From mboxrd@z Thu Jan 1 00:00:00 1970 Delivery-date: Tue, 06 Jan 2026 09:19:16 +0100 Received: from metis.whiteo.stw.pengutronix.de ([2a0a:edc0:2:b01:1d::104]) by lore.white.stw.pengutronix.de with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.96) (envelope-from ) id 1vd2Hc-001pMk-0v for lore@lore.pengutronix.de; Tue, 06 Jan 2026 09:19:16 +0100 Received: from bombadil.infradead.org ([2607:7c80:54:3::133]) by metis.whiteo.stw.pengutronix.de with esmtps (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1vd2Ha-0001qo-15 for lore@pengutronix.de; Tue, 06 Jan 2026 09:19:16 +0100 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: Content-Type:In-Reply-To:From:References:Cc:To:Subject:MIME-Version:Date: Message-ID:Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=dEI+ZAL7JPYHx3GkdrfDFfR1x4naqYwisDf84pnU1HU=; b=qAeT3fajCr5JmEhuoNMbW9+nu4 mBQTvM2VWW0YUNEfiEeEjkCiJFUK2tziyEQqeEhxceU2+cnt6i0pYkX/p6k5fLNxixXWgVcB5MwM4 0wS30nC5vv5JyteHRhh4JZKSXRZ3X9DMIYmMIXfJJ4VRnJN44i0dUaFQ2BQlkqDUlYFEbilkEsGPr xt8lP6ywHrEc0xpYd9onoMOwwoFL91YfOh/TbgCfNyCUO8gEeKfY01zP5gxRydElvyF9c1kjzVFaP 3COr2zXk9mOrNDh0sSyVWTo3QZuanjjuj+l4KTQeex7dvFfcFAuMZDavCoJIdw5fJ6MdGqY71NdEB vfiIZ1BQ==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vd2H7-0000000CbGu-0eLR; Tue, 06 Jan 2026 08:18:45 +0000 Received: from metis.whiteo.stw.pengutronix.de ([2a0a:edc0:2:b01:1d::104]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vd2H3-0000000CbGV-2qrf for barebox@lists.infradead.org; Tue, 06 Jan 2026 08:18:43 +0000 Received: from ptz.office.stw.pengutronix.de ([2a0a:edc0:0:900:1d::77] helo=[127.0.0.1]) by metis.whiteo.stw.pengutronix.de with esmtp (Exim 4.92) (envelope-from ) id 1vd2H2-0001mQ-1V; Tue, 06 Jan 2026 09:18:40 +0100 Message-ID: Date: Tue, 6 Jan 2026 09:18:39 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird To: Sascha Hauer Cc: BAREBOX , "Claude Sonnet 4.5" References: <20260105-pbl-load-elf-v1-0-e97853f98232@pengutronix.de> <20260105-pbl-load-elf-v1-6-e97853f98232@pengutronix.de> <9a2744c4-b115-40e9-9f19-36a291acaeb9@pengutronix.de> Content-Language: en-US From: Ahmad Fatoum In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260106_001842_506928_57323781 X-CRM114-Status: GOOD ( 42.19 ) X-BeenThere: barebox@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "barebox" X-SA-Exim-Connect-IP: 2607:7c80:54:3::133 X-SA-Exim-Mail-From: barebox-bounces+lore=pengutronix.de@lists.infradead.org X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on metis.whiteo.stw.pengutronix.de X-Spam-Level: X-Spam-Status: No, score=-4.0 required=4.0 tests=AWL,BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_NONE autolearn=unavailable autolearn_force=no version=3.4.2 Subject: Re: [PATCH 06/19] elf: implement elf_load_inplace() X-SA-Exim-Version: 4.2.1 (built Wed, 08 May 2019 21:11:16 +0000) X-SA-Exim-Scanned: Yes (on metis.whiteo.stw.pengutronix.de) On 1/5/26 23:42, Sascha Hauer wrote: > On Mon, Jan 05, 2026 at 02:37:13PM +0100, Ahmad Fatoum wrote: >> Hi, >> >> On 1/5/26 12:26 PM, Sascha Hauer wrote: >>> Implement elf_load_inplace() to apply dynamic relocations to an ELF binary >>> that is already loaded in memory. Unlike elf_load(), this function does not >>> allocate memory or copy segments - it only modifies the existing image in >>> place. >>> >>> This is useful for self-relocating loaders or when the ELF has been loaded >>> by external means (e.g., firmware or another bootloader). >> >> Nice. This is more elegant than what I came up with (compressing every >> segment separately). :) >> >>> For ET_DYN (position-independent) binaries, the relocation offset is >>> calculated relative to the first executable PT_LOAD segment (.text section), >>> taking into account the difference between the segment's virtual address >>> and its file offset. >> >> While this may be true for barebox proper, I think in the general case, >> we need to iterate over all segments and take the lowest address. >> The first executable PT_LOAD shouldn't have a special significance in >> this case. >> >>> >>> The entry point is also adjusted to point to the relocated image. >>> >>> Signed-off-by: Sascha Hauer >>> Co-Authored-By: Claude Sonnet 4.5 >>> --- >>> common/elf.c | 152 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ >>> include/elf.h | 8 ++++ >>> 2 files changed, 160 insertions(+) >>> >>> diff --git a/common/elf.c b/common/elf.c >>> index fc2949c285ebb0c0740c68c551926da8d0bb8637..565b283b694773727ef77917cfd8c1d4ee83a8d1 100644 >>> --- a/common/elf.c >>> +++ b/common/elf.c >>> @@ -531,3 +531,155 @@ void elf_close(struct elf_image *elf) >>> >>> free(elf); >>> } >>> + >>> +static void *elf_find_dynamic_inplace(struct elf_image *elf) >> >> const void * >> >>> +{ >>> + void *buf = elf->hdr_buf; >>> + void *phdr = buf + elf_hdr_e_phoff(elf, buf); >>> + int i; >>> + >>> + for (i = 0; i < elf_hdr_e_phnum(elf, buf); i++) { >>> + if (elf_phdr_p_type(elf, phdr) == PT_DYNAMIC) { >>> + u64 offset = elf_phdr_p_offset(elf, phdr); >>> + /* For in-place binary, PT_DYNAMIC is at hdr_buf + offset */ >>> + return elf->hdr_buf + offset; >>> + } >>> + phdr += elf_size_of_phdr(elf); >>> + } >>> + >>> + return