BaseTools/GenFw: Add X64 GOTPCREL Support to GenFw

Adds support for the following X64 ELF relocations to GenFw
  R_X86_64_GOTPCREL
  R_X86_64_GOTPCRELX
  R_X86_64_REX_GOTPCRELX

Background:
The GCC49 and GCC5 toolchains use the small pie model for X64.  In the
small pie model, gcc emits a GOTPCREL relocation whenever C code takes
the address of a global function.  The emission of GOTPCREL is mitigated
by several factors
1. In GCC49, all global symbols are declared hidden thereby eliminating
the emission of GOTPCREL.
2. In GCC5, LTO is used.  In LTO, the complier first creates intermediate
representation (IR) files.  During the static link stage, the LTO compiler
combines all IR files as a single compilation unit, using linker symbol
assistance to generate code.  Any global symbols defined in the IR that
are not referenced from outside the IR are converted to local symbols -
thereby eliminating the emission of GOTPCREL for them.
3. The linker (binutils ld) further transforms any GOTPCREL used with
the movq opcode to a direct rip-relative relocation used with the leaq
opcode.  This linker optimization can be disabled with the option
-Wl,--no-relax.  Furthermore, gcc is able to emit GOTPCREL with other
opcodes
  - pushq opcode for passing arguments to functions.
  - addq/subq opcodes for pointer arithmetic.
These other opcode uses are not transformed by the linker.
Ultimately, in GCC5 there are some emissions of GOTPCREL that survive
all these mitigations - if C code takes the address of a global function
defined in assembly code - and performs pointer arithmetic on the
address - then the GOTPCREL remains in the final linker product.
A GOTPCREL relocation today causes the build to stop since GenFw does
not handle them.  It is possible to eliminate any remaining GOTPCREL
emissions by manually declaring the global symbols causing them to have
hidden visibility.  This patch is offered instead to allow GenFw to
handle any residual GOTPCREL.

Cc: Shi Steven <steven.shi@intel.com>
Cc: Yonghong Zhu <yonghong.zhu@intel.com>
Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Zenith432 <zenith432@users.sourceforge.net>
Reviewed-by: Liming Gao <liming.gao@intel.com>
This commit is contained in:
Zenith432
2018-07-09 20:58:15 +08:00
committed by Liming Gao
parent 99fd30431d
commit ecbaa856da
2 changed files with 219 additions and 1 deletions

View File

@@ -1052,6 +1052,23 @@ typedef struct {
#define R_X86_64_DTPOFF32 21 /* Offset in TLS block */
#define R_X86_64_GOTTPOFF 22 /* PC relative offset to IE GOT entry */
#define R_X86_64_TPOFF32 23 /* Offset in static TLS block */
#define R_X86_64_PC64 24 /* PC relative 64 bit */
#define R_X86_64_GOTOFF64 25 /* 64 bit offset to GOT */
#define R_X86_64_GOTPC3 26 /* 32 bit signed pc relative offset to GOT */
#define R_X86_64_GOT64 27 /* 64-bit GOT entry offset */
#define R_X86_64_GOTPCREL64 28 /* 64-bit PC relative offset to GOT entry */
#define R_X86_64_GOTPC64 29 /* 64-bit PC relative offset to GOT */
#define R_X86_64_GOTPLT64 30 /* like GOT64, says PLT entry needed */
#define R_X86_64_PLTOFF64 31 /* 64-bit GOT relative offset to PLT entry */
#define R_X86_64_SIZE32 32 /* Size of symbol plus 32-bit addend */
#define R_X86_64_SIZE64 33 /* Size of symbol plus 64-bit addend */
#define R_X86_64_GOTPC32_TLSDESC 34 /* GOT offset for TLS descriptor. */
#define R_X86_64_TLSDESC_CALL 35 /* Marker for call through TLS descriptor. */
#define R_X86_64_TLSDESC 36 /* TLS descriptor. */
#define R_X86_64_IRELATIVE 37 /* Adjust indirectly by program base */
#define R_X86_64_RELATIVE64 38 /* 64-bit adjust by program base */
#define R_X86_64_GOTPCRELX 41 /* Load from 32 bit signed pc relative offset to GOT entry without REX prefix, relaxable. */
#define R_X86_64_REX_GOTPCRELX 42 /* Load from 32 bit signed pc relative offset to GOT entry with REX prefix, relaxable. */
#endif /* !_SYS_ELF_COMMON_H_ */