[Bug lto/69866] lto1: internal compiler error: in add_symbol_to_partition_1, at lto/lto-partition.c:158

cvs-commit at gcc dot gnu.org gcc-bugzilla@gcc.gnu.org
Sat Dec 5 18:30:17 GMT 2020


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69866

--- Comment #17 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Maciej W. Rozycki <macro@gcc.gnu.org>:

https://gcc.gnu.org/g:76a553587f3181605c57801c37b0d3e94ce3aca5

commit r11-5795-g76a553587f3181605c57801c37b0d3e94ce3aca5
Author: Maciej W. Rozycki <macro@linux-mips.org>
Date:   Sat Dec 5 18:26:27 2020 +0000

    VAX: Fix the LTO compiler downgrading code to non-PIC model

    Fix a testsuite failure:

    /tmp/ccL65Mmt.s: Assembler messages:
    /tmp/ccL65Mmt.s:36: Warning: Symbol n used as immediate operand in PIC
mode.
    FAIL: gcc.dg/lto/pr55660 c_lto_pr55660_0.o-c_lto_pr55660_1.o link, -O0
-flto -flto-partition=none -fuse-linker-plugin

    where non-PIC code is substituted by the LTO compiler at the link stage
    for what used to be PIC code in the original compilation.  This happens
    because in the de-facto VAX ELF psABI we rely on code being PIC for GOT
    support in dynamic executables and arrange that by having `-fPIC' passed
    to the compiler by default by means of a specs recipe.

    That is however canceled where the LTO wrapper is used, by an internal
    arrangement in the LTO compiler that clears the PIC flag whenever the
    `-flinker-output=exec' option has been used.  This has been deliberately
    introduced with commit 1ff9ed6fb282 ("re PR lto/67548 (LTO drops weak
    binding with "ld -r")")[1]:

    "In the log of PR67548 HJ actually pointed out that we do have API at
    linker plugin side which says what type of output is done.  This is cool
    because we can also use it to drop -fpic when building static binary.
    This is common in Firefox, where some objects are built with -fpic and
    linked to both binaries and libraries."

    with this code:

        case LTO_LINKER_OUTPUT_EXEC: /* Normal executable */
          flag_pic = 0;
          flag_pie = 0;
          flag_shlib = 0;
          break;

    Consequently code like:

    .L6:
            addl3 -8(%fp),$n,%r0
            pushl %r0
            calls $1,foo
            addl2 %r0,-12(%fp)
            incl -8(%fp)
    .L5:

    is produced by the LTO compiler, where a reference to `n' is used that
    is invalid in PIC code, because it uses the immediate addressing mode,
    denoted by the `$' prefix.

    For that not to happen we must never pass `-flinker-output=exec' to the
    LTO compiler unless non-PIC code has been explicitly requested.  Using
    `-flinker-output=dyn' except for relocatable output would seem the
    simplest approach, as it does not fiddle with any of the internal code
    model settings beyond what the command-line options have arranged and
    therefore lets them remain the same as with the original compilation,
    but it breaks as well causing PR lto/69866 to retrigger, as that code
    seems sensitive to `flag_shlib':

    lto1: internal compiler error: in add_symbol_to_partition_1, at
lto/lto-partition.c:152
    0x105be1cb add_symbol_to_partition_1
            .../gcc/lto/lto-partition.c:152
    0x105be443 add_symbol_to_partition_1
            .../gcc/lto/lto-partition.c:194
    0x105be80f add_symbol_to_partition
            .../gcc/lto/lto-partition.c:270
    0x105bee6f add_sorted_nodes
            .../gcc/lto/lto-partition.c:395
    0x105c0903 lto_balanced_map(int, int)
            .../gcc/lto/lto-partition.c:815
    0x105aa91f do_whole_program_analysis
            .../gcc/lto/lto.c:499
    0x105aac97 lto_main()
            .../gcc/lto/lto.c:637
    Please submit a full bug report,
    with preprocessed source if appropriate.
    Please include the complete backtrace with any bug report.
    See <https://gcc.gnu.org/bugs/> for instructions.
    lto-wrapper: fatal error: .../gcc/xgcc returned 1 exit status
    compilation terminated.
    .../usr/bin/vax-netbsdelf-ld: error: lto-wrapper failed
    collect2: error: ld returned 1 exit status
    compiler exited with status 1
    FAIL: gcc.dg/lto/pr69866 c_lto_pr69866_0.o-c_lto_pr69866_1.o link, -O0
-flto -fuse-linker-plugin -fno-fat-lto-objects  (internal compiler error)

