Date: Fri, 2 Jul 2010 08:29:30 +0000 (UTC) From: "Bjoern A. Zeeb" <bz@FreeBSD.org> To: Andriy Gapon <avg@freebsd.org> Cc: freebsd-hackers@freebsd.org, Konstantin Belousov <kib@FreeBSD.org>, Navdeep Parhar <np@freebsd.org>, Peter Wemm <peter@freebsd.org> Subject: Re: elf obj load: skip zero-sized sections early Message-ID: <20100702082754.S14969@maildrop.int.zabbadoz.net> In-Reply-To: <4C246CD0.3020606@freebsd.org> References: <4C246CD0.3020606@freebsd.org>
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On Fri, 25 Jun 2010, Andriy Gapon wrote: Hey, > Proposed patch skips zero sized sections without going into trouble of > allocating section entry (progtab), doing zero-sized memory allocs and copies. > I observe that sometimes zero-sized set_pcpu sections are produced in module > objects, maybe when a module doesn't create any per cpu data of its one, but > references external pcpu data. Not sure. > > Main goal of this patch is to play nice with external debugging tools (e.g. > kgdb) which ignore zero-sized sections outright. Current code effectively > ignores but may apply their alignment to the next non-zero section if its > required alignment is smaller. So the patch should get rid of that side effect > as well as do some very tiny resource conservation. > > This work is based on np@'s investigation and original patch: > http://lists.freebsd.org/pipermail/freebsd-hackers/2009-November/030093.html Have you guys figured this out already? Adding kib to Cc: in case he can help. /bz > diff --git a/sys/boot/common/load_elf_obj.c b/sys/boot/common/load_elf_obj.c > index 4b3aaea..6f3b349 100644 > --- a/sys/boot/common/load_elf_obj.c > +++ b/sys/boot/common/load_elf_obj.c > @@ -221,6 +221,8 @@ __elfN(obj_loadimage)(struct preloaded_file *fp, elf_file_t > ef, u_int64_t off) > for (i = 0; i < hdr->e_shnum; i++) > shdr[i].sh_addr = 0; > for (i = 0; i < hdr->e_shnum; i++) { > + if (shdr[i].sh_size == 0) > + continue; > switch (shdr[i].sh_type) { > case SHT_PROGBITS: > case SHT_NOBITS: > diff --git a/sys/kern/link_elf_obj.c b/sys/kern/link_elf_obj.c > index a337fd0..b0df57d 100644 > --- a/sys/kern/link_elf_obj.c > +++ b/sys/kern/link_elf_obj.c > @@ -555,6 +555,8 @@ link_elf_load_file(linker_class_t cls, const char *filename, > symtabindex = -1; > symstrindex = -1; > for (i = 0; i < hdr->e_shnum; i++) { > + if (shdr[i].sh_size == 0) > + continue; > switch (shdr[i].sh_type) { > case SHT_PROGBITS: > case SHT_NOBITS: > @@ -677,6 +679,8 @@ link_elf_load_file(linker_class_t cls, const char *filename, > /* Size up code/data(progbits) and bss(nobits). */ > alignmask = 0; > for (i = 0; i < hdr->e_shnum; i++) { > + if (shdr[i].sh_size == 0) > + continue; > switch (shdr[i].sh_type) { > case SHT_PROGBITS: > case SHT_NOBITS: > @@ -737,6 +741,8 @@ link_elf_load_file(linker_class_t cls, const char *filename, > ra = 0; > alignmask = 0; > for (i = 0; i < hdr->e_shnum; i++) { > + if (shdr[i].sh_size == 0) > + continue; > switch (shdr[i].sh_type) { > case SHT_PROGBITS: > case SHT_NOBITS: > > -- Bjoern A. Zeeb From August on I will have a life. It's now up to you to do the maths and count to 64. -- Bondorf, Germany, 14th June 2010
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