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Re: RFC: Add GNU_PROPERTY_NEED_PHDRS
- From: Michael Matz <matz at suse dot de>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>
- Cc: Rich Felker <dalias at libc dot org>, Cary Coutant <ccoutant at gmail dot com>, Carlos O'Donell <carlos at redhat dot com>, Florian Weimer <fweimer at redhat dot com>, Szabolcs Nagy <nsz at port70 dot net>, Jan Beulich <JBeulich at suse dot com>, Binutils <binutils at sourceware dot org>, gnu-gabi at sourceware dot org
- Date: Tue, 2 Oct 2018 15:13:53 +0000 (UTC)
- Subject: Re: RFC: Add GNU_PROPERTY_NEED_PHDRS
- References: <CAMe9rOrrshfuAEx3J1E6bZwk7zyMpud-_=YU7rWpj8nx8cgfwQ@mail.gmail.com> <alpine.LSU.2.21.1810021447240.7867@wotan.suse.de> <CAMe9rOq38bLRyNMaMDfdbK=NvFg2YxEwSL3SERL=iapPZ+4COg@mail.gmail.com>
Hi,
On Tue, 2 Oct 2018, H.J. Lu wrote:
> A .note.gnu.property section will lead to a read-only data PT_LOAD segment
> as the first PT_LOAD segment:
Yes, and it's a hack. This section isn't necessary, it merely is the
easiest (?) way you found to force ld to create the PT_LOAD segment you
want. What about linker scripts that filter out all .note sections? You
_still_ want the phdrs to be mapped in that case. You basically replace
the current state (where the phdrs are mapped by accident) with a
different state that still only works by accident. It would be better to
make this work by design not accident.
Ciao,
Michael.
>
> [hjl@gnu-17 ld]$ readelf -WlS tmpdir/pr23428
> There are 16 section headers, starting at offset 0x2ed0:
>
> Section Headers:
> [Nr] Name Type Address Off Size
> ES Flg Lk Inf Al
> [ 0] NULL 0000000000000000 000000
> 000000 00 0 0 0
> [ 1] .note.gnu.property NOTE 0000000000400158 000158
> 000030 00 A 0 0 8
> [ 2] .text PROGBITS 0000000000401000 001000
> 0000ea 00 AX 0 0 16
> [ 3] .rodata PROGBITS 0000000000402000 002000
> 000006 01 AMS 0 0 1
> [ 4] .comment PROGBITS 0000000000000000 002006
> 00002d 01 MS 0 0 1
> [ 5] .debug_aranges PROGBITS 0000000000000000 002040
> 000060 00 0 0 16
> [ 6] .debug_info PROGBITS 0000000000000000 0020a0
> 0002f7 00 0 0 1
> [ 7] .debug_abbrev PROGBITS 0000000000000000 002397
> 000137 00 0 0 1
> [ 8] .debug_line PROGBITS 0000000000000000 0024ce
> 0001a7 00 0 0 1
> [ 9] .debug_frame PROGBITS 0000000000000000 002678
> 000040 00 0 0 8
> [10] .debug_str PROGBITS 0000000000000000 0026b8
> 0002a1 01 MS 0 0 1
> [11] .debug_loc PROGBITS 0000000000000000 002959
> 000295 00 0 0 1
> [12] .debug_ranges PROGBITS 0000000000000000 002bee
> 000020 00 0 0 1
> [13] .symtab SYMTAB 0000000000000000 002c10
> 0001e0 18 14 14 8
> [14] .strtab STRTAB 0000000000000000 002df0
> 000030 00 0 0 1
> [15] .shstrtab STRTAB 0000000000000000 002e20
> 0000ab 00 0 0 1
> Key to Flags:
> W (write), A (alloc), X (execute), M (merge), S (strings), I (info),
> L (link order), O (extra OS processing required), G (group), T (TLS),
> C (compressed), x (unknown), o (OS specific), E (exclude),
> l (large), p (processor specific)
>
> Elf file type is EXEC (Executable file)
> Entry point 0x4010c0
> There are 5 program headers, starting at offset 64
>
> Program Headers:
> Type Offset VirtAddr PhysAddr
> FileSiz MemSiz Flg Align
> LOAD 0x000000 0x0000000000400000 0x0000000000400000
> 0x000188 0x000188 R 0x1000
> LOAD 0x001000 0x0000000000401000 0x0000000000401000
> 0x0000ea 0x0000ea R E 0x1000
> LOAD 0x002000 0x0000000000402000 0x0000000000402000
> 0x000006 0x000006 R 0x1000
> NOTE 0x000158 0x0000000000400158 0x0000000000400158
> 0x000030 0x000030 R 0x8
> GNU_STACK 0x000000 0x0000000000000000 0x0000000000000000
> 0x000000 0x000000 RWE 0x10
>
> Section to Segment mapping:
> Segment Sections...
> 00 .note.gnu.property
> 01 .text
> 02 .rodata
> 03 .note.gnu.property
> 04
> [hjl@gnu-17 ld]$
>
>
>