search for: read_sector_cbios

...xorw %cx, %cx xorb %dh, %dh stc int $0x13 jc 1f cmpw $0xaa55, %bx jne 1f andw $1,%cx /* Bit 0 = fixed disk subset */ jz 1f /* We have EBIOS; patch in the following code at read_sector_cbios: movb $0x42, %ah ; jmp read_common */ movl $0xeb42b4+((read_common-read_sector_cbios-4) << 24), \ (read_sector_cbios) jmp 1f 1: This is my interpretation: David's machine's BIOS returns no carry indicating maybe support. However it doesn'...

...stc > int $0x13 > jc 1f > cmpw $0xaa55, %bx > jne 1f > andw $1,%cx > /* Bit 0 = fixed disk subset */ > jz 1f > > /* We have EBIOS; patch in the following code at > read_sector_cbios: movb $0x42, %ah ; jmp read_common */ > movl $0xeb42b4+((read_common-read_sector_cbios-4) << 24), \ > (read_sector_cbios) > jmp 1f > 1: > > > This is my interpretation: > > David's machine's BIOS returns no carry indic...

Hi, i am looking now at the code which i assume loads the rest of isolinux.bin. The entry point for program execution from the MBR is obviously at http://git.zytor.com/syslinux/syslinux.git/tree/core/isolinux.asm#n186 (Do i get it right that this is the Intel syntax ? (Gronfff)) If POP yields the victim of the most recent not yet popped PUSH, then this does not look correctly coordinated

...hdpfx.S @@ -151,7 +151,7 @@ next: /* Check to see if we have EBIOS */ pushw %dx /* drive number */ - movb $0x41, %ah /* %al == 0 already */ + movb $0x41, %ah movw $0x55aa, %bx xorw %cx, %cx xorb %dh, %dh @@ -167,20 +167,22 @@ next: read_sector_cbios: movb $0x42, %ah ; jmp read_common */ movl $0xeb42b4+((read_common-read_sector_cbios-4) << 24), (read_sector_cbios) - jmp 1f + jmp 2f 1: + xor %cx, %cx /* Clear EBIOS flag. */ +2: popw %dx pushw %cx /* EBIOS flag */ /* Get (C)HS geometry */ movb $0x08, %ah int $...

.../* %al == 0 already */ movw $0x55aa, %bx xorw %cx, %cx xorb %dh, %dh stc int $0x13 popw %dx /* restore drive */ movb $0x08, %ah /* get CHS geometry */ jc 1f cmpw $0xaa55, %bx jne 1f shrw %cx /* Bit 0 = fixed disk subset */ jnc 1f /* We have EBIOS; patch in the following code at read_sector_cbios: movb $0x42, %ah ; jmp read_common */ movl $0xeb42b4+((read_common-read_sector_cbios-4) << 24), \ (read_sector_cbios) /* * read sector size. * Should not fail but if it does I assume that at least * previous 512 value is not overridden */ movb $0x48, %ah movw %sp, %si 1: /*...

...+ push %si + call print_string + .ascii "G\r\n" + pop %si +#endif jmp 1f /* We have non-GPT partition information */ 2: +#ifdef DEBUG_PRINT + push %si + call print_string + .ascii "M\r\n" + pop %si +#endif + movl 8(%si), %ecx #endif 1: @@ -167,14 +181,34 @@ next: read_sector_cbios: movb $0x42, %ah ; jmp read_common */ movl $0xeb42b4+((read_common-read_sector_cbios-4) << 24), \ (read_sector_cbios) - jmp 1f + +#ifdef DEBUG_PRINT + push %si + call print_string + .ascii "E\r\n" + jmp 2f 1: + push %si + call print_string + .ascii "C\r\n" +2: + cal...

...$0x200, -6(%bp) /* -6(%bp) sector size */ /* Check to see if we have EBIOS */ pushw %dx /* drive number */ @@ -86,6 +92,7 @@ next: xorb %dh, %dh stc int $0x13 + popw %dx /* restore drive */ jc 1f cmpw $0xaa55, %bx jne 1f @@ -97,22 +104,32 @@ next: movl $0xeb42b4+((read_common-read_sector_cbios-4) << 24), \ (read_sector_cbios) -1: - popw %dx + /* + * read sector size. + * Should not fail but if it does I assume that at least + * previous 512 value is not overridden + */ + movb $0x48, %ah + movw %sp, %si + jmp 2f /* this can be replaced by a .byte 0xbf to gain + * anot...

