From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on inbox.vuxu.org X-Spam-Level: X-Spam-Status: No, score=-3.0 required=5.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,RCVD_IN_DNSWL_MED,RCVD_IN_MSPIKE_H4, RCVD_IN_MSPIKE_WL autolearn=ham autolearn_force=no version=3.4.4 Received: from second.openwall.net (second.openwall.net [193.110.157.125]) by inbox.vuxu.org (Postfix) with SMTP id 7668A25A7E for ; Mon, 8 Apr 2024 17:32:38 +0200 (CEST) Received: (qmail 15828 invoked by uid 550); 8 Apr 2024 15:32:33 -0000 Mailing-List: contact musl-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Reply-To: musl@lists.openwall.com Received: (qmail 15787 invoked from network); 8 Apr 2024 15:32:33 -0000 Date: Mon, 8 Apr 2024 11:32:44 -0400 From: Rich Felker To: Max Filippov Cc: musl@lists.openwall.com Message-ID: <20240408153244.GW4163@brightrain.aerifal.cx> References: <20240328230116.GM4163@brightrain.aerifal.cx> <20240329014824.GG32430@brightrain.aerifal.cx> <20240403205555.GO4163@brightrain.aerifal.cx> <20240403214555.GP4163@brightrain.aerifal.cx> <20240404140134.GQ4163@brightrain.aerifal.cx> <20240404150053.GR4163@brightrain.aerifal.cx> <20240408144107.GV4163@brightrain.aerifal.cx> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20240408144107.GV4163@brightrain.aerifal.cx> User-Agent: Mutt/1.5.21 (2010-09-15) Subject: Re: [musl] [RFC v2 0/2] xtensa FDPIC port On Mon, Apr 08, 2024 at 10:41:07AM -0400, Rich Felker wrote: > On Thu, Apr 04, 2024 at 11:00:54AM -0400, Rich Felker wrote: > > On Thu, Apr 04, 2024 at 10:01:35AM -0400, Rich Felker wrote: > > > On Thu, Apr 04, 2024 at 01:44:13AM -0700, Max Filippov wrote: > > > > On Wed, Apr 3, 2024 at 2:45 PM Rich Felker wrote: > > > > > > > > > > On Wed, Apr 03, 2024 at 04:55:56PM -0400, Rich Felker wrote: > > > > > > On Tue, Apr 02, 2024 at 07:30:57PM -0700, Max Filippov wrote: > > > > > > > On Thu, Mar 28, 2024 at 6:48 PM Rich Felker wrote: > > > > > > > > On Thu, Mar 28, 2024 at 05:48:50PM -0700, Max Filippov wrote: > > > > > > > > > On Thu, Mar 28, 2024 at 4:00 PM Rich Felker wrote: > > > > > > > > > > On Thu, Mar 28, 2024 at 01:03:17PM -0700, Max Filippov wrote: > > > > > > > > > > > functional/dlopen fails with the > > > > > > > > > > > src/functional/dlopen.c:39: dlsym main failed: (null) > > > > > > > > > > > There's no failure in the dlsym call, but the pointers don't match. > > > > > > > > > > > > > > > > > > > > Is this something related to canonical function descriptors? Is it > > > > > > > > > > musl's fault or a bug in the tooling? I suspect the latter. > > > > > > > > > > > > > > > > > > Yes, dlsym() returns the pointer into def.dso->funcdescs, > > > > > > > > > but (void *)main returns the pointer to the canonical function > > > > > > > > > descriptor. I understand that the linker must use the > > > > > > > > > R_XTENSA_FUNCDESC relocation for the locally defined > > > > > > > > > global symbol instead of the .rofixup entries. > > > > > > > > > > > > > > > > If the xtensa FDPIC ABI is going to be that the linker makes canonical > > > > > > > > function descriptors, I think that's workable, but the dynamic linker > > > > > > > > would need a way to find and usee them. I'm not sure how that would > > > > > > > > work. > > > > > > > > > > > > > > > > The simple (but probably less efficient) way is to copy what SH did > > > > > > > > and have the dynamic linker always be responsible for them (load > > > > > > > > descriptor address from GOT). > > > > > > > > > > > > > > I've built and tested SH FDPIC toolchain, it fails this test in exactly > > > > > > > the