From: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: keir@xen.org, Ross Lagerwall <ross.lagerwall@citrix.com>,
andrew.cooper3@citrix.com, mpohlack@amazon.com,
sasha.levin@oracle.com, xen-devel@lists.xenproject.org
Subject: Re: [PATCH v8.1 14/27] xsplice, symbols: Implement symbol name resolution on address.
Date: Fri, 22 Apr 2016 07:08:34 -0400 [thread overview]
Message-ID: <20160422110834.GF16225@localhost.localdomain> (raw)
In-Reply-To: <571A1E1A02000078000E4AA0@prv-mh.provo.novell.com>
On Fri, Apr 22, 2016 at 04:50:34AM -0600, Jan Beulich wrote:
> >>> On 22.04.16 at 12:28, <konrad.wilk@oracle.com> wrote:
> > On Fri, Apr 22, 2016 at 04:08:10AM -0600, Jan Beulich wrote:
> >> >>> On 22.04.16 at 10:45, <ross.lagerwall@citrix.com> wrote:
> >> > On 04/22/2016 08:51 AM, Jan Beulich wrote:
> >> >>>>> On 22.04.16 at 09:17, <ross.lagerwall@citrix.com> wrote:
> >> >>> On 04/21/2016 01:26 AM, Konrad Rzeszutek Wilk wrote: snip
> >> >>>>>
> >> >>>>>> +static bool_t is_payload_symbol(const struct xsplice_elf
> >> >>>>>> *elf, + const struct
> >> >>>>>> xsplice_elf_sym *sym) +{ + if ( sym->sym->st_shndx ==
> >> >>>>>> SHN_UNDEF || + sym->sym->st_shndx >=
> >> >>>>>> elf->hdr->e_shnum ) + return 0; + + return
> >> >>>>>> (elf->sec[sym->sym->st_shndx].sec->sh_flags & SHF_ALLOC) && +
> >> >>>>>> (ELF64_ST_TYPE(sym->sym->st_info) == STT_OBJECT || +
> >> >>>>>> ELF64_ST_TYPE(sym->sym->st_info) == STT_FUNC);
> >> >>>>>
> >> >>>>> I don't recall having seen a reply to the question on not
> >> >>>>> allowing
> >> >>> STT_NOTYPE here.
> >> >>>>
> >> >>>> Ross, could you elaborate a bit please on this?
> >> >>>
> >> >>>
> >> >>> The payload will typically have many entries like:
> >> >>>
> >> >>> 9: 0000000000000000 0 NOTYPE LOCAL DEFAULT 5 .LC1 10:
> >> >>> 0000000000000006 0 NOTYPE LOCAL DEFAULT 5 .LC2 11:
> >> >>> 000000000000000d 0 NOTYPE LOCAL DEFAULT 5 .LC3 12:
> >> >>> 0000000000000028 0 NOTYPE LOCAL DEFAULT 4 .LC4 13:
> >> >>> 0000000000000058 0 NOTYPE LOCAL DEFAULT 4 .LC5
> >> >>>
> >> >>> used when referencing strings (due to the use of -fPIC). While it
> >> >>> is not a problem for them to go into the symbol table, if more than
> >> >>> one payload is loaded, there will be duplicate conflicting symbols.
> >> >>> So, to prevent these symbols from going into the symbol table, I
> >> >>> disallowed STT_NOTYPE. Perhaps not the best solution but...
> >> >>
> >> >> First of all symbols starting with .L aren't meant to and up in the
> >> >> symbol table at all (i.e. even that of any intermediate .o file). So
> >> >> there's likely (but not necessarily) something wrong with the tool
> >> >> chain used (i.e. normally such symbols wouldn't be needed for e.g.
> >> >> relocations, as those should get converted to section relative
> >> >> ones).
