Re: [PULL 33/36] hw/elf_ops: Ignore loadable segments with zero size

["Alex Bennée" <alex.bennee@linaro.org>]

Philippe Mathieu-Daudé <philmd@linaro.org> writes:

> From: Bin Meng <bmeng@tinylab.org>
>
> Some ELF files really do have segments of zero size, e.g.:
>
> Program Headers:
>   Type           Offset             VirtAddr           PhysAddr
>                  FileSiz            MemSiz              Flags  Align
>   RISCV_ATTRIBUT 0x00000000000025b8 0x0000000000000000 0x0000000000000000
>                  0x000000000000003e 0x0000000000000000  R      0x1
>   LOAD           0x0000000000001000 0x0000000080200000 0x0000000080200000
>                  0x00000000000001d1 0x00000000000001d1  R E    0x1000
>   LOAD           0x00000000000011d1 0x00000000802001d1 0x00000000802001d1
>                  0x0000000000000e37 0x0000000000000e37  RW     0x1000
>   LOAD           0x0000000000000120 0x0000000000000000 0x0000000000000000
>                  0x0000000000000000 0x0000000000000000         0x1000
>
> The current logic does not check for this condition, resulting in
> the incorrect assignment of 'lowaddr' as zero.
>
> There is already a piece of codes inside the segment traversal loop
> that checks for zero-sized loadable segments for not creating empty
> ROM blobs. Let's move this check to the beginning of the loop to
> cover both scenarios.
>
> Signed-off-by: Bin Meng <bmeng@tinylab.org>
> Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
> Message-ID: <20240116155049.390301-1-bmeng@tinylab.org>
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>

This has broken Xtensa system emulation:

  ➜  /bin/sh -c "cd builds/bisect; ninja; make check-tcg"
  [8/8] Linking target qemu-system-xtensa
    BUILD   debian-xtensa-cross
    BUILD   xtensa-softmmu guest-tests
    RUN     xtensa-softmmu guest-tests
    TEST    test_bi on xtensa
    TEST    test_boolean on xtensa
    TEST    test_break on xtensa
    TEST    test_b on xtensa
    TEST    test_bz on xtensa
    TEST    test_cache on xtensa
    TEST    test_clamps on xtensa
    TEST    test_dfp0_arith on xtensa
    TEST    test_exclusive on xtensa
    TEST    test_extui on xtensa
    TEST    test_flix on xtensa
    TEST    test_fp0_arith on xtensa
    TEST    test_fp0_conv on xtensa
    TEST    test_fp0_div on xtensa
    TEST    test_fp0_sqrt on xtensa
    TEST    test_fp1 on xtensa
    TEST    test_fp_cpenable on xtensa
    TEST    test_interrupt on xtensa
    TEST    test_load_store on xtensa
  qemu-system-xtensa: Some ROM regions are overlapping
  These ROM regions might have been loaded by direct user request or by default.
  They could be BIOS/firmware images, a guest kernel, initrd or some other file loaded into guest memory.
  Check whether you intended to load all this guest code, and whether it has been built to load to the correct addresses.

  The following two regions overlap (in the memory address space):
    test_load_store ELF program header segment 1 (addresses 0x0000000000001000 - 0x0000000000001f26)
    test_load_store ELF program header segment 2 (addresses 0x0000000000001ab8 - 0x0000000000001ab8)
  make[1]: *** [Makefile:187: run-test_load_store] Error 1
  make: *** [/home/alex/lsrc/qemu.git/tests/Makefile.include:56: run-tcg-tests-xtensa-softmmu] Error 2

> ---
>  include/hw/elf_ops.h | 71 +++++++++++++++++++++++---------------------
>  1 file changed, 37 insertions(+), 34 deletions(-)
>
> diff --git a/include/hw/elf_ops.h b/include/hw/elf_ops.h
> index 9c35d1b9da..3e966ddd5a 100644
> --- a/include/hw/elf_ops.h
> +++ b/include/hw/elf_ops.h
> @@ -427,6 +427,16 @@ static ssize_t glue(load_elf, SZ)(const char *name, int fd,
>              file_size = ph->p_filesz; /* Size of the allocated data */
>              data_offset = ph->p_offset; /* Offset where the data is located */
>  
> +            /*
> +             * Some ELF files really do have segments of zero size;
> +             * just ignore them rather than trying to set the wrong addr,
> +             * or create empty ROM blobs, because the zero-length blob can
> +             * falsely trigger the overlapping-ROM-blobs check.
> +             */
> +            if (mem_size == 0) {
> +                continue;
> +            }
> +
>              if (file_size > 0) {
>                  if (g_mapped_file_get_length(mapped_file) <
>                      file_size + data_offset) {
> @@ -530,45 +540,38 @@ static ssize_t glue(load_elf, SZ)(const char *name, int fd,
>                  *pentry = ehdr.e_entry - ph->p_vaddr + ph->p_paddr;
>              }
>  
> -            /* Some ELF files really do have segments of zero size;
> -             * just ignore them rather than trying to create empty
> -             * ROM blobs, because the zero-length blob can falsely
> -             * trigger the overlapping-ROM-blobs check.
> -             */
> -            if (mem_size != 0) {
> -                if (load_rom) {
> -                    g_autofree char *label =
> -                        g_strdup_printf("%s ELF program header segment %d",
> -                                        name, i);
> +            if (load_rom) {
> +                g_autofree char *label =
> +                    g_strdup_printf("%s ELF program header segment %d",
> +                                    name, i);
>  
> -                    /*
> -                     * rom_add_elf_program() takes its own reference to
> -                     * 'mapped_file'.
> -                     */
> -                    rom_add_elf_program(label, mapped_file, data, file_size,
> -                                        mem_size, addr, as);
> -                } else {
> -                    MemTxResult res;
> +                /*
> +                 * rom_add_elf_program() takes its own reference to
> +                 * 'mapped_file'.
> +                 */
> +                rom_add_elf_program(label, mapped_file, data, file_size,
> +                                    mem_size, addr, as);
> +            } else {
> +                MemTxResult res;
>  
> -                    res = address_space_write(as ? as : &address_space_memory,
> -                                              addr, MEMTXATTRS_UNSPECIFIED,
> -                                              data, file_size);
> +                res = address_space_write(as ? as : &address_space_memory,
> +                                          addr, MEMTXATTRS_UNSPECIFIED,
> +                                          data, file_size);
> +                if (res != MEMTX_OK) {
> +                    goto fail;
> +                }
> +                /*
> +                 * We need to zero'ify the space that is not copied
> +                 * from file
> +                 */
> +                if (file_size < mem_size) {
> +                    res = address_space_set(as ? as : &address_space_memory,
> +                                            addr + file_size, 0,
> +                                            mem_size - file_size,
> +                                            MEMTXATTRS_UNSPECIFIED);
>                      if (res != MEMTX_OK) {
>                          goto fail;
>                      }
> -                    /*
> -                     * We need to zero'ify the space that is not copied
> -                     * from file
> -                     */
> -                    if (file_size < mem_size) {
> -                        res = address_space_set(as ? as : &address_space_memory,
> -                                                addr + file_size, 0,
> -                                                mem_size - file_size,
> -                                                MEMTXATTRS_UNSPECIFIED);
> -                        if (res != MEMTX_OK) {
> -                            goto fail;
> -                        }
> -                    }
>                  }
>              }

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro