2 files changed, 116 insertions, 6 deletions

diff --git a/scripts/recordmcount.c b/scripts/recordmcount.c
index 37c59654c133..78054a41d134 100644
--- a/scripts/recordmcount.c
+++ b/scripts/recordmcount.c
@@ -118,6 +118,34 @@ umalloc(size_t size)
         return addr;
 }
 
+static unsigned char ideal_nop5_x86_64[5] = { 0x0f, 0x1f, 0x44, 0x00, 0x00 };
+static unsigned char ideal_nop5_x86_32[5] = { 0x3e, 0x8d, 0x74, 0x26, 0x00 };
+static unsigned char *ideal_nop;
+
+static char rel_type_nop;
+
+static int (*make_nop)(void *map, size_t const offset);
+
+static int make_nop_x86(void *map, size_t const offset)
+{
+        uint32_t *ptr;
+        unsigned char *op;
+
+        /* Confirm we have 0xe8 0x0 0x0 0x0 0x0 */
+        ptr = map + offset;
+        if (*ptr != 0)
+                return -1;
+
+        op = map + offset - 1;
+        if (*op != 0xe8)
+                return -1;
+
+        /* convert to nop */
+        ulseek(fd_map, offset - 1, SEEK_SET);
+        uwrite(fd_map, ideal_nop, 5);
+        return 0;
+}
+
 /*
  * Get the whole file as a programming convenience in order to avoid
  * malloc+lseek+read+free of many pieces.  If successful, then mmap
@@ -301,7 +329,11 @@ do_file(char const *const fname)
                         w2(ehdr->e_machine), fname);
                 fail_file();
                 break;
-        case EM_386:     reltype = R_386_32;                   break;
+        case EM_386:
+                reltype = R_386_32;
+                make_nop = make_nop_x86;
+                ideal_nop = ideal_nop5_x86_32;
+                break;
         case EM_ARM:     reltype = R_ARM_ABS32;
                          altmcount = "__gnu_mcount_nc";
                          break;
@@ -312,7 +344,11 @@ do_file(char const *const fname)
         case EM_S390:    /* reltype: e_class    */ gpfx = '_'; break;
         case EM_SH:      reltype = R_SH_DIR32;                 break;
         case EM_SPARCV9: reltype = R_SPARC_64;     gpfx = '_'; break;
-        case EM_X86_64:  reltype = R_X86_64_64;                break;
+        case EM_X86_64:
+                make_nop = make_nop_x86;
+                ideal_nop = ideal_nop5_x86_64;
+                reltype = R_X86_64_64;
+                break;
         }  /* end switch */
 
         switch (ehdr->e_ident[EI_CLASS]) {
diff --git a/scripts/recordmcount.h b/scripts/recordmcount.h
index 7f8d5c4c780f..657dbedd1c7f 100644
--- a/scripts/recordmcount.h
+++ b/scripts/recordmcount.h
@@ -23,6 +23,7 @@
 #undef fn_is_fake_mcount
 #undef MIPS_is_fake_mcount
 #undef sift_rel_mcount
+#undef nop_mcount
 #undef find_secsym_ndx
 #undef __has_rel_mcount
 #undef has_rel_mcount
@@ -49,6 +50,7 @@
 #ifdef RECORD_MCOUNT_64
 # define append_func            append64
 # define sift_rel_mcount        sift64_rel_mcount
+# define nop_mcount             nop_mcount_64
 # define find_secsym_ndx        find64_secsym_ndx
 # define __has_rel_mcount       __has64_rel_mcount
 # define has_rel_mcount         has64_rel_mcount
@@ -77,6 +79,7 @@
 #else
 # define append_func            append32
 # define sift_rel_mcount        sift32_rel_mcount
+# define nop_mcount             nop_mcount_32
 # define find_secsym_ndx        find32_secsym_ndx
 # define __has_rel_mcount       __has32_rel_mcount
 # define has_rel_mcount         has32_rel_mcount
@@ -304,6 +307,70 @@ static uint_t *sift_rel_mcount(uint_t *mlocp,
         return mlocp;
 }
 