    Substitute `-flinker-output=pie' for `-flinker-output=exec' in the specs
    then unless `-no-pie' has also been used, preserving the original intent
    of emitting PIC code by default for executables while keeping the linker
    arrangement unchanged.  The LTO compiler uses the `cc1' spec, so keep
    `cc1plus' unmodified.

    This makes code like:

    .L6:
            movab n,%r0
            addl2 -8(%fp),%r0
            pushl %r0
            calls $1,foo
            addl2 %r0,-12(%fp)
            incl -8(%fp)
    .L5:

    be produced instead corresponding to the fragment quoted above, which is
    valid PIC code as it uses the PC-relative addressing mode denoted by the
    absence of a prefix to `n' (which can be redirected to GOT as required,
    by changing the addressing mode to PC-relative indirect in the operand
    specifier).

    Ideally we would instead default to the PIE model for executables, but
    that triggers a BFD bug where for a change the LTO wrapper is not used:

    .../usr/bin/vax-netbsdelf-ld: /tmp/ccV2sWQt.ltrans0.ltrans.o: warning: GOT
addend of 3 to `n' does not match previous GOT addend of 0
    FAIL: gcc.dg/lto/pr55660 c_lto_pr55660_0.o-c_lto_pr55660_1.o link, -O2
-flto -flto-partition=1to1 -fno-use-linker-plugin

    which is due to assembly code like:

    main:
            .word 0
            subl2 $4,%sp
            movab n,%r0
            movab n+3,%r2
            clrl %r3
            movb $98,%r1
    .L4:

    and consequently object code like:

    00000000 <main>:
       0:   00 00           .word 0x0000 # Entry mask: < >
       2:   c2 04 5e        subl2 $0x4,sp
       5:   9e ef 00 00     movab b <main+0xb>,r0
       9:   00 00 50
                            7: R_VAX_GOT32  n
       c:   9e ef 00 00     movab 12 <main+0x12>,r2
      10:   00 00 52
                            e: R_VAX_GOT32  n+0x3
      13:   d4 53           clrf r3
      15:   90 8f 62 51     movb $0x62,r1

    being produced.  This would be problematic for external `n', because we
    do not support multiple GOT entries for the same symbol referred to with
    different offsets in a single link unit.  In this case however the LTO
    compiler correctly observes that `n' is defined by the executable and
    not preemptible and therefore no GOT entry will be made for it.

    Indeed a valid executable is produced:

    00010548 <main>:
       10548:       00 00           .word 0x0000 # Entry mask: < >
       1054a:       c2 04 5e        subl2 $0x4,sp
       1054d:       9e ef dd 14     movab 11a30 <n>,r0
       10551:       00 00 50
       10554:       9e ef d9 14     movab 11a33 <__bss_start>,r2
       10558:       00 00 52
       1055b:       d4 53           clrf r3
       1055d:       90 8f 62 51     movb $0x62,r1

    despite the warning, but it would be rather bad to have users annoyed
    with this message from BFD, however harmless, especially as it triggers
    outside LTO compilations as well.

    Therefore this change is the best we can do until binutils have been
    fixed.

    References:

    [1] Jan Hubicka, "Getting LTO incremental linking work",
        <https://gcc.gnu.org/ml/gcc-patches/2015-11/msg02986.html>

            gcc/
            * config/vax/elf.h (VAX_CC1_SPEC, VAX_CC1PLUS_SPEC): New macros.
            * config/vax/netbsd-elf.h (CC1_SPEC): Use VAX_CC1_SPEC rather
            than VAX_CC1_AND_CC1PLUS_SPEC.
            (CC1PLUS_SPEC): Use VAX_CC1PLUS_SPEC rather than
            VAX_CC1_AND_CC1PLUS_SPEC.


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