBGC ( image, "COM32 %p: exited to run kernel %p\n",
image, comboot_replacement_image );
image->replacement = comboot_replacement_image;
image_autoload ( image->replacement );
break;

}

comboot_force_text_mode ( );
case COMBOOT_EXIT_COMMAND:
DBGC ( image, "COM32 %p: exited after executing command\n",
image );
break;

DBGC ( image, "COM32 %p returned\n", image );
default:
assert ( 0 );
break;
}

/* Re-register image and return */
register_image ( image );
image_put ( image );
comboot_force_text_mode();

return 0;
}
Expand Down
40 changes: 23 additions & 17 deletions src/arch/i386/image/comboot.c
View file
Expand Up @@ -142,16 +142,16 @@ static int comboot_exec ( struct image *image ) {
comboot_init_psp ( image, seg_userptr );

/* Hook COMBOOT API interrupts */
hook_comboot_interrupts ( );
hook_comboot_interrupts();

DBGC ( image, "executing 16-bit COMBOOT image at %4x:0100\n",
COMBOOT_PSP_SEG );
COMBOOT_PSP_SEG );

/* Temporarily de-register image, so that a "boot" command
* doesn't throw us into an execution loop. Hold a reference
* to avoid the image's being freed.
/* Unregister image, so that a "boot" command doesn't
* throw us into an execution loop. We never
* reregister ourselves; COMBOOT images expect to be
* removed on exit.
*/
image_get ( image );
unregister_image ( image );

/* Store stack segment at 0x38 and stack pointer at 0x3A
Expand Down Expand Up @@ -180,26 +180,32 @@ static int comboot_exec ( struct image *image ) {
"xorw %%bp, %%bp\n\t"
"lret\n\t" )
: : "r" ( COMBOOT_PSP_SEG ) : "eax" );
DBGC ( image, "COMBOOT %p: returned\n", image );
break;

case COMBOOT_RETURN_RUN_KERNEL:
DBGC ( image, "COMBOOT %p: returned to run kernel...\n", image );
comboot_run_kernel ( );
case COMBOOT_EXIT:
DBGC ( image, "COMBOOT %p: exited\n", image );
break;

case COMBOOT_RETURN_EXIT:
case COMBOOT_EXIT_RUN_KERNEL:
DBGC ( image, "COMBOOT %p: exited to run kernel %p\n",
image, comboot_replacement_image );
image->replacement = comboot_replacement_image;
image_autoload ( image->replacement );
break;

}
case COMBOOT_EXIT_COMMAND:
DBGC ( image, "COMBOOT %p: exited after executing command\n",
image );
break;

comboot_force_text_mode ( );
default:
assert ( 0 );
break;
}

DBGC ( image, "COMBOOT %p returned\n", image );
comboot_force_text_mode();

/* Re-register image and return */
register_image ( image );
image_put ( image );

return 0;
}

Expand Down
1 change: 1 addition & 0 deletions src/arch/i386/include/bits/errfile.h
View file
Expand Up @@ -23,6 +23,7 @@
#define ERRFILE_comboot ( ERRFILE_ARCH | ERRFILE_IMAGE | 0x00070000 )
#define ERRFILE_com32 ( ERRFILE_ARCH | ERRFILE_IMAGE | 0x00080000 )
#define ERRFILE_comboot_resolv ( ERRFILE_ARCH | ERRFILE_IMAGE | 0x00090000 )
#define ERRFILE_comboot_call ( ERRFILE_ARCH | ERRFILE_IMAGE | 0x000a0000 )

#define ERRFILE_undi ( ERRFILE_ARCH | ERRFILE_NET | 0x00000000 )
#define ERRFILE_undiload ( ERRFILE_ARCH | ERRFILE_NET | 0x00010000 )
Expand Down
14 changes: 5 additions & 9 deletions src/arch/i386/include/comboot.h
View file
Expand Up @@ -79,18 +79,14 @@ extern int comboot_resolv ( const char *name, struct in_addr *address );
/* setjmp/longjmp context buffer used to return after loading an image */
extern jmp_buf comboot_return;

/* Command line to execute when returning via comboot_return
* with COMBOOT_RETURN_RUN_KERNEL
*/
extern char *comboot_kernel_cmdline;

