[RFC][PATCH 13/13] objtool: recordmcount: Convert do_func() relhdrs

Matt Helsley
2019-05-23T00:04:28Z

Use objtool's ELF data structures to visit the relocation
sections in the top-level ELF file walking function, do_func().
This means we can pass pointers to the relocation header structures
into nested functions and avoid the indexing patterns for them.

These conversions don't use libelf/objtool to change the ELF
file -- it only changes the way we walk the ELF sections and
touch pages for memory mapping made by the old recordmcount code.

Signed-off-by: Matt Helsley <mhelsley@vmware.com>
---
tools/objtool/recordmcount.h | 70 ++++++++++++++++++------------------
1 file changed, 36 insertions(+), 34 deletions(-)

diff --git a/tools/objtool/recordmcount.h b/tools/objtool/recordmcount.h
index ff14d45041f1..0db5cbabbc12 100644
--- a/tools/objtool/recordmcount.h
+++ b/tools/objtool/recordmcount.h
@@ -289,7 +289,7 @@ static unsigned get_mcountsym(Elf_Sym const *const sym0,
return mcountsym;
}

-static void get_sym_str_and_relp(Elf_Shdr const *const relhdr,
+static void get_sym_str_and_relp(GElf_Shdr const *const relhdr,
Elf_Ehdr const *const ehdr,
Elf_Sym const **sym0,
char const **str0,
@@ -297,10 +297,10 @@ static void get_sym_str_and_relp(Elf_Shdr const *const relhdr,
{
Elf_Shdr *const shdr0 = (Elf_Shdr *)(_w(ehdr->e_shoff)
+ (void *)ehdr);
- unsigned const symsec_sh_link = w(relhdr->sh_link);
+ unsigned const symsec_sh_link = relhdr->sh_link;
Elf_Shdr const *const symsec = &shdr0[symsec_sh_link];
- Elf_Shdr const *const strsec = &shdr0[w(symsec->sh_link)];
- Elf_Rel const *const rel0 = (Elf_Rel const *)(_w(relhdr->sh_offset)
+ Elf_Shdr const *const strsec = &shdr0[symsec->sh_link];
+ Elf_Rel const *const rel0 = (Elf_Rel const *)(relhdr->sh_offset
+ (void *)ehdr);

*sym0 = (Elf_Sym const *)(_w(symsec->sh_offset)
@@ -320,9 +320,9 @@ static void get_sym_str_and_relp(Elf_Shdr const *const relhdr,
static uint_t *sift_rel_mcount(uint_t *mlocp,
unsigned const offbase,
Elf_Rel **const mrelpp,
- Elf_Shdr const *const relhdr,
+ GElf_Shdr const *const relhdr,
Elf_Ehdr const *const ehdr,
- unsigned const recsym,
+ unsigned const recsym_index,
uint_t const recval,
unsigned const reltype)
{
@@ -331,8 +331,8 @@ static uint_t *sift_rel_mcount(uint_t *mlocp,
Elf_Sym const *sym0;
char const *str0;
Elf_Rel const *relp;
- unsigned rel_entsize = _w(relhdr->sh_entsize);
- unsigned const nrel = _w(relhdr->sh_size) / rel_entsize;
+ unsigned int rel_entsize = relhdr->sh_entsize;
+ unsigned const nrel = relhdr->sh_size / rel_entsize;
unsigned mcountsym = 0;
unsigned t;

@@ -347,7 +347,7 @@ static uint_t *sift_rel_mcount(uint_t *mlocp,
_w(_w(relp->r_offset) - recval + mcount_adjust);
mrelp->r_offset = _w(offbase
+ ((void *)mlocp - (void *)mloc0));
- Elf_r_info(mrelp, recsym, reltype);
+ Elf_r_info(mrelp, recsym_index, reltype);
if (rel_entsize == sizeof(Elf_Rela)) {
((Elf_Rela *)mrelp)->r_addend = addend;
*mlocp++ = 0;
@@ -367,7 +367,7 @@ static uint_t *sift_rel_mcount(uint_t *mlocp,
* that are not going to be traced. The mcount calls here will be converted
* into nops.
*/
-static int nop_mcount(Elf_Shdr const *const relhdr,
+static int nop_mcount(GElf_Shdr const *const relhdr,
Elf_Ehdr const *const ehdr,
const char *const txtname)
{
@@ -376,9 +376,9 @@ static int nop_mcount(Elf_Shdr const *const relhdr,
Elf_Sym const *sym0;
char const *str0;
Elf_Rel const *relp;
- Elf_Shdr const *const shdr = &shdr0[w(relhdr->sh_info)];
- unsigned rel_entsize = _w(relhdr->sh_entsize);
- unsigned const nrel = _w(relhdr->sh_size) / rel_entsize;
+ Elf_Shdr const *const shdr = &shdr0[relhdr->sh_info];
+ unsigned int rel_entsize = relhdr->sh_entsize;
+ unsigned const nrel = relhdr->sh_size / rel_entsize;
unsigned mcountsym = 0;
unsigned t;
int once = 0;
@@ -470,13 +470,13 @@ static unsigned find_secsym_ndx(unsigned const txtndx,
}

