Date: Fri, 12 Oct 2012 08:28:59 -0500 From: Alex Caudill <alex.caudill@...il.com> To: musl@...ts.openwall.com Subject: Re: PATCH: dl_iterate_phdr() Thanks for the review! To clarify, I meant that the patch is public domain. This version implements most of your changes and attempts support for dlopen()'d libraries and vdso. Some questions: 1.) I guarded link.h with _GNU_SOURCE or _BSD_SOURCE; I'm unclear on whether this is necessary since it isn't a standard header, so please let me know your preference. 2.) I'm unsure of how to replace ElfW(Phdr) in dl_phdr_info - or did you mean that musl should internally use some opaque type for dl_phdr_info? Also, should ElfW() go in elf.h? 3.) The attached dltest.c reveals a problem with dlopen()'d libraries which seems to be related to the locking strategy (see output below). If I don't take the lock and check for current == saved_tail, it "fixes" the example. At the least, I think this reveals a flaw with dlopen("foo", RTLD_NOW) - shouldn't it hold the lock until the dso list has been updated? This function is used by libunwind and (I think) libgcc_eh for C++ exception support, and it's possible that additional fields in dl_phdr_info will be necessary in order for those to work unmodified with musl. I'll look into this today and come up with more tests. Solaris and FreeBSD, at least, have these appended to struct dl_phdr_info: unsigned long long int dlpi_adds; /* total # of loads */ unsigned long long int dlpi_subs; /* total # of unloads */ The dl_iterate_phdr() callback is passed a size arg, and the callback is responsible for checking the size to ensure that the additional fields are present. Don't shoot the messenger! :) TEST OUTPUT: musl: name=./dltest (6 segments) header 0: address= 0x8048034 header 1: address= 0x80480f4 header 2: address= 0x8048000 header 3: address= 0x8049538 header 4: address= 0x804954c header 5: address= 0 name=/lib/ld-musl-i386.so.1 (4 segments) header 0: address=0x28049000 header 1: address=0x280c7714 header 2: address=0x280c77d8 header 3: address=0x28049000 FreeBSD libc: name=/usr/home/alex/dltest (8 segments) header 0: address= 0x8048034 header 1: address= 0x8048134 header 2: address= 0x8048000 header 3: address= 0x80497d0 header 4: address= 0x80497e4 header 5: address= 0x804814c header 6: address= 0x8048784 header 7: address= 0x0 name=libc.so.7 (6 segments) header 0: address=0x2806b000 header 1: address=0x28195000 header 2: address=0x281976b4 header 3: address=0x28195000 header 4: address=0x28194b38 header 5: address=0x2806b000 name=/compat/linux/lib/libavl.so (4 segments) header 0: address=0x281c3000 header 1: address=0x281c5738 header 2: address=0x281c5738 header 3: address=0x281c3000 Download attachment "dynlink.patch" of type "application/octet-stream" (3447 bytes) View attachment "link.h" of type "text/x-chdr" (474 bytes) View attachment "dltest.c" of type "text/x-csrc" (623 bytes)
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