Date: Mon, 06 Sep 2021 16:24:15 +0200 From: Florian Weimer <fweimer@...hat.com> To: "H.J. Lu" <hjl.tools@...il.com> Cc: GNU C Library <libc-alpha@...rceware.org>, GDB <gdb@...rceware.org>, libc-coord@...ts.openwall.com, Daniel Walker <danielwa@...co.com> Subject: Re: [PATCH v6 2/2] Extend struct r_debug to support multiple namespaces * H. J. Lu: > On Mon, Sep 6, 2021 at 2:39 AM Florian Weimer <fweimer@...hat.com> wrote: >> >> * H. J. Lu: >> >> > +* The r_version update in the debugger interface makes the glibc binary >> > + incompatible with GDB binaries built without the following commits: >> > + >> > + c0154a4a21a gdb: Don't assume r_ldsomap when r_version > 1 on Linux >> > + 4eb629d50d4 gdbserver: Check r_version < 1 for Linux debugger interface >> >> Does this incompatibility happen even if audit modules and dlmopen are >> not used? > > Yes. Why? Can't we keep r_version at 1 in this case? >> This puts the assember output from the compiler through the >> preprocessor. That seems to be brittle. I think you would have to >> preprocess the manually written fragment separately. >> >> However, I think we are overdesigning things here. The following in >> dl-debug-symbols-gen.c should work (and the file should have a different >> name then): >> >> /* Alias _r_debug to a prefix of _r_debug_extended. */ >> asm (".set _r_debug, _r_debug_extended\n\t" >> ".type _r_debug, %object\n\t" >> ".symver _r_debug_extended, _r_debug@@" FIRST_VERSION_ld__r_debug_STRING); >> #if __WORDSIZE == 64 >> _Static_assert (sizeof (struct r_debug) == 40, "sizeof (struct r_debug)"); >> asm (".size _r_debug, 40"); >> #else >> _Static_assert (sizeof (struct r_debug) == 20, "sizeof (struct r_debug)"); >> asm (".size _r_debug, 20"); >> #endif >> >> It's not exactly pretty, but at least it's obvious what is going on. >> (Extended asm with input operands is not supported outside of functions.) > > This was the first thing I tried and it didn't work: > > [hjl@...-cfl-2 tmp]$ cat foo.s > .set _r_debug, _r_debug_extended > .globl _r_debug > .type _r_debug, %object > .size _r_debug, 40 > .data > .type _r_debug_extended, %object > .size _r_debug_extended, 48 > .globl _r_debug_extended > _r_debug_extended: > .zero 48 > [hjl@...-cfl-2 tmp]$ gcc -c foo.s > [hjl@...-cfl-2 tmp]$ readelf -sW foo.o | grep _r_debug > 1: 0000000000000000 48 OBJECT GLOBAL DEFAULT 2 _r_debug > 2: 0000000000000000 48 OBJECT GLOBAL DEFAULT 2 _r_debug_extended > [hjl@...-cfl-2 tmp]$ Huh. Does this mean this depends on the symbol definition order in the assembler file? I really hate the post-processing of compiler output. This isn't GHC. 8-> Can we write a portable assembler file instead? Nick Clifton has written down some guidelines: Tips for writing portable assembler with GNU Assembler (GAS) <https://developers.redhat.com/blog/2021/02/26/tips-for-writing-portable-assembler-with-gnu-assembler-gas> There's no initializer, so all we need to know is size and alignment. >> Is this necessary? It makes concurrent access to the list harder and > > When _dl_close_worker is called, it holds GL(dl_load_lock). Why does > this change make concurrent access harder? Something else might want to read the list directly, by starting with DT_DEBUG. Thanks, Florian
Powered by blists - more mailing lists
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.