[Bug target/82303] Better PIE/PIC code generation for kernel code (x86_64 & arm64)

[thgarnie at google dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82303

--- Comment #9 from Thomas Garnier <thgarnie at google dot com> ---
I tested the change against a modified version of the proposed Linux x86_64 PIE
support. The changes removes all the PLT32 and GOT64 entry but I still get
R_X86_64_GOTPC64 & R_X86_64_GOTOFF64 relocations on the head64.c file that is
built with -mcmodel=large (to prevent odd logic on early boot with different
VA).

Do you think the suggested patch can be changed to remove these?

To repro, build the object file with: gcc -mcmodel=large -c -fstatic-pie
./test.c -o test

The objdump -dr output of the testcase:

0000000000000000 <main>:
   0:   55                      push   %rbp
   1:   48 89 e5                mov    %rsp,%rbp
   4:   48 83 ec 20             sub    $0x20,%rsp
   8:   48 8d 05 f9 ff ff ff    lea    -0x7(%rip),%rax        # 8 <main+0x8>
   f:   49 bb 00 00 00 00 00    movabs $0x0,%r11
  16:   00 00 00
                        11: R_X86_64_GOTPC64    _GLOBAL_OFFSET_TABLE_+0x9
  19:   4c 01 d8                add    %r11,%rax
  1c:   89 7d ec                mov    %edi,-0x14(%rbp)
  1f:   48 89 75 e0             mov    %rsi,-0x20(%rbp)
  23:   48 ba 00 00 00 00 00    movabs $0x0,%rdx
  2a:   00 00 00
                        25: R_X86_64_GOTOFF64   _text-0x1023
  2d:   48 8d 14 10             lea    (%rax,%rdx,1),%rdx
  31:   89 55 fc                mov    %edx,-0x4(%rbp)
  34:   8b 55 ec                mov    -0x14(%rbp),%edx
  37:   48 63 d2                movslq %edx,%rdx
  3a:   48 8b 4d e0             mov    -0x20(%rbp),%rcx
  3e:   48 89 ce                mov    %rcx,%rsi
  41:   48 b9 00 00 00 00 00    movabs $0x0,%rcx
  48:   00 00 00
                        43: R_X86_64_GOTOFF64   _text
  4b:   48 8d 3c 08             lea    (%rax,%rcx,1),%rdi
  4f:   48 b9 00 00 00 00 00    movabs $0x0,%rcx
  56:   00 00 00
                        51: R_X86_64_GOTOFF64   memcpy
  59:   48 8d 04 08             lea    (%rax,%rcx,1),%rax
  5d:   ff d0                   callq  *%rax
  5f:   8b 45 fc                mov    -0x4(%rbp),%eax
  62:   c9                      leaveq
  63:   c3                      retq