Let's investigate EFI_SECTION_USER_INTERFACE=0x15 section type:
EFI_SECTION_USER_INTERFACE
Summary:
A leaf section type that contains a Unicode string that contains a human-readable file name.
Prototype:
typedef struct {
EFI_COMMON_SECTION_HEADER CommonHeader;
CHAR16 FileNameString[];
} EFI_USER_INTERFACE_SECTION;
Description:
The user interface file name section is a leaf section that contains a Unicode string that contains a human-readable file name.
This section is optional and is not required for any file types. There must never be more than one user interface file name section contained within a file.
As you can see this section is really simple. Its data is just a CHAR16 string. EDKII has syntax to initialize this section in-place:
FILE FREEFORM = f6ed9cf0-cdc1-40a1-9909-ac6a2f435e23 {
SECTION UI = "MyUI"
}
VolInfo can display string of this section:
$ VolInfo Build/UefiLessonsPkg/RELEASE_GCC5/FV/SIMPLEVOLUME.Fv -x Build/UefiLessonsPkg/RELEASE_GCC5/FV/Guid.xref
VolInfo Version 1.0 Build Developer Build based on Revision: Unknown
ParseGuidBaseNameFile: Build/UefiLessonsPkg/RELEASE_GCC5/FV/Guid.xref
Signature: _FVH (4856465F)
Attributes: 40800
EFI_FVB2_ERASE_POLARITY
EFI_FVB2_ALIGNMENT_16
Header Length: 0x00000048
File System ID: 8c8ce578-8a3d-4f1c-9935-896185c32dd3
Revision: 0x0002
Number of Blocks: 0x00000500
Block Length: 0x00000001
Total Volume Size: 0x00000500
============================================================
File Name: F6ED9CF0-CDC1-40A1-9909-AC6A2F435E23 MyUI
File Offset: 0x00000048
File Length: 0x00000026
File Attributes: 0x00
File State: 0xF8
EFI_FILE_DATA_VALID
File Type: 0x02 EFI_FV_FILETYPE_FREEFORM
------------------------------------------------------------
Type: EFI_SECTION_USER_INTERFACE
Size: 0x0000000E
String: MyUI
There are a total of 1 files in this FV
Intermidiate file for this section would have *.ui extension:
Build/UefiLessonsPkg/RELEASE_GCC5/FV/Ffs/f6ed9cf0-cdc1-40a1-9909-ac6a2f435e23SIMPLEVOLUME/f6ed9cf0-cdc1-40a1-9909-ac6a2f435e23SEC1.ui -C
00000000 0e 00 00 15 4d 00 79 00 55 00 49 00 00 00 |....M.y.U.I...|
0000000e
Another simple section that you might come across is EFI_SECTION_VERSION:
Summary:
A leaf section type that contains a numeric build number and an optional Unicode string that represents the file revision.
Prototype:
typedef struct {
EFI_COMMON_SECTION_HEADER CommonHeader;
UINT16 BuildNumber;
CHAR16 VersionString[];
} EFI_VERSION_SECTION;
Parameters:
CommonHeader Common section header. CommonHeader.Type = EFI_SECTION_VERSION.
BuildNumber A UINT16 that represents a particular build. Subsequent builds have monotonically
increasing build numbers relative to earlier builds.
VersionString A null-terminated Unicode string that contains a text representation of the version. If
there is no text representation of the version, then an empty string must be provided.
Description:
A version section is a leaf section that contains a numeric build number and an optional Unicode string that represents the file revision.
To facilitate versioning of PEIMs, DXE drivers, and other files, a version section may be included in a file.
There must never be more than one version section contained within a file.
The syntax for adding this section is this:
FILE FREEFORM = f6ed9cf0-cdc1-40a1-9909-ac6a2f435e23 {
SECTION BUILD_NUM = 42 VERSION = "MyVersion"
}
Once again VolInfo is able to display the content of this section:
$ VolInfo Build/UefiLessonsPkg/RELEASE_GCC5/FV/SIMPLEVOLUME.Fv -x Build/UefiLessonsPkg/RELEASE_GCC5/FV/Guid.xref
VolInfo Version 1.0 Build Developer Build based on Revision: Unknown
Signature: _FVH (4856465F)
Attributes: 40800
EFI_FVB2_ERASE_POLARITY
EFI_FVB2_ALIGNMENT_16
Header Length: 0x00000048
File System ID: 8c8ce578-8a3d-4f1c-9935-896185c32dd3
Revision: 0x0002
Number of Blocks: 0x00000500
Block Length: 0x00000001
Total Volume Size: 0x00000500
============================================================
File Name: F6ED9CF0-CDC1-40A1-9909-AC6A2F435E23
File Offset: 0x00000048
File Length: 0x00000032
File Attributes: 0x00
File State: 0xF8
EFI_FILE_DATA_VALID
File Type: 0x02 EFI_FV_FILETYPE_FREEFORM
------------------------------------------------------------
Type: EFI_SECTION_VERSION
Size: 0x0000001A
Build Number: 0x002A
Version String: MyVersion
There are a total of 1 files in this FV
Intermidiate file for this section would have *.ver extension:
$ hexdump Build/UefiLessonsPkg/RELEASE_GCC5/FV/Ffs/f6ed9cf0-cdc1-40a1-9909-ac6a2f435e23SIMPLEVOLUME/f6ed9cf0-cdc1-40a1-9909-ac6a2f435e23SEC1.ver -C
00000000 1a 00 00 14 2a 00 4d 00 79 00 56 00 65 00 72 00 |....*.M.y.V.e.r.|
00000010 73 00 69 00 6f 00 6e 00 00 00 |s.i.o.n...|
0000001a
EFI_SECTION_FREEFORM_SUBTYPE_GUID section is very similar to raw, except that its header contains GUID value to describe the data inside the section.