/* Execute comboot_image_cmdline */
extern void comboot_run_kernel ( );
/* Replacement image when exiting with COMBOOT_EXIT_RUN_KERNEL */
extern struct image *comboot_replacement_image;

extern void *com32_external_esp;

#define COMBOOT_RETURN_EXIT 1
#define COMBOOT_RETURN_RUN_KERNEL 2
#define COMBOOT_EXIT 1
#define COMBOOT_EXIT_RUN_KERNEL 2
#define COMBOOT_EXIT_COMMAND 3

extern void comboot_force_text_mode ( void );

Expand Down
143 changes: 82 additions & 61 deletions src/arch/i386/interface/syslinux/comboot_call.c
View file
Expand Up @@ -35,6 +35,8 @@
#include <gpxe/process.h>
#include <gpxe/serial.h>
#include <gpxe/init.h>
#include <gpxe/image.h>
#include <usr/imgmgmt.h>

/** The "SYSLINUX" version string */
static char __data16_array ( syslinux_version, [] ) = "gPXE " VERSION;
Expand Down Expand Up @@ -67,10 +69,8 @@ extern void int22_wrapper ( void );
/* setjmp/longjmp context buffer used to return after loading an image */
jmp_buf comboot_return;

/* Command line to execute when returning via comboot_return
* with COMBOOT_RETURN_RUN_KERNEL
*/
char *comboot_kernel_cmdline;
/* Replacement image when exiting with COMBOOT_EXIT_RUN_KERNEL */
struct image *comboot_replacement_image;

/* Mode flags set by INT 22h AX=0017h */
static uint16_t comboot_graphics_mode = 0;
Expand Down Expand Up @@ -154,66 +154,89 @@ void comboot_force_text_mode ( void ) {


/**
* Run the kernel specified in comboot_kernel_cmdline
* Fetch kernel and optional initrd
*/
void comboot_run_kernel ( )
{
char *initrd;

comboot_force_text_mode ( );

DBG ( "COMBOOT: executing image '%s'\n", comboot_kernel_cmdline );
static int comboot_fetch_kernel ( char *kernel_file, char *cmdline ) {
struct image *kernel;
struct image *initrd = NULL;
char *initrd_file;
int rc;

/* Find initrd= parameter, if any */
if ( ( initrd = strstr ( comboot_kernel_cmdline, "initrd=" ) ) ) {
char old_char = '\0';
char *initrd_end = strchr( initrd, ' ' );

/* Replace space after end of parameter
* with a nul terminator if this is not
* the last parameter
*/
if ( initrd_end ) {
old_char = *initrd_end;
*initrd_end = '\0';
}
if ( ( initrd_file = strstr ( cmdline, "initrd=" ) ) != NULL ) {
char *initrd_end;

/* Replace = with space to get 'initrd filename'
* command suitable for system()
*/
initrd[6] = ' ';
/* skip "initrd=" */
initrd_file += 7;

DBG( "COMBOOT: loading initrd '%s'\n", initrd );
/* Find terminating space, if any, and replace with NUL */
initrd_end = strchr ( initrd_file, ' ' );
if ( initrd_end )
*initrd_end = '\0';

system ( initrd );
DBG ( "COMBOOT: fetching initrd '%s'\n", initrd_file );

/* Restore space after parameter */
if ( initrd_end ) {
*initrd_end = old_char;
/* Allocate and fetch initrd */
initrd = alloc_image();
if ( ! initrd ) {
DBG ( "COMBOOT: could not allocate initrd\n" );
rc = -ENOMEM;
goto err_alloc_initrd;
}
if ( ( rc = imgfetch ( initrd, initrd_file,
register_image ) ) != 0 ) {
DBG ( "COMBOOT: could not fetch initrd: %s\n",
strerror ( rc ) );
goto err_fetch_initrd;
}

/* Restore = */
initrd[6] = '=';
/* Restore space after initrd name, if applicable */
if ( initrd_end )
*initrd_end = ' ';
}

