From: Fangrui Song <maskray@google.com>
To: Florian Weimer <fweimer@redhat.com>
Cc: Jessica Clarke <jrtc27@jrtc27.com>,
Evan Green <evan@rivosinc.com>,
libc-alpha@sourceware.org, slewis@rivosinc.com,
vineetg@rivosinc.com, palmer@rivosinc.com
Subject: Re: [PATCH v8 3/6] riscv: Add __riscv_hwprobe pointer to ifunc calls
Date: Mon, 16 Oct 2023 21:46:41 -0700 [thread overview]
Message-ID: <20231017044641.pw2ccr6exvhtmhkk@google.com> (raw)
In-Reply-To: <87v8bszs20.fsf@oldenburg.str.redhat.com>
On 2023-09-29, Florian Weimer wrote:
>* Jessica Clarke:
>
>> Being able to write portable IFUNC resolvers across Linux, BSDs and
>> other similar OSes is valuable, and this would preclude that. In FreeBSD
>> there are no issues with calling functions from IFUNC resolvers; we just
>> process all non-IRELATIVE relocations before IRELATIVE ones.
>
>Even across multiple objects? In glibc, we rely on relocation order by
>the link editor to put IRELATIVE last, so we don't have that particular
>problem for IRELATIVE, but we have it for regular symbol-based
>relocations that happen to refer to IFUNC symbols because the relocation
>order my not reflect the symbol binding order.
>
>Thanks,
>Florian
As a resolution to
https://sourceware.org/bugzilla/show_bug.cgi?id=13302
("IRELATIVE relocation should come last"), GNU ld places IRELATIVE in
.rela.plt (strange, as IRELATIVE is not lazy).
I think relyong on this is too brittle, as IRELATIVE may be in .rela.dyn . I have just filed
https://sourceware.org/bugzilla/show_bug.cgi?id=30976
("rtld: resolve ifunc relocations after JUMP_SLOT/GLOB_DAT/etc")
based on my examples at https://maskray.me/blog/2021-01-18-gnu-indirect-function#relocation-resolving-order
FreeBSD rtld uses multiple phases and in my analysis
> The approach turns out to be very robust. Many segfault examples on
> glibc work on FreeBSD.
glibc rtld probably does not need to do so much. Just refactoring the loop in elf/dynamic-link.h
so that IRELATIVE, regardless of .rela.dyn or .rela.plt, will work for
my examples. Then the outcome will look good enough to me.
for (int ranges_index = 0; ranges_index < 2; ++ranges_index)
next prev parent reply other threads:[~2023-10-17 4:46 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-01 23:52 [PATCH v8 0/6] RISC-V: ifunced memcpy using new kernel hwprobe interface Evan Green
2023-09-01 23:52 ` [PATCH v8 1/6] riscv: Add Linux hwprobe syscall support Evan Green
2023-09-01 23:52 ` [PATCH v8 2/6] riscv: Add hwprobe vdso call support Evan Green
2023-09-01 23:52 ` [PATCH v8 3/6] riscv: Add __riscv_hwprobe pointer to ifunc calls Evan Green
2023-09-29 18:21 ` Jessica Clarke
2023-09-29 19:40 ` Florian Weimer
2023-09-29 19:49 ` Jessica Clarke
2023-10-17 4:46 ` Fangrui Song [this message]
2023-09-01 23:52 ` [PATCH v8 4/6] riscv: Enable multi-arg ifunc resolvers Evan Green
2023-09-01 23:52 ` [PATCH v8 5/6] riscv: Add ifunc helper method to hwprobe.h Evan Green
2023-09-01 23:52 ` [PATCH v8 6/6] riscv: Add and use alignment-ignorant memcpy Evan Green
2023-09-25 10:28 ` [PATCH v8 0/6] RISC-V: ifunced memcpy using new kernel hwprobe interface Palmer Dabbelt
2023-09-26 2:24 ` enh
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