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Re: [RFC, PATCH, MIPS] Add support for O32 FPXX and program header based ABI information


On 2 May 2014 09:18, Andrew Pinski <pinskia@gmail.com> wrote:
> On Fri, May 2, 2014 at 1:11 AM, Will Newton <will.newton@linaro.org> wrote:
>> On 1 May 2014 22:48, Matthew Fortune <Matthew.Fortune@imgtec.com> wrote:
>>
>> Hi Matthew,
>>
>>> Attached is an initial patch to support the O32 FPXX ABI as described here:
>>>
>>> https://dmz-portal.mips.com/wiki/MIPS_O32_ABI_-_FR0_and_FR1_Interlinking
>>>
>>> This has been discussed at length on GCC and binutils mailing lists and has
>>> approval in principle from MIPS kernel developers at Imagination.
>>>
>>> The proposed ABI was initially reviewed/discussed on the GCC mailing
>>> list starting from the following posts:
>>>
>>> http://gcc.gnu.org/ml/gcc/2014-02/msg00415.html
>>> http://gcc.gnu.org/ml/gcc/2014-03/msg00191.html
>>>
>>> Then refined up to the current spec on binutils with the latest patch here.
>>>
>>> http://sourceware.org/ml/binutils/2014-05/msg00002.html
>>>
>>> To implement this feature I need an additional hook during the loading of
>>> objects to allow a target to inspect the headers (and segments they point
>>> at) to decide if the library is compatible or not. I have made a simple
>>> attempt at this but am quite willing to adapt to better suggestions.
>>>
>>> The current implementation tracks the individual ABI requirements of each
>>> loaded module and caches the information so that program headers are only
>>> inspected once per library. This provides the greatest control but could
>>> theoretically be reduced to simply recording the current state of a process
>>> with a single global value. Since this is an implementation detail this too
>>> is open to debate.
>>>
>>> I think I need to do something relating to caching objects but quite
>>> honestly have no idea on that front. I've used the work from maciej on
>>> NAN2008 handling as a reference for the areas I need to modify for this
>>> implementation but haven't figured that part out.
>>>
>>> I'm also not entirely sure how to go about writing tests for this in glibc
>>> but will look through the test framework to see if anything is possible. I
>>> have attached a basic test that allows all combinations of O32 FP32,
>>> O32 FPXX and O32 FP64 modules to be loaded and tested manually. I have a
>>> hacked patch for qemu to read the new PT_MIPS_ABIFLAGS which I have been
>>> using to test this; I can make that available but will need to rebase to
>>> a public qemu release.
>>>
>>> The corresponding patch to implement O32 FPXX in GCC will hopefully be
>>> posted tomorrow.
>>>
>>> Regards,
>>> Matthew
>>>
>>> 2014-05-01  Matthew Fortune  <matthew.fortune@imgtec.com>
>>>
>>>     * config.h/in (HAVE_MIPS_MODULE_FPXX_DIRECTIVE): Undefine.
>>>     * elf/dl-load.c (open_verify): Add optional hook for phdr check.
>>>     * elf/elf.h (PT_MIPS_ABIFLAGS): Define.
>>>     (Elf_ABIFlags_v0): New structure.
>>>     (AFL_REG_NONE, AFL_REG_32, AFL_REG_64, AFL_REG_128): Define.
>>>     (AFL_ASE_DSP, AFL_ASE_DSP64, AFL_ASE_DSPR2, AFL_ASE_EVA): Likewise.
>>>     (AFL_ASE_MCU, AFL_ASE_MDMX, AFL_ASE_MIPS3D, AFL_ASE_MT): Likewise.
>>>     (AFL_ASE_SMARTMIPS, AFL_ASE_VIRT, AFL_ASE_VIRT64, AFL_ASE_MSA): Likewise.
>>>     (AFL_ASE_MSA64, AFL_ASE_MIPS16, AFL_ASE_MICROMIPS): Likewise.