/* Evade ISO C restriction: no declaration after statement in has_rel_mcount. */
-static char const * __has_rel_mcount(Elf_Shdr const *const relhdr, /* reltype */
+static char const * __has_rel_mcount(GElf_Shdr const *const relhdr, /* reltype */
Elf_Shdr const *const shdr0,
char const *const shstrtab,
char const *const fname)
{
/* .sh_info depends on .sh_type == SHT_REL[,A] */
- Elf_Shdr const *const txthdr = &shdr0[w(relhdr->sh_info)];
+ Elf_Shdr const *const txthdr = &shdr0[relhdr->sh_info];
char const *const txtname = &shstrtab[w(txthdr->sh_name)];

if (w(txthdr->sh_type) != SHT_PROGBITS ||
@@ -485,30 +485,29 @@ static char const * __has_rel_mcount(Elf_Shdr const *const relhdr, /* reltype */
return txtname;
}

-static char const *has_rel_mcount(Elf_Shdr const *const relhdr,
+static char const *has_rel_mcount(GElf_Shdr const *const relhdr,
Elf_Shdr const *const shdr0,
char const *const shstrtab,
char const *const fname)
{
- if (w(relhdr->sh_type) != SHT_REL && w(relhdr->sh_type) != SHT_RELA)
+ if (relhdr->sh_type != SHT_REL && relhdr->sh_type != SHT_RELA)
return NULL;
return __has_rel_mcount(relhdr, shdr0, shstrtab, fname);
}

static unsigned tot_relsize(Elf_Shdr const *const shdr0,
- unsigned nhdr,
const char *const shstrtab,
const char *const fname)
{
+ struct section *sec;
unsigned totrelsz = 0;
- Elf_Shdr const *shdrp = shdr0;
char const *txtname;

- for (; nhdr; --nhdr, ++shdrp) {
- txtname = has_rel_mcount(shdrp, shdr0, shstrtab, fname);
+ list_for_each_entry(sec, &lf->sections, list) {
+ txtname = has_rel_mcount(&sec->sh, shdr0, shstrtab, fname);
if (txtname && is_mcounted_section_name(txtname))
- totrelsz += _w(shdrp->sh_size);
+ totrelsz += sec->sh.sh_size;
}
return totrelsz;
}
@@ -520,13 +519,11 @@ static int do_func(Elf_Ehdr *const ehdr, char const *const fname,
{
Elf_Shdr *const shdr0 = (Elf_Shdr *)(_w(ehdr->e_shoff)
+ (void *)ehdr);
- unsigned const nhdr = w2(ehdr->e_shnum);
Elf_Shdr *const shstr = &shdr0[w2(ehdr->e_shstrndx)];
char const *const shstrtab = (char const *)(_w(shstr->sh_offset)
+ (void *)ehdr);

- Elf_Shdr const *relhdr;
- unsigned k;
+ GElf_Shdr const *relhdr;

/* Upper bound on space: assume all relevant relocs are for mcount. */
unsigned totrelsz;
@@ -540,12 +537,14 @@ static int do_func(Elf_Ehdr *const ehdr, char const *const fname,
unsigned rel_entsize = 0;
unsigned symsec_sh_link = 0;

+ struct section *sec;
+
int result = 0;

if (find_section_by_name(lf, "__mcount_loc") != NULL)
return 0;

- totrelsz = tot_relsize(shdr0, nhdr, shstrtab, fname);
+ totrelsz = tot_relsize(shdr0, shstrtab, fname);
if (totrelsz == 0)
return 0;
mrel0 = umalloc(totrelsz);
@@ -561,24 +560,27 @@ static int do_func(Elf_Ehdr *const ehdr, char const *const fname,
return -1;
}

- for (relhdr = shdr0, k = nhdr; k; --k, ++relhdr) {
- char const *const txtname = has_rel_mcount(relhdr, shdr0,
+ list_for_each_entry(sec, &lf->sections, list) {
+ char const *txtname;
+
+ relhdr = &sec->sh;
+ txtname = has_rel_mcount(relhdr, shdr0,
shstrtab, fname);
if (txtname && is_mcounted_section_name(txtname)) {
uint_t recval = 0;
- unsigned const int recsym = find_secsym_ndx(
- w(relhdr->sh_info), txtname, &recval,
- &shdr0[symsec_sh_link = w(relhdr->sh_link)],
+ unsigned const int recsym_index = find_secsym_ndx(
+ relhdr->sh_info, txtname, &recval,
+ &shdr0[symsec_sh_link = relhdr->sh_link],
ehdr);
- if (recsym == missing_sym) {
+ if (recsym_index == missing_sym) {
result = -1;
goto out;
}

- rel_entsize = _w(relhdr->sh_entsize);
+ rel_entsize = relhdr->sh_entsize;
mlocp = sift_rel_mcount(mlocp,
(void *)mlocp - (void *)mloc0, &mrelp,
- relhdr, ehdr, recsym, recval, reltype);
+ relhdr, ehdr, recsym_index, recval, reltype);
} else if (txtname && (warn_on_notrace_sect || make_nop)) {
/*
* This section is ignored by ftrace, but still
--
2.20.1