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ARM: Resolve thumb_bl fixup in same MCFragment. 

In Thumb1 mode, bl instruction might be selected for branches between
basic blocks in the function if the offset is greater than 2KB.
However, this might cause SEGV because the destination symbol
is not marked as thumb function and the execution mode will be reset
to ARM mode.

Since we are sure that these symbols are in the same data fragment, we
can simply resolve these local symbols, and don't emit any relocation
information for this bl instruction.

llvm-svn: 200842
This commit is contained in:
Logan Chien 2014-02-05 14:15:16 +00:00
parent 99c9d6a0f6
commit d5c48aa3d3
2 changed files with 34 additions and 1 deletions
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9
llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp
View File

@ -565,11 +565,18 @@ void ARMAsmBackend::processFixupValue(const MCAssembler &Asm,
Value |= 1;
}
}
// For Thumb1 BL instruction, it is possible to be a long jump between
// the basic blocks of the same function. Thus, we would like to resolve
// the offset when the destination has the same MCFragment.
if (A && (unsigned)Fixup.getKind() == ARM::fixup_arm_thumb_bl) {
const MCSymbol &Sym = A->getSymbol().AliasedSymbol();
MCSymbolData &SymData = Asm.getSymbolData(Sym);
IsResolved = (SymData.getFragment() == DF);
}
// We must always generate a relocation for BL/BLX instructions if we have
// a symbol to reference, as the linker relies on knowing the destination
// symbol's thumb-ness to get interworking right.
if (A && ((unsigned)Fixup.getKind() == ARM::fixup_arm_thumb_blx ||
(unsigned)Fixup.getKind() == ARM::fixup_arm_thumb_bl ||
(unsigned)Fixup.getKind() == ARM::fixup_arm_blx ||
(unsigned)Fixup.getKind() == ARM::fixup_arm_uncondbl ||
(unsigned)Fixup.getKind() == ARM::fixup_arm_condbl))

26
llvm/test/MC/ARM/thumb-far-jump.s Normal file
View File

@ -0,0 +1,26 @@
@ RUN: llvm-mc < %s -triple thumbv5-linux-gnueabi -filetype=obj -o - \
@ RUN: | llvm-readobj -r | FileCheck %s
.syntax unified
.text
.align 2
.globl main
.type main,%function
.thumb_func
main:
bl end
.space 8192
end:
bl main2
bx lr
.text
.align 2
.globl main2
.type main2,%function
.thumb_func
main2:
bx lr
@ CHECK-NOT: 0x0 R_ARM_THM_CALL end 0x0
@ CHECK: 0x2004 R_ARM_THM_CALL main2 0x0