>>>     (AFL_EXT_XLR, AFL_EXT_OCTEON2, AFL_EXT_OCTEONP): Likewise.
>>>     (AFL_EXT_LOONGSON_3A, AFL_EXT_OCTEON, AFL_EXT_5900): Likewise.
>>>     (AFL_EXT_4010, AFL_EXT_4100, AFL_EXT_3900, AFL_EXT_10000): Likewise.
>>>     (AFL_EXT_SB1, AFL_EXT_4111, AFL_EXT_4120, AFL_EXT_5400): Likewise.
>>>     (AFL_EXT_5500, AFL_EXT_LOONGSON_2E, AFL_EXT_LOONGSON_2F): Likewise.
>>>     (Val_GNU_MIPS_ABI_FP_ANY, Val_GNU_MIPS_ABI_FP_DOUBLE): New enum values.
>>>     (Val_GNU_MIPS_ABI_FP_SINGLE, Val_GNU_MIPS_ABI_FP_SOFT): Likewise.
>>>     (Val_GNU_MIPS_ABI_FP_OLD_64, Val_GNU_MIPS_ABI_FP_XX): Likewise.
>>>     (Val_GNU_MIPS_ABI_FP_64): Likewise.
>>>     * sysdeps/mips/bits/hwcap.h: New file.
>>>     * sysdeps/mips/bits/linkmap.h (struct link_map_machine): Add fpmode
>>>     field.
>>>     * sysdeps/mips/dl-machine.h: Include unistd.h.
>>>     (ELF_MACHINE_NEEDS_PHDR_CHECK): Define.
>>>     (find_mips_abiflags): New static inline function.
>>>     (switch_frmode_to): New static no-inline function.
>>>     (mips_fp_abi, elf_machine_phdr_check): new static function.
>>>     * sysdeps/mips/dl-procinfo.c (_dl_mips_cap_flags): Declare.
>>>     * sysdeps/mips/dl-procinfo.h (_DL_HWCAP_COUNT): Define.
>>>     (HWCAP_IMPORTANT): Define.
>>>     (_dl_procinfo): New static inline function.
>>>     (_dl_hwcap_string, _dl_string_hwcap): Likewise.
>>>     * sysdeps/unix/mips/sysdep.h (_SYS_AUXV_H): Define.
>>>     (bits/hwcap.h): Include.
>>>     * sysdeps/unix/sysv/linux/mips/configure.ac: Check for .module fpxx
>>>     (HAVE_MIPS_MODULE_FPXX_DIRECTIVE): Define.
>>>     * sysdeps/unix/sysv/linux/mips/configure: Regenerate.
>>>     * sysdeps/unix/sysv/linux/mips/getcontext.S
>>>     (HAVE_MIPS_MODULE_FPXX_DIRECTIVE): Use.
>>>     * sysdeps/unix/sysv/linux/mips/setcontext.S: Likewise.
>>>     * sysdeps/unix/sysv/linux/mips/swapcontext.S: Likewise.