same way: pointer loaded directly does not match the pointer > > > > > > > returned by dlsym(). > > > > > > > > > > > > Yes, I've been able to reproduce this and it's a clear bug. There does > > > > > > not seem to be any way the dynamic linker could find these GOTFUNCDESC > > > > > > slots to use them as a canonical address for the function, and > > > > > > moreover, they're not even unique; there would be one per library. > > > > > > > > > > > > The code path for legitimize_pic_address in sh.c that emits > > > > > > GOTFUNCDESC has the wrong logic. A simple fix would be just making > > > > > > that path never be taken, but I'm not sure if that would break use of > > > > > > GOTFUNCDESC for pure-call purposes. > > > > > > > > > > > > The condition should probably be something like: if it's just used for > > > > > > a call (if this is even needed; pure call is probably handled > > > > > > elsewhere) or if the function is static or hidden, use GOTFUNCDESC; > > > > > > otherwise, use GOT. > > > > > > > > > > > > I might try patching it and see what happens. > > > > > > > > > > Attached patch seems to fix it. I'm not sure if this is the most > > > > > idiomatic way to write the predicate in gcc sources, but it should be > > > > > correct. > > > > > > > > It's not what I observe. On my side it doesn't change the result of the > > > > dlopen test, and it also breaks building of all statically-linked tests. > > > > > > > > There are no relocations against the symbol 'main' neither in the test > > > > built with the original gcc nor in the test built with the patched one. > > > > dlopen.o built with the original gcc had R_SH_GOTOFFFUNCDESC > > > > relocation against the symbol 'main', dlopen.o built with the patched > > > > gcc has R_SH_GOTOFF instead. The code generated with the patched > > > > gcc: > > > > > > > > if (dlsym(g, "main") != (void*)main) { > > > > 28c: 50 d1 mov.l 3d0 ,r1 ! 0
> > > > 28e: 8c 31 add r8,r1 > > > > 290: 12 61 mov.l @r1,r1 > > > > 292: 13 62 mov r1,r2 > > > > 294: 8f 91 mov.w 3b6 ,r1 ! 1e0 > > > > 296: ec 31 add r14,r1 > > > > 298: 23 65 mov r2,r5 > > > > 29a: 1c 54 mov.l @(48,r1),r4 > > > > 29c: 83 6c mov r8,r12 > > > > 29e: 4d d6 mov.l 3d4 ,r6 ! 130 > > > > 2a0: 03 06 bsrf r6 > > > > 2a2: 09 00 nop > > > > 2a4: 03 61 mov r0,r1 > > > > 2a6: 4c d2 mov.l 3d8 ,r2 ! 0
> > > > 2a8: 8c 32 add r8,r2 > > > > 2aa: 20 31 cmp/eq r2,r1 > > > > 2ac: 27 89 bt 2fe > > > > .... > > > > 3d8: 00 00 .word 0x0000 > > > > 3d8: R_SH_GOTOFF main > > > > > > > > doesn't look right to me at all. Using R_SH_GOTOFF > > > > for the symbol in text doesn't make sense. Using R_SH_GOT > > > > (AFAIU that's what you meant it to be) doesn't make sense > > > > to me as well, as the value stored in the GOT would be the > > > > address of the main() entry point, not of its descriptor. > > > > > > > > I believe that gcc need to generate R_SH_GOTFUNCDESC > > > > instead of R_SH_GOTOFFFUNCDESC for this test to work > > > > correctly, and that the linker need to put R_SH_FUNCDESC > > > > relocation against that GOT entry, so that the dynamic linker > > > > could put there the address of the function descriptor associated > > > > with the symbol. > > > > > > Indeed I messed this up. Ignore that patch. You're right that use of > > > R_SH_GOTOFFFUNCDESC is wrong -- it's "Used for the FDPIC-relative > > > offset to the function descriptor itself", which is never a constant > > > except for static/hidden functions or when static linking. > > > > > > However, you can test switching it to R_SH_GOTFUNCDESC just by using > > > -fPIC, and