Syslinux - Nov 2015 - Only 2.5G of RAM available when syslinux64.efi boots 32-bit linux 686-pae

Hello,

I'm booting linux-3.16-686-pae kernel (32-bit) via syslinux.efi 64-bit
version.
After boot linux sees only 2.5G of RAM while system has 32G installed.

If I boot the same kernel with GRUB64 efi instead of syslinux 
then amount of RAM available to linux is 32G.

Is this a bug or I'm missing something?

syslinux.cfg:

label live-686-pae
        menu label Linux (686-pae)
        menu default
        linux /live/vmlinuz
        initrd /live/initrd.img
        append boot=live config persistence username=user live-config.utc=no
acpi_osi=Linux live-config.noautologin


Current git: e0be4d87135

Regards,
Andrey

> Hello,
> 
> I'm booting linux-3.16-686-pae kernel (32-bit) via syslinux.efi 64-bit
version.
> After boot linux sees only 2.5G of RAM while system has 32G installed.
> 
> If I boot the same kernel with GRUB64 efi instead of syslinux 
> then amount of RAM available to linux is 32G.
> 
> Is this a bug or I'm missing something?
> 
> syslinux.cfg:
> 
> label live-686-pae
>         menu label Linux (686-pae)
>         menu default
>         linux /live/vmlinuz
>         initrd /live/initrd.img
>         append boot=live config persistence username=user
live-config.utc=no acpi_osi=Linux live-config.noautologin
> 
> 
> Current git: e0be4d87135
> 
> Regards,
> Andrey
 
 
It saddens (me) to see no reply to this email thread at all, especially 
from developers.

C'mon; really? Not even a comment asking to post the _complete_ content 
of the syslinux.cfg file?

No suggestion about kernel options such as 'mem=', 'vmalloc=' or
any
other / similar?

No question about the building environment (nasm, gnu-efi, gcc, 
binutils, mtools...)?

No chance that someone could suggest that updating the gnu-efi 
submodule _might_ _perhaps_ affect the result?

I cannot believe that there is not even one developer that could think 
(and post here) about the potential idea that some code in EFISTUB (or 
whatever is related to EFI in the Linux kernel) needs to be also 
incorporated in Syslinux. Really? There is not one person that could 
think that some development in the EFISTUB code (or similar) during the 
last year-and-a-half / two years might need to be ported to the 
Syslinux code too?

And what about fallback booting methods (a matter that has been 
mentioned here more than once, but it is not clear how much has been 
really done to completely support older kernels)? We have seen problems 
with kernels built with or without certain options in the past. There 
is really not even one subscriber to this Syslinux Mailing List that 
could suggest in this email thread that there might still be some issue 
regarding kernel building options when the kernel is booted by 
Syslinux?

Let's also not forget that Syslinux seems to be "more respectful"
than
GRUB2 when booting (u)efi images. Could this be a factor in how much 
RAM is seen after successfully booting the kernel?

I do not know the reason for the different behavior between 
syslinux.efi X64 and GRUB2.efi X64 when booting this 32-bit pae kernel, 
nor the answers to these questions, but I am at least trying.

Regards,
Ady.
 
> _______________________________________________
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> Unsubscribe or set options at:
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>

>>>
      From: Andrey Plankin via Syslinux <syslinux at zytor.com>
 To: syslinux at zytor.com 
 Sent: Friday, November 20, 2015 11:04 PM
 Subject: [syslinux] Only 2.5G of RAM available then syslinux64.efi boots 32-bit
linux 686-pae
   
Hello,

I'm booting linux-3.16-686-pae kernel (32-bit) via syslinux.efi 64-bit
version.
After boot linux sees only 2.5G of RAM while system has 32G installed.

If I boot the same kernel with GRUB64 efi instead of syslinux 
then amount of RAM available to linux is 32G.