+/*
+ * Read the relocation table again, but this time its called on sections
+ * that are not going to be traced. The mcount calls here will be converted
+ * into nops.
+ */
+static void nop_mcount(Elf_Shdr const *const relhdr,
+                       Elf_Ehdr const *const ehdr)
+{
+        Elf_Shdr *const shdr0 = (Elf_Shdr *)(_w(ehdr->e_shoff)
+                + (void *)ehdr);
+        unsigned const symsec_sh_link = w(relhdr->sh_link);
+        Elf_Shdr const *const symsec = &shdr0[symsec_sh_link];
+        Elf_Sym const *const sym0 = (Elf_Sym const *)(_w(symsec->sh_offset)
+                + (void *)ehdr);
+
+        Elf_Shdr const *const strsec = &shdr0[w(symsec->sh_link)];
+        char const *const str0 = (char const *)(_w(strsec->sh_offset)
+                + (void *)ehdr);
+
+        Elf_Rel const *const rel0 = (Elf_Rel const *)(_w(relhdr->sh_offset)
+                + (void *)ehdr);
+        unsigned rel_entsize = _w(relhdr->sh_entsize);
+        unsigned const nrel = _w(relhdr->sh_size) / rel_entsize;
+        Elf_Rel const *relp = rel0;
+
+        Elf_Shdr const *const shdr = &shdr0[w(relhdr->sh_info)];
+
+        unsigned mcountsym = 0;
+        unsigned t;
+
+        for (t = nrel; t; --t) {
+                int ret = -1;
+
+                if (!mcountsym) {
+                        Elf_Sym const *const symp =
+                                &sym0[Elf_r_sym(relp)];
+                        char const *symname = &str0[w(symp->st_name)];
+                        char const *mcount = gpfx == '_' ? "_mcount" : "mcount";
+
+                        if (symname[0] == '.')
+                                ++symname;  /* ppc64 hack */
+                        if (strcmp(mcount, symname) == 0 ||
+                            (altmcount && strcmp(altmcount, symname) == 0))
+                                mcountsym = Elf_r_sym(relp);
+                }
+
+                if (mcountsym == Elf_r_sym(relp) && !is_fake_mcount(relp))
+                        ret = make_nop((void *)ehdr, shdr->sh_offset + relp->r_offset);
+
+                /*
+                 * If we successfully removed the mcount, mark the relocation
+                 * as a nop (don't do anything with it).
+                 */
+                if (!ret) {
+                        Elf_Rel rel;
+                        rel = *(Elf_Rel *)relp;
+                        Elf_r_info(&rel, Elf_r_sym(relp), rel_type_nop);
+                        ulseek(fd_map, (void *)relp - (void *)ehdr, SEEK_SET);
+                        uwrite(fd_map, &rel, sizeof(rel));
+                }
+                relp = (Elf_Rel const *)(rel_entsize + (void *)relp);
+        }
+}
+
 
 /*
  * Find a symbol in the given section, to be used as the base for relocating
@@ -360,8 +427,7 @@ __has_rel_mcount(Elf_Shdr const *const relhdr,  /* is SHT_REL or SHT_RELA */
                 succeed_file();
         }
         if (w(txthdr->sh_type) != SHT_PROGBITS ||
-            !(w(txthdr->sh_flags) & SHF_EXECINSTR) ||
-            !is_mcounted_section_name(txtname))
+            !(w(txthdr->sh_flags) & SHF_EXECINSTR))
                 return NULL;
         return txtname;
 }
@@ -384,9 +450,11 @@ static unsigned tot_relsize(Elf_Shdr const *const shdr0,
 {
         unsigned totrelsz = 0;
         Elf_Shdr const *shdrp = shdr0;
+        char const *txtname;
 
         for (; nhdr; --nhdr, ++shdrp) {
-                if (has_rel_mcount(shdrp, shdr0, shstrtab, fname))
+                txtname = has_rel_mcount(shdrp, shdr0, shstrtab, fname);
+                if (txtname && is_mcounted_section_name(txtname))
                         totrelsz += _w(shdrp->sh_size);
         }
         return totrelsz;
@@ -422,7 +490,7 @@ do_func(Elf_Ehdr *const ehdr, char const *const fname, unsigned const reltype)
         for (relhdr = shdr0, k = nhdr; k; --k, ++relhdr) {
                 char const *const txtname = has_rel_mcount(relhdr, shdr0,
                         shstrtab, fname);
-                if (txtname) {
+                if (txtname && is_mcounted_section_name(txtname)) {
                         uint_t recval = 0;
                         unsigned const recsym = find_secsym_ndx(
                                 w(relhdr->sh_info), txtname, &recval,
@@ -433,6 +501,12 @@ do_func(Elf_Ehdr *const ehdr, char const *const fname, unsigned const reltype)
                         mlocp = sift_rel_mcount(mlocp,
                                 (void *)mlocp - (void *)mloc0, &mrelp,
                                 relhdr, ehdr, recsym, recval, reltype);
+                } else if (make_nop && txtname) {
+                        /*
+                         * This section is ignored by ftrace, but still
+                         * has mcount calls. Convert them to nops now.
+                         */
+                        nop_mcount(relhdr, ehdr);
                 }
         }
         if (mloc0 != mlocp) {