similar to: [PATCH 3/3] v2: isohdpfx: Ctrl-key press forces load from first hard disk

--- mbr/Makefile | 6 +- mbr/mbr-diag.S | 377 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 382 insertions(+), 1 deletions(-) create mode 100644 mbr/mbr-diag.S diff --git a/mbr/Makefile b/mbr/Makefile index 0bdf7e3..b9d743d 100644 --- a/mbr/Makefile +++ b/mbr/Makefile @@ -17,7 +17,7 @@ topdir = .. include $(topdir)/MCONFIG.embedded -all: mbr.bin gptmbr.bin

--- mbr/Makefile | 6 +- mbr/mbr-diag.S | 371 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 376 insertions(+), 1 deletions(-) create mode 100644 mbr/mbr-diag.S diff --git a/mbr/Makefile b/mbr/Makefile index 0bdf7e3..b9d743d 100644 --- a/mbr/Makefile +++ b/mbr/Makefile @@ -17,7 +17,7 @@ topdir = .. include $(topdir)/MCONFIG.embedded -all: mbr.bin gptmbr.bin

--- mbr/Makefile | 6 +- mbr/mbr-diag.S | 372 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 377 insertions(+), 1 deletions(-) create mode 100644 mbr/mbr-diag.S diff --git a/mbr/Makefile b/mbr/Makefile index 0bdf7e3..b9d743d 100644 --- a/mbr/Makefile +++ b/mbr/Makefile @@ -17,7 +17,7 @@ topdir = .. include $(topdir)/MCONFIG.embedded -all: mbr.bin gptmbr.bin

Hi, FYI syslinux upstream has a bugfix. Both in the 6.xx branch and the 4.xx branch. ----- Forwarded message from syslinux-bot for Martin Str|mberg <ams at ludd.ltu.se> ----- Date: Sat, 15 Apr 2017 10:27:08 -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:

From: MartinS <ams at ludd.ltu.se> isohdp[fp]v.S which says E or C if EBIOS or CBIOS is used. isohdppv.S also says G or M if a GPT or MBR partition is detected. Signed-off-by: MartinS <ams at ludd.ltu.se> --- Comments? diff --git a/mbr/Makefile b/mbr/Makefile index be2bded..7095396 100644 --- a/mbr/Makefile +++ b/mbr/Makefile @@ -21,7 +21,8 @@ include $(MAKEDIR)/embedded.mk all:

Thomas Schmitt said: > I am wondering about the meaning or reason of "+20" in this assembler line: > > movl (32+20)(%si), %ecx > > Why that extra offset 20 on the byte offset 32 which is specified by > GPT specs (UEFI 2.4, 5.3.3) ? (Do i get the language wrong ?) Well I've been looking at this. It seems gptmbr.S

Thomas Schmitt wrote: > My main point of interest is which block is really loaded as first one > of isolinux.bin. [Program snipped.] > (It could be shorter if i did not insist in big endian words.) Why insisting? Anyway appended is a dumper version. I could put up a binery version if needed. Let me know if so. -- MartinS /*

On Sat, Mar 25, 2017 at 06:51:50PM +0100, Geert Stappers via Syslinux wrote: > 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> > Subject: [syslinux:master] mbr/isohdpfx.S: correct pointer for

On Fri, Mar 24, 2017 at 2:55 PM, Martin Str|mberg via Syslinux <syslinux at zytor.com> wrote: > On Fri, Mar 24, 2017 at 05:38:31PM +0100, Thomas Schmitt via Syslinux wrote: >> isohdpfc pushes the CX value to the stack which it gets from INT 13 AH 41. >> Quite surely bit 0 of that CX is not set. But bit 2 "Enhanced Disk Drive" >> could be set. >>

On Fri, Mar 24, 2017 at 05:38:31PM +0100, Thomas Schmitt via Syslinux wrote: > isohdpfc pushes the CX value to the stack which it gets from INT 13 AH 41. > Quite surely bit 0 of that CX is not set. But bit 2 "Enhanced Disk Drive" > could be set. > https://en.wikipedia.org/wiki/INT_13H > > I understand on David's BIOS after > > andw $1,%cx

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

On Wed, Mar 22, 2017 at 12:06:12PM +0100, Thomas Schmitt via Syslinux wrote: > 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 /* -16: Save

The following series of patches add a work-around for a BIOS bug to the MBR code. The user can press a Ctrl key at boot-time to force the MBR to ignore the BIOS-reported drive number (passed in register DL) and use the first hard-disk device (0x80). This works around a common problem that otherwise results in the "Missing operating system" message. If the BIOS-defined boot device order

Version 2 of these patches includes optimisations suggested by H Peter Alvin to save bytes: * Use memory-mapped I/O register to read keyboard shift flags * Don't reload DX from memory; move immediate byte to register Tested using mbr.bin. TJ (3): mbr: Ctrl-key press forces load from first hard disk gptmbr: Ctrl-key press forces load from first hard disk isohdpfx: Ctrl-key press

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

On Tue, Mar 21, 2017 at 09:03:35AM +0100, Thomas Schmitt via Syslinux wrote: > I think we should offer David a binary which he can combine with > the MBR of the ISO and the image with the recognizable blocks. > I will later today upload a binary version of my block producer > and post the URL. > > The combination will be: > 432 bytes from Martin's MBR > 80 bytes

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,

I wrote: > But isohdpfx.S is buggy: ... > /* Check to see if we have EBIOS */ > pushw %dx /* drive number */ > movb $0x41, %ah /* %al == 0 already */ > > Here it claims that al is zero. This is not true. Especially if you Looking at it some more, I've concluded that the bug is the comment. AL doesn't have to be zero and there's no guarantee it

Thomas Schmitt wrote: > I have some problems understanding the details of the program's flow. > > - The code inside PARTITION_SUPPORT is supposed to be inactive with > MBR isohdpfx.bin. It belongs to isohybrid --partok which is equivalent > to MBRs isohdppx*.bin. Debian uses isohdpfx.bin. Yes. isohdpfx.bin is generated from isohdpfx.S in which PARTITION_SUPPORT is not

If EBIOS is detected for this drive it tries to read sector size and use it. If error or no EBIOS 512 is assumed. Buffer to read sector size if always allocated into the stack. CHS informations are not readed as not needed and same space not restoring %dl for drive number. Signed-off-by: Frediano Ziglio <frediano.ziglio at citrix.com> --- mbr/gptmbr.S | 42