It is good to see this ----- Forwarded message from syslinux-bot for Martin Str|mberg <ams at ludd.ltu.se> ----- Date: Sat, 25 Mar 2017 05:54:09 -0700 From: syslinux-bot for Martin Str|mberg <ams at ludd.ltu.se> To: Syslinux commits mailing list <syslinux-commits at zytor.com> Cc: ams at ludd.ltu.se Subject: [syslinux:master] mbr/isohdpfx.S: correct pointer for heads/sectors

This patches add support for dynamic sectors to GPT MBR code. First 3 patches are trick and optimizations to gain some space for the forth patch. I have a modified version of SeaBIOS, some code and some script o test it I'll send on a different mail.

...e if we have EBIOS */ pushw %dx /* drive number */ movb $0x41, %ah /* %al == 0 already */ movw $0x55aa, %bx xorw %cx, %cx xorb %dh, %dh stc int $0x13 jc 1f cmpw $0xaa55, %bx jne 1f andw $1,%cx /* Bit 0 = fixed disk subset */ jz 1f /* We have EBIOS; patch in the following code at read_sector_cbios: movb $0x42, %ah ; jmp read_common */ movl $0xeb42b4+((read_common-read_sector_cbios-4) << 24), \ (read_sector_cbios) #ifdef DEBUG_PRINT push %si call print_string .ascii "E\r\n" jmp 2f 1: push %si call print_string .ascii "C\r\n" 2: pop %si #else 1: #endif...

...S and if the EBIOS assumes a different size of head and cylinder than the MBR does ... that would explain a mislead read attempt. But i understand that INT 13 with AH 8 is used to inquire the C/H/S factors from the BIOS in line 176 ff. So if the BIOS does not lie then the computation at label "read_sector_cbios:" should be correct. Regrettably i still have 4560 pages of the Intel processor manual to read before i can start to handcode an MBR. ~:o) Have a nice day :) Thomas

Hi, given the fact that the conversion has the factor HC*SH = "secpercyl", which is invariant under swapping, there remains as suspect in read_sector_cbios only this division: divb (sectors) There is a suspicious discrepancy in the code: heads = (stack-16) sectors = (stack-18) ... /* here we computer CHS values or just do some dummy computation for EBIOS */ andw $0x3f, %cx /* Sector count */ popw %bx /* EBIOS flag */ pushw %cx /* -...

Hi, funny or enlightening observation: With my qemu-system-i386 it would work if the detected Heads/Cylinder and Sectors/Head factors would change positions ! The effective read operation seems to use H/C = 32 , S/H = 63. The correct LBA would be addressed by H/C = 63 , S/H = 32. -------------------------------------------------------------------------- Reasoning: I have transplanted the

This set of patches add some support for sector size >512. Currently it fixes extlinux, MBR for GPT and ext partitions. Other code is unaffected. This set of patches has been tested on a read Dell machine running a beta firmware.

On 03/18/2017 01:18 AM, Ady Ady via Syslinux wrote: > Some of the things you should / could (re)test / (re)try: > > _ Verify the md5sum of the ISO image. SHA256 verified for downloaded image and for contents of USB flash drive (see below). > _ Is this particular USB device _still_ capable of booting newer > computers? Yes. > What happens if you would try _again_ to boot a

...ssumes a different size of head and cylinder > than the MBR does ... that would explain a mislead read attempt. > But i understand that INT 13 with AH 8 is used to inquire the C/H/S > factors from the BIOS in line 176 ff. So if the BIOS does not lie then > the computation at label "read_sector_cbios:" should be correct. > > Regrettably i still have 4560 pages of the Intel processor manual to read > before i can start to handcode an MBR. ~:o) There is the processor, and then there is the system (chipset, BIOS) in which the processor resides. Figuring out why debian-8.7.1-i386-...