> >> >
> >> > This is not particular to the xsplice build process. Any version of
> >> > GCC+binutils that I've tested with will generate .LC
> >> > symbols for strings into the .o file. Clang generates similar .L.str*
> >> > symbols, in addition to other useless ones like 'NOTYPE LOCAL DEFAULT
> >> > ABS X86_FEATURE_FFXSR'...
> >>
> >> I can confirm the symbols getting generated in the .s file, ...
> >>
> >> > Maybe it uses these .LC symbols rather than section relative ones
> >> > because they point to a mergeable string section, and merging string
> >> > sections would be harder with section relative references?
> >>
> >> ... but I can't confirm them making it into the .o file, not to speak
> >> of being used for relocations. I've tried gcc 4.3.4 as well as 5.3.0
> >> (with and without -fPIC).
> >
> > /home/konrad/xen/xen/arch/x86
> > [konrad@build-external x86]$ readelf --symbols microcode.o | grep \.LC
> > 50: 0000000000000000 0 NOTYPE LOCAL DEFAULT 12 .LC0
> > 51: 00000000000000e8 0 NOTYPE LOCAL DEFAULT 13 .LC5
> > 52: 0000000000000110 0 NOTYPE LOCAL DEFAULT 13 .LC6
> >
> > ?
> > (GCC) 4.4.4 20100503 (Red Hat 4.4.4-2)
>
> Ah, this happens only with optimization, and I had tried only
> without. Looks to indeed be connected to these strings getting
> put into mergeable string sections, instead of just plain .rodata.
>
> >> >> Yet _if_ such symbols make it into the symbol table of a .o, then
> >> >> there is no reason for them to not also make it into the runtime
> >> >> symbol table. Of course similar ones from different modules then
> >> >> shouldn't conflict with one another, and as these are local symbols
> >> >> perhaps the reason for them conflicting is that in the process of
> >> >> creating the runtime symbol table entries you neglect to prefix them
> >> >> with their source or object file names, as is done by
> >> >> xen/tools/symbols.c for the core symbol table? Quite obviously the
> >> >> symbol name generation should match between core and modules...
> >> >>
> >> >
> >> > The build tool does prefix the required functions and objects with their
> >> > source/object file names. The problem is that these are generated
> >> > symbols, so even if you had e.g. keyhandler.c#.LC0, keyhandler.c#.LC1,
> >> > in the symbol table, they might be completed unrelated if you change the
> >> > source even slightly. Having these entries in the symbol table would not
> >> > make any sense.
> >>
> >> Why not? They could still serve as anchor for subsequent patches.
> >
> >>
> >> > Rather than ignoring STT_NOTYPE, an alternative would be to ignore
> >> > symbols starting with ".L".
> >>
> >> That's an option, but as said before, the rules for which symbols to
> >> enter into the symbol table should be consistent for core and modules.
> >
> > And they seem to - see above on the .o file.
>
> Above .o file was a core one, and doesn't tell anyway whether in the
> runtime symbol table the local symbols would be properly prefixed by
> file name. Or did I misunderstand you?
I had 'built_in.o' or 'prelink.o' as the final one in mind - in which the
.LCx are present. But I think you are thinking about 'xen-syms' output.
Looking at the Makefile runes we hit this:
127 $(TARGET)-syms: prelink.o xen.lds $(BASEDIR)/common/symbols-dummy.o
128 $(LD) $(LDFLAGS) -T xen.lds -N prelink.o $(build_id_linker) \
129 $(BASEDIR)/common/symbols-dummy.o -o $(@D)/.$(@F).0
And that ends up causing the .xen-syms.0 file to drop all the .LC0.
However we can't do that. We _have_ to produce an relocatable object
and not do the final linking (so we append -r to the linker invocation).
