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([2804:14d:8084:993e::75d]) by smtp.gmail.com with ESMTPSA id 6a1803df08f44-90a817bb6ccsm16931596d6.13.2026.08.13.08.07.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 13 Aug 2026 08:07:37 -0700 (PDT) Message-ID: Date: Thu, 13 Aug 2026 12:07:33 -0300 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] gdb/record: avoid rax usage in i386-avx-record.exp To: Simon Marchi , gdb-patches@sourceware.org Cc: Christina Joos References: <20260813131022.24873-1-guinevere@redhat.com> <91d78916-4871-4264-8d27-4d221ee424b5@simark.ca> From: Guinevere Larsen In-Reply-To: <91d78916-4871-4264-8d27-4d221ee424b5@simark.ca> X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: LlSR_evCW08-gMXu9mrUEB_SVLn-tI5Nq8Oj5o1EE9c_1786633660 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit 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 On 8/13/26 11:51 AM, Simon Marchi wrote: > On 8/13/26 9:10 AM, Guinevere Larsen wrote: >> My recent commit, 1c04308f0958cbac83bad22703758139ea6969b6: >> >> Author: Guinevere Larsen >> Date: Tue Jun 16 16:03:43 2026 -0300 >> gdb/record: add support for BMI2 instructions >> >> Introduced a few tests that rely on the rax register being set before >> entering the function. This isn't reliable, as programs compiled with >> gcc-14 and earlier will have the register. To avoid compiler versions > This sentence ends abruptly. > > It's not clear to me what the problem is, could you explain it in simple > words :)? > > Simon > oops, sorry, need to do more proofreading I guess. The sentence should be "will have the registered clobbered, saving 0 on it" I haven't looked at the disassembly to know why, but something about how GCC 14 encodes the function calls makes EAX be 0 every time, and the test expects eax to be something else. Moving to a different register sidesteps this -- Cheers, Guinevere Larsen it/its she/her (deprecated)