RFC: Add GNU_PROPERTY_1_GLIBC_2_NEEDED

[H.J. Lu]

/* The needed glibc 2 minor version property for the object file.  */
#define GNU_PROPERTY_1_GLIBC_2_NEEDED   (GNU_PROPERTY_UINT32_OR_LO + 1)

/* The needed glibc 2 minor base version.  */
#define GNU_PROPERTY_1_GLIBC_2_NEEDED_MINOR_BASE 35

/* Set if the object file requires glibc 2 minor version M.  */
#define GNU_PROPERTY_1_GLIBC_2_NEEDED_MINOR_VERSION(m)  \
  (1U << ((m) - GNU_PROPERTY_1_GLIBC_2_NEEDED_MINOR_BASE))

Linker adds glibc versions in GNU_PROPERTY_1_GLIBC_2_NEEDED to DT_VERNEED.
It can be used to embed glibc version dependency in .o files:

[hjl@gnu-cfl-2 elfvers-1]$ ./readelf -n x.o

Displaying notes found in: .note.gnu.property
  Owner                Data size 	Description
  GNU                  0x00000020	NT_GNU_PROPERTY_TYPE_0
      Properties: x86 ISA used:
	x86 feature used: x86
[hjl@gnu-cfl-2 elfvers-1]$ ./readelf -n glibc-2-minor-1.o

Displaying notes found in: .note.gnu.property
  Owner                Data size 	Description
  GNU                  0x00000010	NT_GNU_PROPERTY_TYPE_0
      Properties: 1_glibc_2_needed: 2.35, 2.38
  GNU                  0x00000020	NT_GNU_PROPERTY_TYPE_0
      Properties: x86 ISA used:
	x86 feature used: x86
[hjl@gnu-cfl-2 elfvers-1]$ make x
gcc -B./ -o x x.o glibc-2-minor-1.o
[hjl@gnu-cfl-2 elfvers-1]$ ./readelf -n --version-info x
Version symbols section '.gnu.version' contains 4 entries:
 Addr: 0x00000000004004ae  Offset: 0x0004ae  Link: 6 (.dynsym)
  000:   0 (*local*)       2 (GLIBC_2.34)    3 (GLIBC_2.2.5)   1 (*global*)   

Version needs section '.gnu.version_r' contains 1 entry:
 Addr: 0x00000000004004b8  Offset: 0x0004b8  Link: 7 (.dynstr)
  000000: Version: 1  File: libc.so.6  Cnt: 4
  0x0010:   Name: GLIBC_2.38  Flags: none  Version: 5
  0x0020:   Name: GLIBC_2.35  Flags: none  Version: 4
  0x0030:   Name: GLIBC_2.2.5  Flags: none  Version: 3
  0x0040:   Name: GLIBC_2.34  Flags: none  Version: 2

Displaying notes found in: .note.gnu.property
  Owner                Data size        Description
  GNU                  0x00000040       NT_GNU_PROPERTY_TYPE_0
      Properties: 1_glibc_2_needed: 2.35, 2.38
...
[hjl@gnu-cfl-2 elfvers-1]$ ./x
./x: /lib64/libc.so.6: version `GLIBC_2.38' not found (required by ./x)
./x: /lib64/libc.so.6: version `GLIBC_2.35' not found (required by ./x)
[hjl@gnu-cfl-2 elfvers-1]$


H.J.