If we do not:
ld: warning: cannot find entry symbol _start; defaulting to 0000000000400144
xen_hello_world.o:(.xsplice.funcs+0x10): undefined reference to `xen_extra_version'
ld: xen_hello_world.xsplice: hidden symbol `xen_extra_version' isn't defined
make[3]: *** [xen_hello_world.xsplice] Error 1
I tried for fun to use strip:
xen/xen/arch/x86/test> strip --strip-symbol=".LC0" xen_replace_world.xsplice
strip: not stripping symbol `.LC0' because it is named in a relocation
But it has some hard rules about it.
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next prev parent reply other threads:[~2016-04-22 11:08 UTC|newest]
Thread overview: 126+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-13 22:01 [PATCH v8.1] xSplice v1 design and implementation Konrad Rzeszutek Wilk
2016-04-13 22:01 ` [PATCH v8.1 01/27] Revert "libxc/libxl/python/xenstat/ocaml: Use new XEN_VERSION hypercall" Konrad Rzeszutek Wilk
2016-04-13 22:01 ` [PATCH v8.1 02/27] Revert "HYPERCALL_version_op. New hypercall mirroring XENVER_ but sane." Konrad Rzeszutek Wilk
2016-04-14 16:14 ` Jan Beulich
2016-04-13 22:01 ` [PATCH v8.1 03/27] xsplice: Design document Konrad Rzeszutek Wilk
2016-04-13 22:01 ` [PATCH v8.1 04/27] xen/xsplice: Hypervisor implementation of XEN_XSPLICE_op Konrad Rzeszutek Wilk
2016-04-14 16:36 ` Jan Beulich
2016-04-15 2:28 ` Konrad Rzeszutek Wilk
2016-04-17 8:05 ` Jan Beulich
2016-04-18 7:48 ` Konrad Rzeszutek Wilk
2016-04-18 16:33 ` Jan Beulich
2016-04-19 10:14 ` Konrad Rzeszutek Wilk
2016-04-13 22:01 ` [PATCH v8.1 05/27] libxc: Implementation of XEN_XSPLICE_op in libxc Konrad Rzeszutek Wilk
2016-04-13 22:01 ` [PATCH v8.1 06/27] xen-xsplice: Tool to manipulate xsplice payloads Konrad Rzeszutek Wilk
2016-04-13 22:01 ` [PATCH v8.1 07/27] arm/x86: Use struct virtual_region to do bug, symbol, and (x86) exception tables lookup Konrad Rzeszutek Wilk
2016-04-14 16:50 ` Jan Beulich
2016-04-13 22:01 ` [PATCH v8.1 08/27] arm/x86/vmap: Add vmalloc_xen, vfree_xen and vm_init_type Konrad Rzeszutek Wilk
2016-04-17 20:17 ` Jan Beulich
2016-04-13 22:01 ` [PATCH v8.1 09/27] x86/mm: Introduce modify_xen_mappings() Konrad Rzeszutek Wilk
2016-04-14 4:07 ` Jan Beulich
2016-04-14 13:34 ` Konrad Rzeszutek Wilk
2016-04-13 22:01 ` [PATCH v8.1 10/27] xsplice: Add helper elf routines Konrad Rzeszutek Wilk
2016-04-17 20:55 ` Jan Beulich
2016-04-18 5:53 ` Konrad Rzeszutek Wilk
2016-04-18 6:23 ` Jan Beulich
2016-04-20 16:07 ` Konrad Rzeszutek Wilk
2016-04-20 16:59 ` Jan Beulich
2016-04-13 22:01 ` [PATCH v8.1 11/27] xsplice: Implement payload loading Konrad Rzeszutek Wilk
