Add program property

We introduce .note.gnu.property section to store infomations that linker
or runtime system may use, and we define 4 program property classes to
specifying the merge semantics, it's used for forward compatibility in linker
implementations, allowing linker can correctly handle program property types
even if they are not recognized.

We don't define any program property within this PR, it would be
separate PR like #417

Author: kito-cheng

riscv-elf.adoc

@@ -1085,13 +1085,16 @@ The defined processor-specific section types are listed in <<rv-section-type>>.
 
 | .riscv.attributes          | SHT_RISCV_ATTRIBUTES | none
 | .riscv.jvt                 | SHT_PROGBITS         | SHF_ALLOC + SHF_EXECINSTR
+| .note.gnu.property         | SHT_NOTE             | SHF_ALLOC
 |===
 
 +++.riscv.attributes+++ names a section that contains RISC-V ELF attributes.
 
 +++.riscv.jvt+++ is a linker-created section to store table jump
 target addresses. The minimum alignment of this section is 64 bytes.
 
++++.note.gnu.property+++ names a section that contains a program property note.
+
 === Program Header Table
 
 The defined processor-specific segment types are listed in <<rv-seg-type>>.
@@ -1355,6 +1358,46 @@ value. After the merge, the resulting value will be the non-zero one.
 
 --
 
+=== Program Property
+
+Program property are used to record information about an object file/binary that
+a linker or runtime loader needs to check compatibility.
+
+The program property is divided into different classes, each defining a range
+of program property types and specifying the merge semantics. This is designed
+for forward compatibility in linker implementations, allowing them to correctly
+handle program property types even if they are not recognized.
+
+[[rv-prog-prop-classes]]
+.RISC-V-specific program property classes
+[cols="3,2,2,5"]
+[width=100%]
+|===
+| Name           | Range                    | Data Type | Merge Semantic
+
+| UINT32_AND     | 0xc0000000 ~ 0xc0007fff  | 4-bytes   | A bit is set if it is set in all inputs.
+| UINT32_OR      | 0xc0008000 ~ 0xc000ffff  | 4-bytes   | A bit is set if it is set in any inputs.
+| UINT32_OR_AND  | 0xc0010000 ~ 0xc0017fff  | 4-bytes   | A bit is set if it is set in any inputs and the property is present in all inputs.
+| UINT32_EXACTLY | 0xc0018000 ~ 0xc001ffff  | 4-bytes   | A 32 bit unsigned value is specified if it is set same value in all inputs, tool should report error if mismatched.
+|===
+
+[[rv-prog-prop-class-constants]]
+.Constants for RISC-V-specific program property class
+[cols="3,2"]
+[width=80%]
+|===
+| Name                                 | Value
+
+| GNU_PROPERTY_RISCV_UINT32_AND_LO     | 0xc0000000
+| GNU_PROPERTY_RISCV_UINT32_AND_HI     | 0xc0007fff
+| GNU_PROPERTY_RISCV_UINT32_OR_LO      | 0xc0008000
+| GNU_PROPERTY_RISCV_UINT32_OR_HI      | 0xc000ffff
+| GNU_PROPERTY_RISCV_UINT32_OR_AND_LO  | 0xc0010000
+| GNU_PROPERTY_RISCV_UINT32_OR_AND_HI  | 0xc0017fff
+| GNU_PROPERTY_RISCV_UINT32_EXACTLY_LO | 0xc0018000
+| GNU_PROPERTY_RISCV_UINT32_EXACTLY_HI | 0xc001ffff
+|===
+
 === Mapping Symbol
 
 The section can have a mixture of code and data or code with different ISAs.