Here is definition from the PI specification:
EFI_SECTION_FREEFORM_SUBTYPE_GUID
Summary:
A leaf section type that contains a single EFI_GUID in the header to describe the raw data.
Prototype:
typedef struct {
EFI_COMMON_SECTION_HEADER CommonHeader;
EFI_GUID SubTypeGuid;
} EFI_FREEFORM_SUBTYPE_GUID_SECTION;
Parameters:
CommonHeader Common section header. CommonHeader.Type = EFI_SECTION_FREEFORM_SUBTYPE_GUID.
SubtypeGuid This GUID is defined by the creator of the file. It is a vendor-defined file type.
Description:
A free-form subtype GUID section is a leaf section that contains a single EFI_GUIDin the header to describe the raw data
The syntax for adding this section is this:
SECTION SUBTYPE_GUID <Guid> = <File>
Let's try to use it:
FILE FREEFORM = f6ed9cf0-cdc1-40a1-9909-ac6a2f435e23 {
SECTION SUBTYPE_GUID cf1fce30-b181-4d6a-b860-354c922e5c3e = $(WORKDIR)/hello.txt
}
Here is how VolInfo output looks like in this case:
$ VolInfo Build/UefiLessonsPkg/RELEASE_GCC5/FV/SIMPLEVOLUME.Fv
VolInfo Version 1.0 Build Developer Build based on Revision: Unknown
Signature: _FVH (4856465F)
Attributes: 40800
EFI_FVB2_ERASE_POLARITY
EFI_FVB2_ALIGNMENT_16
Header Length: 0x00000048
File System ID: 8c8ce578-8a3d-4f1c-9935-896185c32dd3
Revision: 0x0002
Number of Blocks: 0x00000500
Block Length: 0x00000001
Total Volume Size: 0x00000500
============================================================
File Name: F6ED9CF0-CDC1-40A1-9909-AC6A2F435E23
File Offset: 0x00000048
File Length: 0x00000033
File Attributes: 0x00
File State: 0xF8
EFI_FILE_DATA_VALID
File Type: 0x02 EFI_FV_FILETYPE_FREEFORM
------------------------------------------------------------
Type: EFI_SECTION_FREEFORM_SUBTYPE_GUID
Size: 0x0000001B
Guid: cf1fce30-b181-4d6a-b860-354c922e5c3e
There are a total of 1 files in this FV
Intermidiate file for this section would have *.guid extension:
$ hexdump Build/UefiLessonsPkg/RELEASE_GCC5/FV/Ffs/f6ed9cf0-cdc1-40a1-9909-ac6a2f435e23SIMPLEVOLUME/f6ed9cf0-cdc1-40a1-9909-ac6a2f435e23SEC1.guid -C
00000000 1b 00 00 18 30 ce 1f cf 81 b1 6a 4d b8 60 35 4c |....0.....jM.`5L|
00000010 92 2e 5c 3e 68 65 6c 6c 6f 21 0a |..\>hello!.|
0000001b
Next there is a couple of sections for executable images. Most often you would use EFI_SECTION_PE32 and include .efi code as your data. But nevertheless here is some info about all of the sections from the caption.
Here in VolInfo output I will show you just the section part, as the rest doesn't have any interesting changes. Also as the build system doesn't check the content of the section data, I will just use the same hello.txt file for the section content that we've created earlier:
EFI_SECTION_PE32
Summary
A leaf section type that contains a complete PE32+ image.
Prototype
typedef EFI_COMMON_SECTION_HEADER EFI_PE32_SECTION;
Description
The PE32+ image section is a leaf section that contains a complete PE32+ image. Normal UEFI
executables are stored within PE32+ images
Example usage:
FILE FREEFORM = f6ed9cf0-cdc1-40a1-9909-ac6a2f435e23 {
SECTION PE32 = $(WORKDIR)/hello.txt
}
VolInfo display for the section:
------------------------------------------------------------
Type: EFI_SECTION_PE32
Size: 0x0000000B
The section file extension is "*.pe32":
$ hexdump Build/UefiLessonsPkg/RELEASE_GCC5/FV/Ffs/f6ed9cf0-cdc1-40a1-9909-ac6a2f435e23SIMPLEVOLUME/f6ed9cf0-cdc1-40a1-9909-ac6a2f435e23SEC1.pe32 -C
00000000 0b 00 00 10 68 65 6c 6c 6f 21 0a |....hello!.|
0000000b
EFI_SECTION_PIC
Summary
A leaf section type that contains a position-independent-code (PIC) image.
