From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pf1-x434.google.com (mail-pf1-x434.google.com [IPv6:2607:f8b0:4864:20::434]) by sourceware.org (Postfix) with ESMTPS id 2E9F33858D35 for ; Wed, 8 Dec 2021 23:52:39 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.4.1 sourceware.org 2E9F33858D35 Received: by mail-pf1-x434.google.com with SMTP id g19so3817766pfb.8 for ; Wed, 08 Dec 2021 15:52:39 -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=crUOPTU/Gb5Qdh0ANzYmJBQ9gm7gDMc9rRvY+gwYf8Y=; b=BgXM9TT2cy9+YFBjcMQJVxYVEMFSIAI0bXdDGvus8naYeW9pT+O2JvemDINnKM9N8A UABN6dEu3kwsx+hpQNO+AWccd7pkuox9mjHcL/mEPiu4lexRH8P3xGTkJJvqOJrCN3qI Z7MKMGzj+xHMrkihvstMl9J0BwRrLnIN1nQYtMJXNCoJ6golyYLKsIT2nxrnv91yi/ur cOD+YmkS6RlFjdlt1aTmbSfGMQh3ppYca2GjUIW94/JLhFi+ExyLOcl9YiasTSaTIJ4T eHwDPVvlAjJ4FULOGv9it050+gXxytjVK7b6THTNB4RCAJwpeOve5j9PMWFxNfN2ykhH wKMw== X-Gm-Message-State: AOAM532cAD/eWYOjbFDtUUZUhGuzEMuC7mqZxKDCJeq8MHjCGcK1Z6hz bf7PtOE+P58W+2qDu58ztSNVcnFH1HkdRn/J4caA3otUR4s= X-Google-Smtp-Source: ABdhPJxmsEkrwULw4XmSOywoV9sylvxGhtHKFmIJMLrRQsMlab/CwP2XHy7kiqVE39r7/lPPylU/GV0QjhmLeZkdIEQ= X-Received: by 2002:a63:4f42:: with SMTP id p2mr31922879pgl.381.1639007558097; Wed, 08 Dec 2021 15:52:38 -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: From: "H.J. Lu" Date: Wed, 8 Dec 2021 15:52:02 -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=-3028.6 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 23:52:41 -0000 On Tue, Dec 7, 2021 at 7:05 PM Rongwei Wang wrote: > > > > On 12/8/21 10:33 AM, H.J. Lu wrote: > > 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]$ > > Learned it! I opened: https://sourceware.org/bugzilla/show_bug.cgi?id=28676 > Thanks. > > > >>> 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.