[llvm-dev] Quick question: How to BuildMI mov64mi32 arbitrary MMB address to memory

[K Jelesnianski via llvm-dev]

Dear All,

I am working on a x86 backend machineFunction pass, where I am trying to
save the hard coded address of an arbitrary machine basic block to memory
in ASM. I know the assembly needed for this but am lost at how to construct
the BuildMI().

Note that these machine basic blocks are not entry's to a function. but in
the middle of the function. so using addGlobalAddress or addExternalSymbol
are no use to me and am trying to avoid having to make a separate jump
table section. Is a jump table section with symbols associated with these
new basic blocks the only option?

In x86 assembly this would look something like:

MOVQ    0x40044540, 0x8(%rsp)     # Store address of trampoline basic block
to stack


The BuildMI looks like:

BuildMI(MBB, MBIt, DL, TII->get(X86::MOV64mi32))
.addImm(0x1) // Scale
.addReg(X86::RSP) // Base
.addImm(0x8) // Disp
.addMBB(my_target_mbb); // Source


So far I have looked into the BuildMI API of LLVM and the only one that
looks relevant is addMBB. While my LLVM pass compiles, my linker complains
(and note that I am compiling with -fPIC):

1)

/usr/bin/ld: /tmp/foo-d523b6.o: Unknown temporary symbol

or 2)

/usr/bin/ld: /tmp/foo-d523b6.o: relocation R_X86_64_32S against `.text' can
not be used when making a shared object; recompile with -fPIC
/usr/bin/ld: final link failed: Nonrepresentable section on output


Any suggestions? Much appreciated for taking a look!


Sincerely,


K Jelesnianski
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