Have you examined the structure EFI_LOAD_OPTION from UefiSpec.h?
I think that you are traversing the structure incorrectly. I cannot be sure
since I am not certain what this mGetVariable function does specifically.
I start by getting the correct size (BufferSize is zero at this first call):
Status = gRT->GetVariable(
VariableName,
(EFI_GUID*)&gEfiGlobalVariableGuid,
NULL,
&BufferSize,
Buffer);
if (Status == EFI_BUFFER_TOO_SMALL) {
Buffer = AllocateZeroPool(BufferSize);
Status = gRT->GetVariable(
VariableName,
(EFI_GUID*)&gEfiGlobalVariableGuid,
NULL,
&BufferSize,
Buffer);
}
To parse the structure I divide it up using the structure. I think your +3 may
be causing lots of issues.
LoadOption = (EFI_LOAD_OPTION *)Buffer;
Description = (CHAR16*)(Buffer + sizeof (EFI_LOAD_OPTION));
DescriptionSize = StrSize (Description);
if (LoadOption->FilePathListLength != 0) {
FilePathList = (UINT8 *)Description + DescriptionSize;
}
After this we can calculate the location of optional data.
OptionalDataOffset = sizeof *LoadOption + DescriptionSize +
LoadOption->FilePathListLength;
The optional data would be found at:
Buffer + OptionalDataOffset
Note that all the pointer math is based on using UINT8* or the raw Buffer
variable which is a UINT8*. Otherwise the size in bytes will not work out.
-Jaben
From: Saqib Khan [mailto:[email protected]]
Sent: Thursday, October 20, 2016 12:30 AM
To: Carsey, Jaben <[email protected]>
Cc: Andrew Fish <[email protected]>; [email protected]; Laszlo Ersek
<[email protected]>
Subject: Re: [edk2] How to get BBS_BBS_DEVICE_PATH from BOOTXXXX variable
Importance: High
BootVariable = mGetVariable(Name, &gEfiGlobalVariableGuid, &BootVariableSize,
NULL);
Ptr = (BootVariable+3);
Print(L" %s",(CHAR16 *)(Ptr));
DevicePath =AllocateZeroPool (*FilePathListLength) ;
Ptr+= StrSize((CHAR16 *)Ptr);
CopyMem (DevicePath, Ptr, *FilePathListLength);
As Carsey suggested i used the same Math in order to get DevicePath but in my
case it is not working
As documentation this data structure is not aligned so i am assuming that just
after description there should be
FilePathList ,so if i CopyMem (*FilePathListLength) bytes to DevicePath i
should get the right value but i am getting garbage.
On Thu, Oct 20, 2016 at 1:41 AM, Carsey, Jaben
<[email protected]<mailto:[email protected]>> wrote:
Have you examined the BCFG command in the UEFI Shell?
It does this exact behavior and the code is at:
ShellPkg\Library\UefiBcfgCommandLib\bcfg.c.
-Jaben
> -----Original Message-----
> From: edk2-devel
> [mailto:[email protected]<mailto:[email protected]>]
> On Behalf Of
> Saqib Khan
> Sent: Wednesday, October 19, 2016 11:18 AM
> To: Andrew Fish <[email protected]<mailto:[email protected]>>
> Cc: [email protected]<mailto:[email protected]>; Laszlo Ersek
> <[email protected]<mailto:[email protected]>>
> Subject: Re: [edk2] How to get BBS_BBS_DEVICE_PATH from BOOTXXXX
> variable
>
> Hi, so i have parsed the structure as follow :
>
>
>
>
>
>
>
> *BootVariable = mGetVariable(Name, &gEfiGlobalVariableGuid,
> &BootVariableSize, NULL);LDAttr = BootVariable[0];FilePathListLength =
> (BootVariable+2);Ptr = (BootVariable+3); // for description *
>
>
>
> *for FilePathList[] Ptr+= StrSize((CHAR16 *)Ptr); CopyMem (Ptr,
> DevicePath, *FilePathListLength);*
>
>
> I am able to get LDAttr ,FilePathListLength and description but
>
> when i try to check DevicePath->Type it always return 0x01( Hardware Device
> Path) for each device .
>
>
> I have hard drive with legacy OS(BBS_DEVICE_PATH). So it should not always
> return 0x01 .What i am doing wrong in parsing ?
>
> Thanks
>
> On Tue, Oct 18, 2016 at 11:37 PM, Andrew Fish
> <[email protected]<mailto:[email protected]>> wrote:
>
> >
> > > On Oct 18, 2016, at 10:40 AM, Laszlo Ersek
> > > <[email protected]<mailto:[email protected]>> wrote:
> > >
> > > On 10/18/16 19:18, Saqib Khan wrote:
> > >> Hi,
> > >> I can not find structure of BOOTXXXX variable, Can any one help how to
> > >> extract device path from BOOTXXXX variable.
> > >
> > > In UEFI-related questions, the UEFI specification has a fair chance to
> > > provide useful information.
> > >
> > > Please refer to "3.1.3 Load Options" in the UEFI v2.6 spec, available
> > > for download from <http://www.uefi.org/specifications>.
> > >
> > > Locating the matching structure definition in the edk2 tree is left as
> > > an exercise to the reader ;)
> > >
> >
> > Chapter 3 Boot Manager.
> >
> > The structure is EFI_LOAD_OPTION but some of the fields are variable
> > length so you have to do math to figure stuff out.
> >
> > Thanks,
> >
> > Andrew Fish
> >
> >
> > > Laszlo
> > >
> > > _______________________________________________
> > > edk2-devel mailing list
> > > [email protected]<mailto:[email protected]>
> > > https://lists.01.org/mailman/listinfo/edk2-devel
> >
> >
>
>
> --
> Regards
> Saqib Ahmed Khanzada
> _______________________________________________
> edk2-devel mailing list
> [email protected]<mailto:[email protected]>
> https://lists.01.org/mailman/listinfo/edk2-devel
--
Regards
Saqib Ahmed Khanzada
_______________________________________________
edk2-devel mailing list
[email protected]
https://lists.01.org/mailman/listinfo/edk2-devel
