Re: [PATCH 1/2] Initial support for GNU_PROPERTY_1_NEEDED

[Adhemerval Zanella via Libc-alpha <libc-alpha@sourceware.org>]

On 03/08/2021 18:59, H.J. Lu via Libc-alpha wrote:
> 1. Add GNU_PROPERTY_1_NEEDED:
> 
>  #define GNU_PROPERTY_1_NEEDED      GNU_PROPERTY_UINT32_OR_LO
> 
> to indicate the needed properties by the object file.
> 2. Add GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS:
> 
>  #define GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS (1U << 0)
> 
> to indicate that the object file requires canonical function pointers and
> cannot be used with copy relocation.
> 3. Scan GNU_PROPERTY_1_NEEDED property and store it in l_1_needed.

It was added by binutils with commit 6320fd00dc374f74658, maybe add on
the commit the version expected to have this support.

LGTM, with a small suggestion below.

Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

> ---
>  elf/elf.h                  | 17 +++++++++++++++++
>  sysdeps/generic/dl-prop.h  |  9 ++++++++-
>  sysdeps/generic/link_map.h |  3 ++-
>  sysdeps/x86/dl-prop.h      | 19 ++++++++++++++-----
>  sysdeps/x86/link_map.h     |  2 ++
>  5 files changed, 43 insertions(+), 7 deletions(-)
> 
> diff --git a/elf/elf.h b/elf/elf.h
> index 4738dfa28f..50f87baceb 100644
> --- a/elf/elf.h
> +++ b/elf/elf.h
> @@ -1312,6 +1312,23 @@ typedef struct
>  /* No copy relocation on protected data symbol.  */
>  #define GNU_PROPERTY_NO_COPY_ON_PROTECTED	2
>  
> +/* A 4-byte unsigned integer property: A bit is set if it is set in all
> +   relocatable inputs.  */
> +#define GNU_PROPERTY_UINT32_AND_LO	0xb0000000
> +#define GNU_PROPERTY_UINT32_AND_HI	0xb0007fff
> +
> +/* A 4-byte unsigned integer property: A bit is set if it is set in any
> +   relocatable inputs.  */
> +#define GNU_PROPERTY_UINT32_OR_LO	0xb0008000
> +#define GNU_PROPERTY_UINT32_OR_HI	0xb000ffff
> +
> +/* The needed properties by the object file.  */
> +#define GNU_PROPERTY_1_NEEDED		GNU_PROPERTY_UINT32_OR_LO
> +
> +/* Set if the object file requires canonical function pointers and
> +   cannot be used with copy relocation.  */
> +#define GNU_PROPERTY_1_NEEDED_INDIRECT_EXTERN_ACCESS (1U << 0)
> +
>  /* Processor-specific semantics, lo */
>  #define GNU_PROPERTY_LOPROC			0xc0000000
>  /* Processor-specific semantics, hi */

Ok.

> diff --git a/sysdeps/generic/dl-prop.h b/sysdeps/generic/dl-prop.h
> index eaee8052b6..207aadb35d 100644
> --- a/sysdeps/generic/dl-prop.h
> +++ b/sysdeps/generic/dl-prop.h
> @@ -47,7 +47,14 @@ static inline int __attribute__ ((always_inline))
>  _dl_process_gnu_property (struct link_map *l, int fd, uint32_t type,
>  			  uint32_t datasz, void *data)
>  {
> -  return 0;
> +  /* Continue until GNU_PROPERTY_1_NEEDED is found.  */
> +  if (type == GNU_PROPERTY_1_NEEDED)
> +    {
> +      if (datasz == 4)
> +	l->l_1_needed = *(unsigned int *) data;

Although the pointer seems to be aligned, I think it would be better to
use memcpy here:

   unsigned int t;
   memcpy (&t, data, sizeof (t));
   l->l_1_needed = t;

(the x86 header might use a more relax since the architecture always
support unaligned access)