when you link, you still get the same problem, because the > > > linker is breaking it by binding at ld-time. So there are at least two > > > bugs in play here. > > > > The offending logic in bfd linker is SYMBOL_FUNCDESC_LOCAL macro in > > bfd/elf32-sh.c. SYMBOL_REFERENCES_LOCAL is not sufficient to conclude > > that the FUNCDESC can be expanded at ld time. I'm not sure how to > > write it yet, but the condition is: > > > > !dynamic_linking || (SYMBOL_REFERENCES_LOCAL && !visible_outside_dso) > > > > The existing elf_hash_table (INFO)->dynamic_sections_created clause > > covers !dynamic_linking mostly except that it will give the wrong > > result for static PIE (which is largely gratuitous for FDPIC, but > > should still be expected to work). > > I have what seem to be working patches for the linker and gcc. > > The bfd link code for sh/fdpic was doing two things wrong: using the > condition "locally defined" rather than "externally visible" for > deciding how to handle function descriptors, and "optimizing" out the > symbol reference even once that was fixed. The patch corrects both > behaviors. > > GCC was wrongly using GOTOFFFUNCDESC rather than GOTFUNCDESC for > locally defined but externally visible symbols. This could be worked > around with -fPIC, but the patch fixes it. (Probably should do > internal too, but nobody uses internal visibility because it's > underspecified and broken.) > > Following the same logic changes should fix the problem on xtensa. > > Rich > --- binutils-2.33.1/bfd/elf32-sh.c.orig 2024-04-04 23:11:28.739136261 +0900 > +++ binutils-2.33.1/bfd/elf32-sh.c 2024-04-08 23:14:24.496915074 +0900 > @@ -61,7 +61,7 @@ > not. If the symbol is protected, we want the local address, but > its function descriptor must be assigned by the dynamic linker. */ > #define SYMBOL_FUNCDESC_LOCAL(INFO, H) \ > - (SYMBOL_REFERENCES_LOCAL (INFO, H) \ > + (!(H) || (H)->dynindx < 0 || (H)->forced_local \ > || ! elf_hash_table (INFO)->dynamic_sections_created) > > #define SH_PARTIAL32 TRUE > @@ -4405,20 +4405,6 @@ > /* Undefined weak symbol which will not be dynamically > resolved later; leave it at zero. */ > goto funcdesc_leave_zero; > - else if (SYMBOL_CALLS_LOCAL (info, h) > - && ! SYMBOL_FUNCDESC_LOCAL (info, h)) > - { > - /* If the symbol needs a non-local function descriptor > - but binds locally (i.e., its visibility is > - protected), emit a dynamic relocation decayed to > - section+offset. This is an optimization; the dynamic > - linker would resolve our function descriptor request > - to our copy of the function anyway. */ > - dynindx = elf_section_data (h->root.u.def.section > - ->output_section)->dynindx; > - relocation += h->root.u.def.section->output_offset > - + h->root.u.def.value; > - } > else if (! SYMBOL_FUNCDESC_LOCAL (info, h)) > { > /* If the symbol is dynamic and there will be dynamic > > --- gcc-11.4.0/gcc/config/sh/sh.c.orig 2024-04-04 05:52:42.125373614 +0900 > +++ gcc-11.4.0/gcc/config/sh/sh.c 2024-04-04 22:54:01.875106654 +0900 > @@ -9147,7 +9147,7 @@ > { > /* Weak functions may be NULL which doesn't work with > GOTOFFFUNCDESC because the runtime offset is not known. */ > - if (SYMBOL_REF_WEAK (orig)) > + if (SYMBOL_REF_WEAK (orig) || (TREE_PUBLIC(SYMBOL_REF_DECL(orig)) && DECL_VISIBILITY (SYMBOL_REF_DECL(orig)) != VISIBILITY_HIDDEN)) > emit_insn (gen_symGOTFUNCDESC2reg (reg, orig)); > else > emit_insn (gen_symGOTOFFFUNCDESC2reg (reg, orig)); > Binutils bug report: https://sourceware.org/bugzilla/show_bug.cgi?id=31619 GCC bug report: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114641