[{"id":3688485,"web_url":"http://patchwork.ozlabs.org/comment/3688485/","msgid":"","list_archive_url":null,"date":"2026-05-08T14:52:25","subject":"Re: [PATCH 3/3] malloc: Remove currently broken memory tagging","submitter":{"id":14312,"url":"http://patchwork.ozlabs.org/api/people/14312/","name":"Florian Weimer","email":"fweimer@redhat.com"},"content":"* Yury Khrustalev:\n\n> Remove AArch64-specific code, that is currently broken, from the\n> core malloc implementation.\n>\n> Code clean-up, no functional change unrelated to memory tagging.\n\nFor future reference, it might be helpful to put into the commit message\nwhy this is broken (highlights are enough).\n\nAs I wrote before, I found the performance unsatisfactory. And I\ncouldn't get it work with sbrk.\n\nWas it actually broken? Maybe I botched my testing, but I could boot on\nAArch64 system where glibc was patched to enable memory tagging\nunconditionally.\n\nThanks,\nFlorian","headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","libc-alpha@sourceware.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","libc-alpha@sourceware.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=hZr06jLw;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=sourceware.org\n (client-ip=38.145.34.32; helo=vm01.sourceware.org;\n envelope-from=libc-alpha-bounces~incoming=patchwork.ozlabs.org@sourceware.org;\n receiver=patchwork.ozlabs.org)","sourceware.org;\n\tdkim=pass (1024-bit key,\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=hZr06jLw","sourceware.org; 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Maybe I botched my testing, but I could boot on\n> AArch64 system where glibc was patched to enable memory tagging\n> unconditionally.\n\nHave you run it on a system that has HWCAP2_MTE? One thing that doesn't\nwork is that calling free(ptr) results in a SIGSEGV if ptr is tagged and\nmemory it points to is also tagged. But of course for this to happen the\nsystem should have HWCAP2_MTE, and Glibc (or your test) should do prctl\nsyscall with PR_SET_TAGGED_ADDR_CTRL and then malloc should use mmap with\nPROT_MTE.\n\nIf you manage to enable memory tagging in malloc correctly, a lot of\nmalloc tests from the Glibc testsuite fail (due to similar segfaults\nresulting from tag mismatch).\n\nThanks,\nYury","headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","libc-alpha@sourceware.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","libc-alpha@sourceware.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=arm.com header.i=@arm.com header.a=rsa-sha256\n header.s=selector1 header.b=hIzPl3lg;\n\tdkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com\n header.a=rsa-sha256 header.s=selector1 header.b=hIzPl3lg;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=sourceware.org\n (client-ip=38.145.34.32; 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Ip=[4.158.2.129];\n Helo=[outbound-uk1.az.dlp.m.darktrace.com]","X-MS-Exchange-CrossTenant-AuthSource":"\n AM1PEPF000252E1.eurprd07.prod.outlook.com","X-MS-Exchange-CrossTenant-AuthAs":"Anonymous","X-MS-Exchange-CrossTenant-FromEntityHeader":"HybridOnPrem","X-BeenThere":"libc-alpha@sourceware.org","X-Mailman-Version":"2.1.30","Precedence":"list","List-Id":"Libc-alpha mailing list ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"libc-alpha-bounces~incoming=patchwork.ozlabs.org@sourceware.org"}},{"id":3688589,"web_url":"http://patchwork.ozlabs.org/comment/3688589/","msgid":"","list_archive_url":null,"date":"2026-05-08T16:29:43","subject":"Re: [PATCH 3/3] malloc: Remove currently broken memory tagging","submitter":{"id":14312,"url":"http://patchwork.ozlabs.org/api/people/14312/","name":"Florian Weimer","email":"fweimer@redhat.com"},"content":"* Yury Khrustalev:\n\n> Have you run it on a system that has HWCAP2_MTE? One thing that doesn't\n> work is that calling free(ptr) results in a SIGSEGV if ptr is tagged and\n> memory it points to is also tagged. But of course for this to happen the\n> system should have HWCAP2_MTE, and Glibc (or your test) should do prctl\n> syscall with PR_SET_TAGGED_ADDR_CTRL and then malloc should use mmap with\n> PROT_MTE.\n\nThe HWCAP2 bit was set, and the prctl call succeeded. It was definitely\nwas not easy to get this point, though.\n\n> If you manage to enable memory tagging in malloc correctly, a lot of\n> malloc tests from the Glibc testsuite fail (due to similar segfaults\n> resulting from tag mismatch).\n\nI went back to my old notes, and found this (regarding test failures in\nparticular):\n\n| There's some issue with the static startup code, and ldconfig from our\n| RPM builds crashes (seems compiler flags dependent). The glibc debug\n| malloc is completely broken because it calls mem2chunk on null\n| pointers, for free(NULL) and realloc(NULL, size). That's not valid in\n| MTE mode. Rebooting with MTE forced on in glibc (for dynamically\n| linked binaries) resulted in a crash in lvm. But it was not as bad as\n| I expected: podman and Go seem to be working.\n\nI think this was with glibc-2.39-derived code, so a bit different from\nthe malloc in the current tree.\n\nThanks,\nFlorian","headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","libc-alpha@sourceware.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","libc-alpha@sourceware.