[Bug ld/23900] New: Can't detect GNU program property generated by older linkers

[hjl.tools at gmail dot com]

https://sourceware.org/bugzilla/show_bug.cgi?id=23900

            Bug ID: 23900
           Summary: Can't detect GNU program property generated by older
                    linkers
           Product: binutils
           Version: 2.32 (HEAD)
            Status: NEW
          Severity: normal
          Priority: P2
         Component: ld
          Assignee: unassigned at sourceware dot org
          Reporter: hjl.tools at gmail dot com
  Target Milestone: ---

Linkers group input note sections with the same name into one output
note section with the same name.  One output note section is placed in
one PT_NOTE segment.  Since new linkers merge input .note.gnu.property
sections into one output .note.gnu.property section, there is only
one NT_GNU_PROPERTY_TYPE_0 note in one PT_NOTE segment with new linkers.
Since older linkers treat input .note.gnu.property section as a generic
note section and just concatenate all input .note.gnu.property sections
into one output .note.gnu.property section without merging them, we may
see invalid NT_GNU_PROPERTY_TYPE_0 note in PT_NOTE segment:

address@hidden tmp]$ cat x.S
#ifdef __LP64__
# define ALIGN 3
#else
# define ALIGN 2
#endif
        .section ".note", "a"
        .p2align ALIGN
        .long 1f - 0f           /* name length.  */
        .long 3f - 1f           /* data length.  */
        /* NT_GNU_PROPERTY_TYPE_0 */
        .long 5                 /* note type.  */
0:
        .asciz "GNU"            /* vendor name.  */
1:
        .p2align ALIGN
        /* GNU_PROPERTY_X86_ISA_1_USED */
        .long 0xc0010000        /* pr_type.  */
        .long 5f - 4f           /* pr_datasz.  */
4:
        .long 0x80000002
5:
        .p2align ALIGN
        /* GNU_PROPERTY_X86_FEATURE_2_USED */
        .long 0xc0010001        /* pr_type.  */
        .long 5f - 4f           /* pr_datasz.  */
4:
        .long 0x9
5:
        .p2align ALIGN
3:

        .text
        .globl _start
_start:
        ret
address@hidden tmp]$ gcc -c x.S -Wa,-mx86-used-note=no
address@hidden tmp]$ ld -o x x.o
address@hidden tmp]$ cat y.s 
        .text
        .globl _start
_start:
        movaps  %xmm0, %xmm1
address@hidden tmp]$ gcc -c y.s -Wa,-mx86-used-note=yes 
address@hidden tmp]$ ld -o y y.o
address@hidden tmp]$ readelf -n x

Displaying notes found in: .note
  Owner                 Data size       Description
  GNU                  0x00000020       NT_GNU_PROPERTY_TYPE_0
      Properties: x86 ISA used: SSE
        Invalid x86 feature used: x86, XMM
address@hidden tmp]$ readelf -n y

Displaying notes found in: .note.gnu.property
  Owner                 Data size       Description
  GNU                  0x00000020       NT_GNU_PROPERTY_TYPE_0
      Properties: x86 ISA used: SSE
        x86 feature used: x86, XMM
address@hidden tmp]$ 

'x' has invalid NT_GNU_PROPERTY_TYPE_0 note. But GNU_PROPERTY_X86_ISA_1_USED
has the GNU_PROPERTY_X86_UINT32_VALID bit set, which can also be set by
-mx86-used-note=yes.  We need a way to mark NT_GNU_PROPERTY_TYPE_0 note in
PT_NOTE segment is valid.

-- 
You are receiving this mail because:
You are on the CC list for the bug.