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Message-ID: <20200609181231.GD1284251@rlwimi.vmware.com>
Date: Tue, 9 Jun 2020 11:12:31 -0700
From: Matt Helsley <mhelsley@...are.com>
To: Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>
CC: <linux-kernel@...r.kernel.org>,
Josh Poimboeuf <jpoimboe@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Steven Rostedt <rostedt@...dmis.org>,
Sami Tolvanen <samitolvanen@...gle.com>,
Julien Thierry <jthierry@...hat.com>
Subject: Re: [RFC][PATCH v4 27/32] objtool: mcount: Generic location and
relocation table types
On Tue, Jun 09, 2020 at 12:11:55PM +0530, Kamalesh Babulal wrote:
> On 6/3/20 1:20 AM, Matt Helsley wrote:
> > Rather than building the exact ELF section data we need and
> > avoiding libelf's conversion step, use more GElf types
> > and then libelf's elfxx_xlatetof() functions to convert
> > the mcount locations (GElf_Addr) and associated relocations.
> >
> > This converts sift_rel_mcount() so that it doesn't use the
> > recordmcount wrapper. The next patch will move it out of the
> > wrapper.
> >
> > Signed-off-by: Matt Helsley <mhelsley@...are.com>
> > ---
> > tools/objtool/recordmcount.c | 44 +++----------
> > tools/objtool/recordmcount.h | 120 ++++++++++++++---------------------
> > 2 files changed, 59 insertions(+), 105 deletions(-)
> >
> > diff --git a/tools/objtool/recordmcount.c b/tools/objtool/recordmcount.c
> > index 06a8f8ddefa7..ef3c360a3db9 100644
> > --- a/tools/objtool/recordmcount.c
> > +++ b/tools/objtool/recordmcount.c
>
> [...]
>
> > -static uint_t *sift_rel_mcount(uint_t *mlocp,
> > - unsigned const offbase,
> > - Elf_Rel **const mrelpp,
> > +static void sift_rel_mcount(GElf_Addr **mlocpp,
> > + GElf_Sxword *r_offsetp,
> > + void **const mrelpp,
> > const struct section * const rels,
> > unsigned const recsym_index,
> > unsigned long const recval,
> > - unsigned const reltype)
> > + unsigned const reltype,
> > + bool is_rela)
> > {
> > - uint_t *const mloc0 = mlocp;
> > - Elf_Rel *mrelp = *mrelpp;
> > - unsigned int rel_entsize = rels->sh.sh_entsize;
> > - unsigned mcountsym = 0;
> > + GElf_Rel *mrelp = *mrelpp;
> > + GElf_Rela *mrelap = *mrelpp;
> > + unsigned int mcount_sym_info = 0;
> > struct reloc *reloc;
> >
> > list_for_each_entry(reloc, &rels->reloc_list, list) {
> > - if (!mcountsym)
> > - mcountsym = get_mcountsym(reloc);
> > -
> > - if (mcountsym == GELF_R_INFO(reloc->sym->idx, reloc->type) && !is_fake_mcount(reloc)) {
> > - uint_t const addend =
> > - _w(reloc->offset - recval + mcount_adjust);
> > - mrelp->r_offset = _w(offbase
> > - + ((void *)mlocp - (void *)mloc0));
> > - Elf_r_info(mrelp, recsym_index, reltype);
> > - if (rel_entsize == sizeof(Elf_Rela)) {
> > - ((Elf_Rela *)mrelp)->r_addend = addend;
> > - *mlocp++ = 0;
> > - } else
> > - *mlocp++ = addend;
> > -
> > - mrelp = (Elf_Rel *)(rel_entsize + (void *)mrelp);
> > + unsigned long addend;
> > +
> > + if (!mcount_sym_info)
> > + mcount_sym_info = get_mcount_sym_info(reloc);
> > +
> > + if (mcount_sym_info != GELF_R_INFO(reloc->sym->idx, reloc->type) || is_fake_mcount(reloc))
> > + continue;
>
> Hi Matt,
>
> I was trying out the patch series on ppc64le and found that __mcount_loc
> and .rela__mcount_loc section pairs do not get generated.
>
> # readelf -S fs/proc/cmdline.o|grep mcount
> #
>
> Debugged the cause to get_mcountsym()'s return type. It returns reloc
> type from GELF_R_INFO() and expects Elf64_Xword a.k.a unsigned long
> to be the return type but get_mcountsym() returns unsigned int on 64-bit.
>
> On power the _mcount is of relocation type R_PPC64_REL24 (info 0x170000000a),
> using unsigned int truncates the value to 0xa and fails the above check.
> Using below fix, that converts mcount_sym_info to use unsigned long, generates
> the __mcount_loc section pairs.
