From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-x436.google.com (mail-pf1-x436.google.com [IPv6:2607:f8b0:4864:20::436]) by sourceware.org (Postfix) with ESMTPS id D907F3858436 for ; Mon, 6 Dec 2021 14:48:45 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org D907F3858436 Received: by mail-pf1-x436.google.com with SMTP id g18so10373833pfk.5 for ; Mon, 06 Dec 2021 06:48:45 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=7XgwunYOdQa30tgaTgj5ht5zvYWHnyn4HhDPdhLFY3A=; b=fJrRyL+BcqnBk+k+SvBWeahWqDoTi6yyEUUcXrW9eTHR5L6EBHphghG8eIxdBbgN8u TKyr22FdfnTVTfglUTKMi8gVPomoDOA9T4E+7p8NygHZbkH2pMLWgEDtWk+fhhFQWxdY 3RwAk+Ns1iVjL6hpqxHep/eXejMO+aZGFzYE1xqNqIlZMeE8Wt6eADvAty87mk/VDzkM XcLJhiGty749yQ5t7+Micwan4BV5sD/GSgyPbKFRswcAKgn5qg2TWqGqDAzPM2BE6Pqb LMkKsX9qu8nxqwU7moJIgWQUAlwzwMxK+tDeT3hWLOIrpJepQKGfnm46ZnqgqCAHA7Ec vS0A== X-Gm-Message-State: AOAM532geA/JLNWGlczzGi3Zu88qL5YT6LPLgufqKzT5zk7C0sooIjCz Z3FdW3rK3yuD44iJpdalCI3I/xLQFHq5INe004NIrg+fV8Y= X-Google-Smtp-Source: ABdhPJyHNeRSDsR3hX2CXC1Dz2SsIZY6sxczwWvUUIqXtwNLw+j2Cj6rAMCyCi+ff8tEHRgQVDMSMc5t90bwV4k8dPA= X-Received: by 2002:a05:6a00:8cd:b0:4a2:82d7:1703 with SMTP id s13-20020a056a0008cd00b004a282d71703mr37811393pfu.43.1638802124876; Mon, 06 Dec 2021 06:48:44 -0800 (PST) MIME-Version: 1.0 References: <20211204045848.71105-1-rongwei.wang@linux.alibaba.com> <20211204045848.71105-2-rongwei.wang@linux.alibaba.com> In-Reply-To: <20211204045848.71105-2-rongwei.wang@linux.alibaba.com> From: "H.J. Lu" Date: Mon, 6 Dec 2021 06:48:09 -0800 Message-ID: Subject: Re: [PATCH RFC 1/1] elf: align the mapping address of LOAD segments with p_align To: Rongwei Wang Cc: GNU C Library , xuyu@linux.alibaba.com, gavin.dg@linux.alibaba.com Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-3029.2 required=5.0 tests=BAYES_00, DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DKIM_VALID_EF, FREEMAIL_FROM, GIT_PATCH_0, RCVD_IN_DNSWL_NONE, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.4 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 06 Dec 2021 14:48:47 -0000 On Fri, Dec 3, 2021 at 9:00 PM Rongwei Wang via Libc-alpha wrote: > > Now, ld.so always map the LOAD segments and aligned by base > page size (e.g. 4k in x86 or 4k, 16k and 64k in arm64). And > this patch improve the scheme here. In this patch, ld.so > can align the mapping address of the first LOAD segment with > p_align when p_align is greater than the current base page > size. This is a bug fix. Please open a glibc bug: https://sourceware.org/bugzilla/enter_bug.cgi with a testcase which should align variables to 2MB in the main program and a shared library. Please include the testcase in your patch and mention the glibc bug in your commit message. > And this change makes code segments using huge pages become > simple and available. > > Signed-off-by: Rongwei Wang > --- > elf/dl-load.c | 1 + > elf/dl-map-segments.h | 54 +++++++++++++++++++++++++++++++++++++++++-- > include/link.h | 3 +++ > 3 files changed, 56 insertions(+), 2 deletions(-) > > diff --git a/elf/dl-load.c b/elf/dl-load.c > index e39980fb19..136cfe2fa8 100644 > --- a/elf/dl-load.c > +++ b/elf/dl-load.c > @@ -1154,6 +1154,7 @@ _dl_map_object_from_fd (const char *name, const char *origname, int fd, > c->dataend = ph->p_vaddr + ph->p_filesz; > c->allocend = ph->p_vaddr + ph->p_memsz; > c->mapoff = ALIGN_DOWN (ph->p_offset, GLRO(dl_pagesize)); > + l->l_load_align = ph->p_align; > > /* Determine whether there is a gap between the last segment > and this one. */ > diff --git a/elf/dl-map-segments.h b/elf/dl-map-segments.h > index ac9f09ab4c..ae03236045 100644 > --- a/elf/dl-map-segments.h > +++ b/elf/dl-map-segments.h > @@ -18,6 +18,47 @@ > > #include > > +static __always_inline void * > +_dl_map_segments_align (const struct loadcmd *c, > + ElfW(Addr) mappref, int fd, size_t alignment, > + const size_t maplength) > +{ > + unsigned long map_start, map_start_align, map_end; > + unsigned long maplen = (maplength >= alignment) ? > + (maplength + alignment) : (2 * alignment); > + > + /* Allocate enough space to ensure that address aligned by > + p_align is included. */ > + map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplen, > + PROT_NONE, > + MAP_ANONYMOUS | MAP_PRIVATE, > + -1, 0); > + if (__glibc_unlikely ((void *) map_start == MAP_FAILED)) { > + /* If mapping a aligned address failed, then ... */ > + map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplength, > + c->prot, > + MAP_COPY|MAP_FILE, > + fd, c->mapoff); > + > + return (void *) map_start; > + } > + map_start_align = ALIGN_UP(map_start, alignment); > + map_end = map_start_align + maplength; > + > + /* Remember which part of the address space this object uses. */ > + map_start_align = (ElfW(Addr)) __mmap ((void *) map_start_align, maplength, > + c->prot, > + MAP_COPY|MAP_FILE|MAP_FIXED, > + fd, c->mapoff); > + if (__glibc_unlikely ((void *) map_start_align == MAP_FAILED)) > + return MAP_FAILED; > + if (map_start_align > map_start) > + __munmap((void *)map_start, map_start_align - map_start); > + __munmap((void *)map_end, map_start + maplen - map_end); > + > + return (void *) map_start_align; > +} > + Please follow the glibc coding format. > /* This implementation assumes (as does the corresponding implementation > of _dl_unmap_segments, in dl-unmap-segments.h) that shared objects > are always laid out with all segments contiguous (or with gaps > @@ -52,11 +93,20 @@ _dl_map_segments (struct link_map *l, int fd, > c->mapstart & GLRO(dl_use_load_bias)) > - MAP_BASE_ADDR (l)); > > - /* Remember which part of the address space this object uses. */ > - l->l_map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplength, > + /* During mapping, align the mapping address of the LOAD segments > + according to own p_align. This helps OS map its code segment to > + huge pages. */ > + if (l->l_load_align > GLRO(dl_pagesize)) { > + l->l_map_start = (ElfW(Addr)) _dl_map_segments_align (c, > + mappref, fd, > + l->l_load_align, maplength); > + } else { > + /* Remember which part of the address space this object uses. */ > + l->l_map_start = (ElfW(Addr)) __mmap ((void *) mappref, maplength, > c->prot, > MAP_COPY|MAP_FILE, > fd, c->mapoff); Please follow the glibc coding format. > + } > if (__glibc_unlikely ((void *) l->l_map_start == MAP_FAILED)) > return DL_MAP_SEGMENTS_ERROR_MAP_SEGMENT; > > diff --git a/include/link.h b/include/link.h > index aea268439c..fc6ce29fab 100644 > --- a/include/link.h > +++ b/include/link.h > @@ -298,6 +298,9 @@ struct link_map > > /* Thread-local storage related info. */ > > + /* Alignment requirement of the LOAD block. */ > + size_t l_load_align; > + > /* Start of the initialization image. */ > void *l_tls_initimage; > /* Size of the initialization image. */ > -- > 2.27.0 > Thanks. -- H.J.