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Mon, 09 May 2022 23:41:06 -0700 (PDT) Date: Mon, 9 May 2022 23:41:02 -0700 From: Fangrui Song To: Alexey Kardashevskiy Subject: Re: [PATCH 1/2] powerpc/vdso: Remove unused ENTRY in linker scripts Message-ID: <20220510064102.pvk3dvqnpihgo3bd@google.com> References: <20220509204635.2539549-1-nathan@kernel.org> <20220509204635.2539549-2-nathan@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: llvm@lists.linux.dev, Nick Desaulniers , patches@lists.linux.dev, Nathan Chancellor , Tom Rix , Paul Mackerras , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On 2022-05-10, Alexey Kardashevskiy wrote: > > >On 5/10/22 06:46, Nathan Chancellor wrote: >>When linking vdso{32,64}.so.dbg with ld.lld, there is a warning about >>not finding _start for the starting address: >> >> ld.lld: warning: cannot find entry symbol _start; not setting start address >> ld.lld: warning: cannot find entry symbol _start; not setting start address >> >>Looking at GCC + GNU ld, the entry point address is 0x0: >> >> $ llvm-readelf -h vdso{32,64}.so.dbg &| rg "(File|Entry point address):" >> File: vdso32.so.dbg >> Entry point address: 0x0 >> File: vdso64.so.dbg >> Entry point address: 0x0 >> >>This matches what ld.lld emits: >> >> $ powerpc64le-linux-gnu-readelf -p .comment vdso{32,64}.so.dbg >> >> File: vdso32.so.dbg >> >> String dump of section '.comment': >> [ 0] Linker: LLD 14.0.0 >> [ 14] clang version 14.0.0 (Fedora 14.0.0-1.fc37) >> >> File: vdso64.so.dbg >> >> String dump of section '.comment': >> [ 0] Linker: LLD 14.0.0 >> [ 14] clang version 14.0.0 (Fedora 14.0.0-1.fc37) >> >> $ llvm-readelf -h vdso{32,64}.so.dbg &| rg "(File|Entry point address):" >> File: vdso32.so.dbg >> Entry point address: 0x0 >> File: vdso64.so.dbg >> Entry point address: 0x0 >> >>Remove ENTRY to remove the warning, as it is unnecessary for the vDSO to >>function correctly. LGTM. e_entry for the vDSO (generally all shared objects, unless invoked directly as the main executable) is unnecessary. >Sounds more like a bugfix to me - _start is simply not defined, I >wonder why ld is not complaining. This is a loose behavior in GNU ld. I know this but did not bother filing a feature request. Now that you mentioned it:) https://sourceware.org/bugzilla/show_bug.cgi?id=29136 (ld: ENTRY(no_such_symbol) in -shared mode does not report a warning) > >Tested-by: Alexey Kardashevskiy >Reviewed-by: Alexey Kardashevskiy > > >> >>Signed-off-by: Nathan Chancellor >>--- >> arch/powerpc/kernel/vdso/vdso32.lds.S | 1 - >> arch/powerpc/kernel/vdso/vdso64.lds.S | 1 - >> 2 files changed, 2 deletions(-) >> >>diff --git a/arch/powerpc/kernel/vdso/vdso32.lds.S b/arch/powerpc/kernel/vdso/vdso32.lds.S >>index 58e0099f70f4..e0d19d74455f 100644 >>--- a/arch/powerpc/kernel/vdso/vdso32.lds.S >>+++ b/arch/powerpc/kernel/vdso/vdso32.lds.S >>@@ -13,7 +13,6 @@ OUTPUT_FORMAT("elf32-powerpcle", "elf32-powerpcle", "elf32-powerpcle") >> OUTPUT_FORMAT("elf32-powerpc", "elf32-powerpc", "elf32-powerpc") >> #endif >> OUTPUT_ARCH(powerpc:common) >>-ENTRY(_start) >> SECTIONS >> { >>diff --git a/arch/powerpc/kernel/vdso/vdso64.lds.S b/arch/powerpc/kernel/vdso/vdso64.lds.S >>index 0288cad428b0..1a4a7bc4c815 100644 >>--- a/arch/powerpc/kernel/vdso/vdso64.lds.S >>+++ b/arch/powerpc/kernel/vdso/vdso64.lds.S >>@@ -13,7 +13,6 @@ OUTPUT_FORMAT("elf64-powerpcle", "elf64-powerpcle", "elf64-powerpcle") >> OUTPUT_FORMAT("elf64-powerpc", "elf64-powerpc", "elf64-powerpc") >> #endif >> OUTPUT_ARCH(powerpc:common64) >>-ENTRY(_start) >> SECTIONS >> { >