From: Kevin Buettner <kevinb@redhat.com>
To: Carl Love via Gdb-patches <gdb-patches@sourceware.org>
Cc: Carl Love <cel@us.ibm.com>, Ulrich Weigand <Ulrich.Weigand@de.ibm.com>
Subject: Re: [PATCH 1/2] PowerPC, function ppc64_sysv_abi_return_value add missing return value convention
Date: Fri, 7 Oct 2022 21:20:32 -0700 [thread overview]
Message-ID: <20221007212032.1944919c@f35-zws-1> (raw)
In-Reply-To: <56392545859f7e949ee1b8fa2198f3928f714bad.camel@us.ibm.com>
Hi Carl,
See my comments below...
On Thu, 06 Oct 2022 09:37:10 -0700
Carl Love via Gdb-patches <gdb-patches@sourceware.org> wrote:
> GDB maintainers:
>
> The following PowerPC specific patch fixes an issue of GDB reporting a
> bogus return value for functions that return a non-trivial value. The
> bogus return values result in five testcase failures for test
> gdb.cp/non-trivial-retval.exp. The issue is the function
> ppc64_sysv_abi_return_value does not return the correct value when the
> valtype->code() is TYPE_CODE_STRUCT and the language_pass_by_reference
> is not trivially_copyable. This patch adds the needed code to return
> RETURN_VALUE_STRUCT_CONVENTION in these cases.
>
> The testcase gdb.cp/non-trivial-retval.exp still fails as gdb now
> correctly reports "Cannot determine contents" instead of the expected
> values, which is correct in this case. The PowerPC ABI uses passes the
> return buffer address in r3. The value of r3 is valid on entry to the
> function but the PowerPC ABI does not guarantee it will not be changed
> in the function. Hence the contents of r3 is not reliable on exit from
> the function. This issue will be addressed by the next patch in this
> patch series.
>
> The patch has been tested on PowerPC and on Intel X86-64 with no
> regression failures.
>
> Please let me know if this patch is acceptable for the GDB mainline.
> Thanks.
>
> Carl Love
>
> -----------------------------------------
> PowerPC, function ppc64_sysv_abi_return_value add missing return value convention
>
> This patch address five testcase failures in gdb.cp/non-trivial-retval.exp.
> The following commit resulted in the five testcases failures on PowerPC. The
> value returned by the function is being reported incorrectly.
>
> commit b1718fcdd1d2a5c514f8ee504ba07fb3f42b8608
> Author: Andrew Burgess <aburgess@redhat.com>
> Date: Mon Dec 13 16:56:16 2021 +0000
>
> gdb: on x86-64 non-trivial C++ objects are returned in memory
>
> Fixes PR gdb/28681. It was observed that after using the `finish`
> command an incorrect value was displayed in some cases. Specifically,
> this behaviour was observed on an x86-64 target.
>
> The function:
>
> enum return_value_convention
> ppc64_sysv_abi_return_value (struct gdbarch *gdbarch, struct value *function,
> struct type *valtype, struct regcache *regcache,
> gdb_byte *readbuf, const gdb_byte *writebuf)
>
> should return RETURN_VALUE_STRUCT_CONVENTION if the valtype->code() is
> TYPE_CODE_STRUCT and if the language_pass_by_reference is not
> trivially_copyable.
>
> This patch adds the need code to return the value
s/need/needed/
> RETURN_VALUE_STRUCT_CONVENTION in the case of this case.
s/the case of //
>
> With this patch, the five test cases still fail but with the message "Value
> returned has type: A. Cannot determine contents". The PowerPC ABI stores the
> address of the buffer containing the function return value in register r3 on
> entry to the function. However, the PowerPC ABI does not guarentee that r3
> will not be modified in the function. So when the function returns, the return
> buffer address cannot be reliably obtained from register r3. Thus the message
> "Cannot determine contents" is appropriate in this case.
