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recordmcount: support >64k sections
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When compiling a kernel with Clang and LTO, we need to run
recordmcount on vmlinux.o with a large number of sections, which
currently fails as the program doesn't understand extended
section indexes. This change adds support for processing binaries
with >64k sections.

Link: https://lkml.kernel.org/r/[email protected]
Link: https://lore.kernel.org/lkml/CAK7LNARbZhoaA=Nnuw0=gBrkuKbr_4Ng_Ei57uafujZf7Xazgw@mail.gmail.com/

Cc: Kees Cook <[email protected]>
Reviewed-by: Matt Helsley <[email protected]>
Signed-off-by: Sami Tolvanen <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>
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@samitolvanen @rostedt
samitolvanen authored and rostedt committed Jun 17, 2020
1 parent b3a9e3b commit 4ef57b2
Showing 1 changed file with 92 additions and 6 deletions.
98 changes: 92 additions & 6 deletions scripts/recordmcount.h
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,11 @@
#undef has_rel_mcount
#undef tot_relsize
#undef get_mcountsym
#undef find_symtab
#undef get_shnum
#undef set_shnum
#undef get_shstrndx
#undef get_symindex
#undef get_sym_str_and_relp
#undef do_func
#undef Elf_Addr
Expand Down Expand Up @@ -58,6 +63,11 @@
# define __has_rel_mcount __has64_rel_mcount
# define has_rel_mcount has64_rel_mcount
# define tot_relsize tot64_relsize
# define find_symtab find_symtab64
# define get_shnum get_shnum64
# define set_shnum set_shnum64
# define get_shstrndx get_shstrndx64
# define get_symindex get_symindex64
# define get_sym_str_and_relp get_sym_str_and_relp_64
# define do_func do64
# define get_mcountsym get_mcountsym_64
Expand Down Expand Up @@ -91,6 +101,11 @@
# define __has_rel_mcount __has32_rel_mcount
# define has_rel_mcount has32_rel_mcount
# define tot_relsize tot32_relsize
# define find_symtab find_symtab32
# define get_shnum get_shnum32
# define set_shnum set_shnum32
# define get_shstrndx get_shstrndx32
# define get_symindex get_symindex32
# define get_sym_str_and_relp get_sym_str_and_relp_32
# define do_func do32
# define get_mcountsym get_mcountsym_32
Expand Down Expand Up @@ -173,6 +188,67 @@ static int MIPS_is_fake_mcount(Elf_Rel const *rp)
return is_fake;
}

static unsigned int get_symindex(Elf_Sym const *sym, Elf32_Word const *symtab,
Elf32_Word const *symtab_shndx)
{
unsigned long offset;
int index;

if (sym->st_shndx != SHN_XINDEX)
return w2(sym->st_shndx);

offset = (unsigned long)sym - (unsigned long)symtab;
index = offset / sizeof(*sym);

return w(symtab_shndx[index]);
}

static unsigned int get_shnum(Elf_Ehdr const *ehdr, Elf_Shdr const *shdr0)
{
if (shdr0 && !ehdr->e_shnum)
return w(shdr0->sh_size);

return w2(ehdr->e_shnum);
}

static void set_shnum(Elf_Ehdr *ehdr, Elf_Shdr *shdr0, unsigned int new_shnum)
{
if (new_shnum >= SHN_LORESERVE) {
ehdr->e_shnum = 0;
shdr0->sh_size = w(new_shnum);
} else
ehdr->e_shnum = w2(new_shnum);
}

static int get_shstrndx(Elf_Ehdr const *ehdr, Elf_Shdr const *shdr0)
{
if (ehdr->e_shstrndx != SHN_XINDEX)
return w2(ehdr->e_shstrndx);

return w(shdr0->sh_link);
}

static void find_symtab(Elf_Ehdr *const ehdr, Elf_Shdr const *shdr0,
unsigned const nhdr, Elf32_Word **symtab,
Elf32_Word **symtab_shndx)
{
Elf_Shdr const *relhdr;
unsigned k;

