[Bug gold/22914] Gold doesn't support .note.gnu.property section (NT_GNU_PROPERTY_TYPE_0)

[ccoutant at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=22914

--- Comment #1 from Cary Coutant <ccoutant at gmail dot com> ---
HJ,

The linux-abi document leaves a few things unspecified:

- Is the .note.gnu.property section SHF_ALLOC or not?

- Does it go in the PT_NOTE segment? Should it be placed at the
beginning of the segment?

- It says the .note.gnu.property section may be combined with other
note sections. (Is that true, or is it missing a "not"?) If the linker
combines it with other SHT_NOTE sections, does the name matter at all?

- Does the linker key off the name of the section, or does it need to
parse all SHT_NOTE sections looking for NT_GNU_PROPERTY_TYPE_0 and
"GNU"? (Neither option is attractive -- I'd much prefer using a custom
section type and program header type, like ARM, MIPS, and Itanium do
for their attributes sections. The linker and loader aren't meant to
be parsing note sections.)

- Where did we end up with note section alignment for 64-bit objects?
Is it still 4-byte aligned?




On Fri, Mar 2, 2018 at 8:31 AM, hjl.tools at gmail dot com
<address@hidden> wrote:
> https://sourceware.org/bugzilla/show_bug.cgi?id=22914
>
>             Bug ID: 22914
>            Summary: Gold doesn't support .note.gnu.property section
>                     (NT_GNU_PROPERTY_TYPE_0)
>            Product: binutils
>            Version: 2.31 (HEAD)
>             Status: NEW
>           Severity: enhancement
>           Priority: P2
>          Component: gold
>           Assignee: ccoutant at gmail dot com
>           Reporter: hjl.tools at gmail dot com
>                 CC: ian at airs dot com
>   Target Milestone: ---
>
> .note.gnu.property section and NT_GNU_PROPERTY_TYPE_0 are specified in
> Linux Extensions to gABI:
>
> https://github.com/hjl-tools/linux-abi/wiki/linux-abi-draft.pdf
>
> address@hidden gold-2]$ cat x.S
> #ifndef NT_GNU_PROPERTY_TYPE_0
> # define NT_GNU_PROPERTY_TYPE_0 5
> #endif
>
> #ifndef GNU_PROPERTY_STACK_SIZE
> # define GNU_PROPERTY_STACK_SIZE 1
> #endif
>
> #if __SIZEOF_PTRDIFF_T__  == 8
> # define ALIGN 3
> #elif __SIZEOF_PTRDIFF_T__  == 4
> # define ALIGN 2
> #endif
>
>         .section ".note.gnu.property", "a"
>         .p2align ALIGN
>
>         .long 1f - 0f           /* name length */
>         .long 5f - 2f           /* data length */
>         .long NT_GNU_PROPERTY_TYPE_0    /* note type */
> 0:      .asciz "GNU"            /* vendor name */
> 1:
>         .p2align ALIGN
> 2:      .long GNU_PROPERTY_STACK_SIZE   /* pr_type.  */
>         .long 4f - 3f   /* pr_datasz.  */
> 3:
>         .dc.a 0x800     /* Stack size.  */
> 4:
>         .p2align ALIGN
> 5:
> address@hidden gold-2]$ cat y.S
> #ifndef NT_GNU_PROPERTY_TYPE_0
> # define NT_GNU_PROPERTY_TYPE_0 5
> #endif
>
> #ifndef GNU_PROPERTY_NO_COPY_ON_PROTECTED
> # define GNU_PROPERTY_NO_COPY_ON_PROTECTED 2
> #endif
>
> #if __SIZEOF_PTRDIFF_T__  == 8
> # define ALIGN 3
> #elif __SIZEOF_PTRDIFF_T__  == 4
> # define ALIGN 2
> #endif
>
>         .section ".note.gnu.property", "a"
>         .p2align ALIGN
>         .long 1f - 0f           /* name length */
>         .long 3f - 2f           /* data length */
>         .long NT_GNU_PROPERTY_TYPE_0    /* note type */
> 0:      .asciz "GNU"            /* vendor name */
> 1:
>         .p2align ALIGN
> 2:      .long GNU_PROPERTY_NO_COPY_ON_PROTECTED /* pr_type.  */
>         .long 0 /* pr_datasz.  */
> 3:
>         .p2align ALIGN
> address@hidden gold-2]$ cat z.S
> #ifndef NT_GNU_PROPERTY_TYPE_0
> # define NT_GNU_PROPERTY_TYPE_0 5
> #endif
>
> #ifndef GNU_PROPERTY_STACK_SIZE
> # define GNU_PROPERTY_STACK_SIZE 1
> #endif
>
> #ifndef GNU_PROPERTY_NO_COPY_ON_PROTECTED
> # define GNU_PROPERTY_NO_COPY_ON_PROTECTED 2
> #endif
>
> #if __SIZEOF_PTRDIFF_T__  == 8
> # define ALIGN 3
> #elif __SIZEOF_PTRDIFF_T__  == 4
> # define ALIGN 2
> #endif
>
>         .section ".note.gnu.property", "a"
>         .p2align ALIGN
>         .long 1f - 0f           /* name length */
>         .long 5f - 2f           /* data length */
>         .long NT_GNU_PROPERTY_TYPE_0    /* note type */
> 0:      .asciz "GNU"            /* vendor name */
> 1:
>         .p2align ALIGN
> 2:      .long GNU_PROPERTY_STACK_SIZE   /* pr_type.  */
>         .long 4f - 3f   /* pr_datasz.  */
> 3:
>         .dc.a 0x111100  /* Stack size.  */
> 4:
>         .p2align ALIGN
>         .long GNU_PROPERTY_NO_COPY_ON_PROTECTED /* pr_type.  */
>         .long 0 /* pr_datasz.  */
>         .p2align ALIGN
> 5:
> address@hidden gold-2]$ cat bar.c
> void
> _start (void)
> {
> }
> address@hidden gold-2]$ make
> gcc -B./  -c -o x.o x.S
> gcc -B./  -c -o y.o y.S
> gcc -B./  -c -o z.o z.S
> gcc -B./  -c -o bar.o bar.c
> ./ld  -o x x.o y.o z.o bar.o
> ld  -o y x.o y.o z.o bar.o
> readelf -n x y
>
> File: x
>
> Displaying notes found in: .note.gnu.property
>   Owner                 Data size       Description
>   GNU                  0x00000010       NT_GNU_PROPERTY_TYPE_0
>       Properties: stack size: 0x800
>   GNU                  0x00000008       NT_GNU_PROPERTY_TYPE_0
>       Properties: no copy on protected
>   GNU                  0x00000018       NT_GNU_PROPERTY_TYPE_0
>       Properties: stack size: 0x111100
>         no copy on protected
>
> Displaying notes found in: .note.gnu.gold-version
>   Owner                 Data size       Description
>   GNU                  0x00000009       NT_GNU_GOLD_VERSION (gold version)
>     Version: gold 1.15
>
> File: y
>
> Displaying notes found in: .note.gnu.property
>   Owner                 Data size       Description
>   GNU                  0x00000018       NT_GNU_PROPERTY_TYPE_0
>       Properties: stack size: 0x111100
>         no copy on protected
> address@hidden gold-2]$
>
> --
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