ELF's DT_ENCODING

ELF's DT_ENCODING

[Jan Beulich]

Commit a7fd11862703 bumped this to 38 without any justification. (By its
name DT_SYMTAB_SHNDX might look to not match the scheme intended to be
used above the boundary, looking more like a d_val kind of tag than a
d_ptr one, but from its description it really is an address. Plus even
that would only justify bumping to 35.)

I think that part of the change wants reverting, unless an up-to-date
spec [1] has moved the marker.

Jan

[1] In search for a new place where the gABI doc would live I found
https://groups.google.com/g/generic-abi/c/9OO5vhxb00Y, but that doesn't
indicate what github project, if any, would have been created. Hence
for now I can only refer to the about 10 years old version on sco.com.

Re: ELF's DT_ENCODING

[Alan Modra]

On Mon, May 22, 2023 at 08:57:00AM +0200, Jan Beulich wrote:
> I think that part of the change wants reverting

Yes, I think it was probably bumped without consulting the spec.  ;-)
ie. it was changed just for readelf.  I'm going to commit the
following after running my normal regression tests.

include/
	* elf/common.h (DT_ENCODING): Set back to 32.
binutils/
	* readelf.c (struct filedata): Don't size dynamic_info array
	using DT_ENCODING.

diff --git a/binutils/readelf.c b/binutils/readelf.c
index b872876a8b6..d8ad58b15dc 100644
--- a/binutils/readelf.c
+++ b/binutils/readelf.c
@@ -304,7 +304,7 @@ typedef struct filedata
   uint64_t *           mipsxlat;
   uint64_t             gnusymidx;
   char *               program_interpreter;
-  uint64_t             dynamic_info[DT_ENCODING];
+  uint64_t             dynamic_info[DT_RELRENT + 1];
   uint64_t             dynamic_info_DT_GNU_HASH;
   uint64_t             dynamic_info_DT_MIPS_XHASH;
   elf_section_list *   symtab_shndx_list;
diff --git a/include/elf/common.h b/include/elf/common.h
index 6f64f05890c..ffa6b60bd2b 100644
--- a/include/elf/common.h
+++ b/include/elf/common.h
@@ -1135,13 +1135,16 @@
 #define DT_FINI_ARRAYSZ 28
 #define DT_RUNPATH	29
 #define DT_FLAGS	30
+
+/* Values in the range [DT_ENCODING, DT_LOOS) use d_un.d_ptr if the
+   value is even, d_un.d_val if odd.  */
+#define DT_ENCODING	32
 #define DT_PREINIT_ARRAY   32
 #define DT_PREINIT_ARRAYSZ 33
 #define DT_SYMTAB_SHNDX    34
 #define DT_RELRSZ	35
 #define DT_RELR		36
 #define DT_RELRENT	37
-#define DT_ENCODING	38
 
 /* Note, the Oct 4, 1999 draft of the ELF ABI changed the values
    for DT_LOOS and DT_HIOS.  Some implementations however, use

-- 
Alan Modra
Australia Development Lab, IBM

Re: ELF's DT_ENCODING

[Fangrui Song]

On Mon, May 22, 2023 at 1:03 AM Alan Modra <amodra@gmail.com> wrote:
>
> On Mon, May 22, 2023 at 08:57:00AM +0200, Jan Beulich wrote:
> > I think that part of the change wants reverting
>
> Yes, I think it was probably bumped without consulting the spec.  ;-)
> ie. it was changed just for readelf.  I'm going to commit the
> following after running my normal regression tests.
>
> include/
>         * elf/common.h (DT_ENCODING): Set back to 32.
> binutils/
>         * readelf.c (struct filedata): Don't size dynamic_info array
>         using DT_ENCODING.
>
> diff --git a/binutils/readelf.c b/binutils/readelf.c
> index b872876a8b6..d8ad58b15dc 100644
> --- a/binutils/readelf.c
> +++ b/binutils/readelf.c
> @@ -304,7 +304,7 @@ typedef struct filedata
>    uint64_t *           mipsxlat;
>    uint64_t             gnusymidx;
>    char *               program_interpreter;
> -  uint64_t             dynamic_info[DT_ENCODING];
> +  uint64_t             dynamic_info[DT_RELRENT + 1];
>    uint64_t             dynamic_info_DT_GNU_HASH;
>    uint64_t             dynamic_info_DT_MIPS_XHASH;
>    elf_section_list *   symtab_shndx_list;
> diff --git a/include/elf/common.h b/include/elf/common.h
> index 6f64f05890c..ffa6b60bd2b 100644
> --- a/include/elf/common.h
> +++ b/include/elf/common.h
> @@ -1135,13 +1135,16 @@
>  #define DT_FINI_ARRAYSZ 28
>  #define DT_RUNPATH     29
>  #define DT_FLAGS       30
> +
> +/* Values in the range [DT_ENCODING, DT_LOOS) use d_un.d_ptr if the
> +   value is even, d_un.d_val if odd.  */
> +#define DT_ENCODING    32
>  #define DT_PREINIT_ARRAY   32
>  #define DT_PREINIT_ARRAYSZ 33
>  #define DT_SYMTAB_SHNDX    34
>  #define DT_RELRSZ      35
>  #define DT_RELR                36
>  #define DT_RELRENT     37
> -#define DT_ENCODING    38
>
>  /* Note, the Oct 4, 1999 draft of the ELF ABI changed the values
>     for DT_LOOS and DT_HIOS.  Some implementations however, use
>
> --
> Alan Modra
> Australia Development Lab, IBM

Thanks to Jan for spotting my mistake and Alan for fixing the issue in
commit bc227f4ccb0778a56ca3d9f27652fd9e5e2747ea (Re: readelf: Support
SHT_RELR/DT_RELR for -r).
Apologies for not taking a closer look at the spec that DT_ENCODING is
defined, when that RELR patch was prepared.



-- 
宋方睿

Re: ELF's DT_ENCODING

[Cary Coutant]

> [1] In search for a new place where the gABI doc would live I found
> https://groups.google.com/g/generic-abi/c/9OO5vhxb00Y, but that doesn't
> indicate what github project, if any, would have been created. Hence
> for now I can only refer to the about 10 years old version on sco.com.

There will be a new spec available soon (I hope). I've rewritten it in
ReStructuredText and will host it on github. We're just waiting for
Xinuos lawyers to approve licensing terms that will make it easier for
people to copy and produce derivative versions.

-cary