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Tue, 10 Mar 2026 23:20:28 -0700 (PDT) Message-ID: Subject: Re: [SH] Check FPSCR.PR for fldi0, fldi1 insns in simulator From: Oleg Endo To: Simon Marchi , gdb-patches@sourceware.org Date: Wed, 11 Mar 2026 15:20:27 +0900 In-Reply-To: <6eb50919-75d8-4725-9afa-e241e4cabab6@simark.ca> References: <016918b6653a40835d2272c3c37d05b0d7e470b6.camel@gmail.com> <6eb50919-75d8-4725-9afa-e241e4cabab6@simark.ca> Content-Type: multipart/mixed; boundary="=-EDxZb7qYSPjDVQ7jhdI2" User-Agent: Evolution 3.54.3 (3.54.3-2.fc41) MIME-Version: 1.0 X-BeenThere: gdb-patches@sourceware.org X-Mailman-Version: 2.1.30 Precedence: list List-Id: Gdb-patches mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: gdb-patches-bounces~public-inbox=simark.ca@sourceware.org --=-EDxZb7qYSPjDVQ7jhdI2 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Wed, 2026-03-11 at 00:27 -0400, Simon Marchi wrote: >=20 > On 2026-03-10 23:02, Oleg Endo wrote: > > Hi, > >=20 > > On SH variants with double-precision FPU the insns fli0 and flid1 requi= re > > that FPSCR.PR must be set to 0, i.e. single-precision mode. The attach= ed > > patch fixes that. > >=20 > > OK to apply? > >=20 > > Best regards, > > Oleg Endo >=20 > I looked for an ISA manual [1] and checked it for fun. For the FLID0, > it says: >=20 > When FPSCR.PR =3D 0, this instruction loads floating-point 0.0 (0x00000= 000) into FRn. >=20 > Curiously, it does not say what happens if `FPSCR.PR =3D 1`. However, > the description for FPSCR.PR says: >=20 > PR: Precision mode > PR =3D 0: Floating-point instructions are executed as single-precision = operations. > PR =3D 1: Floating-point instructions are executed as double-precision = operations (the result of > instructions for which double-precision is not supported is undefined). >=20 > I guess that FLID0 and FLID1 fall into that "is undefined" category? > Do you know what the real hardware does in this case? I have not checked what exactly happens on real hardware. I have checked a few ISA manuals (Renesas, ST). The instruction descriptions doesn't say that FLDI0 / FLID1 raises an exception (when in the wrong mode). So I gues= s it will produce garbage quietly. Maybe some silicon implementations have actually an undocumented but well defined behavior. QEMU traps in this case. We found this while chasing an GCC bug. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D117182 I find using sh-sim for compiler testing quite useful. Hence this patch. >=20 > The patch LGTM, but I am not a maintainer of the sim, so: >=20 > Reviewed-By: Simon Marchi >=20 > One note, please put the relevant information (the body of your email) > into the commit log itself). Yeah, sure I can expand the comment of the commit. Updated patch/commit attached. Best regards, Oleg Endo --=-EDxZb7qYSPjDVQ7jhdI2 Content-Disposition: attachment; filename*0=0002-simsh-check-PFSCRPR-setting-for-fldi0-and-fldi1-insns.pa; filename*1=tch Content-Type: text/x-patch; name="0002-simsh-check-PFSCRPR-setting-for-fldi0-and-fldi1-insns.patch"; charset="UTF-8" Content-Transfer-Encoding: base64 RnJvbSBkY2RhNzE2MzA4ODM3MTUxYTIyYjc2NTM4MWQwMDAzY2M0Yjk3MjNmIE1vbiBTZXAgMTcg MDA6MDA6MDAgMjAwMQpGcm9tOiBPbGVnIEVuZG8gPG9sZWdlbmRvQGdjYy5nbnUub3JnPgpEYXRl OiBXZWQsIDExIE1hciAyMDI2IDExOjU1OjIwICswOTAwClN1YmplY3Q6IFtQQVRDSF0gc2ltL3No OiBjaGVjayBQRlNDUi5QUiBzZXR0aW5nIGZvciBmbGRpMCBhbmQgZmxkaTEgaW5zbnMKCk9uIFNI IHZhcmlhbnRzIHdpdGggZG91YmxlLXByZWNpc2lvbiBGUFUgdGhlIGluc25zIGZsaTAgYW5kIGZs aWQxIGFyZSBvbmx5CmRlZmluZWQgd2hlbiBGUFNDUi5QUiA9IDAuICBUaGUgaGFyZHdhcmUgZG9l cyBub3QgbmVjZXNzYXJpbHkgdHJhcCBidXQgbWlnaHQKcXVpZXRseSBsb2FkIHVuZGVmaW5lZCB2 YWx1ZXMuICBIb3dldmVyLCBxZW11IHRyYXBzIGluIHRoYXQgY2FzZSwgc28gZG8gdGhlCnNhbWUu Ci0tLQogc2ltL3NoL2dlbmNvZGUuYyB8IDEyICsrKysrKysrLS0tLQogMSBmaWxlIGNoYW5nZWQs IDggaW5zZXJ0aW9ucygrKSwgNCBkZWxldGlvbnMoLSkKCmRpZmYgLS1naXQgYS9zaW0vc2gvZ2Vu Y29kZS5jIGIvc2ltL3NoL2dlbmNvZGUuYwppbmRleCA0MjAwOWZjLi45Yzg4MmQyIDEwMDY0NAot LS0gYS9zaW0vc2gvZ2VuY29kZS5jCisrKyBiL3NpbS9zaC9nZW5jb2RlLmMKQEAgLTY0NCwxOCAr NjQ0LDIyIEBAIHN0YXRpYyBvcCB0YWJbXSA9CiAKICAgLyogc2gyZSAqLwogICB7ICIiLCAiIiwg ImZsZGkwIDxGUkVHX04+IiwgIjExMTFubm5uMTAwMDExMDEiLAogICAgIHsKLSAgICAgICJTRVRf RlIgKG4sIChmbG9hdCkgMC4wKTsiLAotICAgICAgIi8qIEZJWE1FOiBjaGVjayBmb3IgRFAgYW5k IChuICYgMSkgPT0gMD8gICovIiwKKyAgICAgICJpZiAoRlBTQ1JfUFIpIiwKKyAgICAgICIgIFJB SVNFX0VYQ0VQVElPTiAoU0lHSUxMKTsiLAorICAgICAgImVsc2UiLAorICAgICAgIiAgU0VUX0ZS IChuLCAoZmxvYXQpIDAuMCk7IiwKICAgICB9LAogICB9LAogCiAgIC8qIHNoMmUgKi8KICAgeyAi IiwgIiIsICJmbGRpMSA8RlJFR19OPiIsICIxMTExbm5ubjEwMDExMTAxIiwKICAgICB7Ci0gICAg ICAiU0VUX0ZSIChuLCAoZmxvYXQpIDEuMCk7IiwKLSAgICAgICIvKiBGSVhNRTogY2hlY2sgZm9y IERQIGFuZCAobiAmIDEpID09IDA/ICAqLyIsCisgICAgICAiaWYgKEZQU0NSX1BSKSIsCisgICAg ICAiICBSQUlTRV9FWENFUFRJT04gKFNJR0lMTCk7IiwKKyAgICAgICJlbHNlIiwKKyAgICAgICIg IFNFVF9GUiAobiwgKGZsb2F0KSAxLjApOyIsCiAgICAgfSwKICAgfSwKIAogICAvKiBzaDJlICov Ci0tCmxpYmdpdDIgMS45LjEKCg== --=-EDxZb7qYSPjDVQ7jhdI2--