From: Alan Modra <amodra@gmail.com>
To: Nick Alcock <nick.alcock@oracle.com>
Cc: binutils@sourceware.org, Indu Bhagat <gitlab@linux-git.oraclecorp.com>
Subject: Re: [PATCH 4/4] libctf: get the offsets of fields of unnamed structs/unions right
Date: Mon, 27 Mar 2023 21:52:34 +1030 [thread overview]
Message-ID: <ZCF8ekefjBi5Ky5R@squeak.grove.modra.org> (raw)
In-Reply-To: <87y1nilc9v.fsf@esperi.org.uk>
On Mon, Mar 27, 2023 at 11:27:40AM +0100, Nick Alcock wrote:
> On 25 Mar 2023, Alan Modra verbalised:
>
> > On Fri, Mar 24, 2023 at 01:36:25PM +0000, Nick Alcock via Binutils wrote:
> >> * testsuite/libctf-lookup/unnamed-field-info*: New test.
> >
> > arm-linux-gnueabi +FAIL: /home/alan/src/binutils-gdb/libctf/testsuite/libctf-lookup/unnamed-field-info.c
> > hppa-linux-gnu +FAIL: /home/alan/src/binutils-gdb/libctf/testsuite/libctf-lookup/unnamed-field-info.c
> > m68k-linux-gnu +FAIL: /home/alan/src/binutils-gdb/libctf/testsuite/libctf-lookup/unnamed-field-info.c
> > microblaze-linux-gnu +FAIL: /home/alan/src/binutils-gdb/libctf/testsuite/libctf-lookup/unnamed-field-info.c
> > mips-linux-gnu +FAIL: /home/alan/src/binutils-gdb/libctf/testsuite/libctf-lookup/unnamed-field-info.c
> > powerpc-linux-gnu +FAIL: /home/alan/src/binutils-gdb/libctf/testsuite/libctf-lookup/unnamed-field-info.c
> > s390-linux-gnu +FAIL: /home/alan/src/binutils-gdb/libctf/testsuite/libctf-lookup/unnamed-field-info.c
> > sh4-linux-gnu +FAIL: /home/alan/src/binutils-gdb/libctf/testsuite/libctf-lookup/unnamed-field-info.c
>
> Weird. I tested on two of those! (arm and powerpc).
>
> Are they all 32-bit platforms? It looks like it.
Yes, and built on x86_64-linux. Which is why things go wrong.
"lookup" is compiled and running on x86_64, thus compiled in offsets
are for the 64-bit host. The test objects are compiled by the
relevant target compiler, in this case all 32-bit. Things would break
with a 32-bit host and 64-bit targets too of course.
> > The fails look like:
> > field b inconsistency: offsetof() says 64 bits, CTF says 32
> > field one inconsistency: offsetof() says 128 bits, CTF says 64
> > field two inconsistency: offsetof() says 192 bits, CTF says 96
> > field three inconsistency: offsetof() says 256 bits, CTF says 128
> > field four inconsistency: offsetof() says 320 bits, CTF says 160
> > field x inconsistency: offsetof() says 384 bits, CTF says 192
> > field y inconsistency: offsetof() says 448 bits, CTF says 256
> > field z inconsistency: offsetof() says 384 bits, CTF says 192
> > field aleph inconsistency: offsetof() says 448 bits, CTF says 224
>
> All failing platforms are 32-bit, and they're all out by a factor of
> two. Just a coincidence, perhaps. (Definitely no more than a vague
> hunch.)
>
> I'll take a look. Maybe I can just make the test less picky -- all we're
> actually interested in for this bug is "CTF says 0". But this is worthy
> of investigation regardless. It's just as likely to be a compiler bug
> as a bug in libctf, I'd guess.
It's funny how we tend to not suspect the test. :)
--
Alan Modra
Australia Development Lab, IBM
next prev parent reply other threads:[~2023-03-27 11:22 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-24 13:36 [PATCH 1/4] libctf: fix assertion failure with no system qsort_r Nick Alcock
2023-03-24 13:36 ` [PATCH 2/4] libctf: work around an uninitialized variable warning Nick Alcock
2023-03-24 13:36 ` [PATCH 3/4] libctf: fix a comment typo Nick Alcock
2023-03-24 13:36 ` [PATCH 4/4] libctf: get the offsets of fields of unnamed structs/unions right Nick Alcock
2023-03-25 6:07 ` Alan Modra
2023-03-27 10:27 ` Nick Alcock
2023-03-27 11:22 ` Alan Modra [this message]
2023-03-27 12:38 ` Nick Alcock
2023-04-06 11:46 ` Nick Alcock
2023-04-08 15:50 ` Nick Alcock
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