Hi,

On Fri, 2024-03-01 at 15:59 +0100, Mark Wielaard wrote:
> This looks correct, but gcc noticed a path to use tu_offset (and
> tu_index) if they weren't initialized or NULL:
> 
> In file included from /home/mark/src/elfutils/libdw/libdwP.h:684,
>                  from /home/mark/src/elfutils/libdw/dwarf_cu_dwp_section_info.c:35:
> In function ‘read_4ubyte_unaligned_1’,
>     inlined from ‘__libdw_package_index’ at /home/mark/src/elfutils/libdw/dwarf_cu_dwp_section_info.c:302:34:
> /home/mark/src/elfutils/libdw/memory-access.h:291:12: error: ‘tu_offset’ may be used uninitialized [-Werror=maybe-uninitialized]
>   291 |   return up->u4;
>       |          ~~^~~~
> /home/mark/src/elfutils/libdw/dwarf_cu_dwp_section_info.c: In function ‘__libdw_package_index’:
> /home/mark/src/elfutils/libdw/dwarf_cu_dwp_section_info.c:268:28: note: ‘tu_offset’ was declared here
>   268 |       const unsigned char *tu_offset;
>       |                            ^~~~~~~~~
> cc1: all warnings being treated as errors
> 
> I couldn't immediately disprove gcc here, so I think it is a good idea
> to add an explicit check for tu_index != NULL.
> 
> diff --git a/libdw/dwarf_cu_dwp_section_info.c b/libdw/dwarf_cu_dwp_section_info.c
> index 3d11c87a..9fdc15bf 100644
> --- a/libdw/dwarf_cu_dwp_section_info.c
> +++ b/libdw/dwarf_cu_dwp_section_info.c
> @@ -297,7 +297,8 @@ __libdw_package_index (Dwarf *dbg, bool tu)
>               cu_index->debug_info_offsets[cui++] = off;
>               cu_offset += cu_index->section_count * 4;
>             }
> -         else if (unit_type == DW_UT_split_type && tui < tu_count)
> +         else if (unit_type == DW_UT_split_type && tu_index != NULL
> +                  && tui < tu_count)
>             {
>               if ((off & UINT32_MAX) != read_4ubyte_unaligned (dbg, tu_offset))
>                 goto not_sorted;
> 
> Which makes gcc happy again.

But not all gcc versions apparently. So I added the following on top.