From: Siddhesh Poyarekar <siddhesh@sourceware.org>
To: Florian Weimer <fweimer@redhat.com>
Cc: "H.J. Lu" <hjl.tools@gmail.com>,
GNU C Library <libc-alpha@sourceware.org>
Subject: Re: [PATCH] ld.so: Handle read-only dynamic section gracefully [BZ #28340]
Date: Thu, 16 Sep 2021 11:34:41 +0530 [thread overview]
Message-ID: <acae7589-37e5-e5e1-742e-c90b7d6af90a@sourceware.org> (raw)
In-Reply-To: <87wnnhnkcp.fsf@oldenburg.str.redhat.com>
On 9/16/21 11:16 AM, Florian Weimer wrote:
> * Siddhesh Poyarekar:
>
>> On 9/16/21 10:18 AM, Florian Weimer wrote:
>>> * H. J. Lu:
>>>
>>>> There is nothing wrong with read-only dynamic segment.
>>> A relocated DYNAMIC array is part of the ABI for !DL_RO_DYN_SECTION.
>>> ELF requires that DT_STRTAB is present. DT_STRTAB needs relocation.
>>> This means that for !DL_RO_DYN_SECTION, the dynamic segment cannot be in
>>> a read-ony LOAD segment for a valid ELF file.
>>
>> I think what H. J. means here is that we just never adjust DT_STRTAB
>> and add l_addr to it every time we use it.
>
> I understood that. But applications expected that DT_STRTAB value has
> been relocated.
>
> See the discussion about the setting of DL_RO_DYN_SECTION for RISC-V and
> libphobos. Quoting libphobos/libdruntime/gcc/sections/elf.d:
>
> | if (dyn.d_tag == DT_STRTAB)
> | {
> | version (CRuntime_Musl)
> | strtab = cast(const(char)*)(info.dlpi_addr + dyn.d_un.d_ptr); // relocate
> | else version (linux)
> | {
> | // This might change in future glibc releases (after 2.29) as dynamic sections
> | // are not required to be read-only on RISC-V. This was copy & pasted from MIPS
> | // while upstreaming RISC-V support. Otherwise MIPS is the only arch which sets
> | // in glibc: #define DL_RO_DYN_SECTION 1
> | version (RISCV_Any)
> | strtab = cast(const(char)*)(info.dlpi_addr + dyn.d_un.d_ptr); // relocate
> | else version (MIPS_Any)
> | strtab = cast(const(char)*)(info.dlpi_addr + dyn.d_un.d_ptr); // relocate
> | else
> | strtab = cast(const(char)*)dyn.d_un.d_ptr;
> | }
Yeah you're right, basically anything that uses dl_iterate_phdr and
subsequently reaches the DYNAMIC segment will be affected by this
change. So if we have to support read-only DYNAMIC then we must
allocate dynamically and relocate there, like we do for vdso.
Siddhesh
next prev parent reply other threads:[~2021-09-16 6:04 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-14 19:09 Siddhesh Poyarekar
2021-09-14 19:15 ` Florian Weimer
2021-09-15 1:14 ` Siddhesh Poyarekar
2021-09-15 14:35 ` H.J. Lu
2021-09-15 15:42 ` Siddhesh Poyarekar
2021-09-15 16:13 ` H.J. Lu
2021-09-15 16:24 ` Siddhesh Poyarekar
2021-09-15 16:34 ` H.J. Lu
2021-09-16 1:43 ` Siddhesh Poyarekar
2021-09-16 2:23 ` H.J. Lu
2021-09-16 3:46 ` Siddhesh Poyarekar
2021-09-16 4:26 ` H.J. Lu
2021-09-16 4:28 ` Siddhesh Poyarekar
2021-09-16 4:30 ` H.J. Lu
2021-09-16 4:48 ` Florian Weimer
2021-09-16 5:36 ` Siddhesh Poyarekar
2021-09-16 5:46 ` Florian Weimer
2021-09-16 6:04 ` Siddhesh Poyarekar [this message]
2021-09-16 14:11 ` Carlos O'Donell
2021-09-16 15:18 ` H.J. Lu
2021-09-16 16:45 ` Siddhesh Poyarekar
2021-09-16 17:38 ` H.J. Lu
2021-09-16 17:58 ` Siddhesh Poyarekar
2021-09-16 22:11 ` H.J. Lu
2021-09-17 2:47 ` Siddhesh Poyarekar
2021-09-17 2:59 ` H.J. Lu
2021-09-17 3:36 ` Siddhesh Poyarekar
2021-09-17 3:42 ` H.J. Lu
2021-09-17 3:44 ` Siddhesh Poyarekar
2021-09-17 3:44 ` Florian Weimer
2021-09-17 3:51 ` Siddhesh Poyarekar
2021-09-16 18:03 ` Florian Weimer
2021-09-16 22:14 ` H.J. Lu
2021-09-17 2:58 ` Siddhesh Poyarekar
2021-09-17 3:46 ` Florian Weimer
2021-09-17 4:00 ` Florian Weimer
2021-09-17 4:12 ` [PATCH] ld.so: Remove DL_RO_DYN_SECTION H.J. Lu
2021-09-17 6:54 ` David Abdurachmanov
2021-09-17 9:01 ` Siddhesh Poyarekar
2021-09-17 15:40 ` H.J. Lu
2021-10-14 12:36 ` [PATCH] ld.so: Handle read-only dynamic section gracefully [BZ #28340] Maciej W. Rozycki
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