From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: by sourceware.org (Postfix, from userid 7814) id C72B63896C1E; Mon, 18 Jan 2021 21:41:29 +0000 (GMT) DKIM-Filter: OpenDKIM Filter v2.11.0 sourceware.org C72B63896C1E Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit From: Fangrui Song To: glibc-cvs@sourceware.org Subject: [glibc/maskray/lld] elf: Replace a --defsym trick with an object file to be compatible with lld X-Act-Checkin: glibc X-Git-Author: Fangrui Song X-Git-Refname: refs/heads/maskray/lld X-Git-Oldrev: 42a0fab9487eea2b128b24d3cc57ef4a44829bbb X-Git-Newrev: 3678e9498ec9a069a33a225dd2e8464bde98dba5 Message-Id: <20210118214129.C72B63896C1E@sourceware.org> Date: Mon, 18 Jan 2021 21:41:29 +0000 (GMT) X-BeenThere: glibc-cvs@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Glibc-cvs mailing list List-Unsubscribe: , List-Archive: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 18 Jan 2021 21:41:29 -0000 https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=3678e9498ec9a069a33a225dd2e8464bde98dba5 commit 3678e9498ec9a069a33a225dd2e8464bde98dba5 Author: Fangrui Song Date: Sat Apr 11 14:21:35 2020 -0700 elf: Replace a --defsym trick with an object file to be compatible with lld The existing code specifies -Wl,--defsym=malloc=0 and other malloc.os definitions before libc_pic.a so that libc_pic.a(malloc.os) is not fetched. This trick is used to avoid multiple definition errors which would happen as a chain result: dl-allobjs.os has an undefined __libc_scratch_buffer_set_array_size __libc_scratch_buffer_set_array_size fetches libc_pic.a(scratch_buffer_set_array_size.os) libc_pic.a(scratch_buffer_set_array_size.os) has an undefined free free fetches libc_pic.a(malloc.os) libc_pic.a(malloc.os) has an undefined __libc_message __libc_message fetches libc_pic.a(libc_fatal.os) libc_fatal.os will cause a multiple definition error (__GI___libc_fatal) >>> defined at dl-fxstatat64.c >>> /tmp/p/glibc/Release/elf/dl-allobjs.os:(__GI___libc_fatal) >>> defined at libc_fatal.c >>> libc_fatal.os:(.text+0x240) in archive /tmp/p/glibc/Release/libc_pic.a lld processes --defsym after all input files, so this trick does not suppress multiple definition errors with lld. Split the step into two and use an object file to make the intention more obvious and make lld work. This is conceptually more appropriate because --defsym defines a SHN_ABS symbol while a normal definition is relative to the image base. See https://sourceware.org/pipermail/libc-alpha/2020-March/111910.html for discussions about the --defsym semantics. Diff: --- elf/Makefile | 11 ++++------- 1 file changed, 4 insertions(+), 7 deletions(-) diff --git a/elf/Makefile b/elf/Makefile index 543800f4be..e242fdc6c3 100644 --- a/elf/Makefile +++ b/elf/Makefile @@ -524,10 +524,6 @@ rtld-stubbed-symbols = \ malloc \ realloc \ -# The GCC arguments that implement $(rtld-stubbed-symbols). -rtld-stubbed-symbols-args = \ - $(patsubst %,-Wl$(comma)--defsym=%=0, $(rtld-stubbed-symbols)) - ifeq ($(have-ssp),yes) # rtld is not built with the stack protector, so these references will # go away in the rebuilds. @@ -536,9 +532,10 @@ endif $(objpfx)librtld.map: $(objpfx)dl-allobjs.os $(common-objpfx)libc_pic.a @-rm -f $@T - $(reloc-link) -o $@.o $(rtld-stubbed-symbols-args) \ - '-Wl,-(' $^ -lgcc '-Wl,-)' -Wl,-Map,$@T - rm -f $@.o + echo '$(patsubst %,.globl %;,$(rtld-stubbed-symbols)) $(patsubst %,%:,$(rtld-stubbed-symbols))' | \ + $(CC) -o $@T.o $(ASFLAGS) -c -x assembler - + $(reloc-link) -o $@.o $@T.o '-Wl,-(' $^ -lgcc '-Wl,-)' -Wl,-Map,$@T + rm -f %@T.o $@.o mv -f $@T $@ # For lld, skip preceding addresses and values before matching the archive and the member.