2016-04-18 6:16 ` Jan Beulich
2016-04-20 15:59 ` Konrad Rzeszutek Wilk
2016-04-20 17:05 ` Jan Beulich
2016-04-20 17:36 ` Konrad Rzeszutek Wilk
2016-04-21 6:41 ` Jan Beulich
2016-04-21 15:15 ` Konrad Rzeszutek Wilk
2016-04-21 15:36 ` Jan Beulich
2016-04-21 16:47 ` Konrad Rzeszutek Wilk
2016-04-22 7:40 ` Jan Beulich
2016-04-13 22:01 ` [PATCH v8.1 12/27] xsplice: Implement support for applying/reverting/replacing patches Konrad Rzeszutek Wilk
2016-04-19 6:27 ` Jan Beulich
2016-04-21 0:28 ` Konrad Rzeszutek Wilk
2016-04-21 6:44 ` Jan Beulich
2016-04-21 20:27 ` Konrad Rzeszutek Wilk
2016-04-22 7:44 ` Jan Beulich
2016-04-22 10:51 ` Konrad Rzeszutek Wilk
2016-04-22 17:26 ` Konrad Rzeszutek Wilk
2016-04-25 7:55 ` Jan Beulich
2016-04-13 22:01 ` [PATCH v8.1 13/27] x86/xen_hello_world.xsplice: Test payload for patching 'xen_extra_version' Konrad Rzeszutek Wilk
2016-04-19 17:40 ` Jan Beulich
2016-04-20 16:10 ` Konrad Rzeszutek Wilk
2016-04-20 17:06 ` Jan Beulich
2016-04-13 22:01 ` [PATCH v8.1 14/27] xsplice, symbols: Implement symbol name resolution on address Konrad Rzeszutek Wilk
2016-04-19 19:31 ` Jan Beulich
2016-04-20 12:55 ` Ross Lagerwall
2016-04-21 0:26 ` Konrad Rzeszutek Wilk
2016-04-21 6:46 ` Jan Beulich
[not found] ` <CACJDEmrucgYZpCDv3EAkDJUOtdcP9P2T=Vine1o2pzUmwJDY1w@mail.gmail.com>
[not found] ` <CACJDEmrzieYh6__MHJH_okoZPk+RA56PuQKv-oid0j1t1po1oQ@mail.gmail.com>
[not found] ` <CACJDEmrdi3sTZjGowkvGP67-_DH3+TLvArC8qZfArsyPb6fpuA@mail.gmail.com>
[not found] ` <CACJDEmrQ6onv-xqYOi3nekioCSASb4c1eZHJ-rzMxU3Wa7SXTQ@mail.gmail.com>
2016-04-21 13:56 ` Konrad Rzeszutek Wilk
2016-04-21 14:25 ` Jan Beulich
2016-04-22 7:17 ` Ross Lagerwall
2016-04-22 7:51 ` Jan Beulich
2016-04-22 8:45 ` Ross Lagerwall
2016-04-22 10:08 ` Jan Beulich
2016-04-22 10:28 ` Konrad Rzeszutek Wilk
2016-04-22 10:50 ` Jan Beulich
2016-04-22 11:08 ` Konrad Rzeszutek Wilk [this message]
2016-04-22 11:18 ` Jan Beulich
2016-04-24 21:41 ` Konrad Rzeszutek Wilk
2016-04-25 8:02 ` Jan Beulich
2016-04-22 11:13 ` Ross Lagerwall
2016-04-22 11:24 ` Jan Beulich
2016-04-22 21:10 ` Konrad Rzeszutek Wilk
2016-04-25 6:41 ` Ross Lagerwall
2016-04-25 8:15 ` Jan Beulich
2016-04-22 14:17 ` Konrad Rzeszutek Wilk
2016-04-13 22:01 ` [PATCH v8.1 15/27] xsplice, symbols: Implement fast symbol names -> virtual addresses lookup Konrad Rzeszutek Wilk
2016-04-19 19:52 ` Jan Beulich
2016-04-22 15:21 ` Konrad Rzeszutek Wilk
2016-04-25 8:38 ` Jan Beulich
2016-04-25 14:12 ` Konrad Rzeszutek Wilk
2016-04-13 22:01 ` [PATCH v8.1 16/27] x86, xsplice: Print payload's symbol name and payload name in backtraces Konrad Rzeszutek Wilk