NULL; /* No PT_DYNAMIC segment */ >>> +} >>> + >>> +/** >>> + * elf_load_inplace() - Apply dynamic relocations to an ELF binary in place >>> + * @elf: ELF image previously opened with elf_open_binary() >>> + * >>> + * This function applies dynamic relocations to an ELF binary that is already >>> + * loaded at its target address in memory. Unlike elf_load(), this does not >>> + * allocate memory or copy segments - it only modifies the existing image. >>> + * >>> + * This is useful for self-relocating loaders or when the ELF has been loaded >>> + * by external means (e.g., loaded by firmware or another bootloader). >>> + * >>> + * The ELF image must have been previously opened with elf_open_binary(). >>> + * >>> + * For ET_DYN (position-independent) binaries, the relocation offset is >>> + * calculated relative to the first executable PT_LOAD segment (.text section). >>> + * >>> + * For ET_EXEC binaries, no relocation is applied as they are expected to >>> + * be at their link-time addresses. >>> + * >>> + * Returns: 0 on success, negative error code on failure >>> + */ >>> +int elf_load_inplace(struct elf_image *elf) >>> +{ >>> + void *dyn_seg; >>> + void *buf, *phdr; >>> + void *elf_buf; >>> + int i, ret; >>> + >>> + buf = elf->hdr_buf; >>> + elf_buf = elf->hdr_buf; >>> + >>> + /* >>> + * First pass: Clear BSS segments (p_memsz > p_filesz). >>> + * This must be done before relocations as uninitialized data >>> + * must be zeroed per C standard. >>> + */ >>> + phdr = buf + elf_hdr_e_phoff(elf, buf); >>> + for (i = 0; i < elf_hdr_e_phnum(elf, buf); i++) { >>> + if (elf_phdr_p_type(elf, phdr) == PT_LOAD) { >>> + u64 p_offset = elf_phdr_p_offset(elf, phdr); >>> + u64 p_filesz = elf_phdr_p_filesz(elf, phdr); >>> + u64 p_memsz = elf_phdr_p_memsz(elf, phdr); >>> + >>> + /* Clear BSS (uninitialized data) */ >>> + if (p_filesz < p_memsz) { >>> + void *bss_start = elf_buf + p_offset + p_filesz; >>> + size_t bss_size = p_memsz - p_filesz; >>> + memset(bss_start, 0x00, bss_size); >> >> How can this be done in-place? If this is padding to get to a page >> boundary, I would assume it's already zero. If it goes beyond a page, >> this will overwrite follow-up segments wouldn't it? >> >> I also find bss_ an unforunate name here as this is applied to all segments. > > The code basically implements this (from > https://refspecs.linuxbase.org/elf/gabi4+/ch5.pheader.html): > > PT_LOAD > The array element specifies a loadable segment, described by > p_filesz and p_memsz. The bytes from the file are mapped to the > beginning of the memory segment. If the segment's memory size > (p_memsz) is larger than the file size (p_filesz), the ``extra'' > bytes are defined to hold the value 0 and to follow the segment's > initialized area > > You are right, this is done for all segments, but de facto the segment > containing the bss section is the only one where p_filesz < p_memsz > is actually used, so "Clear bss segments" doesn't sound too wrong to me. > > I experimented a bit. When I change the linker file to move the bss > section before the data section, the bss section really shows up as > zeroes in the ELF file and p_filesz becomes p_memsz for all segments. > Only when the bss section is at the very end of the binary the bss > section is no longer part of the ELF binary and may hit uninitialized > memory which we really have to memset. Ok. >>> + if (elf->type == ET_DYN) { >>> + u64 text_vaddr = 0; >>> + u64 text_offset = 0; >>> + bool found_text = false; >>> + >>> + /* Find first executable PT_LOAD segment (.text) */ >> >> As mentioned, we should rather get the lowest address across all segments. > > Not sure if this is true. I didn't manage to generate a binary where the > text section is not the first one. When I try to move for example the > data section before the text section then I end up with no executable > segment at all. Something weird is happening there, I haven't fully > understood how the generation of segments from sections work. Quoting your link: An executable or shared object file's base address (on platforms that support the concept) is calculated during execution from three values: the virtual memory load address, the maximum page size, and the lowest virtual address of a program's loadable segment. To compute the base address, one determines the memory address associated with the lowest p_vaddr value for a PT_LOAD segment. This address is truncated to the nearest multiple of the maximum page size. The corresponding p_vaddr value itself is also truncated to the nearest multiple of the maximum page size. The base address is the difference between the truncated memory address and the truncated p_vaddr value. >>> + /* Apply architecture-specific relocations */ >>> + ret = elf_apply_relocations(elf, dyn_seg); >> >> Should I upstream my relocate_image changes that reuse the >> relocate_to_current_adr() code and you rebase on top? > > Show the patch and we'll see. Just sent it. Cheers, Ahmad > > Sascha > -- Pengutronix e.K. | | Steuerwalder Str. 21 | http://www.pengutronix.de/ | 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |