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Levin" Cc: Oleg Nesterov , Michael Ellerman , Eugene Syromyatnikov , Mike Frysinger , Renzo Davoli , Davide Berardi , strace-devel@lists.strace.io, Madhavan Srinivasan , Nicholas Piggin , Christophe Leroy , Naveen N Rao , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 1/7] powerpc: properly negate error in syscall_set_return_value() Message-ID: References: <20250113170925.GA392@strace.io> <20250113171054.GA589@strace.io> <20250114134844.GA10630@strace.io> X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250114134844.GA10630@strace.io> On Tue, Jan 14, 2025 at 03:48:44PM +0200, Dmitry V. Levin wrote: > On Tue, Jan 14, 2025 at 02:00:16PM +0100, Alexey Gladkov wrote: > > On Mon, Jan 13, 2025 at 07:10:54PM +0200, Dmitry V. Levin wrote: > > > Bring syscall_set_return_value() in sync with syscall_get_error(), > > > and let upcoming ptrace/set_syscall_info selftest pass on powerpc. > > > > > > This reverts commit 1b1a3702a65c ("powerpc: Don't negate error in > > > syscall_set_return_value()"). > > > > > > Signed-off-by: Dmitry V. Levin > > > --- > > > arch/powerpc/include/asm/syscall.h | 6 +++++- > > > 1 file changed, 5 insertions(+), 1 deletion(-) > > > > > > diff --git a/arch/powerpc/include/asm/syscall.h b/arch/powerpc/include/asm/syscall.h > > > index 3dd36c5e334a..422d7735ace6 100644 > > > --- a/arch/powerpc/include/asm/syscall.h > > > +++ b/arch/powerpc/include/asm/syscall.h > > > @@ -82,7 +82,11 @@ static inline void syscall_set_return_value(struct task_struct *task, > > > */ > > > if (error) { > > > regs->ccr |= 0x10000000L; > > > - regs->gpr[3] = error; > > > + /* > > > + * In case of an error regs->gpr[3] contains > > > + * a positive ERRORCODE. > > > + */ > > > + regs->gpr[3] = -error; > > > > After this change the syscall_get_error() will return positive value if > > the system call failed. Since syscall_get_error() still believes > > regs->gpr[3] is still positive in case !trap_is_scv(). > > > > Or am I missing something? > > syscall_get_error() does the following in case of !trap_is_scv(): > > /* > * If the system call failed, > * regs->gpr[3] contains a positive ERRORCODE. > */ > return (regs->ccr & 0x10000000UL) ? -regs->gpr[3] : 0; > > That is, in !trap_is_scv() case it assumes that regs->gpr[3] is positive > and is going to return a negative value (-ERRORCODE). Yeah. Now I see it. if (trap_is_scv(regs)) { regs->result = -EINTR; regs->gpr[3] = -EINTR; } else { regs->result = -EINTR; regs->gpr[3] = EINTR; regs->ccr |= 0x10000000; } Two different APIs imply gpr[3] with a different sign. You can add: Reviewed-by: Alexey Gladkov > > It looks like the selftest you mentioned in the commit message doesn't > > check the !trap_is_scv() branch. > > The selftest is architecture-agnostic, it just executes syscalls and > checks whether the data returned by PTRACE_GET_SYSCALL_INFO meets > expectations. Do you mean that syscall() is not good enough for syscall > invocation from coverage perspective on powerpc? > > See also commit d72500f99284 ("powerpc/64s/syscall: Fix ptrace syscall > info with scv syscalls"). > > > -- > ldv -- Rgrds, legion