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[71.211.161.25]) by smtp.gmail.com with ESMTPSA id bi11-20020a05663819cb00b0046b3f7528e9sm654353jab.82.2023.12.21.12.29.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 Dec 2023 12:29:43 -0800 (PST) From: Tom Tromey To: John Baldwin Cc: Tom Tromey , gdb-patches@sourceware.org Subject: Re: [PATCH] Mask x86 segment registers in Windows gdbserver References: <20231219144823.1070597-1-tromey@adacore.com> <3c3d8d0c-8e61-46c0-88d5-fecce4112b59@FreeBSD.org> X-Attribution: Tom Date: Thu, 21 Dec 2023 13:29:42 -0700 In-Reply-To: <3c3d8d0c-8e61-46c0-88d5-fecce4112b59@FreeBSD.org> (John Baldwin's message of "Wed, 20 Dec 2023 14:03:12 -0800") Message-ID: <87wmt72tah.fsf@tromey.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Spam-Status: No, score=-5.2 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE,SPF_HELO_NONE,SPF_PASS,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: >> A test internal to AdaCore prints the segment registers. When run >> using gdbserver, it shows: >> (gdb) print /x $gs >> $6 = 0x2b0000 >> However, the segment registers are only 16 bits -- so this has some >> invalid bits. >> gdb's windows-nat.c has long had a fix for this problem. This patch >> applies the fix to gdbserver as well. John> LGTM. Treating the x86 seg regs as 32-bits has required workarounds in John> various places, but not easily fixable unfortunately. Well, to my surprise, this patch caused regressions in our internal tester. It works again if I explicitly exclude the 'ss' register, like: if (!windows_process.wow64_process) return r >= AMD64_CS_REGNUM && r <= AMD64_GS_REGNUM && r != 19; Now, this seems "ok" to do in some sense. However, I can't explain why native gdb works fine, as it has the same logic in amd64_windows_segment_register_p. I'd welcome any thoughts you (or anybody) might have. Tom