> ---
> gdb/ppc-sysv-tdep.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/gdb/ppc-sysv-tdep.c b/gdb/ppc-sysv-tdep.c
> index f57c261d9dc..14effb93210 100644
> --- a/gdb/ppc-sysv-tdep.c
> +++ b/gdb/ppc-sysv-tdep.c
> @@ -2099,6 +2099,10 @@ ppc64_sysv_abi_return_value (struct gdbarch *gdbarch, struct value *function,
> return RETURN_VALUE_REGISTER_CONVENTION;
> }
>
> + if (!language_pass_by_reference (valtype).trivially_copyable
> + && valtype->code () == TYPE_CODE_STRUCT)
> + return RETURN_VALUE_STRUCT_CONVENTION;
> +
> /* In the ELFv2 ABI, aggregate types of up to 16 bytes are
> returned in registers r3:r4. */
> if (tdep->elf_abi == POWERPC_ELF_V2
> --
> 2.31.1
This change looks good to me, but note the tweaks to the commit log remarks
above.
Kevin
P.S. I'm still looking at part 2.
next prev parent reply other threads:[~2022-10-08 4:20 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-11 22:26 [PATCH] PowerPC, add support for printing non-trivial C++ object for the finish command Carl Love
2022-03-13 5:28 ` Joel Brobecker
2022-03-14 10:43 ` Luis Machado
2022-03-14 13:40 ` Tom Tromey
2022-03-14 13:45 ` Luis Machado
2022-03-14 14:58 ` Ulrich Weigand
[not found] ` <ce6c71356c4a58fcdfb655a6e50c3a24f812e66c.camel@us.ibm.com>
[not found] ` <d9f17525c9a03c20b54015a6a71c36cae50fe4e3.camel@de.ibm.com>
[not found] ` <6ca2276426343756e103995e07ff951d6e26837b.camel@us.ibm.com>
[not found] ` <939797b94ab71f3f7356747d84a1515939cb3dcc.camel@de.ibm.com>
[not found] ` <fccc34c438fda9a35b8a8565e0f5026237e7eab9.camel@us.ibm.com>
[not found] ` <bb5b9b137fc11886964113d4b524526b3c733f4a.camel@us.ibm.com>
[not found] ` <1edb818bd2873a3fa5278f28131089d228a0a4f6.camel@de.ibm.com>
[not found] ` <7c884a865d06890cb325225c65d7a52fdfbd20d2.camel@us.ibm.com>
[not found] ` <846ca96309d2732d3db0e4c323a81105c098fa5f.camel@de.ibm.com>
[not found] ` <5a858dd7b957ecf45cf5b00ffc140a839c8ef023.camel@us.ibm.com>
[not found] ` <b634fecae5e33a3d1a278191c37f306a3b8622f2.camel@de.ibm.com>
[not found] ` <25f2380ced176f58a8e3ea9b70c7e7786988d650.camel@us.ibm.com>
[not found] ` <2b0481466e9ecc33d52c74c3a3b4babb05435f47.camel@de.ibm.com>
[not found] ` <df3b049416ff666e7bd3e3a91e4ea90d34256ea5.camel@us.ibm.com>
[not found] ` <71370ce02bd57827d3b7958772b1594d3591bd16.camel@de.ibm.com>
[not found] ` <ec9dafb1671699b03b28ee4be528711c6988eaa5.camel@us.ibm.com>
[not found] ` <148d8d3efcc8d110119e566027bfd0c65dd02525.camel@de.ibm.com>
[not found] ` <eef62b295e97fc464c22f9d748ff818860137de9.camel@us.ibm.com>
[not found] ` <afd6fa576f479359618b1ee50b08be8932735da8.camel@de.ibm.com>
