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[ELF] Define _GLOBAL_OFFSET_TABLE_ symbol relative to .got

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On many architectures gcc and clang will recognize _GLOBAL_OFFSET_TABLE_ - .
and produce a relocation that can be processed without needing to know the
value of _GLOBAL_OFFSET_TABLE_. This is not always the case; for example ARM
gcc produces R_ARM_BASE_PREL but clang produces the more general
R_ARM_REL32 to _GLOBAL_OFFSET_TABLE_. To evaluate this relocation
correctly _GLOBAL_OFFSET_TABLE_ must be defined to be the either the base of
the GOT or end of the GOT dependent on architecture..

If/when llvm-mc is changed to recognize _GLOBAL_OFFSET_TABLE_ - . this
change will not be necessary for new objects. However there may still be
old objects and versions of clang.

Differential Revision: https://reviews.llvm.org/D34355

llvm-svn: 306282
This commit is contained in:
Peter Smith
2017-06-26 10:22:17 +00:00
parent 1158fe9715
commit 113a59e7db
13 changed files with 197 additions and 27 deletions
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2
lld/ELF/Relocations.cpp
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@@ -361,7 +361,7 @@ static bool isStaticLinkTimeConstant(RelExpr E, uint32_t Type,
// These expressions always compute a constant
if (isRelExprOneOf<R_SIZE, R_GOT_FROM_END, R_GOT_OFF, R_MIPS_GOT_LOCAL_PAGE,
R_MIPS_GOT_OFF, R_MIPS_GOT_OFF32, R_MIPS_GOT_GP_PC,
R_MIPS_TLSGD, R_GOT_PAGE_PC, R_GOT_PC,
R_MIPS_TLSGD, R_GOT_PAGE_PC, R_GOT_PC, R_GOTONLY_PC,
R_GOTONLY_PC_FROM_END, R_PLT_PC, R_TLSGD_PC, R_TLSGD,
R_PPC_PLT_OPD, R_TLSDESC_CALL, R_TLSDESC_PAGE, R_HINT>(E))
return true;