[llvm-dev] lld extra program headers

[Will Song via llvm-dev]

Hello all,

The lld linker appears to generate extra ELF program headers and thus
causes file sizes to be significantly larger than what would get with
ld.gold or ld.bfd.

# readelf -l test.bfd

Elf file type is EXEC (Executable file)
Entry point 0x4000b0
There are 2 program headers, starting at offset 64

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  LOAD           0x0000000000000000 0x0000000000400000 0x0000000000400000
                 0x00000000000000c0 0x00000000000000c0  R E    0x200000
  GNU_STACK      0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000  RW     0x10

 Section to Segment mapping:
  Segment Sections...
   00     .text 
   01     
# readelf -l test.gold

Elf file type is EXEC (Executable file)
Entry point 0x4000b0
There are 2 program headers, starting at offset 64

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  LOAD           0x0000000000000000 0x0000000000400000 0x0000000000400000
                 0x00000000000000c0 0x00000000000000c0  R E    0x1000
  GNU_STACK      0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000  RW     0x10

 Section to Segment mapping:
  Segment Sections...
   00     .text 
   01     
# readelf -l test.lld

Elf file type is EXEC (Executable file)
Entry point 0x201000
There are 4 program headers, starting at offset 64

Program Headers:
  Type           Offset             VirtAddr           PhysAddr
                 FileSiz            MemSiz              Flags  Align
  PHDR           0x0000000000000040 0x0000000000200040 0x0000000000200040
                 0x00000000000000e0 0x00000000000000e0  R      0x8
  LOAD           0x0000000000000000 0x0000000000200000 0x0000000000200000
                 0x0000000000000120 0x0000000000000120  R      0x1000
  LOAD           0x0000000000001000 0x0000000000201000 0x0000000000201000
                 0x0000000000000010 0x0000000000000010  R E    0x1000
  GNU_STACK      0x0000000000000000 0x0000000000000000 0x0000000000000000
                 0x0000000000000000 0x0000000000000000  RW     0x0

 Section to Segment mapping:
  Segment Sections...
   00     
   01     
   02     .text 
   03     

Now obviously disk space is relatively cheap these days but if it could
be avoided, can we avoid generating these unused memory mappings unless
a PT_INTERP section is going to be generated? I could also be
misunderstanding things, and it might be normal to map the program's
program headers into memory (and thus the entire ELF header).

Thanks.