[not found] ` <cb6b19e9d287d2bae4b72627791f2a00af062c48.camel@us.ibm.com>
[not found] ` <ee7101f86b5c8581905c53347fa603dc23ddc2bd.camel@de.ibm.com>
[not found] ` <8decd662134d57e8caf43960a1cdc47723e2bfe3.camel@us.ibm.com>
[not found] ` <f7cad695cf64540bad8c95cf5fd31691711d0eeb.camel@de.ibm.com>
[not found] ` <79d82ed277308ed5ce312bff398e770ab234390a.camel@us.ibm.com>
[not found] ` <63f21a897f452d81a73fb386cb99110a359ef0b7.camel@de.ibm.com>
[not found] ` <be178bc4f356d7f1937458290cb5883eeee9eee1.camel@us.ibm.com>
[not found] ` <dfd935e9414d3dd2c27d1e877d3718ae7510aa07.camel@de.ibm.com>
[not found] ` <97275f61ef101a12cde8e5a45008ed8e479424eb.camel@us.ibm.com>
[not found] ` <b629440707165f46fb466e48b0c95de3bfa334d2.camel@de.ibm.com>
[not found] ` <5a34aaeab59f0099b915d1780c701284a6cf691e.camel@us.ibm.com>
[not found] ` <8aa882863b2f4cef38c22386387c5705bf63c3d5.camel@de.ibm.com>
2022-10-06 16:37 ` [PATCH 1/2] PowerPC, function ppc64_sysv_abi_return_value add missing return value convention Carl Love
2022-10-08 4:20 ` Kevin Buettner [this message]
2022-10-14 23:20 ` Carl Love
2022-10-18 18:55 ` [PATCH 1/2 ver 2] " Carl Love
2022-11-07 20:04 ` [PATCH 1/2 ver 3] " Carl Love
2022-11-14 16:45 ` Ulrich Weigand
2022-11-14 19:38 ` Carl Love
[not found] ` <191f5826b228a7614c084c9704b086851d418c78.camel@us.ibm.com>
[not found] ` <5405a79ecd6ed34646ad77eed0779063ee222d37.camel@de.ibm.com>
2022-10-06 16:36 ` [PATCH 0/2] PowerPC, fix support for printing the function return value for non-trivial values Carl Love
2022-10-18 18:55 ` [PATCH 0/2 version 2] " Carl Love
2022-10-06 16:37 ` [PATCH 2/2] " Carl Love
2022-10-08 4:36 ` Kevin Buettner
2022-10-12 17:01 ` Carl Love
2022-10-14 2:49 ` Kevin Buettner
2022-10-14 7:36 ` Bruno Larsen
2022-10-14 23:25 ` Carl Love
2022-10-14 23:23 ` Carl Love
2022-10-18 1:06 ` Kevin Buettner
2022-10-18 18:26 ` Carl Love
2022-10-18 18:55 ` [PATCH 2/2 ver 2] " Carl Love
2022-10-31 16:07 ` Carl Love
2022-11-07 14:56 ` Bruno Larsen
2022-11-07 19:53 ` Carl Love
2022-11-07 20:04 ` [PATCH 2/2 ver 3] " Carl Love
2022-11-14 16:47 ` Ulrich Weigand
2022-11-15 7:15 ` Tom de Vries
2022-11-15 10:16 ` Ulrich Weigand
2022-11-15 16:04 ` Carl Love
2022-11-15 16:55 ` Simon Marchi
2022-11-15 23:46 ` Carl Love
2022-11-15 17:24 ` Carl Love
2022-11-15 18:05 ` Ulrich Weigand
2022-11-16 1:01 ` Carl Love
2022-11-16 9:52 ` Ulrich Weigand
2022-11-16 10:12 ` Tom de Vries
2022-11-16 10:20 ` Lancelot SIX
2022-11-16 15:56 ` Carl Love
2022-11-16 20:55 ` [PATCH] Change NULL to nullptr in gdb/infcmd.c and gdb/infrun.c Carl Love
2022-11-16 21:15 ` Simon Marchi
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