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H.J. Lu bd7ab16b45 x86-64: Generate branch with PLT32 relocation

Since there is no need to prepare for PLT branch on x86-64, generate
R_X86_64_PLT32, instead of R_X86_64_PC32, if possible, which can be
used as a marker for 32-bit PC-relative branches.

To compile Linux kernel, this patch:

From: "H.J. Lu" <hjl.tools@gmail.com>
Subject: [PATCH] x86: Treat R_X86_64_PLT32 as R_X86_64_PC32

On i386, there are 2 types of PLTs, PIC and non-PIC.  PIE and shared
objects must use PIC PLT.  To use PIC PLT, you need to load
_GLOBAL_OFFSET_TABLE_ into EBX first.  There is no need for that on
x86-64 since x86-64 uses PC-relative PLT.

On x86-64, for 32-bit PC-relative branches, we can generate PLT32
relocation, instead of PC32 relocation, which can also be used as
a marker for 32-bit PC-relative branches.  Linker can always reduce
PLT32 relocation to PC32 if function is defined locally.   Local
functions should use PC32 relocation.  As far as Linux kernel is
concerned, R_X86_64_PLT32 can be treated the same as R_X86_64_PC32
since Linux kernel doesn't use PLT.

is needed.  It is available on hjl/plt32/master branch at

https://github.com/hjl-tools/linux

bfd/

	PR gas/22791
	* elf64-x86-64.c (is_32bit_relative_branch): Removed.
	(elf_x86_64_relocate_section): Check PIC relocations in PIE.
	Remove is_32bit_relative_branch usage.  Disallow PC32 reloc
	against protected function in shared object.

gas/

	PR gas/22791
	* config/tc-i386.c (need_plt32_p): New function.
	(output_jump): Generate BFD_RELOC_X86_64_PLT32 if possible.
	(md_estimate_size_before_relax): Likewise.
	* testsuite/gas/i386/reloc64.d: Updated.
	* testsuite/gas/i386/x86-64-jump.d: Likewise.
	* testsuite/gas/i386/x86-64-mpx-branch-1.d: Likewise.
	* testsuite/gas/i386/x86-64-mpx-branch-2.d: Likewise.
	* testsuite/gas/i386/x86-64-relax-2.d: Likewise.
	* testsuite/gas/i386/x86-64-relax-3.d: Likewise.
	* testsuite/gas/i386/ilp32/reloc64.d: Likewise.
	* testsuite/gas/i386/ilp32/x86-64-branch.d: Likewise.

ld/

	PR gas/22791
	* testsuite/ld-x86-64/mpx1c.rd: Updated.
	* testsuite/ld-x86-64/pr22791-1.err: New file.
	* testsuite/ld-x86-64/pr22791-1a.c: Likewise.
	* testsuite/ld-x86-64/pr22791-1b.s: Likewise.
	* testsuite/ld-x86-64/pr22791-2.rd: Likewise.
	* testsuite/ld-x86-64/pr22791-2a.s: Likewise.
	* testsuite/ld-x86-64/pr22791-2b.c: Likewise.
	* testsuite/ld-x86-64/pr22791-2c.s: Likewise.
	* testsuite/ld-x86-64/x86-64.exp: Run PR ld/22791 tests.

2018-02-13 07:34:36 -08:00

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 	.text
 	.globl	main
 	.type	main, @function
 main:
 	movl	foo(%rip), %eax
 	.size	main, .-main