>
> --- a/tools/objtool/mcount.c
> +++ b/tools/objtool/mcount.c
> @@ -163,7 +163,7 @@ static int is_mcounted_section_name(char const *const txtname)
> strcmp(".cpuidle.text", txtname) == 0;
> }
>
> -static unsigned int get_mcount_sym_info(struct reloc *reloc)
> +static unsigned long get_mcount_sym_info(struct reloc *reloc)
> {
> struct symbol *sym = reloc->sym;
> char const *symname = sym->name;
> @@ -274,7 +274,7 @@ static int nop_mcount(struct section * const rels,
> {
> struct reloc *reloc;
> struct section *txts = find_section_by_index(lf, rels->sh.sh_info);
> - unsigned int mcount_sym_info = 0;
> + unsigned long mcount_sym_info = 0;
> int once = 0;
>
> list_for_each_entry(reloc, &rels->reloc_list, list) {
> @@ -363,7 +363,7 @@ static void sift_rel_mcount(GElf_Addr **mlocpp,
> {
> GElf_Rel *mrelp = *mrelpp;
> GElf_Rela *mrelap = *mrelpp;
> - unsigned int mcount_sym_info = 0;
> + unsigned long mcount_sym_info = 0;
> struct reloc *reloc;
>
> list_for_each_entry(reloc, &rels->reloc_list, list) {
>
> # readelf -S fs/proc/cmdline.o|grep mcount
> [31] __mcount_loc PROGBITS 0000000000000000 00022f10
> [32] .rela__mcount_loc RELA 0000000000000000 00022f20
Fixed for next posting.
I've essentially added this as another patch before it moves into
recordmcount.c, gets renamed to get_mcount_sym_info(), etc. I did it
this way because it only becomes necessary to change the type before
moving the function (and eventually its callers) out of the wrapper.
I feel I should credit you as author or at least co-author of the added
patch since it's basically a "backported" version of the changes you
suggested. I reviewed the process in submitting-patches.rst and propose
the commit message:
objtool: mcount: Extend mcountsym size
Before we can move this function out of the wrapper and into
wordsize-independent code we need to explicitly size the
type returned from get_mcountsym() to preserve the symbol info.
Reported-by: Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>
Signed-off-by: Kamalesh Babulal <kamalesh@...ux.vnet.ibm.com>
Signed-off-by: Matt Helsley <mhelsley@...are.com>
Is that OK with you or do you have another preference?
>
>
> > +
> > + addend = reloc->offset - recval + mcount_adjust;
> > + if (is_rela) {
> > + mrelap->r_offset = *r_offsetp;
> > + mrelap->r_info = GELF_R_INFO(recsym_index, reltype);
> > + mrelap->r_addend = addend;
> > + mrelap++;
> > + **mlocpp = 0;
> > + } else {
> > + mrelp->r_offset = *r_offsetp;
> > + mrelp->r_info = GELF_R_INFO(recsym_index, reltype);
> > + mrelp++;
> > + **mlocpp = addend;
> > }
> > + (*mlocpp)++;
> > + r_offsetp += loc_size;
>
> the offsets generated for rela__mcount_loc section are incorrect:
>
> # readelf -rW fs/proc/meminfo.o
> [...]
> Relocation section '.rela__mcount_loc' at offset 0x59a48 contains 4 entries:
> Offset Info Type Symbol's Value Symbol's Name + Addend
> 0000000000000000 0000000200000026 R_PPC64_ADDR64 0000000000000000 .text + c
> 00000a059c401f38 0000000200000026 R_PPC64_ADDR64 0000000000000000 .text + 64
> 0000000000000000 0000000200000026 R_PPC64_ADDR64 0000000000000000 .text + 7c
> 0000000000000000 0000000600000026 R_PPC64_ADDR64 0000000000000000 .init.text + c
>
> changing the above line to *r_offsetp += loc_size and initializing
> r_offset=0 in do_mcount() generates the correct offset:
>
> # readelf -rW fs/proc/meminfo.o
> [...]
> Relocation section '.rela__mcount_loc' at offset 0x59a48 contains 4 entries:
> Offset Info Type Symbol's Value Symbol's Name + Addend
> 0000000000000000 0000000200000026 R_PPC64_ADDR64 0000000000000000 .text + c
> 0000000000000008 0000000200000026 R_PPC64_ADDR64 0000000000000000 .text + 64
> 0000000000000010 0000000200000026 R_PPC64_ADDR64 0000000000000000 .text + 7c
> 0000000000000018 0000000600000026 R_PPC64_ADDR64 0000000000000000 .init.text + c
Fixed for next posting.
Thank you for testing these out and the fixes!
Cheers,
-Matt Helsley
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