Messages in this thread Patch in this message | | | From | Kamalesh Babulal <> | Subject | Re: [RFC][PATCH v4 27/32] objtool: mcount: Generic location and relocation table types | Date | Tue, 9 Jun 2020 12:11:55 +0530 |
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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@vmware.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
> + > + 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 > } > - *mrelpp = mrelp; > - return mlocp; > + *mrelpp = is_rela ? (void *)mrelap : (void *)mrelp; > } > > -- Kamalesh
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