On Tue, Aug 15, 2017 at 5:51 AM, Richard Biener <rguent...@suse.de> wrote: > On Tue, 15 Aug 2017, Richard Biener wrote: > >> On Mon, 14 Aug 2017, Ian Lance Taylor wrote: >> >> > On Mon, Aug 14, 2017 at 6:17 AM, Richard Biener <rguent...@suse.de> wrote: >> > > On Fri, 4 Aug 2017, Richard Biener wrote: >> > > >> > >> On Fri, 28 Jul 2017, Jason Merrill wrote: >> > >> >> > >> > On 07/28/2017 05:55 PM, Jason Merrill wrote: >> > >> > > On Fri, Jul 28, 2017 at 8:54 AM, Richard Biener <rguent...@suse.de> >> > >> > > wrote: >> > >> > > > On Tue, 4 Jul 2017, Richard Biener wrote: >> > >> > > > >> > >> > > > > On Tue, 20 Jun 2017, Richard Biener wrote: >> > >> > > > > >> > >> > > > > > On Wed, 7 Jun 2017, Richard Biener wrote: >> > >> > > > > > >> > >> > > > > > > On Fri, 19 May 2017, Richard Biener wrote: >> > >> > > > > > > >> > >> > > > > > > > >> > >> > > > > > > > This is a repost (unchanged) of the simple-object ELF >> > >> > > > > > > > support for >> > >> > > > > > > > early LTO debug transfer from IL object to a separate >> > >> > > > > > > > debug-only >> > >> > > > > > > > object >> > >> > > > > > > > file. >> > >> > > > > > > > >> > >> > > > > > > > Bootstrapped and tested on x86_64-unknown-linux-gnu. >> > >> > > > > > > >> > >> > > > > > > Ping. >> > >> > > > > > >> > >> > > > > > Ping^2. >> > >> > > > > >> > >> > > > > Ping^3. >> > >> > > > >> > >> > > > Ping^4. Adding some more global reviewers to CC. >> > >> > > >> > >> > > Looking at it now, sorry for the delay. >> > >> > >> > >> > Actually, the simple-object stuff is more Ian's area. Looking at the >> > >> > other >> > >> > part. >> > >> >> > >> Ian, ping -- we're through with the other part >> > >> (https://gcc.gnu.org/ml/gcc-patches/2017-08/msg00374.html). The >> > >> simple-object part is unchanged at >> > >> >> > >> https://gcc.gnu.org/ml/gcc-patches/2017-05/msg01541.html >> > >> >> > >> nearly unchanged from the post last year (which also includes >> > >> some description): >> > >> >> > >> https://gcc.gnu.org/ml/gcc-patches/2016-09/msg01292.html >> > > >> > > Ian, ping again! (trying now also with the e-mail listed in >> > > MAINTAINERS) >> > > >> > > https://gcc.gnu.org/ml/gcc-patches/2017-05/msg01541.html >> > >> > Sorry about that, for some reason GMail didn't flag this message for me. >> > >> > >> > > + for (ent = buf + entsize; ent < buf + length; ent += entsize) >> > > + { >> > > + unsigned sec = type_functions->fetch_Elf_Word (ent); >> > > + if (pfnret[sec - 1] == 0) >> > > + keep = 1; >> > > + } >> > > + if (keep) >> > > + { >> > > + pfnret[sh_link - 1] = 0; >> > > + pfnret[i - 1] = 0; >> > > + } >> > > + } >> > >> > It seems to me that if you keep any section of an SHT_GROUP, you need >> > to keep all the sections. Otherwise the section indexes in the group >> > will be left dangling. >> >> Note that all sections are "kept", removed sections are just marked >> as SHT_NULL. Which means that indeed some group members might >> be SHT_NULL. >> >> Note that I don't remember if I actually run into any SHT_GROUP >> member being necessary when another is not (IIRC this was with >> debug types sections or so). I'll double-check and add a comment >> where this matters for early-debug (the simple-object code tries >> to be more generic but obviously all testing was done with >> early-debug section copying in mind). > > That said, the callback is supposed to mark interesting stuff as not > deleted. The simple-object interface is only giving some leeway > to simplify things (pulling in the container, directly dependent > sections) to generate a valid ELF output. > >> > The symbol table handling is pretty awful. Can't you just remove the >> > symbols you don't want? You will have to update the sh_info field of >> > the SHT_SYMTAB section, which holds the index of the first STB_GLOBAL >> > symbol in the table. >> >> Maybe that's what I was missing, let me see if I can make it work. >> It looks like if there's no STB_GLOBAL symbol the index is one after >> the last symbol and it seems it is the first ! STB_LOCAL symbol >> ("One greater than the symbol table index of the last local symbol >> (binding STB_LOCAL)"). >> >> Ah, and implementing this now I remember why I chose the "awkward" >> way. This was to preserve symtab indices to not need to rewrite >> relocation sections... There isn't a documented way to make >> an "none" symtab entry (eventually duplicating UND might work >> but IIRC it messes up ordering as UND is STB_LOCAL and thus may >> not appear after the first ! STB_LOCAL symbol). As comments in >> the code indicate I tried to mangle things in a way that makes >> both GNU ld and gold happy... >> >> Any suggestion how to improve things when not removing symbols? >> (I could of course remove things from the end of the symtab) >> Like replacing local symbols with UND and globals with >> a COMMON of zero size (and no name)? >> >> I suppose rewriting relocation sections is possible but I tried >> to do as little as necessary (like not actually removing sections). > > So the following is an update which changes how I remove symbols > by making removed locals copies of UND and removed globals > global commons of size zero: > > Symbol table '.symtab' contains 22 entries: > Num: Value Size Type Bind Vis Ndx Name > 0: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND > 1: 0000000000000000 0 FILE LOCAL DEFAULT ABS t.c > 2: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND > 3: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND > 4: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND > 5: 0000000000000000 0 SECTION LOCAL DEFAULT 4 > 6: 0000000000000000 0 SECTION LOCAL DEFAULT 6 > 7: 0000000000000000 0 SECTION LOCAL DEFAULT 7 > 8: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND > ... > 18: 0000000000000000 0 NOTYPE LOCAL DEFAULT UND > 19: 0000000000000000 0 NOTYPE WEAK HIDDEN 4 t.c.39a678c9 > 20: 0000000000000000 0 OBJECT GLOBAL DEFAULT COM > 21: 0000000000000000 0 OBJECT GLOBAL DEFAULT COM > > Does that look better?
As noted in crossing message, I think SHN_UNDEF is better than SHN_COMMON. Patch is OK with that change, assuming that works. Ian