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=WB0tjlr/;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=sourceware.org\n (client-ip=2620:52:6:3111::32; helo=vm01.sourceware.org;\n envelope-from=libc-alpha-bounces~incoming=patchwork.ozlabs.org@sourceware.org;\n receiver=patchwork.ozlabs.org)","sourceware.org;\n\tdkim=pass (1024-bit key,\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=WB0tjlr/","sourceware.org; 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One thing that doesn't\n>> work is that calling free(ptr) results in a SIGSEGV if ptr is tagged and\n>> memory it points to is also tagged. But of course for this to happen the\n>> system should have HWCAP2_MTE, and Glibc (or your test) should do prctl\n>> syscall with PR_SET_TAGGED_ADDR_CTRL and then malloc should use mmap with\n>> PROT_MTE.\n> \n> The HWCAP2 bit was set, and the prctl call succeeded. It was definitely\n> was not easy to get this point, though.\n> \n>> If you manage to enable memory tagging in malloc correctly, a lot of\n>> malloc tests from the Glibc testsuite fail (due to similar segfaults\n>> resulting from tag mismatch).\n> \n> I went back to my old notes, and found this (regarding test failures in\n> particular):\n> \n> | There's some issue with the static startup code, and ldconfig from our\n> | RPM builds crashes (seems compiler flags dependent). The glibc debug\n> | malloc is completely broken because it calls mem2chunk on null\n> | pointers, for free(NULL) and realloc(NULL, size). That's not valid in\n> | MTE mode. Rebooting with MTE forced on in glibc (for dynamically\n> | linked binaries) resulted in a crash in lvm. But it was not as bad as\n> | I expected: podman and Go seem to be working.\n\nWas podman podmad built with gccgo or golang? If the latter it does not\ngive us much information about memory tagging status since afaik golang\nbinaries do not use libc malloc.\n\n> \n> I think this was with glibc-2.39-derived code, so a bit different from\n> the malloc in the current tree.\n> \n> Thanks,\n> Florian\n>","headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","libc-alpha@sourceware.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","libc-alpha@sourceware.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=linaro.org header.i=@linaro.org header.a=rsa-sha256\n header.s=google header.b=M+cF3u0m;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=sourceware.org\n (client-ip=38.145.34.32; helo=vm01.sourceware.org;\n envelope-from=libc-alpha-bounces~incoming=patchwork.ozlabs.org@sourceware.org;\n receiver=patchwork.ozlabs.org)","sourceware.org;\n\tdkim=pass (2048-bit key,\n unprotected) header.d=linaro.org header.i=@linaro.org header.a=rsa-sha256\n header.s=google header.b=M+cF3u0m","sourceware.org;\n dmarc=pass (p=none dis=none) header.from=linaro.org","sourceware.org; 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charset=UTF-8","Content-Transfer-Encoding":"7bit","X-BeenThere":"libc-alpha@sourceware.org","X-Mailman-Version":"2.1.30","Precedence":"list","List-Id":"Libc-alpha mailing list ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"libc-alpha-bounces~incoming=patchwork.ozlabs.org@sourceware.org"}},{"id":3688599,"web_url":"http://patchwork.ozlabs.org/comment/3688599/","msgid":"","list_archive_url":null,"date":"2026-05-08T16:44:13","subject":"Re: [PATCH 3/3] malloc: Remove currently broken memory tagging","submitter":{"id":14312,"url":"http://patchwork.ozlabs.org/api/people/14312/","name":"Florian Weimer","email":"fweimer@redhat.com"},"content":"* Adhemerval Zanella Netto:\n\n> On 08/05/26 13:29, Florian Weimer wrote:\n>> * Yury Khrustalev:\n>> \n>>> Have you run it on a system that has HWCAP2_MTE? One thing that doesn't\n>>> work is that calling free(ptr) results in a SIGSEGV if ptr is tagged and\n>>> memory it points to is also tagged. But of course for this to happen the\n>>> system should have HWCAP2_MTE, and Glibc (or your test) should do prctl\n>>> syscall with PR_SET_TAGGED_ADDR_CTRL and then malloc should use mmap with\n>>> PROT_MTE.\n>> \n>> The HWCAP2 bit was set, and the prctl call succeeded. It was definitely\n>> was not easy to get this point, though.\n>> \n>>> If you manage to enable memory tagging in malloc correctly, a lot of\n>>> malloc tests from the Glibc testsuite fail (due to similar segfaults\n>>> resulting from tag mismatch).\n>> \n>> I went back to my old notes, and found this (regarding test failures in\n>> particular):\n>> \n>> | There's some issue with the static startup code, and ldconfig from our\n>> | RPM builds crashes (seems compiler flags dependent). The glibc debug\n>> | malloc is completely broken because it calls mem2chunk on null\n>> | pointers, for free(NULL) and realloc(NULL, size). That's not valid in\n>> | MTE mode. Rebooting with MTE forced on in glibc (for dynamically\n>> | linked binaries) resulted in a crash in lvm. But it was not as bad as\n>> | I expected: podman and Go seem to be working.\n>\n> Was podman podmad built with gccgo or golang? If the latter it does not\n> give us much information about memory tagging status since afaik golang\n> binaries do not use libc malloc.\n\nThis was our build which uses OpenSSL cryptography and therefore links\nagainst glibc as well.\n\nThanks,\nFlorian","headers":{"Return-Path":"","X-Original-To":["incoming@patchwork.ozlabs.org","libc-alpha@sourceware.org"],"Delivered-To":["patchwork-incoming@legolas.ozlabs.org","libc-alpha@sourceware.org"],"Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=G8mIUrNW;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=sourceware.org\n (client-ip=2620:52:6:3111::32; helo=vm01.sourceware.org;\n envelope-from=libc-alpha-bounces~incoming=patchwork.ozlabs.org@sourceware.org;\n receiver=patchwork.ozlabs.org)","sourceware.org;\n\tdkim=pass (1024-bit key,\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=G8mIUrNW","sourceware.org; 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