Re: [RFC][PATCH v8 09/20] Define a new dynamic section tag - DT_GNU_FLAGS_1

[Adhemerval Zanella <adhemerval.zanella@linaro.org>]

On 09/02/2021 14:18, Vivek Das Mohapatra via Libc-alpha wrote:
> Define a new flags section DT_GNU_FLAGS_1 (no more bits are available
> in DT_GNU_FLAGS).
> 
> One flag is currently defined: DF_GNU_1_UNIQUE.
> 
> libc and its companion DSOs (libpthread et al) should have this
> section and flag set.
> ---
>  elf/elf.h              |  7 ++++++-
>  elf/get-dynamic-info.h | 12 ++++++++++++
>  include/elf.h          |  2 ++
>  include/link.h         |  1 +
>  4 files changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/elf/elf.h b/elf/elf.h
> index 4f838d4af2..9f9b8e4291 100644
> --- a/elf/elf.h
> +++ b/elf/elf.h
> @@ -895,6 +895,7 @@ typedef struct
>     Dyn.d_un.d_val field of the Elf*_Dyn structure.  This follows Sun's
>     approach.  */
>  #define DT_VALRNGLO	0x6ffffd00
> +#define DT_GNU_FLAGS_1   0x6ffffdf4    /* Open DSO once across all namespaces */
>  #define DT_GNU_PRELINKED 0x6ffffdf5	/* Prelinking timestamp */
>  #define DT_GNU_CONFLICTSZ 0x6ffffdf6	/* Size of conflict section */
>  #define DT_GNU_LIBLISTSZ 0x6ffffdf7	/* Size of library list */

Ok, it matches binutils definition.

> @@ -909,7 +910,7 @@ typedef struct
>  #define DT_SYMINENT	0x6ffffdff	/* Entry size of syminfo */
>  #define DT_VALRNGHI	0x6ffffdff
>  #define DT_VALTAGIDX(tag)	(DT_VALRNGHI - (tag))	/* Reverse order! */
> -#define DT_VALNUM 12
> +#define DT_VALNUM 13
>  
Ok.

>  /* DT_* entries which fall between DT_ADDRRNGHI & DT_ADDRRNGLO use the
>     Dyn.d_un.d_ptr field of the Elf*_Dyn structure.
> @@ -998,6 +999,10 @@ typedef struct
>  #define	DF_1_WEAKFILTER 0x20000000
>  #define	DF_1_NOCOMMON   0x40000000
>  
> +/* State flags selectable in the `d_un.d_val' element of the DT_GNU_FLAGS_1
> +   entry in the dynamic section.  */
> +#define DF_GNU_1_UNIQUE 0x00000001
> +
>  /* Flags for the feature selection in DT_FEATURE_1.  */
>  #define DTF_1_PARINIT	0x00000001
>  #define DTF_1_CONFEXP	0x00000002

Ok, it matches binutils definition.

> diff --git a/elf/get-dynamic-info.h b/elf/get-dynamic-info.h
> index d8ec32377d..d441b39576 100644
> --- a/elf/get-dynamic-info.h
> +++ b/elf/get-dynamic-info.h
> @@ -175,6 +175,18 @@ elf_get_dynamic_info (struct link_map *l, ElfW(Dyn) *temp)
>        if (l->l_flags_1 & DF_1_NOW)
>  	info[DT_BIND_NOW] = info[VERSYMIDX (DT_FLAGS_1)];
>      }
> +  if (info[DT_VALTAGIDX (DT_GNU_FLAGS_1)
> +           + DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGNUM + DT_EXTRANUM] != NULL)
> +    {
> +      l->l_gnu_flags_1 = info[DT_VALTAGIDX (DT_GNU_FLAGS_1)
> +                              + DT_NUM + DT_THISPROCNUM
> +                              + DT_VERSIONTAGNUM + DT_EXTRANUM]->d_un.d_val;
> +
> +      if (__builtin_expect (GLRO(dl_debug_mask) & DL_DEBUG_FILES, 0)
> +	  && l->l_gnu_flags_1 & ~DT_GNU_1_SUPPORTED_MASK)

Use __glibc_likely.

> +	_dl_debug_printf ("\nWARNING: Unsupported flag value(s) of 0x%x in DT_GNU_FLAGS_1.\n",
> +			  l->l_gnu_flags_1 & ~DT_GNU_1_SUPPORTED_MASK);
> +    }
>    if (info[DT_RUNPATH] != NULL)
>      /* If both RUNPATH and RPATH are given, the latter is ignored.  */
>      info[DT_RPATH] = NULL;

Ok.

> diff --git a/include/elf.h b/include/elf.h
> index 14ed67ff67..5eee37c294 100644
> --- a/include/elf.h
> +++ b/include/elf.h
> @@ -25,5 +25,7 @@
>     (DF_1_NOW | DF_1_NODELETE | DF_1_INITFIRST | DF_1_NOOPEN \
>      | DF_1_ORIGIN | DF_1_NODEFLIB | DF_1_PIE)
>  
> +#define DT_GNU_1_SUPPORTED_MASK DF_GNU_1_UNIQUE
> +
>  #endif /* !_ISOMAC */
>  #endif /* elf.h */

Ok.

> diff --git a/include/link.h b/include/link.h
> index b51fa0cbdf..55e0cad71d 100644
> --- a/include/link.h
> +++ b/include/link.h
> @@ -285,6 +285,7 @@ struct link_map
>      unsigned int l_used;
>  
>      /* Various flag words.  */
> +    ElfW(Word) l_gnu_flags_1;
>      ElfW(Word) l_feature_1;
>      ElfW(Word) l_flags_1;
>      ElfW(Word) l_flags;
> 

Ok.