/* Load kernel */
DBG ( "COMBOOT: loading kernel '%s'\n", comboot_kernel_cmdline );
system ( comboot_kernel_cmdline );
DBG ( "COMBOOT: fetching kernel '%s'\n", kernel_file );

free ( comboot_kernel_cmdline );
/* Allocate and fetch kernel */
kernel = alloc_image();
if ( ! kernel ) {
DBG ( "COMBOOT: could not allocate kernel\n" );
rc = -ENOMEM;
goto err_alloc_kernel;
}
if ( ( rc = imgfetch ( kernel, kernel_file,
register_image ) ) != 0 ) {
DBG ( "COMBOOT: could not fetch kernel: %s\n",
strerror ( rc ) );
goto err_fetch_kernel;
}
if ( ( rc = image_set_cmdline ( kernel, cmdline ) ) != 0 ) {
DBG ( "COMBOOT: could not set kernel command line: %s\n",
strerror ( rc ) );
goto err_set_cmdline;
}

/* Boot */
system ( "boot" );
/* Store kernel as replacement image */
comboot_replacement_image = kernel;

DBG ( "COMBOOT: back from executing command\n" );
return 0;

err_set_cmdline:
err_fetch_kernel:
image_put ( kernel );
err_alloc_kernel:
err_fetch_initrd:
image_put ( initrd );
err_alloc_initrd:
return rc;
}


/**
* Terminate program interrupt handler
*/
static __asmcall void int20 ( struct i386_all_regs *ix86 __unused ) {
longjmp ( comboot_return, COMBOOT_RETURN_EXIT );
longjmp ( comboot_return, COMBOOT_EXIT );
}


Expand All @@ -226,7 +249,7 @@ static __asmcall void int21 ( struct i386_all_regs *ix86 ) {
switch ( ix86->regs.ah ) {
case 0x00:
case 0x4C: /* Terminate program */
longjmp ( comboot_return, COMBOOT_RETURN_EXIT );
longjmp ( comboot_return, COMBOOT_EXIT );
break;

case 0x01: /* Get Key with Echo */
Expand Down Expand Up @@ -323,17 +346,15 @@ static __asmcall void int22 ( struct i386_all_regs *ix86 ) {
char cmd[len + 1];
copy_from_user ( cmd, cmd_u, 0, len + 1 );
DBG ( "COMBOOT: executing command '%s'\n", cmd );

comboot_kernel_cmdline = strdup ( cmd );

DBG ( "COMBOOT: returning to run image...\n" );
longjmp ( comboot_return, COMBOOT_RETURN_RUN_KERNEL );
system ( cmd );
DBG ( "COMBOOT: exiting after executing command...\n" );
longjmp ( comboot_return, COMBOOT_EXIT_COMMAND );
}
break;

case 0x0004: /* Run default command */
/* FIXME: just exit for now */
longjmp ( comboot_return, COMBOOT_RETURN_EXIT );
longjmp ( comboot_return, COMBOOT_EXIT_COMMAND );
break;

case 0x0005: /* Force text mode */
Expand Down Expand Up @@ -518,21 +539,21 @@ static __asmcall void int22 ( struct i386_all_regs *ix86 ) {
userptr_t cmd_u = real_to_user ( ix86->segs.es, ix86->regs.bx );
int file_len = strlen_user ( file_u, 0 );
int cmd_len = strlen_user ( cmd_u, 0 );
char file[file_len + 1 + cmd_len + 7 + 1];
char file[file_len + 1];
char cmd[cmd_len + 1];

memcpy( file, "kernel ", 7 );
copy_from_user ( file + 7, file_u, 0, file_len + 1 );
copy_from_user ( file, file_u, 0, file_len + 1 );
copy_from_user ( cmd, cmd_u, 0, cmd_len + 1 );
strcat ( file, " " );
strcat ( file, cmd );

DBG ( "COMBOOT: run kernel image '%s'\n", file );

comboot_kernel_cmdline = strdup ( file );

DBG ( "COMBOOT: returning to run image...\n" );
longjmp ( comboot_return, COMBOOT_RETURN_RUN_KERNEL );
DBG ( "COMBOOT: run kernel %s %s\n", file, cmd );
comboot_fetch_kernel ( file, cmd );
/* Technically, we should return if we
* couldn't load the kernel, but it's not safe
* to do that since we have just overwritten
* part of the COMBOOT program's memory space.
*/
DBG ( "COMBOOT: exiting to run kernel...\n" );
longjmp ( comboot_return, COMBOOT_EXIT_RUN_KERNEL );
}
break;

Expand Down

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