*symtab = NULL;
*symtab_shndx = NULL;

for (relhdr = shdr0, k = nhdr; k; --k, ++relhdr) {
if (relhdr->sh_type == SHT_SYMTAB)
*symtab = (void *)ehdr + relhdr->sh_offset;
else if (relhdr->sh_type == SHT_SYMTAB_SHNDX)
*symtab_shndx = (void *)ehdr + relhdr->sh_offset;

if (*symtab && *symtab_shndx)
break;
}
}

/* Append the new shstrtab, Elf_Shdr[], __mcount_loc and its relocations. */
static int append_func(Elf_Ehdr *const ehdr,
Elf_Shdr *const shstr,
Expand All @@ -188,10 +264,12 @@ static int append_func(Elf_Ehdr *const ehdr,
char const *mc_name = (sizeof(Elf_Rela) == rel_entsize)
? ".rela__mcount_loc"
: ".rel__mcount_loc";
unsigned const old_shnum = w2(ehdr->e_shnum);
uint_t const old_shoff = _w(ehdr->e_shoff);
uint_t const old_shstr_sh_size = _w(shstr->sh_size);
uint_t const old_shstr_sh_offset = _w(shstr->sh_offset);
Elf_Shdr *const shdr0 = (Elf_Shdr *)(old_shoff + (void *)ehdr);
unsigned int const old_shnum = get_shnum(ehdr, shdr0);
unsigned int const new_shnum = 2 + old_shnum; /* {.rel,}__mcount_loc */
uint_t t = 1 + strlen(mc_name) + _w(shstr->sh_size);
uint_t new_e_shoff;

Expand All @@ -201,6 +279,8 @@ static int append_func(Elf_Ehdr *const ehdr,
t += (_align & -t); /* word-byte align */
new_e_shoff = t;

set_shnum(ehdr, shdr0, new_shnum);

/* body for new shstrtab */
if (ulseek(sb.st_size, SEEK_SET) < 0)
return -1;
Expand Down Expand Up @@ -255,7 +335,6 @@ static int append_func(Elf_Ehdr *const ehdr,
return -1;

ehdr->e_shoff = _w(new_e_shoff);
ehdr->e_shnum = w2(2 + w2(ehdr->e_shnum)); /* {.rel,}__mcount_loc */
if (ulseek(0, SEEK_SET) < 0)
return -1;
if (uwrite(ehdr, sizeof(*ehdr)) < 0)
Expand Down Expand Up @@ -434,6 +513,8 @@ static int find_secsym_ndx(unsigned const txtndx,
uint_t *const recvalp,
unsigned int *sym_index,
Elf_Shdr const *const symhdr,
Elf32_Word const *symtab,
Elf32_Word const *symtab_shndx,
Elf_Ehdr const *const ehdr)
{
Elf_Sym const *const sym0 = (Elf_Sym const *)(_w(symhdr->sh_offset)
Expand All @@ -445,7 +526,7 @@ static int find_secsym_ndx(unsigned const txtndx,
for (symp = sym0, t = nsym; t; --t, ++symp) {
unsigned int const st_bind = ELF_ST_BIND(symp->st_info);

if (txtndx == w2(symp->st_shndx)
if (txtndx == get_symindex(symp, symtab, symtab_shndx)
/* avoid STB_WEAK */
&& (STB_LOCAL == st_bind || STB_GLOBAL == st_bind)) {
/* function symbols on ARM have quirks, avoid them */
Expand Down Expand Up @@ -516,21 +597,23 @@ static unsigned tot_relsize(Elf_Shdr const *const shdr0,
return totrelsz;
}


/* Overall supervision for Elf32 ET_REL file. */
static int do_func(Elf_Ehdr *const ehdr, char const *const fname,
unsigned const reltype)
{
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)];
unsigned const nhdr = get_shnum(ehdr, shdr0);
Elf_Shdr *const shstr = &shdr0[get_shstrndx(ehdr, shdr0)];
char const *const shstrtab = (char const *)(_w(shstr->sh_offset)
+ (void *)ehdr);

Elf_Shdr const *relhdr;
unsigned k;

Elf32_Word *symtab;
Elf32_Word *symtab_shndx;

/* Upper bound on space: assume all relevant relocs are for mcount. */
unsigned totrelsz;

Expand Down Expand Up @@ -561,6 +644,8 @@ static int do_func(Elf_Ehdr *const ehdr, char const *const fname,
return -1;
}

find_symtab(ehdr, shdr0, nhdr, &symtab, &symtab_shndx);

for (relhdr = shdr0, k = nhdr; k; --k, ++relhdr) {
char const *const txtname = has_rel_mcount(relhdr, shdr0,
shstrtab, fname);
Expand All @@ -577,6 +662,7 @@ static int do_func(Elf_Ehdr *const ehdr, char const *const fname,
result = find_secsym_ndx(w(relhdr->sh_info), txtname,
&recval, &recsym,
&shdr0[symsec_sh_link],
symtab, symtab_shndx,
ehdr);
if (result)
goto out;
Expand Down

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