>>> ---
>>>  config.h.in                                |    6 +-
>>>  elf/dl-load.c                              |    7 +
>>>  elf/elf.h                                  |   97 ++++++++++++-
>>>  sysdeps/mips/bits/hwcap.h                  |   23 +++
>>>  sysdeps/mips/bits/linkmap.h                |    1 +
>>>  sysdeps/mips/dl-machine.h                  |  218 ++++++++++++++++++++++++++++
>>>  sysdeps/mips/dl-procinfo.c                 |   16 ++
>>>  sysdeps/mips/dl-procinfo.h                 |   50 +++++-
>>>  sysdeps/unix/mips/sysdep.h                 |    3 +
>>>  sysdeps/unix/sysv/linux/mips/configure     |   27 ++++
>>>  sysdeps/unix/sysv/linux/mips/configure.ac  |   15 ++
>>>  sysdeps/unix/sysv/linux/mips/getcontext.S  |    4 +
>>>  sysdeps/unix/sysv/linux/mips/setcontext.S  |    4 +
>>>  sysdeps/unix/sysv/linux/mips/swapcontext.S |    4 +
>>>  14 files changed, 462 insertions(+), 13 deletions(-)
>>>  create mode 100644 sysdeps/mips/bits/hwcap.h
>>>
>>> diff --git a/config.h.in b/config.h.in
>>> index 40797e7..05da98a 100644
>>> --- a/config.h.in
>>> +++ b/config.h.in
>>> @@ -241,8 +241,12 @@
>>>  /* The pt_chown binary is being built and used by grantpt.  */
>>>  #undef HAVE_PT_CHOWN
>>>
>>> -/* ports/sysdeps/mips/configure.in  */
>>> +/* sysdeps/mips/configure.in  */
>>>  /* Define if using the IEEE 754-2008 NaN encoding on the MIPS target.  */
>>>  #undef HAVE_MIPS_NAN2008
>>>
>>> +/* sysdeps/unix/sysv/linux/mips/configure.in  */
>>> +/* Define if the assembler supports the .module fp=xx directive.  */
>>> +#undef HAVE_MIPS_MODULE_FPXX_DIRECTIVE
>>> +
>>>  #endif
>>> diff --git a/elf/dl-load.c b/elf/dl-load.c
>>> index 6501ff2..43aacdc 100644
>>> --- a/elf/dl-load.c
>>> +++ b/elf/dl-load.c
>>> @@ -1866,6 +1866,13 @@ open_verify (const char *name, struct filebuf *fbp, struct link_map *loader,
>>>             }
>>>         }
>>>
>>> +#ifdef ELF_MACHINE_NEEDS_PHDR_CHECK
>>> +      if (!__builtin_expect (
>>> +            elf_machine_phdr_check (phdr, ehdr->e_phnum, fbp->buf, fbp->len,
>>> +                                    fd, loader), 1))
>>> +       goto close_and_out;
>>> +#endif
>>> +
>>>        /* Check .note.ABI-tag if present.  */
>>>        for (ph = phdr; ph < &phdr[ehdr->e_phnum]; ++ph)
>>>         if (ph->p_type == PT_NOTE && ph->p_filesz >= 32 && ph->p_align >= 4)
>>> diff --git a/elf/elf.h b/elf/elf.h
>>> index 40e87b2..dccdee9 100644
>>> --- a/elf/elf.h
>>> +++ b/elf/elf.h
>>> @@ -1631,9 +1631,10 @@ typedef struct
>>>
>>>  /* Legal values for p_type field of Elf32_Phdr.  */
>>>
>>> -#define PT_MIPS_REGINFO        0x70000000      /* Register usage information */
>>> -#define PT_MIPS_RTPROC  0x70000001     /* Runtime procedure table. */
>>> -#define PT_MIPS_OPTIONS 0x70000002
>>> +#define PT_MIPS_REGINFO          0x70000000    /* Register usage information. */
>>> +#define PT_MIPS_RTPROC   0x70000001    /* Runtime procedure table. */
>>> +#define PT_MIPS_OPTIONS          0x70000002
