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Re: [PATCH] [PR libc/18801] PIE binary with STT_GNU_IFUNC symbol and TEXTREL segfaults on x86_64
- From: Sriraman Tallam <tmsriram at google dot com>
- To: "H.J. Lu" <hjl dot tools at gmail dot com>
- Cc: Paul Pluzhnikov <ppluzhnikov at google dot com>, GLIBC Devel <libc-alpha at sourceware dot org>, Ian Lance Taylor <iant at google dot com>, David Li <davidxl at google dot com>
- Date: Tue, 11 Aug 2015 17:55:33 -0700
- Subject: Re: [PATCH] [PR libc/18801] PIE binary with STT_GNU_IFUNC symbol and TEXTREL segfaults on x86_64
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On Tue, Aug 11, 2015 at 5:02 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Tue, Aug 11, 2015 at 3:57 PM, Sriraman Tallam <tmsriram@google.com> wrote:
>> On Tue, Aug 11, 2015 at 3:54 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>> On Tue, Aug 11, 2015 at 3:37 PM, Paul Pluzhnikov <ppluzhnikov@google.com> wrote:
>>>> On Tue, Aug 11, 2015 at 3:31 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>>
>>>>> No. I am proposing that linker issues an error if there is TEXTREL
>>>>> with IFUNC unless "-z now'" is used, assuming that this doesn't
>>>>> require changes to ld.so nor SELinux.
>>>>
>>>> Ah, ok. But that *doesn't* help current crash at all: "-z now" will
>>>> force IFUNC resolver (if any) to be called, and that call will fail
>>>> since we are currently removing execute protections.
>>>> (This is in fact the situation we've discovered the crash in originally.)
>>>
>>> Can you try adding -Wl,-z,execstack?
>>
>> Yes, making the stack executable will solve the problem. My test case
>> needed ".note.GNU-stack" specifically for this.
>
> Given SELinux issue, I don't think we should change ld.so. Instead,
> we can change ld to issue an error for TEXTREL with IFUNC and
> suggest -fPIE and -Wl,-z,execstack as workaround.
I am not sure I understand the problem. What is wrong with the patch?
Why should IFUNC+TEXTREL be disallowed?
Thanks
Sri
>
>
> --
> H.J.