From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-x42b.google.com (mail-pf1-x42b.google.com [IPv6:2607:f8b0:4864:20::42b]) by sourceware.org (Postfix) with ESMTPS id D88743858406 for ; Wed, 8 Dec 2021 02:33:57 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org D88743858406 Received: by mail-pf1-x42b.google.com with SMTP id g18so1175039pfk.5 for ; Tue, 07 Dec 2021 18:33:57 -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=d/gwaYO1Io7Ge0/BelIT5d9pQct3AWaRfyRBB3BDeew=; b=U6cVFrDzYX799Axe9arNO+T8FwnzCqe994xlrItS1nYjo9raWHNh8yy3BBAvgiMbfJ u9XUGn2uZXZRKD/xb3ZMHP43MZySzDJkuatpAZ9iPeaOz8HxHikAqA3BF3bO8yRogsBE uaqFbIKYuhvDhflggeXhWOQXqZuaW7nz2zgeCglD+QwX/Lgo/ogNjx5KaBaYQIYE1qzG hDdmnlnJ3MR/GlpFo151dhIleY+AnCtFhCsORGA9apLVOOUCSjazszMRAVG5hQt5ayCq 9GT9UzKti5fA9jFPaY2P8CW3/VHLAqmmCmiqeObgQtTtYOS67GfuB3MQD/nQ7sAdV2BD Yf5A== X-Gm-Message-State: AOAM530o2WD56F0wNeo4TCUsDshHEsByGzmNDDJ7FyzR6WpbWJx39UWf MpwgLtyjXXfIwUBltiXvo4r1lEZgs6Q9rTLGQ6i+4dOZt7k= X-Google-Smtp-Source: ABdhPJzoh8mGfvJuNUFoSxJc/QfdS/5iJB3dTYbzrSvH4FWp7UOhFMxzNC8/eWfzejltM7vva61VkDvbZyK8/WD112A= X-Received: by 2002:a05:6a00:234e:b0:4ae:2e0d:cc68 with SMTP id j14-20020a056a00234e00b004ae2e0dcc68mr2946070pfj.60.1638930836900; Tue, 07 Dec 2021 18:33:56 -0800 (PST) MIME-Version: 1.0 References: <20211204045848.71105-1-rongwei.wang@linux.alibaba.com> <20211204045848.71105-2-rongwei.wang@linux.alibaba.com> <53904314-f919-5965-a9cf-20c1b43eb47a@linux.alibaba.com> In-Reply-To: <53904314-f919-5965-a9cf-20c1b43eb47a@linux.alibaba.com> From: "H.J. Lu" Date: Tue, 7 Dec 2021 18:33:21 -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=-3028.7 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: Wed, 08 Dec 2021 02:34:00 -0000 On Tue, Dec 7, 2021 at 6:14 PM Rongwei Wang wrote: > > Hi hjl > > On 12/6/21 10:48 PM, H.J. Lu wrote: > > 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.cgiOK > > And I requesting the account. > > > > with a testcase which should align variables to 2MB in the main > By the way, I have a question about whether we need to align each LOAD > segments? In our patch, we only fixed the mapping address for the first > LOAD segment. I think the first one should be sufficient. You can verify it with a 2MB aligned variable in PIE: [hjl@gnu-cfl-2 tmp]$ cat x.c #include int foo __attribute__((aligned(0x200000))) = 1; int main () { printf ("foo: %p\n", &foo); } [hjl@gnu-cfl-2 tmp]$ gcc -no-pie x.c [hjl@gnu-cfl-2 tmp]$ ./a.out foo: 0x800000 [hjl@gnu-cfl-2 tmp]$ gcc x.c -fpie -pie [hjl@gnu-cfl-2 tmp]$ ./a.out foo: 0x55c529afe000 [hjl@gnu-cfl-2 tmp]$ > > 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. > OK > > Thanks. > > > >> + } > >> 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.