Is this a bug or I'm missing something?

syslinux.cfg:

label live-686-pae
? ? ? ? menu label Linux (686-pae)
? ? ? ? menu default
? ? ? ? linux /live/vmlinuz
? ? ? ? initrd /live/initrd.img
? ? ? ? append boot=live config persistence username=user live-config.utc=no
acpi_osi=Linux live-config.noautologin


Current git: e0be4d87135

Regards,
Andrey
<<<
1) I think this problem is not related to appended kernel variables.2) Syslinux
allocates and free EFI memory before calling ExitBootServices()but even if SL
forgets freeing memory I cannot belive SL ever allocates 32-2.5=29.5GB or
so.Then the problem does not look like not released SL allocated memory...

Questions
1) If you boot the PAE kernel with syslinux32.efi do you see the same problem?
2) Have you tried booting in different PCs to rule out some FW related issue?
Debugging this is not simple but it can be done calling
EFI_BOOT_SERVICES.GetMemoryMap()as soon as the syslinux64.efi runs and before
calling ExitBootServices()
then parsing the returned array of EFI_MEMORY_DESCRIPTORS we can see what's
going on.
Best,Patrick

On Sat, Nov 21, 2015 at 1:04 AM, Andrey Plankin via Syslinux
<syslinux at zytor.com> wrote:
> Hello,
>
> I'm booting linux-3.16-686-pae kernel (32-bit) via syslinux.efi 64-bit
version.
> After boot linux sees only 2.5G of RAM while system has 32G installed.
Why not use a 64-bit kernel with such a large machine?

Do you have the config used to build that kernel?  I'm specifically
looking for any config line with "EFI" in it.
> If I boot the same kernel with GRUB64 efi instead of syslinux
> then amount of RAM available to linux is 32G.
>
> Is this a bug or I'm missing something?
It's certainly unexpected behavior but booting a 32-bit kernel from a
64-bit EFI is also a little unexpected.  Syslinux will definitely try
to use the EFI stub in the kernel to boot the kernel.  I can't speak
for GRUB but it has done some forced behaviors in the past.

Could you post the memory map that Linux uses in both cases?  dmesg
should be able to help.
> syslinux.cfg:
>
> label live-686-pae
>         menu label Linux (686-pae)
>         menu default
>         linux /live/vmlinuz
>         initrd /live/initrd.img
>         append boot=live config persistence username=user
live-config.utc=no acpi_osi=Linux live-config.noautologin
Is this the entire file or just an excerpt?  If an excerpt, I'd wonder
if there's any other stray APPEND.  What does your kernel show as the
command line?
> Current git: e0be4d87135
So a build of Syslinux from that commit.

-- 
-Gene

> On Sat, Nov 21, 2015 at 1:04 AM, Andrey Plankin via Syslinux
> <syslinux at zytor.com> wrote:
> > Hello,
> >
> > I'm booting linux-3.16-686-pae kernel (32-bit) via syslinux.efi
64-bit version.
> > After boot linux sees only 2.5G of RAM while system has 32G installed.
> 
> Why not use a 64-bit kernel with such a large machine?
> 
> Do you have the config used to build that kernel?  I'm specifically
> looking for any config line with "EFI" in it.
> 
> > If I boot the same kernel with GRUB64 efi instead of syslinux
> > then amount of RAM available to linux is 32G.
> >
> > Is this a bug or I'm missing something?
> 
> It's certainly unexpected behavior but booting a 32-bit kernel from a
> 64-bit EFI is also a little unexpected.  Syslinux will definitely try
> to use the EFI stub in the kernel to boot the kernel.  I can't speak
> for GRUB but it has done some forced behaviors in the past.
> 
> Could you post the memory map that Linux uses in both cases?  dmesg
> should be able to help.
> 
> > syslinux.cfg:
> >
> > label live-686-pae
> >         menu label Linux (686-pae)
> >         menu default
> >         linux /live/vmlinuz
> >         initrd /live/initrd.img
> >         append boot=live config persistence username=user
live-config.utc=no acpi_osi=Linux live-config.noautologin
> 
> Is this the entire file or just an excerpt?  If an excerpt, I'd wonder
> if there's any other stray APPEND.  What does your kernel show as the
> command line?
> 
> > Current git: e0be4d87135
> 
> So a build of Syslinux from that commit.
> 
> -- 
> -Gene
 
 
While we wait for a reply from Andrey...


