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Re: port-amd64/54052: bump STACK_ALIGNBYTES for COMPAT_LINUX
The following reply was made to PR port-amd64/54052; it has been noted by GNATS.
From: Rin Okuyama <rokuyama.rk%gmail.com@localhost>
To: Joerg Sonnenberger <joerg%bec.de@localhost>, gnats-bugs%NetBSD.org@localhost
Cc: port-amd64-maintainer%netbsd.org@localhost, gnats-admin%netbsd.org@localhost,
Subject: Re: port-amd64/54052: bump STACK_ALIGNBYTES for COMPAT_LINUX
Date: Tue, 12 Mar 2019 17:55:47 +0900
On 2019/03/12 7:54, Joerg Sonnenberger wrote:
> On Mon, Mar 11, 2019 at 05:50:00AM +0000, rokuyama.rk%gmail.com@localhost wrote:
>> Linux binaries with glibc >= 2.23 randomly crashes in dynamic linker.
>> By bisectioning, the cause turns out to be this commit
> So the real problem is that ld.so doesn't do what any normal startup
> code does by aligning the stack explicitly. *sigh*
I don't get what you means...
(1) The bottom of stack (i.e., %rsp = &argc) is required to be aligned
to 16-byte boundary by "System V ABI - AMD64 Architecture Processor
(see pp. 29-30).
(2) However, we align it to only 8-byte boundary; we don't define
STACK_ALIGNBYTES for amd64, and __ALIGNBYTES = (8 - 1) is used instead:
1394 static size_t
1395 calcstack(struct execve_data * restrict data, const size_t gaplen)
1415 /* make the stack "safely" aligned */
1416 return STACK_LEN_ALIGN(stacklen, STACK_ALIGNBYTES);
(3) If the bottom of stack is aligned to 16-byte boundary, ld.so for
Linux works fine.
Therefore, I think that ld.so is legal within System V ABI. Isn't it?
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