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[87.115.72.67]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49996100184sm282265415e9.1.2026.08.18.03.18.41 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Aug 2026 03:18:41 -0700 (PDT) From: Andrew Burgess To: Sebastian Huber , gdb-patches@sourceware.org Subject: Re: [PATCH 3/4] sim/mips: Deliver the reserved instruction exception In-Reply-To: <20260816234357.278358-4-sebastian.huber@embedded-brains.de> References: <20260816234357.278358-1-sebastian.huber@embedded-brains.de> <20260816234357.278358-4-sebastian.huber@embedded-brains.de> Date: Tue, 18 Aug 2026 11:18:40 +0100 Message-ID: <87tsor20lb.fsf@redhat.com> MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 9K_zr6RXO6wRJctXfoRggXEC3AVPKuhcQqmj1rxYMU8_1787048322 X-Mimecast-Originator: redhat.com Content-Type: text/plain 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 Sebastian Huber writes: > The ReservedInstruction and CoProcessorUnusable cases of > signal_exception() compute CAUSE, SR and EPC and set PC to the exception > handler address, and then assign PC = EPC, which discards all of it. > The client resumes on the faulting instruction rather than in its > handler, so it raises the same exception again and never advances. The > address error cases immediately above deliberately do not do this and > say so in a comment. > > The consequence is that a target which handles the exception never runs. > A compiler emits rdhwr to read the thread pointer for every access to a > thread-local object on every MIPS target, because the instruction exists > since MIPS32r2 and the operating system is expected to emulate it where > the processor lacks it. The R3900 lacks it. > > Signed-off-by: Sebastian Huber Please remove the 'Signed-off-by' tag from all commits. This tag has no meaning for the GDB project, but might in the future. Sorry I missed giving this feedback on the earlier patches. Otherwise: Approved-By: Andrew Burgess Thanks, Andrew > --- > sim/mips/interp.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/sim/mips/interp.c b/sim/mips/interp.c > index a2757ec5ef7..5dbd1482b99 100644 > --- a/sim/mips/interp.c > +++ b/sim/mips/interp.c > @@ -1992,7 +1992,8 @@ signal_exception (SIM_DESC sd, > > case ReservedInstruction: > case CoProcessorUnusable: > - PC = EPC; > + /* Leave PC at the exception handler address. This allows emulating > + an instruction the CPU lacks. */ > sim_engine_halt (SD, CPU, NULL, PC, > sim_stopped, SIM_SIGILL); > > -- > 2.51.0