[Bug 1767223] Re: multilib selects wrong start files

[Thomas Preud'homme]

This bug is due to newlib built against an older version of gcc-arm-
none-eabi. It will be fixed by rebuilding newlib using the same source.

** Package changed: gcc-arm-none-eabi (Ubuntu) => newlib (Ubuntu)

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Title:
  multilib selects wrong start files

Status in newlib package in Ubuntu:
  Confirmed

Bug description:
  The multilib setup is not working in the bionic version of gcc-arm-
  none-eabi (gcc v6.3.1). For example, if I build a project with
  "-mcpu=cortex-m4" or "-march=armv7e-m" and link with:

  arm-none-eabi-gcc -o someoutput.elf  object1.o object2.o -mthumb -Wl
  ,--gc-sections -ffast-math -march=armv7-m -Tlinker_script.ld

  I get as output:

  /usr/lib/gcc/arm-none-eabi/6.3.1/../../../arm-none-eabi/bin/ld: error: /usr/lib/gcc/arm-none-eabi/6.3.1/../../../arm-none-eabi/lib/crt0.o: Conflicting CPU architectures 13/1
  /usr/lib/gcc/arm-none-eabi/6.3.1/../../../arm-none-eabi/bin/ld: failed to merge target specific data of file /usr/lib/gcc/arm-none-eabi/6.3.1/../../../arm-none-eabi/lib/crt0.o

  arm-none-eabi-readelf -A on any of my object files produces:

  Attribute Section: aeabi
  File Attributes
    Tag_CPU_name: "Cortex-M4"
    Tag_CPU_arch: v7E-M
    Tag_CPU_arch_profile: Microcontroller
    Tag_THUMB_ISA_use: Thumb-2
    Tag_ABI_PCS_wchar_t: 4
    Tag_ABI_FP_number_model: Finite
    Tag_ABI_align_needed: 8-byte
    Tag_ABI_align_preserved: 8-byte, except leaf SP
    Tag_ABI_enum_size: small
    Tag_ABI_optimization_goals: Prefer Speed
    Tag_CPU_unaligned_access: v6

  But "arm-none-eabi-readelf -A /usr/lib/gcc/arm-none-eabi/6.3.1
  /../../../arm-none-eabi/lib/crt0.o" gives

  Attribute Section: aeabi
  File Attributes
    Tag_CPU_arch: v4
    Tag_ARM_ISA_use: Yes

  If I define "void _init(void){}" and use -nostartfiles, compilation
  finishes but the resulting binary does not work. I have not examined
  the output file but it appears that it has somehow linked to code
  containing ARM as well as thumb code:

  # readelf -A someoutput.elf
  Attribute Section: aeabi
  File Attributes
    Tag_CPU_name: "Cortex-M4"
    Tag_CPU_arch: v7E-M
    Tag_CPU_arch_profile: Microcontroller
    Tag_ARM_ISA_use: Yes
    Tag_THUMB_ISA_use: Thumb-2
    Tag_ABI_PCS_wchar_t: 4
    Tag_ABI_FP_denormal: Needed
    Tag_ABI_FP_exceptions: Needed
    Tag_ABI_FP_number_model: IEEE 754
    Tag_ABI_align_needed: 8-byte
    Tag_ABI_align_preserved: 8-byte, except leaf SP
    Tag_ABI_enum_size: small
    Tag_ABI_optimization_goals: Prefer Speed
    Tag_CPU_unaligned_access: v6

  I can work around the problem by manually specifying compatible
  versions of libc and libgcc with -nostdlib:

  -nostdlib /usr/lib/arm-none-eabi/newlib/thumb/libc.a /usr/lib/gcc/arm-
  none-eabi/6.3.1/thumb/v7e-m/libgcc.a

  This produces a working binary. However, there is still something
  wrong because readelf -A still includes "Tag_ARM_ISA_use: Yes":

  Attribute Section: aeabi
  File Attributes
    Tag_CPU_name: "Cortex-M4"
    Tag_CPU_arch: v7E-M
    Tag_CPU_arch_profile: Microcontroller
    Tag_ARM_ISA_use: Yes
    Tag_THUMB_ISA_use: Thumb-2
    Tag_ABI_PCS_wchar_t: 4
    Tag_ABI_FP_denormal: Needed
    Tag_ABI_FP_exceptions: Needed
    Tag_ABI_FP_number_model: IEEE 754
    Tag_ABI_align_needed: 8-byte
    Tag_ABI_align_preserved: 8-byte, except leaf SP
    Tag_ABI_enum_size: small
    Tag_ABI_optimization_goals: Prefer Speed
    Tag_CPU_unaligned_access: v6

  Previously, using xenial and gcc v4, readelf gives the following output on the output binary:
  Attribute Section: aeabi
  File Attributes
    Tag_CPU_name: "7E-M"
    Tag_CPU_arch: v7E-M
    Tag_CPU_arch_profile: Microcontroller
    Tag_THUMB_ISA_use: Thumb-2
    Tag_ABI_PCS_wchar_t: 4
    Tag_ABI_FP_denormal: Needed
    Tag_ABI_FP_exceptions: Needed
    Tag_ABI_FP_number_model: IEEE 754
    Tag_ABI_align_needed: 8-byte
    Tag_ABI_enum_size: small
    Tag_ABI_optimization_goals: Prefer Speed
    Tag_CPU_unaligned_access: v6

  (Also, what happened to gdb-arm-none-eabi?)

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