[Bug ld/20608] New: Relocation truncated to fit: R_ARM_THM_JUMP24 for relocation to PLT entry.

[peter.smith at linaro dot org]

https://sourceware.org/bugzilla/show_bug.cgi?id=20608

            Bug ID: 20608
           Summary: Relocation truncated to fit: R_ARM_THM_JUMP24 for
                    relocation to PLT entry.
           Product: binutils
           Version: 2.25
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: peter.smith at linaro dot org
  Target Milestone: ---

I'm raising this as a result of an investigation of a buildbot failure found
whilst trying to link libclang.so https://llvm.org/bugs/show_bug.cgi?id=27813 

The exact error the buildbot was intermittently seeing was:
DebugHandlerBase.cpp:(.text._ZN4llvm8DenseMapIPKNS_12MachineInstrEPNS_8MCSymbolENS_12DenseMapInfoIS3_EENS_6detail12DenseMapPairIS3_S5_EEE4growEj[_ZN4llvm8DenseMapIPKNS_12MachineInstrEPNS_8MCSymbolENS_12DenseMapInfoIS3_EENS_6detail12DenseMapPairIS3_S5_EEE4growEj]+0x18a):
relocation truncated to fit: R_ARM_THM_JUMP24 against symbol `operator
delete(void*)@@GLIBCXX_3.4' defined in .text section in
/usr/lib/gcc/arm-linux-gnueabihf/4.8/libstdc++.so
collect2: error: ld returned 1 exit status

This sounds similar to https://sourceware.org/bugzilla/show_bug.cgi?id=12965
but that has been fixed for some time.

The failure on the buildbot is with binutils 2.24, but I've also reproducible
on 2.25 (the latest ARM build that I have available). 

I don't have access to the original objects from the clang build, but I've made
a reproducer for what I think the problem is.

It needs a shared object or some other means of generating a PLT entry for a
symbol. The b.w instruction with the R_ARM_THUMB_JUMP24 relocation needs to be
in range of the ARM part of the PLT entry, but not in range of the inline Thumb
state change that the b.w needs to target. If the instruction is closer the b.w
can reach the inline state change, it the instruction is further away than the
ARM part then a stub is generated.

The test case is highly sensitive to the distance between the .plt entry and
the b.w. I'm using the (Linaro GCC 5.3-2016.02) 5.3.1 20160113 release.

-- shared.c -- 
int func(void) {
    return 0;
}
arm-linux-gnueabihf-gcc shared.c --shared -fPIC -o shared.so

-- space.s --
 .text
 .syntax unified
 .thumb
 .global sp
 .type sp,%function
 .space (1024 * 1024 * 16) - 0x108
 .space 2 // Will fail values 2 or 4
 .global func2
 .type func2,%function
func2:
 b.w func

arm-linux-gnueabihf-gcc space.s -fPIC --shared  -O2 -o test.axf shared.so
-mthumb
(.text+0xfffefa): relocation truncated to fit: R_ARM_THM_JUMP24 against symbol
`func' defined in .text section in shared.so
collect2: error: ld returned 1 exit status

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