>>> +#define PT_MIPS_ABIFLAGS  0x70000003   /* FP mode requirement. */
>>>
>>>  /* Special program header types.  */
>>>
>>> @@ -1755,6 +1756,96 @@ typedef struct
>>>
>>>  typedef Elf32_Addr Elf32_Conflict;
>>>
>>> +typedef struct
>>> +{
>>> +  /* Version of flags structure.  */
>>> +  Elf32_Half version;
>>> +  /* The level of the ISA: 1-5, 32, 64.  */
>>> +  unsigned char isa_level;
>>> +  /* The revision of ISA: 0 for MIPS V and below, 1-n otherwise.  */
>>> +  unsigned char isa_rev;
>>> +  /* The size of general purpose registers.  */
>>> +  unsigned char gpr_size;
>>> +  /* The size of co-processor 1 registers.  */
>>> +  unsigned char cpr1_size;
>>> +  /* The size of co-processor 2 registers.  */
>>> +  unsigned char cpr2_size;
>>> +  /* The floating-point ABI.  */
>>> +  unsigned char fp_abi;
>>> +  /* Mask of processor-specific extensions.  */
>>> +  Elf32_Word isa_ext;
>>> +  /* Mask of ASEs used.  */
>>> +  Elf32_Word ases;
>>> +  /* Mask of general flags.  */
>>> +  Elf32_Word flags1;
>>> +  Elf32_Word flags2;
>>> +} Elf_ABIFlags_v0;
>>> +
>>> +/* Values for the register size bytes of an abi flags structure.  */
>>> +
>>> +#define AFL_REG_NONE         0x00       /* No registers.  */
>>> +#define AFL_REG_32           0x01       /* 32-bit registers.  */
>>> +#define AFL_REG_64           0x02       /* 64-bit registers.  */
>>> +#define AFL_REG_128          0x03       /* 128-bit registers.  */
>>> +
>>> +/* Masks for the ases word of an ABI flags structure.  */
>>> +
>>> +#define AFL_ASE_DSP          0x00000001 /* DSP ASE.  */
>>> +#define AFL_ASE_DSP64        0x00000002 /* DSP ASE (64-bit).  */
>>> +#define AFL_ASE_DSPR2        0x00000004 /* DSP R2 ASE.  */
>>> +#define AFL_ASE_EVA          0x00000008 /* Enhanced VA Scheme.  */
>>> +#define AFL_ASE_MCU          0x00000010 /* MCU (MicroController) ASE.  */
>>> +#define AFL_ASE_MDMX         0x00000020 /* MDMX ASE.  */
>>> +#define AFL_ASE_MIPS3D       0x00000040 /* MIPS-3D ASE.  */
>>> +#define AFL_ASE_MT           0x00000080 /* MT ASE.  */
>>> +#define AFL_ASE_SMARTMIPS     0x00000100 /* SmartMIPS ASE.  */
>>> +#define AFL_ASE_VIRT         0x00000200 /* VZ ASE.  */
>>> +#define AFL_ASE_VIRT64       0x00000400 /* VZ ASE (64-bit).  */
>>> +#define AFL_ASE_MSA          0x00000800 /* MSA ASE.  */
>>> +#define AFL_ASE_MSA64        0x00001000 /* MSA ASE (64-bit).  */
>>> +#define AFL_ASE_MIPS16       0x00002000 /* MIPS16 ASE.  */
>>> +#define AFL_ASE_MICROMIPS     0x00004000 /* MICROMIPS ASE.  */
>>> +#define AFL_ASE_XPA          0x00002000 /* XPA ASE.  */
>>> +
>>> +/* Masks for the isa_ext word of an ABI flags structure.  */
>>> +
>>> +#define AFL_EXT_XLR          0x00000020 /* RMI Xlr instruction.  */
>>> +#define AFL_EXT_OCTEON2              0x00000100 /* Cavium Networks Octeon2.  */
>>> +#define AFL_EXT_OCTEONP              0x00000200 /* Cavium Networks OcteonP.  */
>>> +#define AFL_EXT_LOONGSON_3A   0x00000400 /* Loongson 3A.  */
