[for-linus][PATCH 01/17] recordmcount: support >64k sections

Steven Rostedt
2020-06-18T23:57:06Z

From: Sami Tolvanen <samitolvanen@google.com>

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/20200424193046.160744-1-samitolvanen@google.com
Link: https://lore.kernel.org/lkml/CAK7LNARbZhoaA=Nnuw0=gBrkuKbr_4Ng_Ei57uafujZf7Xazgw@mail.gmail.com/

Cc: Kees Cook <keescook@chromium.org>
Reviewed-by: Matt Helsley <mhelsley@vmware.com>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
---
scripts/recordmcount.h | 98 +++++++++++++++++++++++++++++++++++++++---
1 file changed, 92 insertions(+), 6 deletions(-)

diff --git a/scripts/recordmcount.h b/scripts/recordmcount.h
index 74eab03e31d4..f9b19524da11 100644
--- a/scripts/recordmcount.h
+++ b/scripts/recordmcount.h
@@ -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
@@ -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
@@ -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
@@ -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,
@@ -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;

@@ -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;
@@ -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)
@@ -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)
@@ -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 */
@@ -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;

@@ -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);
@@ -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;
--
2.26.2