> +      return 0;
> +    }
> +  return 1;
>  }
>  
>  #endif /* _DL_PROP_H */
> diff --git a/sysdeps/generic/link_map.h b/sysdeps/generic/link_map.h
> index a056184690..9f482b8c20 100644
> --- a/sysdeps/generic/link_map.h
> +++ b/sysdeps/generic/link_map.h
> @@ -1 +1,2 @@
> -/* No architecture specific definitions.  */
> +/* GNU_PROPERTY_1_NEEDED of this object.  */
> +unsigned int l_1_needed;
> diff --git a/sysdeps/x86/dl-prop.h b/sysdeps/x86/dl-prop.h
> index 56bd020b3c..385548fad3 100644
> --- a/sysdeps/x86/dl-prop.h
> +++ b/sysdeps/x86/dl-prop.h
> @@ -97,6 +97,7 @@ _dl_process_property_note (struct link_map *l, const ElfW(Nhdr) *note,
>  
>    const ElfW(Addr) start = (ElfW(Addr)) note;
>  
> +  unsigned int needed_1 = 0;
>    unsigned int feature_1_and = 0;
>    unsigned int isa_1_needed = 0;
>    unsigned int last_type = 0;
> @@ -141,7 +142,8 @@ _dl_process_property_note (struct link_map *l, const ElfW(Nhdr) *note,
>  	      last_type = type;
>  
>  	      if (type == GNU_PROPERTY_X86_FEATURE_1_AND
> -		  || type == GNU_PROPERTY_X86_ISA_1_NEEDED)
> +		  || type == GNU_PROPERTY_X86_ISA_1_NEEDED
> +		  || type == GNU_PROPERTY_1_NEEDED)
>  		{
>  		  /* The sizes of types which we are searching for are
>  		     4 bytes.  There is no point to continue if this

Ok.

> @@ -151,12 +153,18 @@ _dl_process_property_note (struct link_map *l, const ElfW(Nhdr) *note,
>  
>  		  /* NB: Stop the scan only after seeing all types which
>  		     we are searching for.  */
> -		  _Static_assert ((GNU_PROPERTY_X86_ISA_1_NEEDED >
> -				   GNU_PROPERTY_X86_FEATURE_1_AND),
> +		  _Static_assert (((GNU_PROPERTY_X86_ISA_1_NEEDED
> +				    > GNU_PROPERTY_X86_FEATURE_1_AND)
> +				   && (GNU_PROPERTY_X86_FEATURE_1_AND
> +				       > GNU_PROPERTY_1_NEEDED)),
>  				  "GNU_PROPERTY_X86_ISA_1_NEEDED > "
> -				  "GNU_PROPERTY_X86_FEATURE_1_AND");
> +				  "GNU_PROPERTY_X86_FEATURE_1_AND && "
> +				  "GNU_PROPERTY_X86_FEATURE_1_AND > "
> +				  "GNU_PROPERTY_1_NEEDED");
>  		  if (type == GNU_PROPERTY_X86_FEATURE_1_AND)
>  		    feature_1_and = *(unsigned int *) ptr;
> +		  else if (type == GNU_PROPERTY_1_NEEDED)
> +		    needed_1 = *(unsigned int *) ptr;
>  		  else
>  		    {
>  		      isa_1_needed = *(unsigned int *) ptr;

Ok.

> @@ -187,9 +195,10 @@ _dl_process_property_note (struct link_map *l, const ElfW(Nhdr) *note,
>      }
>  
>    /* We get here only if there is one or no GNU property note.  */
> -  if (isa_1_needed != 0 || feature_1_and != 0)
> +  if (needed_1 != 0 || isa_1_needed != 0 || feature_1_and != 0)
>      {
>        l->l_property = lc_property_valid;
> +      l->l_1_needed = needed_1;
>        l->l_x86_isa_1_needed = isa_1_needed;
>        l->l_x86_feature_1_and = feature_1_and;
>      }

Ok.

> diff --git a/sysdeps/x86/link_map.h b/sysdeps/x86/link_map.h
> index 4c46a25f83..0c7e25dc96 100644
> --- a/sysdeps/x86/link_map.h
> +++ b/sysdeps/x86/link_map.h
> @@ -29,3 +29,5 @@ unsigned int l_x86_feature_1_and;
>  
>  /* GNU_PROPERTY_X86_ISA_1_NEEDED of this object.  */
>  unsigned int l_x86_isa_1_needed;
> +
> +#include <sysdeps/generic/link_map.h>
> 

Ok.