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[192.0.220.237]) by smtp.gmail.com with ESMTPSA id bz12-20020a05622a1e8c00b0039a1146e0e1sm2144667qtb.33.2022.10.18.08.36.09 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Oct 2022 08:36:10 -0700 (PDT) Date: Tue, 18 Oct 2022 11:36:07 -0400 From: Mark Johnston To: Paul Floyd Cc: freebsd-hackers Subject: Re: AMD64 14.0-CURRENT memory layout changes Message-ID: References: <578a011d-0c3f-3f91-48ca-17999a6515a9@gmail.com> <259246b0-9592-3aa8-2a1a-52609ac5357c@gmail.com> List-Id: Technical discussions relating to FreeBSD List-Archive: https://lists.freebsd.org/archives/freebsd-hackers List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-hackers@freebsd.org MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <259246b0-9592-3aa8-2a1a-52609ac5357c@gmail.com> X-Rspamd-Queue-Id: 4MsHyM4x6Yz3Sq4 X-Spamd-Bar: -- Authentication-Results: mx1.freebsd.org; dkim=pass header.d=gmail.com header.s=20210112 header.b="ftCMdza/"; dmarc=none; spf=pass (mx1.freebsd.org: domain of markjdb@gmail.com designates 2607:f8b0:4864:20::72f as permitted sender) smtp.mailfrom=markjdb@gmail.com X-Spamd-Result: default: False [-2.70 / 15.00]; NEURAL_HAM_MEDIUM(-1.00)[-1.000]; NEURAL_HAM_LONG(-1.00)[-1.000]; NEURAL_HAM_SHORT(-1.00)[-0.998]; MID_RHS_NOT_FQDN(0.50)[]; FORGED_SENDER(0.30)[markj@freebsd.org,markjdb@gmail.com]; R_SPF_ALLOW(-0.20)[+ip6:2607:f8b0:4000::/36:c]; R_DKIM_ALLOW(-0.20)[gmail.com:s=20210112]; MIME_GOOD(-0.10)[text/plain]; FROM_HAS_DN(0.00)[]; PREVIOUSLY_DELIVERED(0.00)[freebsd-hackers@freebsd.org]; TO_MATCH_ENVRCPT_SOME(0.00)[]; DMARC_NA(0.00)[freebsd.org]; MLMMJ_DEST(0.00)[freebsd-hackers@freebsd.org]; RCVD_IN_DNSWL_NONE(0.00)[2607:f8b0:4864:20::72f:from]; RCVD_VIA_SMTP_AUTH(0.00)[]; DWL_DNSWL_NONE(0.00)[gmail.com:dkim]; FROM_NEQ_ENVFROM(0.00)[markj@freebsd.org,markjdb@gmail.com]; DKIM_TRACE(0.00)[gmail.com:+]; TO_DN_ALL(0.00)[]; RCVD_COUNT_THREE(0.00)[3]; ARC_NA(0.00)[]; RCPT_COUNT_TWO(0.00)[2]; MIME_TRACE(0.00)[0:+]; FREEMAIL_TO(0.00)[gmail.com]; ASN(0.00)[asn:15169, ipnet:2607:f8b0::/32, country:US]; FREEMAIL_ENVFROM(0.00)[gmail.com]; RCVD_TLS_LAST(0.00)[] X-ThisMailContainsUnwantedMimeParts: N On Tue, Oct 18, 2022 at 02:13:46PM +0200, Paul Floyd wrote: > > > > > How is 14.0 working out what address to use for the stack? > > (The above is with ASLR all off) > > > Answering my own question: > > it's in auxv (from __thr_get_main_stack_base) > > > /usr/include/sys/elf_common.h:#define AT_USRSTACKBASE 35 /* Top > of user stack */ > > I haven't yet added this (or AT_USRSTACKLIM) to the client auxv that > Valgrind synthesizes. > > > I'm still not certain that will fix it - I would have expected > __thr_get_main_stack_base to fallback to using sysctl. I think this is a compatibility bug in elf_aux_info(). The values of AT_USRSTACKBASE and AT_USRSTACKLIM can never legitimately be zero, I think, so we can use that to test. diff --git a/lib/libc/gen/auxv.c b/lib/libc/gen/auxv.c index af59a2dda90a..2f043f8814cf 100644 --- a/lib/libc/gen/auxv.c +++ b/lib/libc/gen/auxv.c @@ -381,15 +381,21 @@ _elf_aux_info(int aux, void *buf, int buflen) break; case AT_USRSTACKBASE: if (buflen == sizeof(u_long)) { - *(u_long *)buf = usrstackbase; - res = 0; + if (usrstackbase != 0) { + *(u_long *)buf = usrstackbase; + res = 0; + } else + res = ENOENT; } else res = EINVAL; break; case AT_USRSTACKLIM: if (buflen == sizeof(u_long)) { - *(u_long *)buf = usrstacklim; - res = 0; + if (usrstacklim != 0) { + *(u_long *)buf = usrstacklim; + res = 0; + } else + res = ENOENT; } else res = EINVAL; break;