2016-04-19 20:09 ` Jan Beulich
2016-04-13 22:01 ` [PATCH v8.1 17/27] xsplice: Add support for bug frames Konrad Rzeszutek Wilk
2016-04-19 20:17 ` Jan Beulich
2016-04-21 0:29 ` Konrad Rzeszutek Wilk
2016-04-21 6:49 ` Jan Beulich
2016-04-22 10:10 ` Konrad Rzeszutek Wilk
2016-04-22 10:28 ` Jan Beulich
2016-04-22 10:54 ` Konrad Rzeszutek Wilk
2016-04-22 10:58 ` Jan Beulich
2016-04-22 11:10 ` Konrad Rzeszutek Wilk
2016-04-13 22:01 ` [PATCH v8.1 18/27] xsplice: Add support for exception tables Konrad Rzeszutek Wilk
2016-04-19 20:31 ` Jan Beulich
2016-04-13 22:02 ` [PATCH v8.1 19/27] xsplice: Add support for alternatives Konrad Rzeszutek Wilk
2016-04-20 6:28 ` Jan Beulich
2016-04-21 0:30 ` Konrad Rzeszutek Wilk
2016-04-21 6:55 ` Jan Beulich
2016-04-21 0:31 ` Konrad Rzeszutek Wilk
2016-04-21 6:56 ` Jan Beulich
2016-04-22 16:06 ` Konrad Rzeszutek Wilk
2016-04-13 22:02 ` [PATCH v8.1 20/27] build_id: Provide ld-embedded build-ids Konrad Rzeszutek Wilk
2016-04-20 7:14 ` Jan Beulich
2016-04-21 0:33 ` Konrad Rzeszutek Wilk
2016-04-21 6:59 ` Jan Beulich
2016-04-21 20:30 ` Konrad Rzeszutek Wilk
2016-04-22 16:16 ` Konrad Rzeszutek Wilk
2016-04-13 22:02 ` [PATCH v8.1 21/27] xsplice: Print build_id in keyhandler and on bootup Konrad Rzeszutek Wilk
2016-04-13 22:02 ` [PATCH v8.1 22/27] XENVER_build_id/libxc: Provide ld-embedded build-id Konrad Rzeszutek Wilk
2016-04-14 15:03 ` Wei Liu
2016-04-14 15:04 ` Daniel De Graaf
2016-04-20 7:19 ` Jan Beulich
2016-04-13 22:02 ` [PATCH v8.1 23/27] libxl: info: Display build_id of the hypervisor Konrad Rzeszutek Wilk
2016-04-14 15:06 ` Wei Liu
2016-04-13 22:02 ` [PATCH v8.1 24/27] xsplice: Stacking build-id dependency checking Konrad Rzeszutek Wilk
2016-04-20 7:49 ` Jan Beulich
2016-04-22 10:46 ` Konrad Rzeszutek Wilk
2016-04-22 10:55 ` Jan Beulich
2016-04-13 22:02 ` [PATCH v8.1 25/27] xsplice/xen_replace_world: Test-case for XSPLICE_ACTION_REPLACE Konrad Rzeszutek Wilk
2016-04-20 11:12 ` Jan Beulich
2016-04-13 22:02 ` [PATCH v8.1 26/27] xsplice: Prevent duplicate payloads from being loaded Konrad Rzeszutek Wilk
2016-04-20 11:16 ` Jan Beulich
2016-04-13 22:02 ` [PATCH v8.1 27/27] MAINTAINERS/xsplice: Add myself and Ross as the maintainers Konrad Rzeszutek Wilk
2016-04-14 14:26 ` [PATCH v8.1] xSplice v1 design and implementation Konrad Rzeszutek Wilk
2016-04-14 14:29 ` Julien Grall
2016-04-14 15:12 ` Andrew Cooper
2016-04-14 15:17 ` Jan Beulich
2016-04-15 0:55 ` Konrad Rzeszutek Wilk
2016-04-17 8:00 ` Jan Beulich
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