Prototype
typedef EFI_COMMON_SECTION_HEADER EFI_PIC_SECTION;
Description
A PIC image section is a leaf section that contains a position-independent-code (PIC) image.
Example usage:
FILE FREEFORM = f6ed9cf0-cdc1-40a1-9909-ac6a2f435e23 {
SECTION PIC = $(WORKDIR)/hello.txt
}
VolInfo output for the section:
------------------------------------------------------------
Type: EFI_SECTION_PIC
Size: 0x0000000B
The section file extension is "*.pic":
$ hexdump Build/UefiLessonsPkg/RELEASE_GCC5/FV/Ffs/f6ed9cf0-cdc1-40a1-9909-ac6a2f435e23SIMPLEVOLUME/f6ed9cf0-cdc1-40a1-9909-ac6a2f435e23SEC1.pic -C
00000000 0b 00 00 11 68 65 6c 6c 6f 21 0a |....hello!.|
0000000b
EFI_SECTION_COMPATIBILITY16
Summary:
A leaf section type that contains an IA-32 16-bit executable image.
Prototype:
typedef EFI_COMMON_SECTION_HEADER EFI_COMPATIBILITY16_SECTION;
Description:
A Compatibility16 image section is a leaf section that contains an IA-32 16-bit executable image.
IA-32 16-bit legacy code that may be included in PI Architecture firmware is stored in a 16-bit
executable image.
Example usage:
FILE FREEFORM = f6ed9cf0-cdc1-40a1-9909-ac6a2f435e23 {
SECTION COMPAT16 = $(WORKDIR)/hello.txt
}
VolInfo output for the section:
------------------------------------------------------------
Type: EFI_SECTION_COMPATIBILITY16
Size: 0x0000000B
The section file extension is "*.com16":
$ hexdump Build/UefiLessonsPkg/RELEASE_GCC5/FV/Ffs/f6ed9cf0-cdc1-40a1-9909-ac6a2f435e23SIMPLEVOLUME/f6ed9cf0-cdc1-40a1-9909-ac6a2f435e23SEC1.com16 -C
00000000 0b 00 00 16 68 65 6c 6c 6f 21 0a |....hello!.|
0000000b
EFI_SECTION_TE
Summary
A leaf section that contains a Terse Executable (TE) image.
Prototype
typedef EFI_COMMON_SECTION_HEADER EFI_TE_SECTION;
Description
The terse executable section is a leaf section that contains a Terse Executable (TE) image. A TE
image is an executable image format specific to the PI Architecture that is used for storing
executable images in a smaller amount of space than would be required by a full PE32+ image.
Example usage:
FILE FREEFORM = f6ed9cf0-cdc1-40a1-9909-ac6a2f435e23 {
SECTION TE = $(WORKDIR)/hello.txt
}
You would find that in this case build actually checks the file content. Build fails with the error:
DOS header signature was not found in /<...>/hello.txt image.
But if you would use correct file, the VolInfo would show you EFI_SECTION_TE section.
The section file extension is "*.te":
Creation of this type of section is not supported by edk2. There is no syntax for it. But nevertheless here is definition from the specification:
EFI_SECTION_DISPOSABLE
Summary:
An encapsulation section type in which the section data is disposable.
Prototype:
typedef EFI_COMMON_SECTION_HEADER EFI_DISPOSABLE_SECTION;
Description:
A disposable section is an encapsulation section in which the section data may be disposed of during the process of creating or updating a firmware image without significant impact on the usefulness of the file.
There are also sections for the dependency expressions for DXE and PEI stages. You probably wouldn't write them yourself, but here is their description for completeness:
EFI_SECTION_PEI_DEPEX
Summary:
A leaf section type that is used to determine dispatch order for a PEIM.
Prototype:
typedef EFI_COMMON_SECTION_HEADER EFI_PEI_DEPEX_SECTION;
Description:
The PEI dependency expression section is a leaf section that contains a dependency expression that is used to determine dispatch order for a PEIM. See the Platform Initialization Pre-EFI Initialization Core Interface Specification for details regarding the format of the dependency expression.
EFI_SECTION_DXE_DEPEX
Summary:
A leaf section type that is used to determine the dispatch order for a DXE driver.
Prototype:
typedef EFI_COMMON_SECTION_HEADER EFI_DXE_DEPEX_SECTION;
Description
The DXE dependency expression section is a leaf section that contains a dependency expression that is used to determine the dispatch order for a DXE driver. See the Platform Initialization Driver Execution Environment Core Interface Specification for details regarding the format of the dependency expression.
The section file extension for these sections is "*.dpx"