[llvm-bugs] [Bug 34768] New: Fix aeabi_cfcmp.S and aeabi_cdcmp.S for Thumb2 MachO targets

via llvm-bugs llvm-bugs at lists.llvm.org
Thu Sep 28 09:16:04 PDT 2017


            Bug ID: 34768
           Summary: Fix aeabi_cfcmp.S and aeabi_cdcmp.S for Thumb2 MachO
           Product: compiler-rt
           Version: unspecified
          Hardware: PC
                OS: All
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: compiler-rt
          Assignee: unassignedbugs at nondot.org
          Reporter: manojgupta at google.com
                CC: llvm-bugs at lists.llvm.org
            Blocks: 34715

Peter Smith <Peter.Smith at arm.com> wrote:
To hazard a guess at what the problem is when compiling with Thumb2 using

The bne __aeabi_cdcmple is a Thumb2 conditional branch to a symbol defined in a
separate section (thanks to the subsections_via_symbols). In ELF there is a
relocation directive R_ARM_THM_JMP19 I think. Whereas I don't think that there
is one defined for Mach-O.

Personally if these symbols are in different sections it isn't ideal to use a
conditional branch in Thumb2 even when a relocation exists as the range is only
+- 1 MiB. I suggest when compiling in Thumb2 we separate the comparison and do
an unconditional branch.

This is blocking form landing fix for PR 34715.

Referenced Bugs:

[Bug 34715] compiler-rt builtins are broken for thumb
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