>>> +#define AFL_EXT_OCTEON       0x00000800 /* Cavium Networks Octeon.  */
>>> +#define AFL_EXT_5900         0x00004000 /* MIPS R5900 instruction.  */
>>> +#define AFL_EXT_4650         0x00010000 /* MIPS R4650 instruction.  */
>>> +#define AFL_EXT_4010         0x00020000 /* LSI R4010 instruction.  */
>>> +#define AFL_EXT_4100         0x00040000 /* NEC VR4100 instruction.  */
>>> +#define AFL_EXT_3900         0x00080000 /* Toshiba R3900 instruction.  */
>>> +#define AFL_EXT_10000        0x00100000 /* MIPS R10000 instruction.  */
>>> +#define AFL_EXT_SB1          0x00200000 /* Broadcom SB-1 instruction.  */
>>> +#define AFL_EXT_4111         0x00400000 /* NEC VR4111/VR4181 instruction.  */
>>> +#define AFL_EXT_4120         0x00800000 /* NEC VR4120 instruction.  */
>>> +#define AFL_EXT_5400         0x01000000 /* NEC VR5400 instruction.  */
>>> +#define AFL_EXT_5500         0x02000000 /* NEC VR5500 instruction.  */
>>> +#define AFL_EXT_LOONGSON_2E   0x40000000 /* ST Micro Loongson 2E.  */
>>> +#define AFL_EXT_LOONGSON_2F   0x80000000 /* ST Micro Loongson 2F.  */
>>> +
>>> +/* Object attribute values.  */
>>> +enum
>>> +{
>>> +  /* Not tagged or not using any ABIs affected by the differences.  */
>>> +  Val_GNU_MIPS_ABI_FP_ANY = 0,
>>> +  /* Using hard-float -mdouble-float.  */
>>> +  Val_GNU_MIPS_ABI_FP_DOUBLE = 1,
>>> +  /* Using hard-float -msingle-float.  */
>>> +  Val_GNU_MIPS_ABI_FP_SINGLE = 2,
>>> +  /* Using soft-float.  */
>>> +  Val_GNU_MIPS_ABI_FP_SOFT = 3,
>>> +  /* Using -mips32r2 -mfp64.  */
>>> +  Val_GNU_MIPS_ABI_FP_OLD_64 = 4,
>>> +  /* Using -mfpxx.  */
>>> +  Val_GNU_MIPS_ABI_FP_XX = 5,
>>> +  /* Using -mips32r2 -mfp64.  */
>>> +  Val_GNU_MIPS_ABI_FP_64 = 6
>>> +};
>>>
>>>  /* HPPA specific definitions.  */
>>>
>>> diff --git a/sysdeps/mips/bits/hwcap.h b/sysdeps/mips/bits/hwcap.h
>>> new file mode 100644
>>> index 0000000..96575d2
>>> --- /dev/null
>>> +++ b/sysdeps/mips/bits/hwcap.h
>>> @@ -0,0 +1,23 @@
>>> +/* Defines for bits in AT_HWCAP.
>>> +   Copyright (C) 2014 Free Software Foundation, Inc.
>>> +   This file is part of the GNU C Library.
>>> +
>>> +   The GNU C Library is free software; you can redistribute it and/or
>>> +   modify it under the terms of the GNU Lesser General Public
>>> +   License as published by the Free Software Foundation; either
>>> +   version 2.1 of the License, or (at your option) any later version.
>>> +
>>> +   The GNU C Library is distributed in the hope that it will be useful,
>>> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
>>> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>>> +   Lesser General Public License for more details.
>>> +
>>> +   You should have received a copy of the GNU Lesser General Public
>>> +   License along with the GNU C Library; if not, see
>>> +   <http://www.gnu.org/licenses/>.  */
>>> +
>>> +#ifndef _SYS_AUXV_H
>>> +# error "Never include <bits/hwcap.h> directly; use <sys/auxv.h> instead."
