[Bug gold/20523] New: powerpc64le kernel build with additional cross section references fails

[npiggin at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=20523

            Bug ID: 20523
           Summary: powerpc64le kernel build with additional cross section
                    references fails
           Product: binutils
           Version: 2.28 (HEAD)
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: gold
          Assignee: ccoutant at gmail dot com
          Reporter: npiggin at gmail dot com
                CC: ian at airs dot com
  Target Milestone: ---

Making a small change to the way Linux is linked, moving some text to a
different output section:

diff --git a/arch/powerpc/kernel/vmlinux.lds.S
b/arch/powerpc/kernel/vmlinux.lds.S
index c157b8d..03178df 100644
--- a/arch/powerpc/kernel/vmlinux.lds.S
+++ b/arch/powerpc/kernel/vmlinux.lds.S
@@ -49,8 +49,7 @@ SECTIONS
                ALIGN_FUNCTION();
                HEAD_TEXT
                _text = .;
-               /* careful! __ftr_alt_* sections need to be close to .text */
-               *(.text .text.* .fixup __ftr_alt_* .ref.text)
+               *(.text .text.* .fixup .ref.text)
                SCHED_TEXT
                LOCK_TEXT
                KPROBES_TEXT
@@ -63,7 +62,6 @@ SECTIONS
                *(.got2)
                __got2_end = .;
 #endif /* CONFIG_PPC32 */
-
        } :kernel

        . = ALIGN(PAGE_SIZE);
@@ -92,6 +90,10 @@ SECTIONS
        __init_begin = .;
        INIT_TEXT_SECTION(PAGE_SIZE) :kernel

+       .__ftr_alternates.text : AT(ADDR(.__ftr_alternates.text) - LOAD_OFFSET)
{
+               *(__ftr_alt*);
+       }
+
        /* .exit.text is discarded at runtime, not link time,
         * to deal with references from __bug_table
         */

Results in gold failing to link the kernel

../binutils/binutils-gdb/gold/ld-new: stub group size is too large; retrying
with 22020096
../binutils/binutils-gdb/gold/ld-new: stub group size is too large; retrying
with 16515072
arch/powerpc/kernel/head_64.o(__ftr_alt_97+0x40): error: relocation overflow
try relinking with a smaller --stub-group-size
arch/powerpc/kernel/head_64.o(__ftr_alt_97+0x7c): error: relocation overflow
try relinking with a smaller --stub-group-size
arch/powerpc/kernel/head_64.o(__ftr_alt_97+0xbc): error: relocation overflow
try relinking with a smaller --stub-group-size
arch/powerpc/lib/built-in.o(__ftr_alt_97+0x8): error: relocation overflow
try relinking with a smaller --stub-group-size

Where some of the instructions in __ftr_alt* have conditional branches back to
.text that will be out of range and require a trampoline:

40:   00 00 82 41     beq     40 <__ftr_alt_97+0x40>


Linking with ld.bfd succeeds. The "careful!" comment in the linker script is
related to these relocations but should not cause this failure (runtime code
patching in the kernel cannot cope with __ftr_alt patch code using branch
trampolines).

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