From: Willy Tarreau Date: Wed, 8 Jan 2025 08:31:41 +0000 (+0100) Subject: DEV: ncpu: make the wrapper work both as a lib and executable X-Git-Tag: v3.2-dev3~3 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ca773e1a2a4ed4992aba2ac26bf35011a7b8c11d;p=thirdparty%2Fhaproxy.git DEV: ncpu: make the wrapper work both as a lib and executable It's convenient to have a share lib be able to also work as a wrapper. But recent glibc broke support for this dual-mode thing some time ago: https://patchwork.ozlabs.org/project/glibc/patch/20190312130235.8E82C89CE49C@oldenburg2.str.redhat.com/ https://stackoverflow.com/questions/59074126/loading-executable-or-executing-a-library Trying to preload such an executable indeed returns: ERROR: ld.so: object '/path/to/ncpu.so' from LD_PRELOAD cannot be preloaded (cannot dynamically load position-independent executable): ignored. Note that the code still supports it since libc.so is both an executable and a lib. The approach taken here is the same as in the nousr.so wrapper. It consists in dropping the DF_1_PIE flag from the resulting executable since it's what the dynamic linker is looking for. This flag is found in FLAGS_1 in the .dynamic section. As readelf -a suggests, it's after the tag 0x6ffffffb. The value is 0x08000000. We're using objdump to figure the length and offset of the struct, dd to extract the 3 parts, and sed to patch the binary. It's likely that it will only work on 64-bit little endian, though tests should be performed to see what to do on other platforms. At least on x86_64, ld.so is happy and it continues to be possible to use the binary as a .so, and that the platform where most of the development happens so that's fine. In any case the wrapper and the standard shared lib are still made two distinct files so that it's possible to use the non-patched version on unsupported OSes or architectures. --- diff --git a/Makefile b/Makefile index f6cc556c0d..9bf63a280d 100644 --- a/Makefile +++ b/Makefile @@ -1022,7 +1022,7 @@ help: IGNORE_OPTS=help install install-man install-doc install-bin \ uninstall clean tags cscope tar git-tar version update-version \ opts reg-tests reg-tests-help admin/halog/halog dev/flags/flags \ - dev/haring/haring dev/poll/poll dev/tcploop/tcploop + dev/haring/haring dev/ncpu/ncpu dev/poll/poll dev/tcploop/tcploop ifneq ($(TARGET),) ifeq ($(filter $(firstword $(MAKECMDGOALS)),$(IGNORE_OPTS)),) @@ -1059,6 +1059,9 @@ dev/haring/haring: dev/haring/haring.o dev/hpack/%: dev/hpack/%.o $(cmd_LD) $(ARCH_FLAGS) $(LDFLAGS) -o $@ $^ $(LDOPTS) +dev/ncpu/ncpu: + $(cmd_MAKE) -C dev/ncpu ncpu V='$(V)' + dev/poll/poll: $(cmd_MAKE) -C dev/poll poll CC='$(CC)' OPTIMIZE='$(COPTS)' V='$(V)' @@ -1072,7 +1075,7 @@ dev/udp/udp-perturb: dev/udp/udp-perturb.o $(cmd_LD) $(ARCH_FLAGS) $(LDFLAGS) -o $@ $^ $(LDOPTS) # rebuild it every time -.PHONY: src/version.c dev/poll/poll dev/tcploop/tcploop +.PHONY: src/version.c dev/ncpu/ncpu dev/poll/poll dev/tcploop/tcploop src/calltrace.o: src/calltrace.c $(DEP) $(cmd_CC) $(TRACE_COPTS) -c -o $@ $< @@ -1138,7 +1141,7 @@ clean: distclean: clean $(Q)rm -f admin/iprange/iprange admin/iprange/ip6range admin/halog/halog $(Q)rm -f admin/dyncookie/dyncookie - $(Q)rm -f dev/haring/haring dev/poll/poll dev/tcploop/tcploop + $(Q)rm -f dev/haring/haring dev/ncpu/ncpu{,.so} dev/poll/poll dev/tcploop/tcploop $(Q)rm -f dev/hpack/decode dev/hpack/gen-enc dev/hpack/gen-rht $(Q)rm -f dev/qpack/decode diff --git a/dev/ncpu/Makefile b/dev/ncpu/Makefile index 2c1c42feb9..4307c99d4a 100644 --- a/dev/ncpu/Makefile +++ b/dev/ncpu/Makefile @@ -4,12 +4,28 @@ CC = cc OPTIMIZE = -O2 -g DEFINE = INCLUDE = -OBJS = ncpu.so +OBJS = ncpu.so ncpu +OBJDUMP = objdump all: $(OBJS) -%.so: %.c - $(cmd_CC) $(OPTIMIZE) $(DEFINE) $(INCLUDE) -fPIC -shared -o $@ $^ +%.o: %.c + $(cmd_CC) $(OPTIMIZE) $(DEFINE) $(INCLUDE) -shared -fPIC -c -o $@ $^ + +%.so: %.o + $(cmd_CC) -pie -o $@ $^ + $(Q)rm -f $^ + +%: %.so + $(call qinfo, PATCHING)set -- $$($(OBJDUMP) -j .dynamic -h $^ | fgrep .dynamic); \ + ofs=$$6; size=$$3; \ + dd status=none bs=1 count=$$((0x$$ofs)) if=$^ of=$^-p1; \ + dd status=none bs=1 skip=$$((0x$$ofs)) count=$$((0x$$size)) if=$^ of=$^-p2; \ + dd status=none bs=1 skip=$$((0x$$ofs+0x$$size)) if=$^ of=$^-p3; \ + sed -e 's,\xfb\xff\xff\x6f\x00\x00\x00\x00\x00\x00\x00\x08,\xfb\xff\xff\x6f\x00\x00\x00\x00\x00\x00\x00\x00,g' < $^-p2 > $^-p2-patched; \ + cat $^-p1 $^-p2-patched $^-p3 > "$@" + $(Q)rm -f $^-p* + $(Q)chmod 755 "$@" clean: - rm -f $(OBJS) *.[oas] *~ + rm -f $(OBJS) *.[oas] *.so-* *~