>>> +#endif
>>> +
>>> +#define HWCAP_MIPS_UFR 0x00000001
>>> diff --git a/sysdeps/mips/bits/linkmap.h b/sysdeps/mips/bits/linkmap.h
>>> index a6df782..dfbc3be 100644
>>> --- a/sysdeps/mips/bits/linkmap.h
>>> +++ b/sysdeps/mips/bits/linkmap.h
>>> @@ -1,4 +1,5 @@
>>>  struct link_map_machine
>>>    {
>>>      ElfW(Addr) plt; /* Address of .plt */
>>> +    ElfW(Word) fpmode; /* Overall FP mode */
>>>    };
>>> diff --git a/sysdeps/mips/dl-machine.h b/sysdeps/mips/dl-machine.h
>>> index 5a07c0b..b10c228 100644
>>> --- a/sysdeps/mips/dl-machine.h
>>> +++ b/sysdeps/mips/dl-machine.h
>>> @@ -32,6 +32,7 @@
>>>  #include <sgidefs.h>
>>>  #include <sys/asm.h>
>>>  #include <dl-tls.h>
>>> +#include <unistd.h>
>>>
>>>  /* The offset of gp from GOT might be system-dependent.  It's set by
>>>     ld.  The same value is also */
>>> @@ -107,6 +108,223 @@ elf_machine_matches_host (const ElfW(Ehdr) *ehdr)
>>>      }
>>>  }
>>>
>>> +#define ELF_MACHINE_NEEDS_PHDR_CHECK
>>> +
>>> +static inline const ElfW(Phdr) *
>>> +find_mips_abiflags (const ElfW(Phdr) *phdr, ElfW(Half) phnum)
>>> +{
>>> +  const ElfW(Phdr) *ph;
>>> +
>>> +  for (ph = phdr; ph < &phdr[phnum]; ++ph)
>>> +    if (ph->p_type == PT_MIPS_ABIFLAGS)
>>> +      return ph;
>>> +  return NULL;
>>> +}
>>> +
>>> +#if _MIPS_SIM == _ABIO32
>>> +/* Modify the mode of the floating-point registers.  This function must not
>>> +   be inlined as it relies on the calling-convention to only need to save
>>> +   restore the callee-saved registers around the mode switch.  */
>>> +
>>> +static __attribute__ ((noinline)) void
>>> +switch_frmode_to (int newmode)
>>> +{
>>> +  asm volatile
>>> +      ("addu $sp, $sp, -48\n"
>>> +       "sdc1 $f20, 0($sp)\n"
>>> +       "sdc1 $f22, 8($sp)\n"
>>> +       "sdc1 $f24, 16($sp)\n"
>>> +       "sdc1 $f26, 24($sp)\n"
>>> +       "sdc1 $f28, 32($sp)\n"
>>> +       "sdc1 $f30, 40($sp)\n"
>>> +       "beq %0, $0, 1f\n"
>>> +       "ctc1 $0, $4\n"
>>> +       "b 2f\n"
>>> +       "1:\n"
>>> +       "ctc1 $0, $1\n"
>>> +       "2:\n"
>>> +       "ldc1 $f20, 0($sp)\n"
>>> +       "ldc1 $f22, 8($sp)\n"
>>> +       "ldc1 $f24, 16($sp)\n"
>>> +       "ldc1 $f26, 24($sp)\n"
>>> +       "ldc1 $f28, 32($sp)\n"
>>> +       "ldc1 $f30, 40($sp)\n"
>>> +       "addu $sp, $sp, -48\n" :: "r"(newmode));
>>> +}
>>> +#endif
>>> +
>>> +static const char *
>>> +mips_fp_abi (int val)
>>> +{
>>> +  switch (val)
>>> +    {
>>> +    case Val_GNU_MIPS_ABI_FP_ANY:
>>> +      return "no float";
>>> +    case Val_GNU_MIPS_ABI_FP_DOUBLE:
>>> +      return "Hard float (DP)";
>>> +    case Val_GNU_MIPS_ABI_FP_SINGLE:
>>> +      return "Hard float (SP)";
>>> +    case Val_GNU_MIPS_ABI_FP_SOFT:
>>> +      return "Soft float";
>>> +    case Val_GNU_MIPS_ABI_FP_OLD_64:
>>> +      return "Unsupported FP64";
>>> +    case Val_GNU_MIPS_ABI_FP_XX:
>>> +      return "Hard float (32-bit CPU, Any FPU)";
>>> +    case Val_GNU_MIPS_ABI_FP_64:
>>> +      return "Hard float (32-bit CPU, 64-bit FPU)";
>>> +    default:
>>> +      return "Unknown FP ABI";
>>> +    }