According to the report, syslinux.efi X64 is successfully booting the 
32-bit kernel. In theory, this should / would mean that the kernel was 
built with CONFIG_EFI_MIXED, among others.

As far as I know, the EFISTUB code doesn't know how to boot a kernel 
with a different architecture / bitness than the firmware. If this is 
(still) correct, then syslinux.efi X64 should be using the (latest) EFI 
handover protocol to be able to boot this 32-bit kernel (not the 
EFISTUB code).

According to the report, both grub2 and Syslinux are booting this 
32-bit kernel; with the difference being somehow related to the PAE 
feature.

Without PAE, the kernel would be able to see less than 4GB of RAM. 
According to the report, grub2 somehow is being able to boot this 
kernel with its PAE feature enabled (thus, the kernel / OS sees the 
whole RAM) while syslinux.efi seems to "block" the potential 
availability of at least part of the available RAM.

Is there any assumption in syslinux.efi about the available RAM when 
booting mixed architecture / bitness kernels? Is there some kind of 
(RAM) limitation / assumption in syslinux.efi for 32-bit? Are PAE 
kernels actually supported by the EFI handover implementation in 
syslinux.efi? If I am not mistaken, these seem to be the key points to 
be reviewed.

Regards,
Ady.

PS: The EFI-related code in the Linux kernel (e.g. EFI handover 
protocol) has seen (additional) developments during the last 1.5~2 
years. Perhaps it's time to contact Matt Fleming, or at least to visit 
the current efi code and update the Syslinux's code accordingly / if 
needed?

Regards,
Ady.
> _______________________________________________
> Syslinux mailing list
> Submissions to Syslinux at zytor.com
> Unsubscribe or set options at:
> http://www.zytor.com/mailman/listinfo/syslinux
>

On Mon, Nov 23, 2015 at 3:06 PM, Ady via Syslinux <syslinux at zytor.com>
wrote:
> It saddens (me)
> C'mon; really?
As you asked.

-- 
-Gene

2015-11-21 7:04 UTC+01:00, Andrey Plankin via Syslinux <syslinux at
zytor.com>:
> Hello,
>
> I'm booting linux-3.16-686-pae kernel (32-bit) via syslinux.efi 64-bit
> version.
> After boot linux sees only 2.5G of RAM while system has 32G installed.
>
> If I boot the same kernel with GRUB64 efi instead of syslinux
> then amount of RAM available to linux is 32G.
>
> Is this a bug or I'm missing something?
Is it possible to have access to the kernel you're trying to boot?


Celelibi

2015-11-27 5:42 UTC+01:00, Celelibi <celelibi at
gmail.com>:
> 2015-11-21 7:04 UTC+01:00, Andrey Plankin via Syslinux
> <syslinux at zytor.com>:
>> Hello,
>>
>> I'm booting linux-3.16-686-pae kernel (32-bit) via syslinux.efi
64-bit
>> version.
>> After boot linux sees only 2.5G of RAM while system has 32G installed.
>>
>> If I boot the same kernel with GRUB64 efi instead of syslinux
>> then amount of RAM available to linux is 32G.
>>
>> Is this a bug or I'm missing something?
>
> Is it possible to have access to the kernel you're trying to boot?
(Shamless third message in a row.)

It looks like there is no automatic build of the sysappend string in
UEFI. So you may try adding the following option in your config.
sysappend CPU=6:P

You may also try the less prefered kernel option "forcepae" documented
as follow:

	forcepae [X86-32]
			Forcefully enable Physical Address Extension (PAE).
			Many Pentium M systems disable PAE but may have a
			functionally usable PAE implementation.
			Warning: use of this parameter will taint the kernel
			and may cause unknown problems.

So, enable it at your own risks.
BTW, what CPU are you trying to boot?

Celelibi