Re: [PATCH] Fix: Sign extensions for DW_FORM_addrx were never considered

[Can Acar <canacar@imcan.dev>]

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To be perfectly responsible here, I need to state that I have not run the
testsuite, because I couldn't get it working on my machine. It could be
possible for me to set up a virtual environment where I can run the test
suites if required.

Best regards,
Can

On Thu, Oct 23, 2025 at 2:42 PM Can Acar <canacar@imcan.dev> wrote:

> DW_FORM_addr is converted (sign-extended) to a signed value when
> the dwarf size is less than the size of unrelocated_addr, if the
> target architecture "naturally" sign extends an address (bfd.c).
>
> However, the same handling was not done for DW_FORM_addrx. This
> meant that for example, trying to `list` a function with an
> address >= 0x80000000 on (some?) 32-bit mips targets, when
> that address was encoded using DW_FORM_addrx, was broken.
>
> This patch fixes this issue by plumbing read_addr_index_1 into
> unit_head::read_address, which is the function used to extract
> information from DW_FORM_addr, and so it handles this case
> correctly.
> ---
>  gdb/dwarf2/read.c | 21 ++++++++++-----------
>  1 file changed, 10 insertions(+), 11 deletions(-)
>
> diff --git a/gdb/dwarf2/read.c b/gdb/dwarf2/read.c
> index 955893c5f0c..e83d6ca38ae 100644
> --- a/gdb/dwarf2/read.c
> +++ b/gdb/dwarf2/read.c
> @@ -15350,12 +15350,14 @@ dwarf2_per_objfile::read_line_string (const
> gdb_byte *buf,
>
>  static unrelocated_addr
>  read_addr_index_1 (dwarf2_per_objfile *per_objfile, unsigned int
> addr_index,
> -                  std::optional<ULONGEST> addr_base, int addr_size)
> +                  std::optional<ULONGEST> addr_base, unit_head *cu_header)
>  {
>    struct objfile *objfile = per_objfile->objfile;
>    bfd *abfd = objfile->obfd.get ();
>    const gdb_byte *info_ptr;
>    ULONGEST addr_base_or_zero = addr_base.has_value () ? *addr_base : 0;
> +  unsigned int ignore_bytes_read;
> +  unsigned char addr_size = cu_header->addr_size;
>
>    per_objfile->per_bfd->addr.read (objfile);
>    if (per_objfile->per_bfd->addr.buffer == NULL)
> @@ -15368,10 +15370,7 @@ read_addr_index_1 (dwarf2_per_objfile
> *per_objfile, unsigned int addr_index,
>            objfile_name (objfile));
>    info_ptr = (per_objfile->per_bfd->addr.buffer + addr_base_or_zero
>               + addr_index * addr_size);
> -  if (addr_size == 4)
> -    return (unrelocated_addr) bfd_get_32 (abfd, info_ptr);
> -  else
> -    return (unrelocated_addr) bfd_get_64 (abfd, info_ptr);
> +  return cu_header->read_address(abfd, info_ptr, &ignore_bytes_read);
>  }
>
>  /* Given index ADDR_INDEX in .debug_addr, fetch the value.  */
> @@ -15380,7 +15379,7 @@ static unrelocated_addr
>  read_addr_index (struct dwarf2_cu *cu, unsigned int addr_index)
>  {
>    return read_addr_index_1 (cu->per_objfile, addr_index,
> -                           cu->addr_base, cu->header.addr_size);
> +                           cu->addr_base, &cu->header);
>  }
>
>  /* Given a pointer to an leb128 value, fetch the value from .debug_addr.
> */
> @@ -15403,9 +15402,9 @@ dwarf2_read_addr_index (dwarf2_per_cu *per_cu,
> dwarf2_per_objfile *per_objfile,
>  {
>    struct dwarf2_cu *cu = per_objfile->get_cu (per_cu);
>    std::optional<ULONGEST> addr_base;
> -  int addr_size;
> +  unit_head *cu_header;
>
> -  /* We need addr_base and addr_size.
> +  /* We need addr_base and header (only some fields of which are used
> later).
>       If we don't have PER_CU->cu, we have to get it.
>       Nasty, but the alternative is storing the needed info in PER_CU,
>       which at this point doesn't seem justified: it's not clear how
> frequently
> @@ -15424,17 +15423,17 @@ dwarf2_read_addr_index (dwarf2_per_cu *per_cu,
> dwarf2_per_objfile *per_objfile,
>    if (cu != NULL)
>      {
>        addr_base = cu->addr_base;
> -      addr_size = cu->header.addr_size;
> +      cu_header = &cu->header;
>      }
>    else
>      {
>        cutu_reader reader (*per_cu, *per_objfile, nullptr, nullptr, false,
>                           language_minimal);
>        addr_base = reader.cu ()->addr_base;
> -      addr_size = reader.cu ()->header.addr_size;
> +      cu_header = &reader.cu ()->header;
>      }
>
> -  return read_addr_index_1 (per_objfile, addr_index, addr_base,
> addr_size);
> +  return read_addr_index_1 (per_objfile, addr_index, addr_base,
> cu_header);
>  }
>
>  /* Given a DW_FORM_GNU_str_index value STR_INDEX, fetch the string.
> --
> 2.50.1 (Apple Git-155)
>
>

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