>>> +}
>>> +
>>> +static int __attribute_used__
>>> +elf_machine_phdr_check (const ElfW(Phdr) *phdr, ElfW(Half) phnum,
>>> +                       char * buf, int len, int fd, struct link_map * map)
>>> +{
>>> +  const ElfW(Phdr) *ph = find_mips_abiflags (phdr, phnum);
>>> +  struct link_map *l;
>>> +  Lmid_t nsid;
>>> +  int req_abi = Val_GNU_MIPS_ABI_FP_DOUBLE;
>>> +  Elf_ABIFlags_v0 *mips_abiflags = NULL;
>>> +
>>> +  /* Read the attributes section.  */
>>> +  if (ph != NULL)
>>> +    {
>>> +      ElfW(Addr) size = ph->p_filesz;
>>> +
>>> +      if (ph->p_offset + size <= (size_t) len)
>>> +       mips_abiflags = (Elf_ABIFlags_v0 *) (buf + ph->p_offset);
>>> +      else
>>> +       {
>>> +         mips_abiflags = alloca (size);
>>> +         __lseek (fd, ph->p_offset, SEEK_SET);
>>> +         if (__libc_read (fd, (void *) mips_abiflags, size) != size)
>>> +           {
>>> +             if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_LIBS, 0))
>>> +               _dl_debug_printf ("   Unable to read PT_MIPS_ABIFLAGS\n");
>>> +             return 0;
>>> +           }
>>> +       }
>>> +      if (size < sizeof (Elf_ABIFlags_v0))
>>> +       {
>>> +         if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_LIBS, 0))
>>> +           _dl_debug_printf ("   contains malformed PT_MIPS_ABIFLAGS\n");
>>> +         return 0;
>>> +       }
>>> +      req_abi = mips_abiflags->fp_abi;
>>> +    }
>>> +
>>> +  /* ANY is compatible with anything.  */
>>> +  if (req_abi == Val_GNU_MIPS_ABI_FP_ANY)
>>> +    return 1;
>>> +
>>> +  /* Check that the new mode does not conflict with any currently
>>> +     loaded object.  */
>>> +  for (nsid = 0; nsid < DL_NNS; ++nsid)
>>> +    for (l = GL(dl_ns)[nsid]._ns_loaded; l != NULL; l = l->l_next)
>>> +      {
>>> +       bool success = true;
>>> +       if (l->l_mach.fpmode == 0)
>>> +         {
>>> +           l->l_mach.fpmode = Val_GNU_MIPS_ABI_FP_DOUBLE;
>>> +           ph = find_mips_abiflags (l->l_phdr, l->l_phnum);
>>> +           if (ph)
>>> +             {
>>> +               if (ph->p_filesz < sizeof (Elf_ABIFlags_v0))
>>> +                 {
>>> +                   if (__builtin_expect (GLRO(dl_debug_mask)
>>> +                                         & DL_DEBUG_LIBS, 0))
>>> +                     _dl_debug_printf ("   malformed PT_MIPS_ABIFLAGS found\n");
>>> +                   return 0;
>>> +                 }
>>> +
>>> +               mips_abiflags = (Elf_ABIFlags_v0 *) (l->l_addr + ph->p_vaddr);
>>> +               l->l_mach.fpmode = mips_abiflags->fp_abi;
>>> +             }
>>> +         }
>>> +       switch (req_abi)
>>> +         {
>>> +         case Val_GNU_MIPS_ABI_FP_ANY:
>>> +           /* Can't happen, see above.  */
>>> +           break;
>>> +         case Val_GNU_MIPS_ABI_FP_DOUBLE:
>>> +           if (l->l_mach.fpmode != Val_GNU_MIPS_ABI_FP_DOUBLE
>>> +#if _MIPS_SIM == _ABIO32
>>> +               && l->l_mach.fpmode != Val_GNU_MIPS_ABI_FP_XX
>>> +#endif
>>> +               && l->l_mach.fpmode != Val_GNU_MIPS_ABI_FP_ANY)
>>> +             success = false;
>>> +           break;
>>> +         case Val_GNU_MIPS_ABI_FP_SINGLE:
>>> +           if (l->l_mach.fpmode != Val_GNU_MIPS_ABI_FP_SINGLE
>>> +               && l->l_mach.fpmode != Val_GNU_MIPS_ABI_FP_ANY)
>>> +             success = false;
>>> +           break;
>>> +         case Val_GNU_MIPS_ABI_FP_SOFT:
>>> +           if (l->l_mach.fpmode != Val_GNU_MIPS_ABI_FP_SOFT
>>> +               && l->l_mach.fpmode != Val_GNU_MIPS_ABI_FP_ANY)
>>> +             success = false;
>>> +           break;
>>> +#if _MIPS_SIM == _ABIO32
>>> +         case Val_GNU_MIPS_ABI_FP_XX:
>>> +           if (l->l_mach.fpmode != Val_GNU_MIPS_ABI_FP_XX
>>> +               && l->l_mach.fpmode != Val_GNU_MIPS_ABI_FP_DOUBLE
>>> +               && l->l_mach.fpmode != Val_GNU_MIPS_ABI_FP_64
>>> +               && l->l_mach.fpmode != Val_GNU_MIPS_ABI_FP_ANY)
>>> +             success = false;
>>> +           break;
>>> +         case Val_GNU_MIPS_ABI_FP_64:
>>> +           if (l->l_mach.fpmode != Val_GNU_MIPS_ABI_FP_64
>>> +               && l->l_mach.fpmode != Val_GNU_MIPS_ABI_FP_XX
>>> +               && l->l_mach.fpmode != Val_GNU_MIPS_ABI_FP_ANY)
>>> +             success = false;
>>> +           break;
>>> +#endif
>>> +         default:
>>> +           success = false;
>>> +         }
>>> +
>>> +       if (!success)
>>> +         {
>>> +           if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_LIBS, 0))
>>> +             _dl_debug_printf ("   uses %s, already loaded %s\n",
>>> +                               mips_fp_abi (req_abi),
>>> +                               mips_fp_abi (l->l_mach.fpmode));
>>> +           return 0;
>>> +         }
>>> +      }
>>> +
>>> +#if _MIPS_SIM == _ABIO32
>>> +  if (req_abi == Val_GNU_MIPS_ABI_FP_DOUBLE
>>> +      || req_abi == Val_GNU_MIPS_ABI_FP_64)
>>> +    {
>>> +      if (GLRO(dl_hwcap) & HWCAP_MIPS_UFR)
>>> +       {
>>> +         int status;
>>> +         /* Obtain UFR mode information.  */
>>> +         asm volatile ("cfc1 %0,$1\n": "=r"(status));
>>> +         if (status == 0 && req_abi == Val_GNU_MIPS_ABI_FP_64)
>>> +           switch_frmode_to (1);
>>> +         else if (status == 1 && req_abi == Val_GNU_MIPS_ABI_FP_DOUBLE)
>>> +           switch_frmode_to (0);
>>> +
>>> +         asm volatile ("cfc1 %0,$1\n": "=r"(status));
>>
>> I would be inclined to make these inline asm statements into a
>> function with a descriptive name, and potentially the status values
>> could usefully be named too.
>>
>>> +         if ((status == 0 && req_abi == Val_GNU_MIPS_ABI_FP_64)
>>> +             || (status == 1 && req_abi == Val_GNU_MIPS_ABI_FP_DOUBLE))
>>> +           _dl_signal_error (0, map->l_name, NULL, "Unable to set FP mode");
>>
>> Under what circumstances can this error occur?
>
> The hardware does not support the requested mode.

Maybe "Hardware does not support mode %s" would be a more helpful
message in this case.

-- 
Will Newton
Toolchain Working Group, Linaro


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